veterinary anesthesia
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Copyright © 2001 by Butterworth–Heinemann
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Every effort has been made to ensure that the drug dosage schedules withinthis text are accurate and conform to standards accepted at time of publication.However, as treatment recommendations vary in the light of continuingresearch and clinical experience, the reader is advised to verify drug dosageschedules herein with information found on product information sheets. This isespecially true in cases of new or infrequently used drugs.
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Library of Congress Cataloging-in-Publication DataCornick-Seahorn, Janyce L.
Veterinary anesthesia / Janyce L. Cornick-Seahorn.p. cm. — (The Practical veterinarian)
Includes bibliographical references (p. ).ISBN 0-7506-7227-7 (alk. paper)
1. Veterinary anesthesia. I. Title. II. Series.SF914 .C67 2000636.089’796—dc21 00-044452
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Series Preface
The Practical Veterinarian series was developed to help
veterinary students, veterinarians, and veterinary techni-
cians find answers to common questions quickly. Unlike
larger textbooks, which are filled with detailed informa-
tion and meant to serve as reference books, all the books
in The Practical Veterinarian series are designed to cut to
the heart of the subject matter. Not meant to replace the
reference texts, the guides in our series complement the
larger books by serving as an introduction to each topic
for those learning the subject matter for the first time or
as a quick review for those who already have mastered
the basics of each subject.
The titles for the books in our series are selected to
provide information for the most common subjects one
would encounter in veterinary school and veterinary
practice. The authors are experienced and established
clinicians who can present the subject matter in an easy-
to-understand format. This helps both the first-time stu-
dent of the subject and the seasoned practitioner assess
information often difficult to comprehend.
It is our hope that the books in The Practical Veteri-
narian series will meet the needs of readers and serve as
a constant source of practical and important informa-
tion. We welcome comments and suggestions that will
vii
help us improve future editions of the books in this
series.
Shawn P. Messonnier, D.V.M.
viii Series Preface
Preface
Veterinary Anesthesia summarizes what I hope is practical,
useful information for learning the basic and clinical
principles and the daily practice of anesthesia. I would
like to thank my husband, Tom, and my children, Brad
and Sam, without whom this project would not have had
such meaning. I would like to thank my parents, without
whom I would not have had the opportunity to achieve
my goals nor the desire to share my knowledge, as I hope
I have in this endeavor.
I thank my mentor in anesthesia, Dr. Sandee Harts-
field, who continues to be a friend and unending source
of knowledge and common sense regarding the art of
anesthesia. I thank my mentor in large animal internal
medicine, Dr. Kent Carter, who instilled in me a logical
and thorough approach to case management.
I also thank my editor, Leslie Kramer, whose opti-
mism and enthusiasm gave me support every step of the
way.
And, most of all, I thank God for my profession and
the opportunity to accrue the information and knowl-
edge that I feel are most pertinent to teach veterinary
students and guide practitioners, many of whom I have
been fortunate to interact with at some level of their
careers.
ix
The book is not comprehensive but includes those
drug dosages, techniques, and procedures I feel are per-
tinent to the daily practice of veterinary medicine. Many
of the recommendations and dosages are based on clini-
cal experience, which I hope will complement and
enhance the clinical practice of anesthesia.
J.L.C-S.
x Preface
1
Introduction to Anesthesiaand Patient Preparation
Anesthesia is defined as total loss of sensation in a bodypart or the whole body, induced by a drug or drug com-bination that depresses activity of nervous tissue periph-erally (local and regional anesthesia) or centrally(general anesthesia). Anesthesia and chemical restraintare reversible processes essential to the practice of vet-erinary medicine, providing safe and effective patientimmobilization to minimize stress and pain and facilitatea wide variety of procedures.
1
General Principles of Anesthetic Management
Regardless of species and procedure, these guidelinesshould be applied to all patients:
1. Critical evaluation of history, physical examination,and laboratory data. Know your patient!
2. Weigh the benefits of the procedure against thepotential detrimental effects of anesthesia.
3. Stabilize and correct any identified abnormalities, ifpossible, prior to anesthesia.
4. Be organized to minimize anesthesia time.
5. Identify and prepare for potential complications.
6. Select the anesthetic protocol based on the patientand existing abnormalities.
7. Establish intravenous access whenever possible andfeasible.
8. Secure and maintain a patent airway whenever pos-sible and feasible.
9. Use supplemental oxygen when indicated, based onpatient and duration of procedure.
10. Use a maintenance regimen that will minimizeadverse effects.
11. Provide ventilatory support.
12. Monitor vital body systems, including cardiovascular,respiratory, and central nervous systems.
2 Introduction to Anesthesia and Patient Preparation
13. Identify and correct any abnormalities that arise dur-ing the anesthetic period.
14. Continue monitoring and support until vital signsare stable.
15. Use appropriate analgesia and sedation postopera-tively to minimize pain and distress.
Patient Preparation
“For every mistake that is made for not knowing, a hundred are made for not looking.”
—Anonymous
Patient preparation includes evaluation of the signal-ment, history, and pertinent laboratory data that mightaffect the patient’s response to anesthesia. Patients thencan be categorized according to physical status, whichhelps in the selection of an anesthetic protocol anddetermines the likelihood (risk) for occurrence of a car-diopulmonary emergency during the anesthetic period(Table 1–1).
Physical examination should always include assess-ment of temperature, heart rate, respiratory rate, mucousmembrane color and moistness, pulse quality, thoracicauscultation, and abdominal palpation, even in seem-ingly healthy patients. Normal values for a variety ofspecies are listed in Table 1–2. Minimal laboratory data inphysical status I patients should include packed cell vol-ume (PCV) and total protein for all species (exceptions
Introduction to Anesthesia and Patient Preparation 3
being animals in which venipuncture cannot be per-formed without some level of anesthesia). Blood ureanitrogen (uric acid in avian species) is advised but prob-ably not necessary in most healthy patients. Normalranges of these values for a variety of species are given inTable 1–3. History and physical examination findings
4 Introduction to Anesthesia and Patient Preparation
Table 1–1 Classification of Physical Status
Category Physical Status Examples
I Normal healthy Patient presented forpatient elective procedure
II Patient with mild Skin tumor, fracturesystemic disease without shock
III Patient with severe but Fever, dehydration, not incapacitating anemia, cachexia, early systemic disease renal or cardiac disease
IV Patient with severe Uremia, cardiac life-threatening decompensation, systemic disease septicemia, emaciation
V Moribund patient not Profound shock, expected to survive terminal malignancy, with or without severe traumaintervention
E E is added to category to designate that anesthesia is being performed on an emergency basis.
Adapted from the American Society of Anesthesiologists.
Introduction to Anesthesia and Patient Preparation 5
Table 1–2 Normal Values for Temperature, Pulse Rate,and Respiratory Rate for Several Veterinary Species
Heart Respiratory Species Temperature ºF Rate/Minute Rate/Minute
Birds
Pet birds* 102–105 120–500 10–75
Raptors 102–104 107–310 12–25
Ratites 99–104 60–190 6–12 (resting, mild ambi-ent tempera-ture)
Cat 100.5–102.5 110–200 15–26
Cow 100.5–102.5 60–80 8–20
Dog 101–103 89–140 8–20
Ferret 100–104 200–400 33–36
Goat 101–103 70–135 12–25
Horse 99.5–101.5 25–50 8–12
Llama 99.5–102 60–80 10–30
Rabbit 101.5–104 130–325 30–60
Sheep 102–104 60–90 15–30
Pig 100–103 60–90 10–30
Pot-belly pig 102–103 70–80 13–18 (80–100: (25–40: neonates) neonates/
juveniles)
*Ranges tend to correlate inversely with the size of the bird.
6 Introduction to Anesthesia and Patient Preparation
Tab
le 1
–3
Norm
al (
Aw
ake)
Ran
ges
for
Hem
atocr
it, To
tal Pro
tein
, W
hite B
lood C
ell
Count, a
nd S
ele
cted C
hem
istr
y Val
ues
for
Seve
ral Ve
terinar
y Speci
es
Sp
eci
es
PC
V (
%)
TP
(gm
/dl)
WB
C �
10
3B
UN
(m
g/d
l)
Cre
ati
nin
e (
mg/d
l)
Bird
s* Pet
bird
s35–50
2.5
–5.0
3.0
–12.0
2.3
–14.0
mg/
dl (U
ric a
cid)
Rap
tors
43–49
2.6
5–5.1
4.6
–12
4.5
–14 m
g/dl (U
ric a
cid)
Rat
ites
40–50
2.4
–5.3
8–24
1–14 m
g/dl (U
ric a
cid)
Cat
27–45
6.0
–7.
55.5
–18
15–31
0.7
–1.8
Cow
23–43
6.0
–7.
54–12
7–30
0.6
–1.8
Dog
35–54
5.5
–7.
56.5
–18
6–30
0.5
–1.6
Ferret
48–50
6.0
7.0–9.3
19–27
0.4
–0.5
Goat
22–38
6.1
–7.
44–13
12–25
0.7
–1.5
Hors
e25–48
5.7
–7.
96–12
10–30
0.9
–1.8
Llam
a25–45
4.9
–7.
98–23
9–33
1.1
–3.2
Rab
bit
36–48
5.4
–7.
59–11
17–23
0.8
–1.8
Shee
p30–50
6.3
–7.
14–12
5–26
0.9
–2.0
Pig
30–50
6.0
–8.0
6.5
–20
8–24
0.8
–2.7
Note
: Th
ese
norm
al v
alues
should
be
use
d a
s ge
ner
al g
uid
elin
es, a
s va
riatio
n e
xist
s bet
wee
n r
efer
ence
ran
ges
for
indi-
vidual
labora
torie
s.
*Wid
e va
riatio
n e
xist
s am
ong
avia
n s
pec
ies.
Val
ues
list
ed a
re to b
e use
d o
nly
as
gener
al g
uid
elin
es.
(abnormal organ system function, geriatric patients) willdictate the need for more complete laboratory evalua-tion including a complete blood count; serum chemistrypanel, which should include total CO2 (metabolic acid-base status) and electrolyte concentrations; and urinaly-sis. Unprompted extensive laboratory screening has notbeen found to improve outcome for surgical patients ineither human or veterinary medicine. Further diagnosticevaluation, such as thoracic and abdominal radiographsor ultrasonography, echocardiography, and organ spe-cific evaluation (i.e., bile acid assay) should be based onabnormal physical examination and primary bloodchemistry findings.
Fasting
In general, patients should be fasted for 6–12 hours priorto induction of anesthesia, with water withheld for vari-able periods of time to minimize risk of aspiration andregurgitation and to decrease gastrointestinal volume.There is disparity in the literature regarding length offasting, due largely to personal experience and prefer-ence. Table 1–4 lists recommended fasting times for sev-eral common domestic species. Slightly longer periodsare recommended when prolonged or abdominal sur-geries are to be performed. Very young and very smallpatients should not be fasted due to risk of hypoglycemia.Water withholding is unnecessary in most species with theexception being ruminants and camelids (see Table 1–4).
Introduction to Anesthesia and Patient Preparation 7
8 Introduction to Anesthesia and Patient Preparation
Table 1–4 Recommended Fasting and Water WithholdingTimes for Several Veterinary Species
WaterSpecies Recommended Fasting Time* Restriction**
Birds
Pet birds 1–3 hr (the smaller the bird, ≤1 hrthe shorter the fast; >300 gms: maximum 10 hr usually is tolerated)
Raptors 6–12 hr (up to 24 hr in large 2 hrraptors)
Ratites 12–24 hr 2 hr
Cat 6–8 hr 6 hr
Cow 24–48 hr 12–24 hr
Dog 6–8 hr 6 hr
Ferret 4–6 hr 2 hr
Goat 12–24 hr 2–8 hr
Horse 6–12 hr Not necessary
Llama 12–24 hr 8 hr
Rabbit† 8 hr Not necessary
Sheep 12–24 hr 2–8 hr
Pig 8–12 hr Not necessary
Note: Fasting times for many species vary in the literature; as a general rule, thelonger the procedure, the longer is the fast.
*Fasting is not recommended for neonates of any species or for very small patientsbecause high metabolic rates and limited glycogen stores cause increased risk fordevelopment of hypoglycemia. Fasting should be abbreviated or omitted in animalswith diseases that can precipitate hypoglycemia, such as insulinoma and diabetesmellitus. (continues)
Record Keeping
Proper patient preparation minimizes but cannot elimi-nate the risk of anesthesia. Thorough record keepingwill encourage vigilant patient monitoring and allow theveterinarian not only to evaluate perianesthetic eventsretrospectively for future reference but to provide rele-vant and documented information should litigationoccur. The anesthetic record should include animalname and case number, owner name, signalment,weight, physical and laboratory examination results,physical status, procedure performed, all anestheticagents (premedications, induction agents, maintenanceagents) administered including dose (in mg) or concen-tration (inhalant agents), route and time of administra-tion, duration of anesthesia, supportive measures (i.e.,fluid type and rate of administration), a chronologicrecording of vital signs, postoperative analgesic agentsadministered, vital signs recorded during recovery andany complications encountered. Figure 1–1 provides anexample of an anesthetic record to facilitate completerecord keeping.
Introduction to Anesthesia and Patient Preparation 9
Table 1–4 (Continued)**Water deprivation should be eliminated or abbreviated in patients with significantrenal disease (unless IV fluids are provided to assure normal hydration preopera-tively) or during high ambient environmental temperatures (i.e., ruminants).†While the practice has been recommended in the literature, fasting of rabbits isconsidered unnecessary since this species does not vomit and a prolonged fastcan promote gastrointestinal stasis.
10
Figure 1-1 An example of an anesthetic record, which facili-tates sequential recording of vital signs and summarizes drugsadministered and events occurring during the anesthetic period.
2
Pharmacology and Application of Parenteral Anesthetic Agents
A plethora of injectable agents are available in veterinarypractice to fulfill the need for premedication, induction,maintenance, and postoperative analgesia; to alleviateanxiety and motor activity (chemical restraint); and toprovide profound muscle relaxation (neuromuscularblocking agents) when indicated. While some agents,such as the dissociative drugs, serve multiple roles (pre-medication, induction, and maintenance), parenteraldrugs are summarized according to primary effects andbriefly described in Table 2–1. The “ideal” anestheticagent is described in Table 2–2. Because no drug avail-able today possesses all the “ideal” qualities, anestheticselection is a compromise based on the patient, the
11
procedure, and the available agents, equipment, andexpertise. Inhalation agents come closest to possessingthe majority of qualities described for an “ideal” anes-thetic agent and will be discussed in Chapter 4.
Premedication agents are used to aid in animalrestraint (calming effect), reduce anxiety, provide anal-gesia, provide muscle relaxation, decrease the require-ments for potentially more dangerous drugs used forinduction and maintenance, promote smooth transitionfrom consciousness to unconsciousness and vice versaduring the induction and recovery periods, respectively,and minimize autonomic reflex activity. Induction agentsare used to provide a smooth transition from conscious-ness to unconsciousness, which facilitates intubation andtransition to the maintenance protocol. Some agents usedfor induction also are useful, as repeat boluses or con-stant rate infusion, for maintenance of anesthesia (seeTable 2–1). Other drugs (adjunct agents, Table 2–1)serve a variety of roles including sparing the more car-diorespiratory depressing drugs used for induction andmaintenance and muscle relaxation.
The following alphabetical list (by chemical name)summarizes drugs that might be used in veterinary anes-thesia (MOA is mechanism of action; DOA is duration ofaction, these numbers are only guidelines as DOA isinfluenced significantly by concurrently administereddrugs and individual patient status). Route of adminis-tration for every agent is listed in parentheses after DOAand includes intravenous (IV), intramuscular (IM),
12 Pharmacology and Application of Parenteral Anesthetic Agents
subcutaneous (SC), and per os (PO). In general, theonset of effect occurs within 5 minutes for drugs admin-istered intravenously. When drugs are administeredintramuscularly, onset of effect is in 15 minutes; subcuta-neous administration requires a slightly longer time totake effect (20–30 minutes). Common tradenames(USA; UK* or USA and UK**) for some of the agentshave been listed in parentheses after the chemical name.Drug dosages are listed in Appendix 1 and in those chap-ters discussing protocols for individual animal species.
Drug: Acepromazine (Promace; Acetylpro-mazine*)
Class: Phenothiazine tranquilizer (major)
MOA: Antiadrenergic, anticholinergic, antihist-aminic, antidopaminergic
DOA: Dose dependent; 2–3 hr (prolonged inhepatic-compromised, geriatric, andpediatric patients); (IV, IM, SC, PO)
Effect: Calming effect; decreased motor activity;antiemetic; no analgesia
Adverse: Hypotension, penile paralysis (equine),decreased seizure threshold, prolongedduration with liver disease; anecdotalreports of profound respiratory and car-diovascular depression in Boxers
Approved: Horses, cats, dogs
Pharmacology and Application of Parenteral Anesthetic Agents 13
Drug: Alfentanil (Alfenta; Rapifen*): Schedule II
Class: Opioid agonist
MOA: Activates µ opioid receptors
DOA: <30 minutes; used as constant rate infu-sion; (IV)
Effect: Analgesia, sedation
Adverse: Respiratory depression, bradycardia,excitement in some species
Approved: None; rarely used in veterinary medicine
Drug: Atipamezole (Antisedan)
Class: Alpha2 receptor antagonist
MOA: Blocks alpha1 and alpha2 receptors
DOA: >120 minutes; (IM)
Effect: Reverses effects of alpha2 agonists
Adverse: Excitement, tremors, salivation, vomiting,diarrhea
Approved: Dogs
Drug: Atracurium (Tracrium**)
Class: Competitive nondepolarizing neuromus-cular blocking agent
MOA: Competitive blockade of acetylcholinereceptors at neuromuscular junction
DOA: <30 minutes (undergoes Hofmann elimi-nation: spontaneous nonenzymatic
14 Pharmacology and Application of Parenteral Anesthetic Agents
degradation at body pH; also metabo-lized by esterases); (IV)
Effect: Reversible skeletal muscle relaxation
Adverse: Respiratory paralysis (must support respi-ration), minimal cardiovascular effects,may cause histamine release
Approved: None
Drug: Atropine
Class: Anticholinergic
MOA: Competitive blockade of muscarinicreceptors
DOA: 60–90 min (some species variation); (IV,IM, SC)
Effect: Parasympatholytic: increased heart rate,decreased salivation/secretions, dilatedpupils; gastrointestinal stasis, increasesphysiologic dead space (bronchodilation)
Adverse: Tachycardia, arrhythmias, colic (equine)
Approved: Dogs, cats, cattle, horses, sheep
Drug: Azaperone (Stresnil**)
Class: Butyrophenone tranquilizer (major)
MOA: Antiadrenergic, anticholinergic, antihist-aminic, antidopaminergic
DOA: 2–4 hr; (IV, IM)
Pharmacology and Application of Parenteral Anesthetic Agents 15
Effect: Calming effect; decreased motor activity;antiemetic; no analgesia
Adverse: Extrapyramidal effects (tremors, rigidity)are more common compared to acepro-mazine; personality change possible;hypotension
Approved: Swine
Drug: Bupivacaine (Marcaine**): 0.5%
Class: Local anesthetic agent (amide)
MOA: Blocks nerve transmission by blocking Nachannel and preventing excitation-conduction process
DOA: 4–6 hr; (epidural, local infiltration)
Effect: Reversible prevention of nerve transmis-sion; thus motor, sensory, and autonomicfunction is temporarily inhibited
Adverse: CNS excitation, seizures, respiratoryparalysis, hypotension, hypothermia, ven-tricular arrhythmias
Approved: None
Drug: Buprenorphine (Buprenex; Temgesic*;Vetergesic*): Schedule V
Class: Opioid partial agonist
MOA: Activates opioid receptors in brain andspinal cord
16 Pharmacology and Application of Parenteral Anesthetic Agents
DOA: 6–12 hr; (IV, IM, SC)
Effect: Analgesia; minimal sedation
Adverse: Respiratory depression (less than withpure opioid agonists), bradycardia, flatu-lence, defecation, hypothermia; may bemore difficult to reverse due to highreceptor affinity
Approved: None
Drug: Butorphanol (Torbugesic**; Torbutrol**): Schedule IV
Class: Opioid agonist/antagonist
MOA: Activates (�) and blocks (µ) opioidreceptors in brain and spinal cord
DOA: 1–2 hr; (IV, IM, SC, PO)
Effect: Analgesia, sedation
Adverse: Respiratory depression (less than withpure opioids), bradycardia, flatulence,defecation, hypothermia
Approved: Horses, dogs
Drug: Carfentanil (Wildnil): Schedule II(requires DEA special user’s permit)
Class: Opioid agonist
MOA: Activates opioid µ receptors
DOA: Prolonged if not reversed; (IM)
Pharmacology and Application of Parenteral Anesthetic Agents 17
Effect: Analgesia, sedation, immobilization
Adverse: Hypoventilation, excitement (somespecies), hypothermia, muscle fascicula-tions
Approved: Animal use only, reserved for use inimmobilization of wildlife and exoticspecies
Drug: Chloral hydrate: Schedule IV
Class: Sedative-hypnotic
MOA: CNS depression is due to active metabolites
DOA: Dose dependent: <2 hr for sedativedosages; (IV, PO)
Effect: Sedation at low doses; general anestheticat high doses; poor analgesic effects
Adverse: Minimal at sedative dosages; anestheticdoses have high incidence of cardiopul-monary arrest
Approved: None; once available in combinationwith pentobarbital and magnesium sul-fate for use in large animals
Drug: cis-Atracurium (Nimbex)
Class: Competitive nondepolarizing neuromus-cular blocking agent
18 Pharmacology and Application of Parenteral Anesthetic Agents
MOA: Competitive blockade of acetylcholinereceptors of neuromuscular junction
DOA: <20–30 min (undergoes Hofmann elimi-nation: spontaneous nonenzymaticdegradation at body pH); (IV)
Effect: Reversible skeletal muscle relaxation
Adverse: Respiratory paralysis (must control respi-ration), minimal cardiovascular effects
Approved: None
Drug: Desflurane (Suprane)
Class: Methyl ether inhalation agent
MOA: Reversible depression of central nervoussystem
DOA: Not applicable
Effect: Unconsciousness, analgesia, musclerelaxation
Adverse: Dose-dependent cardiopulmonarydepression (slightly less than otherinhalation agents at equivalent MAC con-centrations)
Approved: None
Drug: Detomidine (Dormosedan)
Class: Alpha2 agonist
MOA: Activates CNS alpha2 receptors, whichinhibit neurotransmitter release in brain
Pharmacology and Application of Parenteral Anesthetic Agents 19
DOA: Dose dependent; 75–120 min; (IV, IM)
Effect: Sedation, analgesia, muscle relaxation
Adverse: Bradycardia, conduction disturbances,hypotension, respiratory depression,hypoxia
Approved: Horses
Drug: Diazepam (Valium**): Schedule IV
Class: Benzodiazepine tranquilizer (minor)
MOA: Activates CNS benzodiazepine receptors,which increase inhibitory neurotransmit-ters (i.e., GABA, glycine)
DOA: <3 hr; (IV, IM, PO)
Effect: Mild sedation, muscle relaxation,enhances effect of concurrently usedagents
Adverse: Excitement in some species (horses,dogs), hepatoxicity has been reportedwith PO administration in cats
Approved: Dog
Drug: Diprenorphine (Revivon*, M50-50)
Class: Opioid agonist/antagonist
MOA: Blocks opioid receptors
DOA: Short (renarcotization following reversalof potent opioids has been reported);(IV, IM)
20 Pharmacology and Application of Parenteral Anesthetic Agents
Effect: Used to antagonize etorphine
Adverse: Opioid sedation and respiratory depres-sion may persist with overdose
Approved: Animal use only, for reversal of etorphinein wildlife and exotic species
Drug: Edrophonium (Tensilon)
Class: Acetylcholinesterase inhibitor
MOA: Inhibits acetylcholinesterase and allowsaccumulation of ACh, enhances AChrelease, induces repetitive firing of themotor nerve terminal
DOA: Onset of action is rapid (1–2 min); dura-tion relatively short; (IV)
Effect: Antagonize nondepolarizing neuromus-cular blockers to restore neuromusculartransmission
Adverse: Parasympathetic stimulation: bradycar-dia, airway constriction, increased secretions
Approved: None
Drug: Enflurane (Ethrane**): an isomer of isoflurane
Class: Methyl ether: inhalation agent
MOA: Reversible depression of central nervoussystem
Pharmacology and Application of Parenteral Anesthetic Agents 21
DOA: Not applicable
Effect: Unconsciousness, muscle relaxation
Adverse: Dose-dependent cardiac and respiratorydepression
Approved: None
Drug: Etomidate (Amidate; Hypnomidate*)
Class: Imidazole
MOA: Nonbarbiturate sedative-hypnotic
DOA: <10 min; (IV)
Effect: Rapid loss of consciousness of short dura-tion, minimal cardiopulmonary depres-sion
Adverse: Pain on injection, myoclonus, vomiting(minimized with premedication); depres-sion of adrenal function
Approved: None
Drug: Etorphine (M-99): Schedule II
Class: Opioid agonist
MOA: Activates µ opioid receptors
DOA: <2 hr; (IV, IM)
Effect: Sedation, analgesia, immobilization,80–1,000 times as potent as morphine
Adverse: Profound respiratory depression, brady-cardia, hypertension
22 Pharmacology and Application of Parenteral Anesthetic Agents
Approved: Animal use only: exotic animal immobi-lization
Drug: Fentanyl (Sublimaze**): Schedule II
Class: Opioid agonist
MOA: Activates µ opioid receptors
DOA: <1 hr; used as constant rate infusion (IV)or transdermal patch
Effect: Analgesia, sedation, 75–125 times aspotent as morphine
Adverse: Respiratory depression, bradycardia,excitement in some species
Approved: None
Drug: Flumazenil (Romazicon)
Class: Benzodiazepine receptor antagonist
MOA: Competes with benzodiazepines forreceptor
DOA: 2–3 hr; (IV)
Effect: Specific reversal of benzodiazepine tran-quilizers
Adverse: Rare
Approved: None
Drug: Gallamine (Flaxedil**): currently notavailable commercially
Pharmacology and Application of Parenteral Anesthetic Agents 23
Class: Nondepolarizing neuromuscular blocker
MOA: Competitive blockade of acetylcholinereceptors of neuromuscular junction;prevents muscle contraction
DOA: <30 min; (IV)
Effect: Reversible skeletal muscle relaxation
Adverse: Respiratory paralysis, tachycardia, hyper-tension
Approved: None (has been used in reptiles forimmobilization)
Drug: Glycopyrrolate (Robinul)
Class: Anticholinergic
MOA: Blocks effect of acetylcholine at mus-carinic receptors
DOA: 2–4 hr; (IV, IM, SC)
Effect: Parasympatholytic: increased heart rate,decreased respiratory secretions,increases physiologic dead space (bron-chodilation), does not cross placental orblood-brain barrier
Adverse: Ileus, sinus tachycardia
Approved: Dog, cat
Drug: Guaifenesin (Guailaxin; Glycerol guaiacolate)
Class: Central-acting muscle relaxant
24 Pharmacology and Application of Parenteral Anesthetic Agents
MOA: Depresses internuncial neuron transmis-sion; central-acting muscle relaxant
DOA: Dose dependent; 30 min; (IV)
Effect: Muscle relaxation, sedation
Adverse: Very safe although overdose can occur,which manifests as forelimb rigidity fol-lowed by respiratory paralysis
Approved: Horses
Drug: Halothane (Fluothane**)
Class: Fluorinated hydrocarbon inhalationanesthetic
MOA: Reversible depression of central nervoussystem
DOA: Not applicable
Effect: Unconsciousness, muscle relaxation
Adverse: Dose-dependent cardiopulmonarydepression, ventricular arrhythmias
Approved: Dogs, cats, nonfood animals
Drug: Isoflurane (Aerrane, Isoflo; Forane**)
Class: Methyl ether inhalation anesthetic
MOA: Reversible depression of central nervoussystem
DOA: Not applicable
Effect: Unconsciousness, muscle relaxation
Pharmacology and Application of Parenteral Anesthetic Agents 25
Adverse: Dose-dependent cardiopulmonarydepression (relatively less thanhalothane)
Approved: Horses, dogs
Drug: Ketamine (Ketaset; Ketalar*; Vetalar**)
Class: Dissociative agent
MOA: Depresses thalamoneocortical system;activates limbic system; analgesic effectsare associated with opioid (agonist) andN-methyl-D-aspartate receptor (antago-nist) interaction
DOA: Dose and species dependent; 15–60 min;(IV, IM)
Effect: Catalepsy, superficial analgesia, poorvisual analgesia, amnesia, immobility
Adverse: Muscle rigidity, seizures, increased secre-tions, negative inotropic agent but central catecholamine release causesincreased ABP and HR, increased ocularand intracranial pressure
Approved: Cats, primates
Drug: Lidocaine (Xylocaine**): 2.0%
Class: Local anesthetic agent (amide)
MOA: Blocks sodium influx and thus preventsnerve depolarization and conduction
26 Pharmacology and Application of Parenteral Anesthetic Agents
DOA: 90–200 min; (epidural, local infiltration)
Effect: Blocks pain, motor, and sympatheticfibers; also used IV to treat ventriculararrhythmias
Adverse: Hypotension due to vasodilation; respira-tory arrest is possible when given epidu-rally; seizures at high doses
Approved: None
Drug: Medetomidine (Dormitor)
Class: Alpha2 agonist
MOA: Activates CNS alpha2 receptors, whichinhibit neurotransmitter release in brain
DOA: Dose and species dependent; 60–120min; (IV, IM, SC)
Effect: Sedation, analgesia, muscle relaxation
Adverse: Bradycardia, conduction disturbances,hypotension, respiratory depression,hypoxia
Approved: Dogs
Drug: Meperidine (Demerol; Pethidine*):Schedule II
Class: Opioid agonist
MOA: Activates µ receptors in CNS and otherorgans
Pharmacology and Application of Parenteral Anesthetic Agents 27
DOA: <2 hr; (IM, SC)
Effect: Analgesia, sedation, increases venouscapacitance
Adverse: Respiratory depression, flatulence, con-stipation, bradycardia, can cause hista-mine release with rapid IV injection,excitement possible in cats, horses
Approved: None
Drug: Mepivicaine (Carbocaine-V): 1–2%
Class: Local anesthetic agent (amide)
MOA: Blocks sodium influx and thus preventsnerve depolarization and conduction
DOA: 120–240 min; (epidural, local infiltration)
Effect: Blocks pain, motor and sympatheticfibers
Adverse: Hypotension due to vasodilation and res-piratory arrest are possible when givenepidurally; seizures and cardiotoxicitywith overdose
Approved: None
Drug: Methohexital (Brevital; Brevane; Brietal*): Schedule IV
Class: Ultrashort-acting oxybarbiturate
MOA: Sedative-hypnotic; CNS depression byaction on barbiturate receptors
28 Pharmacology and Application of Parenteral Anesthetic Agents
DOA: <15 min; (IV)
Effect: Sedation to unconsciousness (dosedependent)
Adverse: Respiratory depression (apnea), myocar-dial depression, excitement, muscletremors, seizures during recovery
Approved: None
Drug: Methoxyflurane (Metofane**;Penthrane)
Class: Methyl ether inhalation anesthetic
MOA: Reversible depression of central nervoussystem
DOA: Not applicable
Effect: Unconsciousness, analgesia, musclerelaxation
Adverse: Dose-dependent cardiopulmonarydepression; prolonged recovery; renal toxi-city due to metabolites
Approved: Small and large animals, birds
Drug: Midazolam (Versed; Hypnovel*): Schedule IV
Class: Benzodiazepine tranquilizer (minor)
MOA: Activates CNS benzodiazepine receptors,which increase inhibitory neurotransmit-tors (i.e., GABA, glycine)
Pharmacology and Application of Parenteral Anesthetic Agents 29
DOA: <2 hr (duration is slightly less thandiazepam); (IV, IM, SC)
Effect: Mild sedation, muscle relaxation; workswell IV or IM
Adverse: Excitement in some species, respiratorydepression
Approved: None
Drug: Morphine (Duromorph**): Schedule II
Class: Opioid agonist
MOA: Activates µ opioid receptors in CNS andother organs
DOA: 4 hr; (IM, SC, PO)
Effect: Analgesia, sedation, alleviates pulmonaryedema by increasing venous capacitance;provides 10–24 hr of analgesia as far for-ward as the thoracic limbs when adminis-tered epidurally.
Adverse: Respiratory depression, flatulence, con-stipation, histamine release with IVadministration; excitement possible inhorses and cats
Approved: None
Drug: Nalbuphine (Nubain)
Class: Opioid agonist/antagonist
30 Pharmacology and Application of Parenteral Anesthetic Agents
MOA: Antagonizes µ receptor, activates kappareceptors
DOA: 2–3 hr; (IV, IM, SC)
Effect: Analgesia, sedation
Adverse: Minimal respiratory depression
Approved: None
Drug: Nalmefene (Revex)
Class: Opioid antagonist
MOA: Antagonizes all opioid receptors
DOA: Longer acting than naloxone; (IV, IM,SC)
Effect: Reverses effects of opioid agonists,including respiratory depression andanalgesia
Adverse: Stimulates sympathetic nervous system;potential for cardiac arrhythmias
Approved: None
Drug: Naloxone (Narcan**)
Class: Opioid antagonist
MOA: Antagonizes all opioid receptors
DOA: 30–45 min; (IV, IM, SC)
Effect: Reverses the effects of opioid agonists,including respiratory depression and
Pharmacology and Application of Parenteral Anesthetic Agents 31
analgesia; has been used in the treatmentof hemorrhagic shock
Adverse: Stimulates sympathetic nervous system:potential for cardiac arrhythmias
Approved: None
Drug: Naltrexone (Trexonil)
Class: Opioid antagonist
MOA: Antagonizes all opioid receptors
DOA: Longer acting than naloxone; (IV, IM,SC)
Effect: Reverses the effects of opioid agonists,including respiratory depression andanalgesia; available as an oral prepara-tion for humans
Adverse: Stimulates sympathetic nervous system:potential for cardiac arrhythmias
Approved: Used for reversal of carfentanil in exoticspecies
Drug: Neostigmine (Prostigmine; Stiglyn)
Class: Acetylcholinesterase inhibitor
MOA: Inhibits acetylcholinesterase and allowsaccumulation of ACh, enhances AChrelease, induces repetitive firing of themotor nerve terminal
32 Pharmacology and Application of Parenteral Anesthetic Agents
DOA: Onset of action is 7–10 min; duration ofaction is relatively short; (IV)
Effect: Antagonize nondepolarizing neuromus-cular blockers to restore neuromusculartransmission, onset of action is rapid
Adverse: Parasympathetic stimulation includingbradycardia, airway constriction,increased secretions
Approved: None
Drug: Oxymorphone (Numorphan):Schedule II
Class: Opioid agonist
MOA: Activates µ receptors
DOA: 2–6 hr; (IV, IM, SC)
Effect: Analgesia, sedation
Adverse: Respiratory depression, bradycardia,excitement in some species
Approved: Dogs, cats
Drug: Pancuronium (Pavulon**)
Class: Competitive nondepolarizing neuromus-cular blocker
DOA: 30–45 min; (IV)
MOA: Competitive blockade of acetylcholinereceptors of neuromuscular junction
Pharmacology and Application of Parenteral Anesthetic Agents 33
Effect: Reversible skeletal muscle paralysis
Adverse: Respiratory paralysis (must control venti-lation), minimal cardiovascular effectsalthough may cause transient tachycar-dia; prolonged effect in renal- andhepatic-compromised patients
Approved: None
Drug: Pentazocine (Talwin): Schedule IV
Class: Opioid agonist/antagonist
MOA: Activates (�) and blocks (µ) opioidreceptors in brain and spinal cord: lowpotency
DOA: <2 hr; (IM, SC)
Effect: Analgesia, sedation; 0.1–0.3 timespotency of morphine
Adverse: Respiratory depression (less than withpure opioids), bradycardia, flatulence,defecation, hypothermia
Approved: Horses, dogs
Drug: Pentobarbital (Nembutal; Beuthanasia-D): Schedule II
Class: Short-acting oxybarbiturate
MOA: Sedative-hypnotic; CNS depression byaction on barbiturate receptors
34 Pharmacology and Application of Parenteral Anesthetic Agents
DOA: Species and dose dependent; <1.5 hr;(IV, PO)
Effect: Sedation to unconsciousness
Adverse: CNS/respiratory depression (apnea),myocardial depression, leukopenia,splenic engorgement, excitement (stageII) due to inadequate quantity or rate ofdosing
Approved: Dogs
Drug: Phenobarbital: Schedule IV
Class: Long-acting oxybarbiturate; routesinclude IV and PO
MOA: Sedative/hypnotic; CNS depression byaction on barbiturate receptors
DOA: Dose dependent; 12–24 hr; (IV, PO)
Effect: Sedation to unconsciousness (dosedependent); used to control seizures: (16mg/kg IV, 2–4 mg/kg PO BID (small ani-mal); 2–10 mg/kg IV/PO every 8–12 hr(equine)
Adverse: CNS/respiratory depression (apnea),myocardial depression, polyuria/polydip-sia/polyphagia
Approved: None
Pharmacology and Application of Parenteral Anesthetic Agents 35
Drug: Procaine (Novocaine)
Class: Local anesthetic (ester linked)
MOA: Blocks sodium influx and thus preventsnerve depolarization and conduction
DOA: 60–90 min; (local infiltration)
Effect: Blocks pain, motor, and sympatheticfibers
Adverse: May cause allergic reaction
Approved: None
Drug: Propofol (Rapinovet**)
Class: Alkyl phenol structure
MOA: Sedative/hypnotic: CNS depression byenhancing GABA activity in the brainand decreasing cerebral metabolic rate
DOA: <15 min; (IV)
Effect: Sedation to unconsciousness dependingon dosage; muscle relaxation
Adverse: Respiratory depression (apnea) especiallyif administered rapidly, myocardialdepression, hypotension, Heinz body for-mation (oxidative injury) in cats whengiven repeatedly due to phenolic struc-ture
Approved: Dogs
36 Pharmacology and Application of Parenteral Anesthetic Agents
Drug: Pyridostigmine (Regonol)
Class: Acetylcholinesterase inhibitor
MOA: Inhibit acetylcholinesterase and allowaccumulation of ACh, enhance AChrelease, induce repetitive firing of themotor nerve terminal
DOA: Onset of action is 12–16 min and dura-tion 40% longer than neostigmine andedrophonium; (IV)
Effect: Antagonize nondepolarizing neuromus-cular blockers to restore neuromusculartransmission
Adverse: Parasympathetic stimulation, includingbradycardia, airway constriction,increased secretions
Approved: None
Drug: Romifidine (Sedivet*)
Class: Alpha2 agonist
MOA: Activates CNS alpha2 receptors, whichinhibit neurotransmitter release in brain
DOA: Dose dependent; >120 min; (IV, IM, SC)
Effect: Sedation, analgesia, muscle relaxation
Adverse: Bradycardia, conduction disturbances,hypotension, respiratory depression,hypoxia
Pharmacology and Application of Parenteral Anesthetic Agents 37
Approved: Not currently approved in the UnitedStates, but studies have been publishedfor dosages in dogs and horses
Drug: Sevoflurane (Ultrane)
Class: Methyl ether inhalation agent
MOA: Reversible depression of central nervoussystem
DOA: Not applicable
Effect: Unconsciousness, muscle relaxation
Adverse: Dose-dependent cardiopulmonarydepression (similar to isoflurane)
Approved: None
Drug: Succinylcholine (Anectine**; Sucostrin;Scoline*)
Class: Depolarizing noncompetitive neuromus-cular blocker
MOA: Depolarizes nicotinic receptors on mus-cle motor end plate and prevents neuro-muscular transmission.
DOA: <15 min; (IV)
Effect: Nonreversible (short-duration) skeletalmuscle paralysis
Adverse: Respiratory paralysis (necessary equip-ment to provide mechanical ventilationshould be available if this drug is used);
38 Pharmacology and Application of Parenteral Anesthetic Agents
prolonged effect with hepatic-compromising diseases due to depend-ency on metabolism by the liver-derivedenzyme, pseudocholinesterase; muscle fasciculations; hyperkalemia; known trigger of malignant hyperthermia
Approved: None
Drug: Sufentanil (Sufenta): Schedule II
Class: Opioid agonist
MOA: Activates µ opioid receptors
DOA: <1 hr; used as constant rate infusion;(IV)
Effect: Analgesia, sedation
Adverse: Respiratory depression, bradycardia,muscle twitching
Approved: None; rarely used in veterinary medicine
Drug: Thiopental (Pentothal; Intraval*):Schedule III
Class: Ultrashort-acting thiobarbiturate
MOA: Sedative/hypnotic; CNS depression byaction on barbiturate receptors
DOA: <15 min; (IV)
Effect: Sedation to unconsciousness (dosedependent), stage II delerium can occurwith inadequate or perivascular dosages
Pharmacology and Application of Parenteral Anesthetic Agents 39
Adverse: Respiratory depression (apnea), myocar-dial depression, cardiac arrhythmias
Approved: Dogs
Drug: Tiletamine; Zolazepam (Telazol):Schedule III
Class: Dissociative agent combined with benzo-diazepine
MOA: Tiletamine: depresses thalamoneocorticalsystem; activates limbic system; analgesiceffects are associated with opioid (ago-nist) and N-methyl-D-aspartate receptor(antagonist) interaction; zolazepam actson benzodiazepine receptors
DOA: Dose and species dependent; 20–80 min;(IM, IV)
Effect: Catalepsy, superficial analgesia, amnesia,immobility, muscle relaxation
Adverse: Increased secretions, muscle rigidity insome species, negative inotrope but cen-tral catecholamine release promotesincreased BP and HR, increased ocularand intracranial pressure
Approved: Cats, dogs
Drug: Tolazoline (Tolazine)
Class: Alpha1 and alpha2 receptor antagonist
40 Pharmacology and Application of Parenteral Anesthetic Agents
MOA: Occupies and antagonizes alpha2 recep-tors (least specific for the alpha2 recep-tor)
DOA: 2 hr; (IV, IM)
Effect: Reverses effects of alpha2 agonists
Adverse: Hypotension with rapid injection due tovasodilatory effect, excitement, tremors,salivation, tachypnea
Approved: Horses
Drug: Tubocurarine (Curare)
Class: Competitive nondepolarizing neuromus-cular blocker
MOA: Competitive blockade of acetylcholinereceptors of neuromuscular junction
DOA: <30 min; (IV)
Effect: Reversible skeletal muscle relaxation
Adverse: Respiratory paralysis (must control respi-ration), causes histamine release thatresults in hypotension and bronchocon-striction
Approved: None
Drug: Vecuronium (Norcuron)
Class: Competitive nondepolarizing neuromus-cular blocker
Pharmacology and Application of Parenteral Anesthetic Agents 41
MOA: Competitive blockade of acetylcholinereceptors of neuromuscular junction
DOA: <30 min; (IV)
Effect: Reversible skeletal muscle relaxation
Adverse: Respiratory paralysis (must control respi-ration), minimal cardiovascular effects;significant hepatic dysfunction will pro-long effect
Approved: None
Drug: Xylazine (Rompun**; Ansed)
Class: Alpha2 agonist
MOA: Activates CNS alpha2 receptors, whichinhibit neurotransmitter release in brain
DOA: Dose and species dependent; 15–30 min(analgesia); 1–2 hr (sedation); (IV, IM,SC)
Effect: Sedation, analgesia, muscle relaxation
Adverse: Bradycardia, conduction disturbances,hypotension, respiratory depression,hypoxia
Approved: Horses (10% formulation); dogs and cats(2% formulation); deer and elk
42 Pharmacology and Application of Parenteral Anesthetic Agents
Drug: Yohimbine (Yobine)
Class: Alpha2 antagonist
MOA: Blocks alpha2 receptors; also has antisero-tonin activity
DOA: <1 hr; (IV, IM)
Effect: Reverses effects of alpha2 agonists
Adverse: Hypotension with rapid injection due tovasodilatory effect, excitement, tremors,salivation, tachypnea
Approved: Dogs
Pharmacology and Application of Parenteral Anesthetic Agents 43
Tab
le 2
–1
Cat
ego
ries
and M
ajor
Effect
s of
Inje
ctab
le A
nest
hetic
Age
nts
Use
d in
Vete
rinar
y M
edic
ine (
text
has
speci
fic
agent
info
rmat
ion)
Use
/Cate
go
ryEff
ect
s/C
om
men
ts
Pre
med
icati
on
s
Antic
holin
ergic
sD
ecre
ase
secr
etio
ns,
pre
vent
bra
dyc
ardia
Atropin
e
Gly
copyr
rola
te
Tranquili
zers
Alle
viat
e an
xiet
y an
d d
ecre
ase
moto
r ac
tivity
; pro
vide
no
anal
gesi
a, s
yner
gize
act
ivity
of
oth
er a
gents
; pro
mote
m
usc
le r
elax
atio
n
Maj
or
tran
quili
zers
:
Ace
pro
maz
ine
Use
is
rela
tivel
y co
mm
on in a
ll sp
ecie
s(p
hen
oth
iazi
ne)
Aza
per
one
Use
is
pre
dom
inan
tly in s
win
e an
d s
om
e ex
otic
spec
ies
(buty
rophen
one)
Min
or
tran
quili
zers
:
Dia
zepam
M
inim
al s
edat
ion u
nle
ss c
om
bin
ed w
ith o
pio
id o
r al
pha 2
(ben
zodia
zepin
e)ag
onis
t
Mid
azola
m
More
rap
id o
nse
t of
effe
ct a
nd n
ot
pai
nfu
l w
hen
giv
en IM
or
44 Pharmacology and Application of Parenteral Anesthetic Agents
(ben
zodia
zepin
e)SC
(co
mpar
ed t
o d
iaze
pam
, w
hic
h is
reco
mm
ended
for
IVuse
only
)
Ben
zodia
zepin
eSp
ecifi
c re
vers
al a
gent
for
ben
zodia
zepin
esanta
gonis
t
Flum
azen
il
Alp
ha
2ag
onis
tsPro
vide
anal
gesi
a, s
edat
ion, an
d m
usc
le r
elax
atio
n; ca
rdio
vas-
cula
r ef
fect
s ar
e pro
found (
conduct
ion d
istu
rban
ces,
hyp
ote
nsi
on)
but
usu
ally
wel
l-tole
rate
d in h
ealth
y pat
ients
;si
gnifi
cant
spar
ing
effe
ct w
hen
use
d p
rior
to inhal
ant
anes
-th
esia
Xyla
zine
Short
est
dura
tion o
f ef
fect
; �
2:�
1se
lect
ivity
bin
din
g ra
tio
= 1
60
Det
om
idin
eLo
nge
st d
ura
tion o
f ef
fect
; �
2:�
1se
lect
ivity
bin
din
g ra
tio =
260
Med
etom
idin
eG
reat
est
�2:�
1se
lect
ivity
bin
din
g ra
tio =
1620
Rom
ifidin
eN
ot
curren
tly a
ppro
ved f
or
use
in U
nite
d S
tate
s; �
2:�
1
sele
ctiv
ity b
indin
g ra
tio =
340
Alp
ha
2an
tago
nis
tsSp
ecifi
c re
vers
al a
gents
for
alpha 2
agonis
ts; m
ay p
rom
ote
hyp
ote
nsi
on t
hro
ugh
vas
odila
tory
effec
ts e
spec
ially
when
adm
inis
tere
d r
apid
ly IV
Yohim
bin
e�
2:�
1se
lect
ivity
bin
din
g ra
tio =
40
(contin
ues
)
Pharmacology and Application of Parenteral Anesthetic Agents 45
Tab
le 2
–1
(Continued)
Use
/Cate
go
ryEff
ect
s/C
om
men
ts
Tola
zolin
eN
onsp
ecifi
c an
tago
nis
t of
�1
and �
2re
cepto
rs
Atip
amez
ole
�2:�
1se
lect
ivity
bin
din
g ra
tio =
8526
Opio
ids
Pro
vide
anal
gesi
a an
d s
edat
ion (
deg
ree
of
effe
cts
vary
with
ag
ent)
; use
d f
or
pre
emptiv
e an
d p
ost
oper
ativ
e an
alge
sia.
(Anal
gesi
c pote
nci
es r
elat
ive
to m
orp
hin
e [1
] ar
e lis
ted in
par
enth
eses
for
each
age
nt.)
Opio
id (
µ)
agonis
ts:
Maj
or
side
effe
ct is
resp
irato
ry d
epre
ssio
n; gr
eate
st p
ote
ntia
l fo
r ab
use
Morp
hin
e(1
)
Mep
erid
ine
(0.5
)
Hyd
rom
orp
hone
(5)
Oxy
morp
hone
(8–10)
Fenta
nyl
(75–125)
Alfe
nta
nil
(20–75)
Sufe
nta
nil
(600–1000)
Car
fenta
nil
(10,0
00)
Etorp
hin
e(8
0–1000)
46 Pharmacology and Application of Parenteral Anesthetic Agents
Part
ial µ
agonis
t:Le
ss r
espira
tory
dep
ress
ion
Bupre
norp
hin
e(2
5–50)
Opio
id a
gonis
t (�
)/Le
ss r
espira
tory
dep
ress
ion c
om
par
ed t
o µ
agonis
tsan
tago
nis
ts (
µ):
Buto
rphan
ol
Com
monly
use
d in v
eter
inar
y m
edic
ine;
moder
ate
anal
gesi
a;
may
be
use
d t
o r
ever
se µ
agonis
ts; (2
–5)
Nal
buphin
eN
ot
sched
ule
d b
ut
min
imal
ly e
ffec
tive
as a
n a
nal
gesi
c ag
ent;
may
be
use
d t
o r
ever
se µ
agonis
ts; (0
.5)
Penta
zoci
ne
(0.1
)
Nal
orp
hin
eU
sed f
or
anta
gonis
t ef
fect
, ra
rely
use
d c
linic
ally
Dip
renorp
hin
eU
sed f
or
anta
gonis
t ef
fect
; sh
ort
dura
tion o
f ac
tion m
ay a
llow
”r
enar
cotiz
atio
n“
afte
r re
vers
al
Opio
id a
nta
gonis
ts:
Use
d “
to e
ffec
t” t
o r
ever
se o
pio
id a
gonis
ts a
nd a
gonis
t/an
tago
nis
ts
Nal
oxo
ne
Short d
ura
tion o
f ac
tion m
ay a
llow
“re
nar
cotiz
atio
n”
afte
r re
vers
al
Nal
trex
one
Nal
mef
ene
Dis
soci
ativ
e agen
tsD
ose
-dep
enden
t ef
fect
pro
vides
quie
ting
and im
mobili
zatio
n
at low
dose
s an
d g
ener
al a
nes
thes
ia a
t hig
her
dosa
ges,
som
atic
anal
gesi
a; p
oor
visc
eral
anal
gesi
a(c
ontin
ues
)
Pharmacology and Application of Parenteral Anesthetic Agents 47
Tab
le 2
–1
(Continued)
Use
/Cate
go
ryEff
ect
s/C
om
men
ts
Ket
amin
e
Tile
tam
ine
(Tel
azol™
)C
om
mer
cial
pro
duct
com
bin
ed w
ith z
ola
zepam
in 1
:1 (
mg)
rat
io
Chlo
ral hyd
rate
Sedat
ive/
hyp
notic
: use
d f
or
larg
e an
imal
sed
atio
n; no longe
r use
d a
s la
rge
anim
al g
ener
al a
nes
thet
ic d
ue
to n
arro
wsa
fety
mar
gin a
nd p
rolo
nge
d r
ecove
ries;
effec
tive
IV, PO
,re
ctal
ly
Ind
uct
ion
/main
ten
an
ce a
gen
ts
Barb
ituate
sSh
ort a
nd u
ltras
hort-a
ctin
g; h
igh p
H m
akes
them
irrita
ting
to
tissu
es
Pento
bar
bita
lSh
ort-a
ctin
g oxy
bar
bitu
rate
; re
cove
ry >
6–24 h
r; r
arel
y use
d f
or
clin
ical
anes
thes
ia d
ue
to a
vaila
bili
ty o
f ag
ents
with
shorter
dura
tion o
f ef
fect
Met
hohex
ital
Ultr
ashort-a
ctin
g oxy
bar
bitu
rate
(ra
pid
ly m
etab
oliz
ed);
not
com
monly
use
d
Thio
pen
tal
Ultr
ashort-a
ctin
g th
iobar
bitu
rate
(ra
pid
ly r
edis
trib
ute
d):
ris
k of
rough
, pro
longe
d r
ecove
ry if
use
d a
s re
pea
ted b
olu
s or
inpre
sence
of
hep
atic
dis
ease
; co
mm
on u
se in v
eter
inar
ypra
ctic
e
48 Pharmacology and Application of Parenteral Anesthetic Agents
Dis
soci
ativ
e agen
tsSe
e ea
rlier
; w
hile
met
abolis
m is
rela
tivel
y ra
pid
, re
pea
t dosa
ges
of
dis
soci
ativ
es w
ill c
ontrib
ute
to r
ough
, pro
longe
dre
cove
ries
(esp
ecia
lly t
ileta
min
e)
Pro
pofo
lPro
duce
s ra
pid
loss
of
consc
iousn
ess;
rec
ove
ry is
fast
due
to
rapid
met
abolis
m, m
akin
g it
use
ful fo
r in
duct
ion a
nd
mai
n-
tenan
ce
Etom
idat
ePro
duce
s ra
pid
loss
of
consc
iousn
ess;
rec
ove
ry is
fast
due
to
rapid
met
abolis
m, m
akin
g it
use
ful fo
r in
duct
ion a
nd
mai
n-
tenan
ce
Ad
jun
ct a
gen
ts
Gly
cery
l gu
aiac
ola
te
Cen
tral
-act
ing
musc
le r
elax
ant
use
d in lar
ge a
nim
als
to r
educe
(g
uai
fenes
in)
require
men
ts o
f in
duct
ion a
nd m
ainte
nan
ce a
gents
; 5 a
nd
10%
(hors
es o
nly
) so
lutio
ns—
10%
solu
tion c
ause
s hem
ol-
ysis
in s
pec
ies
oth
er t
han h
ors
es
Neu
rom
usc
ula
r Act
at
neu
rom
usc
ula
r ju
nct
ion t
o b
lock
neu
rotran
smis
sion,
blo
ckin
g a
gen
tsre
sulti
ng
in m
usc
le p
aral
ysis
; ve
ntil
atory
support is
require
d;
use
ful ad
junct
for
ocu
lar,
orthoped
ic, an
d a
bdom
inal
pro
ce-
dure
s an
d f
or
pat
ients
that
res
ist
mec
han
ical
ven
tilat
ion;
spar
ing
effe
ct o
n c
oncu
rren
tly u
sed d
rugs
; no inher
ent
analg
esic
effec
ts
(contin
ues
)
Pharmacology and Application of Parenteral Anesthetic Agents 49
Tab
le 2
–1
(Continued)
Use
/Cate
go
ryEff
ect
s/C
om
men
ts
Nondep
ola
rizin
g C
om
pet
itive
(re
vers
ible
) in
terfer
ence
with
ace
tylc
holin
e at
co
mpet
itive
post
synap
tic m
usc
le m
embra
ne;
man
y ag
ents
curren
tly
agen
ts:
avai
lable
with
var
iable
dura
tion o
f ac
tion, ca
rdio
vasc
ula
r
effe
cts,
abili
ty t
o induce
his
tam
ine
rele
ase,
dura
tion a
nd
onse
t of
effe
ct a
nd c
ost
(te
xt d
escr
iptio
ns
are
give
n o
nly
for
those
with
curren
t or
his
toric
al, an
d r
elat
ivel
y co
mm
on, use
in v
eter
inar
y m
edic
ine)
Turb
ocu
rarin
eU
se is
larg
ely
rese
rved
for
rese
arch
Gal
lam
ine
Use
is
larg
ely
rese
rved
for
rese
arch
and s
om
e ex
otic
spec
ies
Pancu
roniu
mRel
ativ
ely
long
dura
tion o
f ef
fect
Vecu
roniu
mIn
term
edia
te d
ura
tion o
f ef
fect
Atrac
uriu
mSh
ort
dura
tion o
f ef
fect
cis-
Atrac
uriu
mSh
ort
dura
tion o
f ef
fect
Miv
acuriu
mSh
ort
dura
tion o
f ef
fect
Rocu
roniu
mIn
term
edia
te d
ura
tion o
f ef
fect
Doxa
curiu
mRel
ativ
ely
long
dura
tion o
f ef
fect
50 Pharmacology and Application of Parenteral Anesthetic Agents
Dep
ola
rizin
g N
onre
vers
ible
dep
ola
rizat
ion o
f post
synap
tic m
usc
le m
embra
ne
nonco
mpet
itive
ag
ents
:
Succ
inyl
cholin
eU
ltras
hort
act
ing,
rap
id o
nse
t; si
de
effe
cts
pre
clude
routin
e use
Ace
tylc
holin
este
rase
Rev
erse
com
pet
itive
NM
Bs
by
allo
win
g ac
etyl
cholin
e to
acc
u-
inhib
itors
:m
ula
te a
t sy
nap
tic c
left a
nd r
esto
re n
orm
al m
usc
le f
unct
ion;
side
effe
cts
are
asso
ciat
ed w
ith s
timula
tion o
f m
usc
arin
icre
cepto
rs a
nd p
reve
nte
d b
y prio
r ad
min
istrat
ion o
f an
anti-
cholin
ergi
c ag
ent
Edro
phoniu
m
Neo
stig
min
e
Pyr
idost
igm
ine
Pharmacology and Application of Parenteral Anesthetic Agents 51
Table 2–2 Properties of an “Ideal” Anesthetic Agent
1. Does not require metabolism for termination of action andelimination (reversible or respiratory elimination).
2. Permits rapid and easily controlled induction, changes inanesthetic depth and recovery.
3. Is not irritating to any tissue.
4. Does not depress cardiopulmonary function.
5. Produces adequate muscle relaxation and analgesia for sur-gical procedures.
6. Is compatible with other drugs.
7. Is nontoxic to the patient and humans.
8. Is inexpensive, stable, and noninflammable.
9. Requires no special equipment for administration.
52 Pharmacology and Application of Parenteral Anesthetic Agents
3
Local/Regional Anesthetic Techniques
Local and regional anesthesia always has been an inte-gral part of large animal practice for economic and prac-tical reasons. The availability and convenience of avariety of general anesthesia options minimized the needto apply these agents in small animals. However, with theever-increasing awareness of pain management in all vet-erinary species, local and regional techniques are gain-ing popularity in small animal practice. Application oflocal and regional agents in animals undergoing generalanesthesia will provide preemptive analgesia and spareanesthetic requirements. While historically such tech-niques have been associated with the local anestheticagents, other drugs, including opioids, alpha2 agonists,and ketamine have been reported to possess analgesic
53
properties when applied by these routes. This chapterdiscusses mainly the application of local anestheticagents used to produce local and regional anesthesia(complete loss of sensation to a body part or region) butalso includes dosage and application of the alpha2 ago-nists. Clinical application of opioids to produce regionalanalgesia (loss of sensitivity to pain) is discussed in Chap-ter 8 (“Pain Management”).
Local anesthetic agents reversibly block actionpotentials along nerve axons by interference with volt-age-gated sodium channels. Two classes (based on theintermediate chain of the molecule), the esters and theamides (Table 3–1), determine drug biotransformation.Esters are readily hydrolyzed in the blood by plasmacholinesterase made in the liver, while amides requirebiotransformation by liver microsomal enzymes. Eventhough lidocaine is well-known for its usefulness intra-venously to treat cardiac ventricular arrhythmias, it andlocal anesthetic agents have several potential adverseeffects, including formation of cardiac arrhythmias(Table 3–2). These adverse effects are minimized whenaccidental intravenous injection is avoided and dosagesremain within recommended maximum safe limits.
The time to effect, potency, and duration of effectdepend on the agent’s physical and chemical properties(see Table 3–1). Lipid solubility influences intrinsicpotency and protein binding is probably the primarydeterminant of duration. The dissociation constant(pKa) is thought to determine the speed of action. The
54 Local/Regional Anesthetic Techniques
Local/Regional Anesthetic Techniques 55
Tab
le 3
–1
Pro
pert
ies
of
Sele
cted L
oca
l A
nest
hetic
Age
nts
Use
d in V
ete
rinar
y M
edic
ine
Agen
tLip
id
pK
aP
rote
in
On
set
of
Du
rati
on
(T
rad
e N
am
e)
Cla
ssP
ote
ncy
*So
lub
ilit
yB
ind
ing
Eff
ect
(min
)
Pro
cain
eEs
ter
—1
8.9
6%
Slow
60–90
(Novo
cain
e)
Chlo
ropro
cain
eEs
ter
11
9.1
7%
Fast
30–60
(Nes
acai
ne)
Lidoca
ine
Am
ide
23.6
7.7
65%
Fast
90–200
(Xyl
oca
ine)
Mep
ivac
aine
Am
ide
22
7.6
75%
Fast
120–240
(Car
boca
ine)
Bupiv
acai
ne
Am
ide
830
8.1
95%
Inte
rme-
180–600
(Mar
cain
e)dia
te
Tetrac
aine
Este
r8
80
8.6
80%
Slow
180–600
(Ponto
cain
e)
*Pote
ncy
is r
elat
ive
to p
roca
ine
(1).
56 Local/Regional Anesthetic Techniques
Table 3–2 Potential Toxic Effects of Local Anesthetics
• Central nervous system
Muscle tremors
Convulsions
Respiratory depression
Generalized CNS depression
• Cardiovascular system
Depression of myocardial contractility
Hypotension
Bradycardia
Ventricular tachycardia/fibrillation: This response hasbeen reported with bupivacaine and may be refractory totreatment and fatal
• Methemoglobinemia
This response most often is linked to benzocaine buthas been reported with other agents
• Allergic reactions
Associated with para-aminobenzoic acid (PABA), ametabolite of the ester local anesthetics and of methyl-paraben, a preservative used in many of the local anesthetics
• Tissue toxicity
Local anesthetic injection has been shown to causereversible skeletal muscle damage and, rarely, neuronaldamage
uncharged base form is most lipid soluble, diffusingreadily across the nerve sheath; dissociation is favored byincreasing pH. This is why efficacy is decreased ininflamed and infected (low pH) tissues.
Local anesthetic agents show a preferential effect onnerve fibers with the order (most to least sensitive) beingpreganglionic sympathetic (B fibers) > small sensory (A-delta fibers) > motor (A-alpha fibers). Sensitivity ofunmyelinated pain (C) fibers to local anesthetic agents issimilar to B fibers, but blockade may be affected by fac-tors other than those influencing the myelinated fibers.Sensation disappears in the order of pain, cold, warmth,touch, then joint and deep pressure and recovers in thereverse order.
Of the many local anesthetic agents available, only afew are commonly used in veterinary medicine, includ-ing lidocaine, mepivacaine, and bupivacaine. A topical5% eutectic mixture of lidocaine and prilocaine (EMLAcream, Astra Pharmaceuticals) applied to unbroken skinalso is effective when applied to animals for such proce-dures as venipuncture but must be applied at least 15–30min in advance. While many techniques have beendescribed for the common domestic species, Tables 3–3through 3–5 describe selected local anesthetic tech-niques that have shown relatively common applicationfor local/regional anesthesia or pain management. Fig-ures 3–1 through 3–4 illustrate the sites for injection forseveral techniques described in Table 3–3.
Local/Regional Anesthetic Techniques 57
Tab
le 3
–3
Sele
cted L
oca
l A
nest
hetic
Tech
niq
ues
in D
ogs
and C
ats
Nerv
es
Are
a A
nest
heti
zed
Tech
niq
ue*
Do
sage
Infrao
rbita
lU
pper
lip
, nose
, ro
of
of
Inse
rt n
eedle
1 c
m c
rania
l0.5
–2 m
l**
(Fig
. 3–1A)
nas
al c
avity
, sk
in c
rania
l to
(an
d a
dva
nce
to)
to infrao
rbita
l fo
ram
enin
frao
rbita
l fo
ram
en e
ither
in
tra-
or
extrao
rally
Trig
emin
alEy
e, o
rbit,
conju
ctiv
a, e
ye-
Inse
rt n
eedle
ven
tral
to z
ygo-1–2 m
l**
(ophth
alm
ic
lids,
ski
n o
f fo
rehea
d:
mat
ic p
roce
ss a
t le
vel of
div
isio
n)
glove
aki
nes
ia m
ay o
ccur
late
ral ca
nth
us,
cra
nia
l to
(Fig
. 3–1C
)ra
mus
of
man
dib
le in
med
ioca
udal
dire
ctio
n t
o
orb
ital fis
sure
Max
illar
y M
axill
a, u
pper
tee
th a
nd
Inse
rt n
eedle
at
90º
angl
e0.2
5–1 m
l**
(Fig
. 3–1B)
lip, nose
ventral
to b
ord
er o
f zy
gom
atic
arc
h, 0.5
cm
caudal
to lat
eral
can
thus
Men
tal
Low
er lip
Inse
rt n
eedle
rost
ral to
1–2 m
l**
(Fig
. 3–1E)
men
tal fo
ram
en a
t le
vel
of
2nd p
rem
ola
r
58 Local/Regional Anesthetic Techniques
Man
dib
ula
rC
hee
k, c
anin
e, inci
sor
teet
h,
Inse
rt n
eedle
at
low
er0.5
–1 m
l**
(infe
rior
muco
sa a
nd s
kin o
f ch
inan
gle
of
jaw
, 1.5
cm
al
veola
r br.)
ro
stra
l to
angu
lar
pro
cess
;(F
ig. 3–1D
)ad
vance
1.5
cm
dors
ally
al
ong
med
ial su
rfac
e of
ram
us
Bra
chia
l ple
xus
Are
a dis
tal to
and incl
udin
g22 g
a, 7
.5 c
m n
eedle
4–6 m
g/kg
(F
ig. 3–2)
the
elbow
inse
rted
med
ial to
(L
)sh
ould
er join
t to
war
d
1.5
–2 m
g/kg
cost
och
ondra
l ju
nct
ion
(B)
par
alle
l to
ver
tebra
e.
Inje
ct w
hile
with
dra
win
g nee
dle
. Asp
irate
firs
t. O
nse
t re
quire
s 20–30
min
IV r
egio
nal
Are
a dis
tal to
tourn
iquet
Apply
tourn
iquet
after
2–3 m
l L
(BIE
R-b
lock
)des
angu
inat
ion o
f lim
b
dilu
ted t
o
with
Esm
arch
ban
dag
e.
5–10 m
l In
ject
into
super
ficia
l w
ith s
alin
eve
in. Li
mit
to 2
hr
(contin
ues)
Local/Regional Anesthetic Techniques 59
Tab
le 3
–3
(Continued)
Nerv
es
Are
a A
nest
heti
zed
Tech
niq
ue*
Do
sage
Inte
rcost
alFo
r th
ora
coto
my,
rib
Blo
ck m
inim
um
of
50.2
5–1 m
l B
frac
ture
s, p
leura
l sp
ace
(2 c
rania
l an
d
per
site
dra
inag
e2 c
audal
to s
ite).
B:
≤3
Cau
dal
bord
er o
f rib
m
g/kg
nea
r in
terv
erte
bra
l fo
ram
en
Inte
rple
ura
lSa
me
as f
or
inte
rcost
al
Req
uire
s pla
cem
ent
of
1–2 m
l B
regi
onal
blo
ckin
terp
leura
l ca
thet
er
Epid
ura
l Anes
thes
ia c
audal
to
22 g
a, 2
.5–7.
5 c
m s
pin
al1 m
l/5 k
g re
gional
um
bili
cus
nee
dle
(25 g
a hyp
o-
L,B; M
axi-
(Fig
. 3–3)
der
mic
nee
dle
for
mum
of
6
pat
ients
<2 k
g). Lu
mbo-
ml has
sa
cral
spac
e: n
eedle
bee
nin
troduce
d o
n d
ors
al
advi
sed
mid
line
just
cau
dal
to
line
bet
wee
n ilia
c w
ings
. N
eedle
adva
nce
d u
ntil
dis
tinct
“pop”
is f
elt
(inte
r-
60 Local/Regional Anesthetic Techniques
arcu
ate
ligam
ent)
. M
ay
obse
rve
tail
flick
. C
hec
k fo
r C
SF (
if pre
sent
dec
reas
e dose
by
50%
or
with
dra
w 1
–2 m
m)
Dig
ital blo
ck
Pro
vide
anal
gesi
a fo
rSu
per
ficia
l ra
dia
l n:
0.1
–0.3
ml
(Fig
. 3–4)
onyc
hec
tom
ydors
om
edia
l ca
rpus;
B p
er s
ite
uln
ar n
(dors
al
≤3 m
g/kg
cuta
neo
us
br)
: la
tera
l ca
rpus;
med
ian n
&
uln
ar n
(pal
mar
br)
: pal
mar
car
pus
L =
lidoca
ine;
B =
bupiv
acai
ne
*U
se 2
5 g
a nee
dle
unle
ss o
ther
wis
e in
dic
ated
.
**D
ose
is for
2%
lidoca
ine
or
0.5
% b
upiv
acai
ne
in d
ogs
. The
dose
in c
ats
is 0
.25–0.5
ml.
Tota
l dosa
ge for
lidoca
ine
should
not ex
ceed
4–5 m
g/kg
for
lidoca
ine
and 2
mg/
kg for
bupiv
acai
ne
for
eith
er s
pec
ies.
Local/Regional Anesthetic Techniques 61
Tab
le 3
–4
Sele
cted L
oca
l A
nest
hetic
Tech
niq
ues
in H
ors
es
Nerv
e(s
)A
rea A
nest
heti
zed
Tech
niq
ue
Do
sage*
Supra
orb
ital
Upper
lid
Inse
rt 2
5 g
a nee
dle
into
5 m
l(f
ronta
l)su
pra
orb
ital fo
ram
en loca
ted
5–7 c
m a
bove
med
ial
canth
us
at d
epth
of
1.5
–2 c
m,
inje
ctin
g sh
allo
w t
o d
eep
Auric
ulo
pal
peb
ral
Aki
nes
ia o
f upper
In
sert n
eedle
into
dep
ress
ion
5 m
llid
only
caudal
to m
andib
le a
t ve
ntral
edge
of
zygo
mat
ic a
rch
Cau
dal
epid
ura
lTa
il, p
erin
eum
In
sert 1
8–22 g
a hyp
oder
mic
0.2
–0.3
caudal
nn.
incl
udin
gor
spin
al n
eedle
into
1st
mg/
sacr
al n
n.
rect
um
, vu
lva,
in
terc
occ
ygea
l sp
ace
with
kgva
gina,
pre
vents
nee
dle
per
pen
dic
ula
r to
stra
inin
gsk
in s
urf
ace
or
poin
t dire
cted
ve
ntrocr
ania
l (3
0°)
. Pla
cing
dro
p o
f ag
ent
into
nee
dle
hub
will
ver
ify p
roper
loca
tion a
s flu
id is
aspira
ted into
epid
ura
l sp
ace.
Addin
g xy
lazi
ne
(0.1
7
62 Local/Regional Anesthetic Techniques
mg/
kg)
or
det
om
idin
e (0
.06
mg/
kg)
to t
he
lidoca
ine
will
in
crea
se d
ura
tion o
f an
alge
sia
Note
: Th
ese
are
just
a few
com
monly
use
d lo
cal a
nes
thet
ic tec
hniq
ues
in h
ors
es. F
or
des
crip
tions
of ad
diti
onal
blo
cks
for
the
hea
d, f
or
dia
gnost
ic n
erve
and jo
int blo
cks,
and tec
hniq
ues
for
lapar
oto
my, r
efer
to “
Rec
om
men
ded
Rea
din
g.”
*Dosa
ge is
for
2%
lidoca
ine.
Tab
le 3
–5
Sele
cted L
oca
l A
nest
hetic
Tech
niq
ues
in R
um
inan
ts a
nd S
win
e
Nerv
e(s
)A
rea A
nest
heti
zed
Tech
niq
ue
Do
sage*
Infil
trat
ion
Para
lum
bar
foss
aLi
ne
blo
ck o
f in
cisi
on s
ite.
50 m
lIn
verted
L t
echniq
ue:
cra
nia
l 50–100 m
lan
d d
ors
al t
o inci
sion s
ite.
Des
ensi
tize
skin
firs
t, th
en inje
ct
dee
per
to d
esen
sitiz
e m
usc
le
and p
erito
neu
m
Pro
xim
al
Para
lum
bar
foss
aD
esen
sitiz
e su
bcu
taneo
us
site
s 15 m
l dee
p,
para
vertebra
lfo
r nee
dle
entry
with
1–2 m
l L.
5 m
l af
ter
(dors
al a
nd
Use
14 g
a nee
dle
to g
uid
ew
ithdra
w-
ing
(contin
ues)
Local/Regional Anesthetic Techniques 63
Tab
le 3
–5
(Continued)
Nerv
e(s
)A
rea A
nest
heti
zed
Tech
niq
ue
Do
sage*
ventral
br.
of
16–18 g
a, 1
1–15 c
m n
eedle
.nee
dle
T1
3, L1
, L2
)En
try
site
s ar
e 5 c
m o
ff m
idlin
e 1–2 c
m,
(2.5
–3 c
m f
or
smal
l ru
min
ants
).
per
site
Pass
nee
dle
dow
n t
o c
rania
l Sm
all
aspec
t of
tran
sver
se p
roce
ss
rum
inan
ts:
and “
wal
k off”
front
edge
of
2–3 m
l/pro
cess
(+
1 c
m).
site
T13: front
of
tran
sver
se
(tota
l pro
cess
of
L1dose
)
L1: front
of
tran
sver
se p
roce
ss
of
L2L2
: front
of
tran
sver
se p
roce
ss
of
L3
Dis
tal
Para
lum
bar
foss
aN
erve
s ar
e des
ensi
tized
at
dis
tal
20 m
l para
vertebra
l en
ds
of
tran
sver
se p
roce
sses
of
ventral
,(s
ame
as f
or
L1, L2
, an
d L
3. 18 g
a, 7
.5 c
m5 m
l pro
xim
al b
lock
)nee
dle
is
inse
rted
ven
tral
to
dors
alpro
cess
and inje
ctio
n m
ade
64 Local/Regional Anesthetic Techniques
in f
an-s
hap
ed p
atte
rn. N
eedle
is
with
dra
wn a
nd r
einse
rted
dors
al t
o p
roce
ss
IV r
egio
nal
in
Are
a dis
tal to
Apply
tourn
iquet
or
cuff (
>200
30 m
l; ca
ttle
and
tourn
iquet
mm
Hg)
to lim
b. In
ject
into
3–10 m
l sm
all ru
mi-
super
ficia
l ve
in w
ith 2
0–25 g
afo
r sm
all
nan
tsnee
dle
clo
se t
o s
urg
ical
site
. ru
min
ants
Apply
pre
ssure
to s
ite t
o a
void
an
d s
win
ehem
atom
a. A
nes
thes
ia o
nse
t is
5–10 m
in a
nd p
ersi
sts
until
tour-
niq
uet
is
rem
ove
d (
max
: (≤
2 h
r).
Pete
rson e
ye
Eye,
orb
it, o
rbic
u-
SC infil
trat
ion a
t notc
h f
orm
ed15 m
lblo
ckla
ris o
culi
musc
le.
by
zygo
mat
ic a
nd t
empora
l ab
duce
ns,
Fa
cilit
ates
pro
cess
es o
f m
alar
bone.
troch
lear
, en
ucl
eatio
nU
se 1
4 g
a nee
dle
inse
rted
at
ocu
lom
oto
r, w
hen
com
bin
edsa
me
site
as
guid
e fo
r 18 g
a,ophth
alm
ic,
with
auric
ulo
-11 c
m n
eedle
dire
cted
horiz
onta
lm
axill
ary
and
pal
peb
ral blo
ckan
d s
lightly
post
erio
r to
man
dib
ula
r brr.
reac
h s
olid
bone
(site
of
of
trig
emin
al
orb
itoro
tundum
wher
e ner
ves
ner
veex
it) a
nd inje
ct(c
ontin
ues)
Local/Regional Anesthetic Techniques 65
Tab
le 3
–5
(Continued)
Nerv
e(s
)A
rea A
nest
heti
zed
Tech
niq
ue
Do
sage*
Auric
olo
pal
peb
ral
Eyel
ids
Sam
e si
te a
s ab
ove
. W
ithdra
w
10 m
lnee
dle
and r
edire
ct p
ost
eria
lly,
late
ral to
zyg
om
atic
arc
h a
nd
inje
ct d
urin
g in
sertio
n t
o 5
–7.
5
cm. U
pper
lid
may
req
uire
lo
cal in
filtrat
ion 2
–3 c
m f
rom
lid
mar
gin.
Bovi
ne d
ehorn
Horn
and b
ase
Tem
pora
l rid
ge, 2 c
m f
rom
horn
5–10 m
lco
rnual
bra
nch
of
horn
bas
e, d
epth
of
1–2.5
cm
.of
zygo
mat
ico-
Ner
ve is
pal
pab
le h
ere.
Inje
ctte
mpora
l n.
2–3 c
m r
ost
ral to
horn
with
(of trig
emin
al n
.)18 g
a nee
dle
. Asp
irate
firs
t.An S
C r
ing
blo
ck a
round t
he
horn
bas
e m
ay b
e nee
ded
fo
r co
smet
ic d
ehorn
and
larg
e horn
s
Caprine d
ehorn
Horn
and b
ase
1. H
alfw
ay b
etw
een lat
eral
sa
me
ner
ve a
sof
horn
canth
us
and lat
eral
horn
pre
vious
(1)
bas
e: inse
rt n
eedle
(22
66 Local/Regional Anesthetic Techniques
plu
s co
rnual
br.
ga, 2.5
cm
) cl
ose
to c
audal
2–3 m
l/si
teof
infrat
roch
lear
rid
ge o
f su
pra
orb
ital pro
cess
(<10 m
g/n. (2
)1–1.5
cm
dee
p.
kg m
axi-
2. H
alfw
ay b
etw
een m
edia
l m
um
)ca
nth
us
and m
edia
l horn
bas
e: inse
rt n
eedle
dors
al
and p
aral
lel to
dors
om
edia
l m
argi
n o
f orb
it, inje
ct in lin
e.
Deb
uddin
g of
kids:
rin
g blo
ck,
0.5
ml/
horn
Caudal epid
ura
lTa
il, p
erin
eum
Inse
rt 1
8–22 g
a hyp
oder
mic
or
5–6 m
l:(c
occ
ygea
l an
d
incl
udin
g re
ctum
,sp
inal
nee
dle
into
1st
inte
r-ca
ttle
sacr
al n
n.)
vu
lva,
vag
ina,
cocc
ygea
l sp
ace
with
nee
dle
0.2
2 m
g/kg
rum
inan
ts
pre
vents
per
pen
dic
ula
r to
ski
n s
urfac
efo
r lla
mas
cam
elid
sst
rain
ing
or
poin
t dire
cted
ven
trocr
ania
lan
d s
mal
l(3
0º)
. Pla
cing
dro
p o
f ag
ent
rum
inan
tsin
to n
eedle
hub w
ill v
erify
pro
per
loca
tion a
s flu
id is
aspira
ted into
epid
ura
l sp
ace.
Addin
g xy
lazi
ne
(0.0
5 m
g/kg
fo
r ca
ttle
, 0.1
7 m
g/kg
for
Local/Regional Anesthetic Techniques 67
(contin
ues)
Tab
le 3
–5
(Continued)
Nerv
e(s
)A
rea A
nest
heti
zed
Tech
niq
ue
Do
sage*
llam
as)
to lid
oca
ine
will
in
crea
se d
ura
tion o
f an
alge
sia
Cra
nia
l epid
ura
lAnes
thes
ia c
audal
Te
chniq
ue
is s
imila
r to
that
use
d2–4 m
g/kg
(sm
all
to d
iaphra
gmin
dog.
Site
is
bet
wee
n L
9(r
umin
ant)
rum
inan
ts
and S
1. O
nse
t: 2–15 m
in.
0.8
–1 m
g/kg
and p
igs)
Rea
r lim
b p
aral
ysis
per
sist
s up
(pig
s)to
2 h
r. Red
uce
dose
by
50%
if
CSF
is
note
d in n
eedle
. Req
uire
s 18–20 g
a, 6
–16 c
m
nee
dle
, sh
ortes
t fo
r sm
all
rum
inan
ts; lo
nge
st f
or
larg
e pig
s. S
win
e: x
ylaz
ine
(1–2
mg/
kg)
or
det
om
idin
e 0.5
m
g/kg
) to
lid
oca
ine
will
incr
ease
dura
tion o
f an
alge
sia
SC: su
bcu
taneo
us
*Dosa
ge is
for
2%
lidoca
ine
(L).
68 Local/Regional Anesthetic Techniques
69
Figu
re 3
–1
Needle
pla
cem
ent
for
loca
l an
est
hetic
inje
ctio
n o
f th
e (
A)
infr
aorb
ital
, (B
) m
axil-
lary
, (C
) ophth
amic
div
isio
n o
f th
e t
rige
min
al, (D
) m
enta
l, an
d (
E)
man
dib
ula
r (i
nfe
rior
alve
ola
rbra
nch
) nerv
es.
(R
eprinte
d w
ith p
erm
issi
on f
rom
Thurm
on, et
al.,
eds.
, Lu
mb a
nd J
ones’
Vete
ri-
nary
Anest
hesi
a, 3rd
ed.,
Bal
tim
ore
: W
illia
ms
& W
ilkin
s, 1
996, pag
e 4
30.)
70
Figure 3–2 Needle placement for brachial plexus block medialto shoulder joint, lateral aspect of left thoracic limb; 2 is the sec-ond rib. (Reprinted with permission from Muir and Hubbell, eds.,Handbook of Veterinary Anesthesia, 2nd ed., St. Louis: Mosby,1995, page 100.)
71
Figu
re 3
–3
Needle
pla
cem
ent
(A)
into
the lum
bosa
cral
epid
ura
l sp
ace o
f dogs
and c
ats.
Pal
pat
ion
of
the d
ors
al ilia
c w
ings
and d
ors
al p
roce
ss o
f lu
mbar
vert
ebra
7 w
ill g
uid
e p
lace
ment
on t
he m
idlin
eju
st c
audal
to a
lin
e d
raw
n b
etw
een t
he w
ings
and just
cra
nia
l to
the f
irst
sac
ral ve
rtebra
. (R
eprinte
dw
ith p
erm
issi
on f
rom
Thurm
on e
t al
., eds.
, Lu
mb a
nd J
ones’
Vete
rinary
Anest
hesi
a, 3rd
ed.,
Bal
tim
ore
:W
illia
ms
& W
ilkin
s, 1
996, pag
e 4
35.)
72
Figure 3–4 Diagram of right forepaw of a cat illustrating sitesfor injection of local anesthetic to provide analgesia for onychec-tomy. (Reprinted with permission from Pascoe, Local and regionalanesthesia and analgesia, in Seminars in Veterinary Medicine andSurgery (Small Animal) 1997;12(2):435.)
4
Inhalation Agents
Inhalation agents provide the most versatile and readilycontrolled method of general anesthesia and are espe-cially well suited for prolonged and complex proceduresand for common as well as uncommon veterinaryspecies. The anesthetic agents are carried in oxygen;thus, patients receive an enriched oxygen mixture andmost often are intubated, which assures a protected air-way and provides a method for ventilatory support. Themain disadvantages of these agents are the expense ofequipment necessary to deliver the agent and, despitethe ability to readily control the concentration delivered,vigilant monitoring is essential to avoid excessive anes-thetic depth, which can rapidly lead to patient mortality.
73
Inhalant anesthetics are vapors (a liquid at ambienttemperature and pressure; these include all potentinhalant agents) or gases (a gas at ambient temperatureand pressure, such as nitrous oxide) administered intothe respiratory tract and absorbed from alveoli into theblood to create a partial pressure (tension). This partialpressure allows the gas to pass from the blood to the brain, wherethe agents exert reversible generalized central nervous systemdepression, the degree of which has been described asdepth of anesthesia (Table 4–1).
Some of the physicochemical characteristics deter-mine the action and margin of safety of the agents anddictate how they are supplied and the equipmentneeded for safe delivery, as well as how they are taken upby the lung, distributed within the body, and eliminated.Vapor pressure is a measure of the agent’s ability to evapo-rate (volatility) and must be sufficient to provide ade-quate concentration in the vapor state to produceanesthesia under ambient conditions. Saturated vaporpressure represents the maximum achievable vapor con-centration for a given liquid at a given temperature (andbarometric pressure); it is determined by dividing vaporpressure by barometric pressure (e.g., Halothane:244/760 = 32% saturated vapor pressure). The greater isthe vapor pressure, the greater the concentration ofinhalant deliverable to the patient (and environment).
The boiling point, defined as the temperature atwhich the vapor pressure is equal to atmospheric pres-sure, is greater than room temperature for all inhalant
74 Inhalation Agents
Inhalation Agents 75
Tab
le 4
–1
Sta
ges
and C
har
acte
rist
ics
of
Genera
l A
nest
hesi
a
Sta
ge/
Pu
lse
Refl
exe
s O
cula
r
Mu
scle
To
ne
Desc
rip
tio
nR
ate
AB
PR
esp
irati
on
Lo
stR
efl
exe
s Lo
st
I/Anal
gesi
a⇑
⇑Reg
ula
r ±
⇑*
All
pre
sent
All
pre
sent
Norm
al
II/D
eler
ium
⇑⇑
Erra
tic ±
⇑*
All
pre
sent
Pre
sent:
Exce
ssiv
enys
tagm
us
move
men
t
III/S
urg
ical
Pla
ne
1,
⇓**
N⇓
Lary
nge
alD
imin
ished
⇓
light
Pla
nes
2
⇓⇓
**⇓
⇓Pe
dal
Lacr
imat
ion,
⇓⇓
and 3
, pal
peb
ral
med
ium
Pla
ne
4,
⇓⇓
**⇓
⇓⇓
, irr
egula
rC
orn
eal
⇓⇓
⇓
dee
p
IV⇓
⇓⇓
Bar
ely
Apnea
⇓⇓
⇓
pal
pab
le
Note
: W
hen
unaf
fect
ed b
y par
ente
ral a
gents
adm
inis
tere
d (
antic
holin
ergi
c ag
ents
, opio
ids)
, pupils
are
dila
ted d
urin
gst
ages
I a
nd II,
are
norm
al o
r co
nst
ricte
d in
pla
nes
1–3, a
nd a
re d
ilate
d in
pla
ne
4 a
nd s
tage
IV.
In c
attle
, eye
posi
tion is
a re
liable
indic
ator
of dep
th. T
he
eye
move
s from
cen
tral
to v
entral
as
surg
ical
anes
thet
ic d
epth
is a
chie
ved. A
s an
esth
e-si
a bec
om
es d
eeper
, the
eye
retu
rns
to c
entral
loca
tion.
(contin
ues
)
agents except nitrous oxide (N2O); therefore, all are liq-uids at room temperature except N2O, which is suppliedfor use in blue cylinders compressed to its liquid state at750 psi. Hence, the pressure gauge on a tank of N2Odoes not indicate the quantity of gas remaining until allliquid is converted to a gas state and pressure begins todecrease as the gas empties.
The quantity of inhalant agent delivered is discussedclinically as concentration in volume percentage, which rep-resents the percentage of the agent in relation to the car-rier gas mixture (oxygen alone or combined with N2O).
The molecular weight, unique for each vapor, is thatweight which occupies 22.4 liters under standard condi-tions (0°C [273 K, absolute scale] and 760 mmHg [baro-metric pressure at 1 atmosphere sea level]). The specificgravity is the ratio of the weight of a unit volume of onesubstance to a similar volume of water under similar con-ditions (20°C). Molecular weight and agent specific grav-ity are properties that allow determination of the volumeof vapor yielded by 1 ml of anesthetic liquid (Figure4–1). From this calculation, the cost of using an inhalantagent may be approximated, based on percentage deliv-ered, total carrier gas flow, and time (see Figure 4–1).
76 Inhalation Agents
Table 4–1 (Continued)
ABP = arterial blood pressure
N = normal
*Breath holding may occur.
**Rate depends on other contributing factors, including premedications, body temperature, fluid balance.
77
Figure 4–1 Calculations to determine volume of vapor from 1ml of anesthetic liquid at 20ºC (calculations 1–4) and averageanesthetic liquid usage per unit time (calculations 5 and 6), usingisoflurane as an example.
1. 1 ml liquid isoflurane � 1.49 g/ml (spe-cific gravity) � 1.49 gm
2. 1.49 gm � 185 (molecular weight) �0.0081 mol of liquid
3. 0.0081 mol � 22400 ml/mol (1 mol of gas� 22.4 L) � 181.4 ml at 273 K (0°C)
4. 181.4 ml vapor � 293/273 K � 194.7 mlvapor/ml liquid isoflurane at 20°C and 760 mmHg
For example, assume 2% isoflurane deliverywith total flow (flowmeter setting) of 2L/minute.
5. 2% � 100 � 2 L/minute � 60 min � 2400ml isoflurane vapor per hour
6. 2400 ml isoflurane vapor/hr � 194.7 mlvapor/ml liquid � 12.3 ml liquid/hr
The solubility (partition) coefficient, the extent to whicha gas will dissolve in a given solvent, is expressed as a con-centration ratio of the anesthetic in the solvent and gasphases. The blood/gas solubility coefficient (Table 4–2)predicts the speed of induction, recovery, and change inanesthetic depth for an inhalant. The lower is the coeffi-cient, the more rapid the action of the agent. Theoil/gas solubility coefficient is the ratio of the concen-tration of an inhalant in oil and gas phases at equilib-rium, correlates inversely with anesthetic potency (asrepresented by the minimum alveolar concentration),and describes the capacity of lipids for the inhalant. Thelower is the oil/gas solubility coefficient, the lower thepotency and thus the higher the MAC value.
Several factors control anesthetic delivery to thelungs and uptake by the blood; these are summarized inTable 4–3. When equilibrium between delivery anduptake (by blood and tissue) is achieved and the alveolarpartial pressure reaches a steady state, the partial pres-sure in the brain is controlled by the partial pressure inthe alveoli.
The minimum alveolar concentration (MAC) is a meas-urement of inhalation agent potency, which refers to thequantity of an agent required to produce a desiredeffect. MAC, which provides a method for comparing thepotency of one agent to another (see Table 4–2), isdefined as the minimum alveolar concentration of ananesthetic agent at one atmosphere that produces immo-bility in 50% of patients exposed to a noxious stimulus.
78 Inhalation Agents
Inhalation Agents 79
Tab
le 4
–2
Phys
icoch
em
ical
Pro
pert
ies
and M
inim
um
Alv
eola
r C
once
ntr
atio
n(M
AC
) of
Inhal
ant
Anest
hetic
Age
nts
Halo
-Is
o-
Meth
o-
Sevo
-P
rop
ert
yD
esf
lura
ne
En
flu
ran
eth
an
efl
ura
ne
xyfl
ura
ne
flu
ran
eN
2O
Mole
cula
r168
185
197
185
165
200
44
wei
ght
Liquid
1.4
71.5
21.8
61.4
91.4
21.5
2—
spec
ific
grav
ity
(20°C
; gm
/ml)
ml va
por/
209.7
197.
5227
194.7
206.9
182.7
—m
l liq
uid
(2
0°C
)
Boili
ng
poin
t 23.5
57
50
49
105
59
–89
(°C
)
Vapor pre
ssure
664
172
243
240
23
160
—m
mH
G
at 2
0°C
(contin
ues
)
80 Inhalation Agents
Tab
le 4
–2
(Continued)
Halo
-Is
o-
Meth
o-
Sevo
-P
rop
ert
yD
esf
lura
ne
En
flu
ran
eth
an
efl
ura
ne
xyfl
ura
ne
flu
ran
eN
2O
Blo
od/g
as
0.4
22.0
2.5
41.4
615.0
0.6
80.4
7par
titio
n
coef
ficie
nt
(37°C
)
Oil/
gas
18.7
96
224
91
970
47
1.4
0par
titio
n
coef
ficie
nt
(37°C
)
MAC
* (%
)7.
1–9.7
2.0
–2.3
0.8
–1.1
1.3
–1.6
0.2
3–0.2
92.1
–2.6
150– 200
Bio
tran
s-0.0
22.4
20–25
0.1
750
3.0
0.0
04
form
atio
n(%
of
met
abolit
es)
*M
AC
var
ies
slig
htly
am
ong
spec
ies
and in
div
idual
s. T
he
valu
e gi
ven is
an a
vera
ge o
r ra
nge
der
ived
fro
m v
alues
reported
for
seve
ral s
pec
ies.
As
a gen
eralr
ule
, conce
ntrat
ions
require
d for
clin
ical
purp
ose
s ar
e ap
pro
xim
atel
y 2–3
times
the
MAC
val
ue
imm
edia
tely
follo
win
g in
duct
ion (
mas
k in
duct
ion m
ay r
equire
3–5 tim
es M
AC
) an
d 1
.5–2 tim
esM
AC
val
ue
for
anes
thet
ic m
ainte
nan
ce.
Inhalation Agents 81
Table 4–3 Factors That Increase the Rate of Rise ofInhalant Anesthetic Tension (Partial Pressure) in the Alveoli
I. Increased delivery of anesthetic to the lungs
A. Increased inspired concentration (the higher is theinspired concentration administered, the more rapid therate of rise of the alveolar concentration)
1. Increased vaporizer setting
2. Increased fresh gas inflow (this effect is significant dur-ing the induction phase when uptake is significant)
3. Decreased breathing circuit volume (the smaller isthe circuit volume, the more rapidly the inspired con-centration is affected by concentration delivered fromthe vaporizer)
4. Second gas effect: Passive increase in inspired con-centration of an anesthetic gas due to rapid uptake oflarge volumes of a less soluble agent used in a highconcentration (N2O), therefore the increased concen-tration accelerates the rate of rise of the second gasin the alveoli; 50% N2O augments inflow into alveoliand accelerates uptake of the second gas in mixture(e.g., halothane, isoflurane), which is used at muchlower concentrations
B. Increased alveolar ventilation
1. Occurs with application of mechanical ventilation
2. Occurs with a decrease in dead space ventilation
3. Relative to functional residual capacity (FRC; volumeremaining in lungs after normal expiration). Thesmaller is the FRC, the less time it takes to “wash in”
(continues)
Therefore, methoxyflurane (MAC = 0.23) currently isthe most potent inhalant agent available. Anestheticrequirements are altered by a variety of factors, which arelisted in Table 4–4, but not by duration of anesthesia, sex,or metabolic acid/base or potassium imbalance.
Inhalation agents affect organ systems in addition tothe central nervous system. Inhalant agents decreaseelectrical activity of the cerebral cortex as brain concen-tration increases, as indicated by decreased frequencyand amplitude of EEG activity; however, due to extremevariability, the EEG alone is not a reliable index of anes-thetic depth. And, the agent enflurane has epileptogenicpotential, which greatly limits its usefulness in veterinarymedicine.
82 Inhalation Agents
Table 4–3 (Continued)
the “new” gas mixture. FRC is decreased in pregnancy and in a variety of primary respiratorydiseases
II. Decreased removal (uptake) from the alveoli
A. Decreased blood/gas solubility coefficient
B. Decreased cardiac output
C. Decreased alveolar to venous anesthetic partial pres-sure difference: the magnitude of difference is relatedto the amount of anesthetic uptake by the tissues andthe largest gradient occurs during induction when tis-sue uptake is greatest
Inhalation Agents 83
Inhalants depress respiratory function in a dose-dependent manner and respiratory arrest occurs at 2–3MAC. Of the currently available agents, respiratorydepression occurs in the following order from most toleast at equipotent concentrations: enflurane >desflurane ≥ isoflurane = methoxyflurane ≥ sevoflurane> halothane. Halothane has been reported to produce aparadoxic tachypnea in some patients, and the mecha-nism is unknown.
Table 4–4 Factors That Affect Anesthetic Requirements(MAC)
Increase in requirements:
Hyperthermia
Hypernatremia
CNS stimulants: amphetamine, ephedrine, physostigmine
Decrease in requirements:
Hypothermia
Hyponatremia
Pregnancy
PaO2 <40 mmHg
Pa CO2 >95 mmHg
Mean arterial blood pressure <50 mmHg
Old age
CNS depressants: N2O, opioids, acepromazine, benzodi-azepines, alpha2 agonists, ketamine, thiopental, propofol
84 Inhalation Agents
All agents depress cardiovascular performance in adose-dependent manner, associated with a negativeinotropic effect, decreased sympathoadrenal activity, andvasodilation. Halothane is noted for its cardiac sensitiza-tion to epinephrine-induced arrhythmias. This occurs toa much lesser extent with methoxyflurane and isnegligible with the other agents. Vasodilation increaseswith increasing depth of isoflurane anesthesia, whichcontributes to hypotension. Myocardial depression is rel-atively less with isoflurane, desflurane, and sevofluranethan halothane, methoxyflurane, and enflurane. Desflu-rane, while similar to isoflurane in cardiovascular effects,is reported to sustain autonomic activity better and main-tain a relatively constant heart rate and, overall, is mostsparing of cardiovascular function.
While all of the inhalation agents are capable ofcausing hepatocellular injury due to reduced oxygen deliv-ery, isoflurane, sevoflurane, and desflurane better main-tain hepatic blood flow and oxygenation, especiallyduring prolonged periods. Halothane has been specifi-cally though rarely associated with fulminant hepaticnecrosis in humans and some animal species and shouldbe avoided in animals with identified hepatic abnormal-ities. This effect is probably influenced by such concur-rent factors as hypoxemia, N2O administration, priorinduction of hepatic drug-metabolizing enzymes, andmechanical ventilation.
All agents decrease renal blood flow and glomerularfiltration rate in a dose-related manner. The effect is
Inhalation Agents 85
exacerbated by preexisting dehydration and hemody-namic abnormalities and may be minimized by intraop-erative fluid therapy. Methoxyflurane is most nephrotoxicand was removed from human use for this reason. Thecause is associated with methoxyflurane biotransforma-tion, which releases free fluoride ions that cause directtubular damage resulting in nonoliguric renal failure.Enflurane and sevoflurane also produce free fluorideions secondary to biotransformation, and sevofluraneyields a nephrotoxic compound, olefin, when it reactswith carbon dioxide absorbents; however, neither seemsto result in concentrations great enough to cause signifi-cant renal damage.
All potent volatile anesthetic agents can triggermalignant hyperthermia but halothane is the most potentof the commonly used agents. Malignant hyperthermiais a pharmacogenetic, often fatal, myopathy of humansand swine typically characterized by increased tempera-ture, muscle rigidity, metabolic acidosis, hyperkalemia,and striated muscle deterioration due to a defect in cal-cium homeostasis at the cellular level. It has beenreported in horses, dogs, cats, birds, deer, and otherwildlife species, but a genetic link has not been eluci-dated in these species. In wildlife species, the syndromeis referred to as capture myopathy.
Anesthetic elimination (and recovery) is influencedby alveolar ventilation, cardiac output, agent solubility,and duration of anesthesia (the longer is the duration,the greater the extent of tissue saturation). When a
86 Inhalation Agents
rebreathing circuit is used (Chapter 5), purging the cir-cuit with oxygen by engaging the oxygen flush valve orincreasing oxygen flow rate will facilitate elimination aswill continued assisted ventilation. While it may seemintuitive to simply disconnect the patient from thebreathing system, this deprives the patient of oxygen sup-plementation and increases contamination of the workenvironment with exhaled anesthetic agent.
Biotransformation is unique to each anesthetic agent(see Table 4–2) and occurs primarily in the liver. Thepotential for acute and chronic toxicities (Table 4–5)associated with environmental exposure to inhaledagents increases with increased biotransformation tometabolites. This is a major reason why methoxyflurane(metabolized up to 50%) no longer is used in human
Table 4–5 Adverse Side Effects Associated with Environmental Exposure to Inhalation Agents
Reproduction disorders Abortion, malformations
Malignancy
Vital organ dysfunction Hepatopathy, renal pathologicchanges, behavioral changes(headache, fatigue, decreasedperformance)
N2O Neutropenia, megaloblastic anemia (decreased vitamin B12 &methionine synthetase synthesis
Inhalation Agents 87
medicine and has lost favor in veterinary medicine, rep-resenting a significant health hazard to patients and per-sonnel. Practices to minimize workplace contamination(Table 4–6) with inhalant agents should be utilized tominimize human exposure.
Table 4–6 Work Practices That Help Minimize Environ-mental Contamination of the Workplace with InhalantAnesthetics
1. Use a scavenger system
2. Educate all personnel about the potential health hazards
3. Keep equipment and vaporizers in good condition
4. Identify and repair leaks in system by an established routine
5. Fill vaporizers at the end of the day
6. Fill vaporizers in a well-ventilated area
7. Inflate endotracheal tube cuffs adequately
8. Avoid the use of mask and chamber inductions and main-tenance whenever possible
9. Keep patients on O2 as long as possible to scavengeexpired anesthetic gases
10. Avoid or minimize exposure with the use of respiratorswith organic vapor cartridges (available from medical sup-ply companies) during the first trimester of pregnancy(while the first trimester is the most vulnerable period,steps to minimize exposure should be practiced through-out the pregnancy)
Nitrous oxide will not provide general anesthesiaalone due to its low potency (see Table 4–2) but is usedas a percentage of the carrier gas (50–70%) to decreaserequirements of the more potent agents and speedinduction, due to its second gas effect (see Table 4–3).While cardiopulmonary effects are minimal, somecontraindications are associated with its use and it hasbeen associated with specific toxic effects (see Table4–5). Nitrous oxide rapidly diffuses into closed gasspaces (while nitrogen slowly diffuses out) and will causeexpansion of the space and respiratory compromise(e.g., pneumothorax, intestinal obstruction); therefore,it is contraindicated in these situations. Nitrous oxiderarely is used in large animal species because of the largevolume of gas contained in the gastrointestinal tract andpotential for excessive distension as well as the need for100% oxygen to maintain adequate oxygenation duringinhalation anesthesia. Diffusion hypoxia can occur withN2O use, due to its rapid exit from the blood into thelungs when delivery is ended. It is essential that 100%oxygen delivery be continued for at least 5 min after N2Ois discontinued.
Inhalant agents offer the most versatile method formaintenance of anesthesia available today. Isofluranecurrently is the most commonly used and favored agentin veterinary medicine, although sevoflurane, with itslower solubility, offers benefits that may rival isofluranewhen it becomes a more economical option. Halothane
88 Inhalation Agents
remains in common use, despite its arrhythmogenicpotential, slower onset and cessation of action, andgreater potential for cardiovascular depression.Halothane historically has been preferred in equineanesthesia, at least for elective procedures, due toreports of smoother recoveries (than isoflurane).Recently, use of sevoflurane has been reported to pro-duce smooth, rapid recoveries and may gain widespreaduse in equine anesthesia in the future. Inhalant anesthe-sia requires vigilant monitoring (Chapter 6) and is notwithout potential detrimental effects to both the patientand the work environment.
Inhalation Agents 89
5
Anesthetic Equipment
The Anesthesia Machine
Basic components of an anesthesia machine include acompressed gas source, pressure-reducing valve (pres-sure regulator), flowmeter, and vaporizer. Compressed(carrier, fresh) gas sources are oxygen and N2O. WhileN2O commonly is used in human anesthesia, use in vet-erinary medicine is limited mainly to dogs and cats tospare requirements for the more potent inhalant agents.In addition to liquid bulk tanks for oxygen, sourcesinclude large tanks (e.g., H tanks with 6,910 L capacity foroxygen or 14,520 L for N2O) connected by high-pres-sure, color-coded (green for oxygen, blue for N2O) hose
91
known as DISS (diameter index and safety system) andsmall tanks (E tanks: 655 L capacity for oxygen, 1,590 Lfor N2O), which may be connected, via a hanger yolkwith a self-contained pressure regulator and pressuregauge, directly to a small animal machine. A pin indexsystem configuration (Figure 5–1) prevents inadvertentinterchange of medical gases. Compressed gas tanks arefilled under pressure (2200 psi for oxygen; 750 psi forN2O) and always must be handled carefully. The pres-sure gauge reading for oxygen tanks decreases linearlywith decreasing content, providing an indication ofavailable oxygen remaining.
Pressure regulators reduce the pressure exiting thecompressed gas source to a constant and safe pressure of50–60 psi to provide a constant pressure to the flowmeter.Flowmeters control and indicate the rate of flow of oxygenand N2O delivered to the common gas outlet or throughan out-of-system vaporizer. Gas moves from bottom totop around a float, which indicates flow rate in L (orml)/min. Most flowmeter floats are cylindrical and readin the middle; alternate-shaped floats are read at the top.Flowmeters are calibrated at 20°C and 760 mmHg. Flowknobs usually are color coded and oxygen flowmeterknobs usually are larger than other knobs on themachine to minimize human error.
Vaporizers deliver a controlled concentration of potentinhalant to the patient breathing system. Currently, thesafest vaporizers are out of (breathing) circle (VOC;Figure 5–2), precision, agent specific, concentration
92 Anesthetic Equipment
93
Figure 5–1 Diagram of the pin index safety system, illustratingthe spacing between the valve outlet and pin holes in the valvebodies for oxygen and N2O cylinders. The numbering system iden-tifies each pin hole site. (Reprinted with permission from CE Short,Principles and Practice of Veterinary Anesthesia, Baltimore:Williams & Wilkins, 1987, page 397.)
calibrated, and variable bypass, which are temperature,flow, and back-pressure compensated. Because vaporiz-ers different than those just described remain in use inveterinary practice, we provide a brief review of thesevaporizers.
The two major exceptions that remain in veterinarymedical use are nonprecision in-the-circle vaporizers(Stephens, Ohio #8) and multiagent measured-flow, out-of-circle vaporizers (Copper Kettle, Vernitrol). In-the-cir-cle vaporizers (VIC) almost always are located on theinspiratory side of the breathing system and the patientbreathes through the vaporizer. Vaporization and anes-thetic concentration in the breathing system is con-trolled by patient ventilation (increased ventilation willincrease vaporization); the arbitrary settings on thevaporizers (Ohio #8, 0–10; Stephens, off–8) indicate theamount of inspiratory flow diverted into the vaporizationchamber. These vaporizers are nonprecision, low resist-ance, and not temperature compensated, meaning thedelivered concentration is unknown and can changeunpredictably, the anesthesia often being referred to asqualitative (versus quantitative). Inspired concentrationincreases with increased temperature, increased ventila-tion (spontaneous or mechanical), and decreased freshgas flow into the breathing circuit. Mechanical ventila-tion is contraindicated with VICs. The Ohio #8, with itswick to increase surface area, was designed specificallyfor methoxyflurane (low volatility). Guidelines for use
94 Anesthetic Equipment
95
Figu
re 5
–2
Dia
gra
m o
f va
porize
r an
d b
reat
hin
g co
mponent
loca
tion f
or
VO
C (
vaporize
r out
of
circ
le).
(R
eprinte
d w
ith p
erm
issi
on f
rom
CE S
hort
, Pri
nci
ple
s and P
ract
ice o
f Ve
teri
nary
Anest
hesi
a,
Bal
tim
ore
: W
illia
ms
& W
ilkin
s, 1
987,
pag
e 4
03.)
with isoflurane and halothane (with wick removed) havebeen published; however, this practice is discourageddue to the high volatility of these agents and theincreased potential to deliver fatal concentrations. TheStephens vaporizer has been used for halothane andisoflurane (and sevoflurane) and is intended for use witha low-flow circle breathing system. A wick is provided foruse with methoxyflurane as well. Vigilant monitoring willhelp assure that excessive concentrations are not deliv-ered to the patient.
Measured-flow vaporizers allow use of multipleagents because they contain two oxygen flowmeters, onefor diluent flow and one for vaporizer flow. The appro-priate flow setting for both flowmeters must be calcu-lated to deliver the desired concentration of the specificagent used (Figure 5–3). Originally, a special circularslide rule to determine flowmeter settings was includedwith these vaporizers (see Figure 5–3).
Two other features of anesthesia machines needmention. While not essential, most anesthesia machineshave an oxygen flush valve (OFV), which supplies oxygento the common gas outlet or directly to the breathing cir-cuit at an unmetered rate of 35–75 L/min. The OFV flowbypasses the vaporizer in contemporary machines, butolder machines to which precision vaporizers wereadded later may direct oxygen, with flush activation,through the vaporizer, with the potential to increaseanesthetic output if the vaporizer is turned on. Whenusing an anesthesia machine, the circuitry should be
96 Anesthetic Equipment
97
Figure 5–3 Circular slide rule for calculation of oxygen flowsfor an anesthetic machine with a measured-flow VOC vaporizer(Verni-trol, Copper Kettle). The rule can be used for multiple anes-thetic agents and a variety of total oxygen flow rates over a rangeof temperatures. Calculations can be made according to the fol-lowing equations (using halothane as the anesthetic agent):
1. Saturated vapor pressure (halothane) � 243 � 760 � 32%;desired TGF (total gas flow) � 2 L/min; desired halothane con-centration [%Hal] � 1.5%
2. Halothane vapor leaving vaporizer � desired %Hal � TGF � 1.5% � 2000 ml � 30 ml
(continues)
followed and understood prior to use. The OFV is usedto flush (remove) anesthetic from the rebreathing sys-tem during recovery or when problems with anestheticdepth are identified; using it to fill the rebreathing bagin an attempt to ventilate and deepen the patient’s anes-thesia is ineffective, as its purpose is to dilute anestheticconcentration within the breathing circle. The OFVshould not be used in pediatric circuits or nonrebreath-ing systems, both of which have small volumes, due to thedanger of overpressurizing the patient’s respiratory sys-tem. The common gas outlet is the site from which gasesthat have passed through the flowmeter, vaporizer(VOC), or OFV exit the anesthesia machine for deliveryto the breathing system. Some vaporizers, purchased sep-arately and added to a machine, have been placedbetween the common gas outlet and the breathing cir-cuit, which increases the risk of delivering excessive con-
98 Anesthetic Equipment
Figure 5–3 (Continued)
3. To provide 30 ml halothane vapor leaving vaporizer: TGF exitingvaporizer � 30 ml � 32%(sat VP) �94 ml.
4. 94 ml (TGF exiting vaporizer) � 30 ml (halothane vapor) � 64ml oxygen entering vaporization chamber (vaporizer flowmetersetting).
5. Bypass oxygen flowmeter setting � 2000 ml (total flow) � 94ml � 1906 ml
(Reprinted with permission from Thurmon et al., eds., Lumb andJones’ Veterinary Anesthesia, 3rd ed., Baltimore: Williams andWilkins, 1996, page 387.)
centrations should the vaporizer be tilted or the oxygenflush valve engaged when the vaporizer is on.
Anesthesia Breathing Systems
The breathing system connects the anesthesia machine(via the fresh gas inlet) to the patient (via mask or endo-tracheal tube). Two types of circuits are used in veteri-nary medicine. The circle rebreathing system is the mostcommon circuit used and is standard equipment onmost anesthesia machines. Pediatric, standard adult(small animal), and large animal circuits differ primarilyin their internal diameters, rebreathing bag, and overallvolume and size of the carbon dioxide absorbent canis-ter. Pediatric and adult circuits have the same sizeabsorbent canister and differ only in the size of thebreathing tubes and rebreathing bag used (Table 5–1).
Circle systems have the same basic components,including:
• The Y-piece (patient connection). • Two breathing tubes (between the Y-piece and one-
way valves).
• Paired one-way valves (inspiratory and expiratory),which prevent rebreathing of exhaled gases beforethey pass through the absorbent canister.
• Fresh gas inlet (site of entry of gases from the com-mon gas outlet).
Anesthetic Equipment 99
100 Anesthetic Equipment
Tab
le 5
–1
Siz
es
and R
eco
mm
endat
ions
for
Fresh
Gas
Flo
w R
ates
of
Circl
e S
yste
ms
and N
onre
bre
athin
g Sy
stem
s Bre
ath
ing
Dia
mete
rR
eb
reath
ing
Fresh
Gas
Flow
Syst
em
Tub
e
Bag V
olu
me*
Pati
en
t Siz
eR
ate
(m
l/kg/m
in)
Circ
le Pedia
tric
15 m
m0.5
–1 L
<7kg
4–11 (
close
d)
Adult
22 m
m1 L
8–15 k
g10–20 (
low
flo
w)
2 L
16–30 k
g25–35 (
sem
i-cl
ose
d)
3 L
31–45 k
g5 L
46–135 k
gLa
rge
anim
al50 m
m15 a
nd 2
0 L
135–330 k
g6–10
30 L
>330
Nonre
bre
ath
ing
<5–7 k
g200–600**
Bai
ns
syst
em (
Map
leso
ncl
assi
ficat
ion T
ype
D,
modifi
ed)
Ayr
e’s
T-pie
ce
(Map
leso
n c
lass
ifica
tion
Type
E) N
orm
an e
lbow
Anesthetic Equipment 101
(Map
leso
n c
lass
ifica
tion
Type
E) J
acks
on-R
ees
Syst
em (
a m
odifi
ed
Ayr
e’s
T-pie
ce; M
aple
son
clas
sific
atio
n T
ype
E)
*Reb
reat
hin
g bag
siz
e m
ay b
e es
timat
ed b
y m
ulti
ply
ing
6 �
tidal
volu
me
(10 m
l/kg
) �
BW
(kg
).
**Rec
om
men
dat
ions
for
tota
l fre
sh g
as flo
w a
re q
uite
var
iable
in the
liter
ature
but,
in g
ener
al, a
re 2
–3 tim
es m
inute
ventil
atio
n (
170–350 m
l/kg
/min
ute
for
dogs
and c
ats)
to p
reve
nt re
bre
athin
g of ca
rbon d
ioxide.
• Pop-off (relief) valve, which vents gases to the scav-enger system and prevents excessive pressure withinthe system.
• Rebreathing bag, which provides peak demands dur-ing inspiration, a mechanism for manually assistingventilation, and a method for observing sponta-neous ventilation.
• Pressure manometer, usually attached at absorbentcanister and calibrated in cm H2O to assess pressureachieved during assisted ventilation.
• Absorbent canister.
The absorbent canister is filled with either soda limeor barium lime granules (calcium hydroxide is the pri-mary component of both), which neutralize exhaledCO2. The reaction (CO2 � H2O → H2CO3 � 2NaOH �Ca(OH)2 → CaCO2 � Na2CO3 � 4H2O � heat) isexhaustive and produces a change in the granules,including heat generation, soft to hard, and a colorchange (most often white to violet). As a general rule,absorbent granules should be changed after 6–8 hr ofuse or when the color reaction is apparent in approxi-mately two thirds of the granules.
Nonrebreathing systems have no chemical absorbentand depend on a high fresh-gas flow rate to removeexhaled CO2 from the breathing system. They are lessefficient than the rebreathing system; the oxygen andanesthetic agent are wasted; more anesthetic agent must
102 Anesthetic Equipment
be scavenged, with a greater potential for environmentalcontamination; and patient heat and humidity is notconserved, so that patient cooling due to convective heatloss is greater. The main advantage is less resistance to breath-
ing; hence, the recommendation for use in small (<5–7kg) patients. They also are lightweight, easy to position,inexpensive (to purchase), and allow rapid changes ininspired anesthetic concentration. Several systems, classi-fied collectively by the Mapleson system, are available; ingeneral, only four are used in veterinary medicine (seeTable 5–1), with the Bains coaxial system being the mostpopular. The Bains system is a tube (inspired fresh gasdelivery) within a tube (carries exhaled gases away fromthe patient to the reservoir bag and scavenging system)and can be fitted with a pressure manometer (with anadditional equipment piece that also has a relief valveand accommodates the reservoir bag).
Waste Gas Scavenging
Several medical problems have been linked to exposureto waste anesthetic gases (see Table 4–5). Guidelines tominimize workplace contamination (see Table 4–6)include a scavenging system on all anesthesia machines tocollect and eliminate waste gases from the workplace. Agas-collecting connection (the pop-off or relief valve), aninterface, and a disposal system compose the scavengingsystem assembly. The interface prevents transfer of pres-sure changes from the disposal system to the breathing
Anesthetic Equipment 103
104 Anesthetic Equipment
system. It includes positive and negative pressure reliefmechanisms and, for active systems, a reservoir bag toprovide visual assessment of its proper function.
Disposal systems are passive or active. Passive systemsinclude piping waste gases into nonrecirculating ventila-tion systems, directly to the atmosphere, and throughabsorption devices (F/air canisters are portable and neu-tralize inhaled gases with the exception of N2O but havea limited useful life, making them expensive and variablein effectiveness).
Active systems include piped vacuum and active ductsystems. A piped vacuum system is convenient whenalready in place and when location of exit for passive dis-charge is inconvenient. An active duct system with highvolume flow and low negative pressure is ideal for wastegas removal. Tubing for the connecting parts of the scav-enging system ideally should be readily discernible fromthe breathing circuit. Table 5–2 is a simple guide to per-forming routine checks of the anesthesia machine andto detecting leaks from the breathing circuit.
Ventilators
Controlled ventilation is unnecessary for the majority ofanesthetized veterinary patients, but a variety of patientcircumstances will prompt the need for intermittent pos-itive pressure ventilation (IPPV). Indications includeapnea; documentation of severe hypoventilation(↑PaCO2); intrathoracic surgery; patient factors such as
Anesthetic Equipment 105
Table 5–2 Recommendations for Routine Assessment ofAnesthesia Machine and Breathing Circuit to Minimize Riskof Malfunction and Environmental Pollution
1. Machine check
a. Check anesthetic level in vaporizer and fill if indicated(preferably, at time when room is not in use).
b. Check tightness of filler cap.
c. Make sure vaporizer setting is in off position.
2. Oxygen supply and delivery
a. Check cylinder pressure (50–60 psi) and assess quan-tity of oxygen available.
b. For machines equipped with N2O source and flowmeter,turn on N2O flow and turn off oxygen supply; N2O floatshould drop to zero. (This should be performed at leastweekly.)
c. Verify proper flowmeter function. Float should movefreely the entire length of flowmeter tube.
3. Check breathing circuit
a. Assure all fittings are tight.
b. Check absorbant canister for need to change soda limeand assure canister is properly positioned and tightly fitted.
c. Confirm proper function of unidirectional valves of circleby inhaling and exhaling through Y-piece and observingappropriate movement.
d. Check for leaks: Close the relief valve, occlude the Y-piece, pressurize the circuit to 30 cm H2O; pressureshould remain stable or drop slowly (<250 ml/min).Open the relief valve to assure release of pressure.
(continues)
obesity, abdominal distention, or primary lung dysfunc-tion; use of an intraoperative neuromuscular blockingagent; surgery lasting more than 90 min; the need forhyperventilation in cases of head trauma; and facilitationof a stable plane of surgical anesthesia by enhancinganesthetic agent delivery and uptake.
Maintaining a PaCO2 between 35 and 45 mmHg isthe general goal of IPPV; however, there is controversyregarding the desired high-end range for PaCO2, with 50mmHg commonly recommended. Moderate increases inPaCO2 support arterial blood pressure through endoge-nous catecholamine release. Intermittent positive pres-sure ventilation decreases cardiovascular function by
106 Anesthetic Equipment
Table 5–2 (Continued)
4. Check waste gas scavenging system
a. Confirm connection to relief valve.
b. Connect or activate active scavenging system or verifypatency of passive system.
5. Check ventilator function (when applicable).
a. Turn on prior to connection to breathing circuit (mayrequire partially occluding connecting tubing) to assurefunction and appropriate settings.
b. Verify proper connection to breathing circuit, whichincludes closing the relief valve.
c. The scavenging system must be connected to the venti-lator relief valve when in use.
impeding venous return to the heart (and therefore dias-tolic filling). The benefits of IPPV, compared to thepotential detrimental effects, should be considered inevery patient. High-risk patients with inadequate vascu-lar volume or compromised cardiac function may nottolerate IPPV well, as evidenced by exacerbation of lowarterial blood pressure values.
Even though IPPV has a negative effect on cardio-vascular performance, this is minimized by assuring ade-quate intravascular volume, using inotropes to enhancecardiovascular performance (Chapter 7), and applyingIPPV within the recommended guidelines (Table 5–3).
Ventilators are classified broadly, based on mode ofoperation, including pressure cycled and volume cycled.Ventilators require electricity, compressed gas, or bothfor operation. The timing of pressure-cycled ventilators isinfluenced by a preset peak inspiratory pressure limit.Inspiration will continue until a preset pressure isachieved, regardless of the volume delivered. While thistype of operation is safer, in that it will not allow deliveryof excessive pressure during the inspiratory phase, tidalvolume delivered may be inadequate (depending onlung and breathing system compliance). The tidal vol-ume delivered tends to decrease over time unless theventilator periodically is reset to compensate for the tem-poral decrease in lung compliance.
Volume-cycled ventilators deliver a preset tidal volumeregardless of peak pressure achieved. Most ventilators of
Anesthetic Equipment 107
this type have settings that limit the maximum pressureachieved to assure patient safety. Maximum pressure dur-ing the inspiratory phase increases as patient compliancedecreases. Leaks in the breathing circuit do not becomereadily apparent with volume-cycled operation, while
108 Anesthetic Equipment
Table 5–3 Recommended Settings for Mechanical Ventilation
Setting Guidelines
Tidal volume* 15–20 ml/kg (small animals)
10–15 ml/kg (large animals)
Inspiratory time <1.5 sec (small animals)
<3 sec (large animals)
I:E (inspiratory to expiratory) ≤1:2ratio
Peak inspiratory pressure 12–20 cm H2O (small animals)
20–30 cm H2O (large animals)
Respiratory frequency 8–14 (dogs)
10–14 (cats)
6–10 (horse and cow)
8–12 (small ruminants and pigs)
*Ventilator tidal volume is set slightly higher than the actual patient needs, to allowfor increases in breathing system and airway volume when positive pressure isdelivered. Setting tidal volume too low will permit development of atelectasis. Whenlower tidal volume must be used (e.g., on animals with abdominal distention ordiaphragmatic hernia), the rate should be increased accordingly.
leaks usually are readily apparent with pressure-cycledventilators.
While ventilators historically have been classified aspressure or volume cycled, the terms are somewhat mis-leading because most often a timing mechanism controlsthe change from the inspiratory phase to the expiratoryphase, with inspiratory time being a major determinantof the cycle. Ventilators also are classified according todirection of bellows movement during expiration. Ascending(during expiration) bellows are considered safer,because they will not fill if a disconnection occurs in thebreathing circuit, thus quickly alerting the anesthetist toa problem.
Even though an anesthetized animal may appear tobe ventilating adequately, as indicated by a normal spon-taneous respiratory rate and a “normal”-appearing tidalvolume, some degree of respiratory depression is pres-ent. The subsequent elevation of PaCO2 may be quanti-tated by arterial blood gas analysis or continuouslyreading capnometers, which visually display a value forend-tidal carbon dioxide, an indirect measure of PaCO2.Anesthesia-associated hypercapnia during spontaneousventilation tends to increase with the duration of theanesthesia. This stresses the importance of minimizinganesthesia time and providing ventilatory support, eithermanually or mechanically, for prolonged proceduresand high-risk patients.
Anesthetic Equipment 109
6
Monitoring Anesthesia
Based on suggestions by the American College of Veteri-nary Anesthesiologists (ACVA) for monitoring anes-thetized veterinary patients, personnel should be “awareof the patient’s status at all times during anesthesia andrecovery.” No monitoring tool or device can take theplace of constant human observation; available equip-ment is meant to enhance the observation skills of theattending anesthetist. Keeping a record of perianestheticevents (see Figure 1–1) will provide a legal documentand facilitate appropriate observation and temporalrecording of relevant measured parameters and events.Monitoring provides ongoing determination of patientphysiologic status, allowing early recognition and treat-ment of abnormalities and a way to assess therapeutic
111
efficacy. Recommended monitoring methods anddevices are targeted to assure adequate circulation, oxy-genation, and ventilation. The best treatment for anes-thetic complications is prevention. But, when they dooccur, early recognition usually will allow correction withminimal intervention and long-term detrimental effects.
Monitoring efforts concentrate on three bodysystems—the central nervous system (including ocular,musculoskeletal, and other reflexes), the cardiovascularsystem, and the respiratory system—and should includeperiodic temperature assessment. The following guide-lines should be considered:
1. Evaluation of integrated responses, using one ormore parameters for multiple body system assess-ment, allows more accurate and representativeongoing patient assessment than reliance on a singleparameter.
2. Even though a variety of monitoring devices is avail-able, it is best to choose one or two for routine useand become familiar with their benefits and limita-tions, remembering that they are a supplement tomonitoring not a replacement.
3. The monitoring plan should increase in complexity(more quantitative measurements) as patient andprocedure risk increase.
4. Noninvasive monitors are relatively easy to use butresults can be highly variable; the data provided are
112 Monitoring Anesthesia
best viewed as trends (qualitative) over time ratherthan quantitative measurements.
5. In general, invasive monitoring techniques are moreaccurate but more expensive to provide, requiregreater technical skill, and usually are reserved forhigh-risk patients and procedures (horses are anexception, for which invasive arterial blood pressuremonitoring is used routinely during inhalation anes-thesia regardless of patient status).
6. Keeping an anesthetic record provides a method oftracking trends in measured parameters (e.g., heartrate, respiratory rate, blood pressure) and providesinformation for subsequent anesthetic episodes inthat patient.
Signs of the various stages of inhalation anesthesiaare listed in Table 4–1. General anesthesia includes uncon-
sciousness, insensitivity to pain, muscle relaxation, and absence
of reflex response. The degree required for each of theseeffects depends largely on the procedure. While no clearline divides stages and planes of anesthesia, planes 2 and3 of stage III are the desired levels for most procedures.Confounding factors that complicate evaluation accord-ing to stage, include variation in species response toanesthetic agents, premedication agents administered,PaO
2and PaCO
2values, and the patient’s physical status.
Monitoring Anesthesia 113
Tab
le 6
–1
Par
amete
rs M
onitore
d a
nd A
pplic
able
Tech
niq
ues
Use
d D
uring
Genera
lA
nest
hesi
a
Para
mete
rM
eth
od
Co
mm
en
ts
Res
pira
tory
monito
ring
Res
pira
tory
rat
e,
Thora
cic
move
men
tSu
bje
ctiv
e only
. N
o indic
atio
ndep
th, an
d c
har
acte
rReb
reat
hin
g bag
of
adeq
uac
y of
ventil
atio
n.
move
men
tAppro
pria
te f
or
asse
ssin
g ch
ange
s ove
r tim
e.
Esophag
eal st
etho-
May
be
atta
ched
to e
arpie
ces
or
scope
amplif
ier; a
lso d
etec
ts h
eart s
ounds
Res
pira
tory
(ap
nea
) In
terfac
ed b
etw
een E
T tu
be
monito
ran
d b
reat
hin
g sy
stem
. D
etec
tsex
hal
ed b
reat
h b
y ch
ange
in t
em-
per
ature
and p
rovi
des
an a
udib
lebee
p. M
ay n
ot
be
sensi
tive
enough
for
very
sm
all pat
ients
.
Tidal
and m
inute
volu
me
Ventil
om
etry
Ventil
om
eter
is
applie
d t
o e
xpira
tory
side
of
pat
ient
bre
athin
g ci
rcuit
End-tid
al C
O2
(ETC
O2)
Cap
nom
etry
Pro
vides
bre
athin
g ra
te a
nd
ETC
O2
valu
e.
114 Monitoring Anesthesia
Cap
nogr
aphy
Als
o d
ispla
ys g
raph o
f ex
pire
d C
O2
(Fig
ure
6–1)
Hem
ogl
obin
sat
ura
tion
Puls
e oxi
met
erH
emogl
obin
oxy
gen s
atura
tion a
nd
(SaO
2or
SpO
2)
puls
e ra
te
Arter
ial blo
od g
as a
nal
ysis
Labora
tory
blo
od g
as
Most
acc
ura
te a
sses
smen
t of
(PaC
O2
and P
aO2)
anal
yzer
adeq
uac
y of
ventil
atio
n a
nd
Han
dhel
d a
nal
yzer
sblo
od o
xyge
nat
ion
Card
iova
scula
r m
onito
ring
Hea
rt r
ate
Pre
cord
ial au
sculta
tion
Esophag
eal st
etho-
Als
o a
vaila
ble
with
sel
f-sc
ope
conta
ined
ECG
lea
ds
(Hes
ka
Corp
., Fo
rt C
olli
ns,
CO
)
ECG
Rec
ord
s m
yoca
rdia
l el
ectric
al a
ctiv
itybu
t gi
ves
no in
dica
tion
of a
dequ
acy
of p
erfu
sion
Puls
e ra
te a
nd q
ual
ityPa
lpat
ion
Subje
ctiv
e; s
ites
vary
am
ong
spec
ies:
Can
ine—
dors
al p
edal
, lin
gual
, fe
mora
l
Felin
e—fe
mora
l, �
lingu
al a
nd
dors
al p
edal
(contin
ues
)
Monitoring Anesthesia 115
Tab
le 6
–1
(Continued)
Para
mete
rM
eth
od
Co
mm
en
ts
Equin
e—fa
cial
, tran
sver
se f
acia
l, dors
al m
etat
arsa
lRum
inan
t—au
ricula
r, co
ccyg
eal,
dig
ital
Swin
e—fe
mora
l, au
ricula
r, co
ccyg
eal,
bra
chia
lPuls
e oxi
met
ryPro
vides
puls
e ra
te a
nd indire
ct
asse
ssm
ent
of
blo
od o
xyge
nat
ion
(SaO
2; Fi
gure
6–2)
Art
eria
l blo
od p
ress
ure
N
onin
vasi
veTw
o m
ethods
(both
req
uire
cuff*)
:(A
BP)
1. O
scill
om
etric
—pro
vides
hea
rt r
ate
plu
s sy
stolic
, m
ean, an
d d
iast
olic
AB
P a
t pre
set
inte
rval
s.2. D
opple
r cr
ysta
l pro
be—
applie
d
ove
r ar
tery
dis
tal to
a c
uff w
ithm
anom
eter
. Sk
in o
ver
arte
ry m
ust
be
close
ly c
lipped
, ge
l ap
plie
d
and p
robe
taped
in p
lace
, w
hic
ham
plif
ies
sound o
f puls
e. R
elia
bly
116 Monitoring Anesthesia
mea
sure
s sy
stolic
AB
P o
nly
.**Als
opro
vides
contin
uous
audito
ryin
form
atio
n o
n p
uls
e rh
ythm
and
qual
ity. Le
ss a
uto
mat
ed t
han
osc
illom
etric
tec
hniq
ue.
Inva
sive
†Pro
vides
contin
uous,
acc
ura
te
read
out
of
SAP,
MAP,
and D
AP.
Req
uire
s ar
teria
l ca
thet
er a
ttac
hed
to a
pre
ssure
tra
nsd
uce
r an
dre
cord
ing
dev
ice
or
sphyg
mo-
man
om
eter
(M
AP o
nly
) vi
asa
line-
fille
d t
ubin
g. S
ensi
tive
mon-
itor
of
anes
thet
ic d
epth
, es
pec
ially
use
ful in
hors
es.
Site
s fo
r arter
ial ca
thet
eriz
atio
n:
Can
ine—
dors
al p
edal
, lin
gual
, fe
mora
lFe
line—
fem
ora
l, dors
al p
edal
Equin
e—fa
cial
, tran
sver
se f
acia
l, dors
al m
etat
arsa
l(c
ontin
ues
)
Monitoring Anesthesia 117
Tab
le 6
–1
(Continued)
Para
mete
rM
eth
od
Co
mm
en
ts
Rum
inan
t—au
ricula
rSw
ine—
auric
ula
r, fe
mora
l
Cen
tral
ven
ous
pre
ssure
Mea
sure
d w
ith c
athet
erRef
lect
s th
e bal
ance
bet
wee
n b
lood
(CVP)
pla
ced into
ante
rior
volu
me
and c
apac
ity a
nd h
elps
vena
cava
via
jugu
lar
avoid
pulm
onar
y ed
ema
and
vein
and c
onnec
ted
ove
rhyd
ratio
n w
ith r
apid
flu
idto
man
om
eter
or
adm
inis
trat
ion in h
igh-ris
kpre
ssure
tra
nsd
uce
r pat
ients
.ze
roed
at
thora
cic
Norm
al va
lues
:in
let
0–10 c
m H
2O
(sm
all an
imal
)5–15 c
m H
2O
(aw
ake
hors
es)
25–35 c
m H
2O
(an
esth
etiz
ed
hors
es)
Urin
e outp
ut
Urin
ary
cath
eter
con-
Indire
ct m
easu
re o
f org
annec
ted t
o c
lose
d
per
fusi
on. Es
pec
ially
colle
ctio
n s
yste
mim
portan
t in
ren
al d
isea
se.
Norm
al:
1–2 m
l/kg
/hr
118 Monitoring Anesthesia
Note
s: T
he
goal
of re
spira
tory
monito
ring
is to d
eter
min
e an
d m
ainta
in a
deq
uac
y of ve
ntil
atio
n (
norm
al P
aCO
2an
dPa
O2). T
he
goal
of ca
rdio
vasc
ula
r m
onito
ring
is to m
onito
r th
e el
ectric
al a
ctiv
ity o
f th
e hea
rt a
nd e
nsu
re a
deq
uat
e per
fu-
sion o
f vi
tal o
rgan
s, p
artic
ula
rly the
bra
in, h
eart, a
nd k
idney
s.
SAP =
sys
tolic
AB
P; M
AP =
mea
n A
BP; D
AP =
dia
stolic
AB
P.
*C
uff
wid
th is
appro
xim
atel
y 40%
the
circ
um
fere
nce
of th
e ap
pen
dag
e.
**As
a ge
ner
al r
ule
, when
the
syst
olic
AB
P is
90–100 m
mH
g, m
ean A
BP is
60–70 m
mH
g.†A m
inim
um
mea
n A
BP o
f 60–70 m
mH
g is
consi
der
ed n
eces
sary
to a
ssure
per
fusi
on o
f vi
tal o
rgan
s in
all
spec
ies.
Cat
-tle
may
dem
onst
rate
hig
her
val
ues
durin
g ge
ner
al a
nes
thes
ia a
nd r
ecum
ben
cy, e
spec
ially
as
dura
tion o
f an
esth
esia
incr
ease
s (e
.g.,
mea
n A
BP =
100–150 m
mH
g). H
ors
es h
ave
bee
n r
eported
to e
xhib
it hig
h v
alues
, whic
h in
crea
se o
ver
time
in a
ssoci
atio
n w
ith tourn
iquet
applic
atio
n (
star
ting
appro
xim
atel
y 45 m
in a
fter
tourn
iquet
pla
cem
ent)
.
Monitoring Anesthesia 119
Assessment of the cardiovascular and respiratorysystems incorporate subjective and objective data thatindicate the state of circulation, oxygenation, and venti-lation. Table 6–1 lists the parameters that may beassessed and methods and equipment available. Table6–2 provides details on the principles and operation ofthe capnograph and pulse oximeter. Table 6–3 lists nor-mal values for some measured parameters in a variety ofspecies. Table 6–4 lists some potential abnormalities thatmay develop during general anesthesia, potential causesto be investigated, and an approach to management.
120 Monitoring Anesthesia
Tab
le 6
–2
Princi
ple
s of
Opera
tion a
nd S
ignific
ance
of
Info
rmat
ion P
rovi
ded b
yM
onitoring
Equip
ment
Use
d in V
ete
rinar
y M
edic
ine
Eq
uip
men
tP
rin
cip
les
of
Op
era
tio
nP
rob
e S
ite(s
)/So
urc
e o
f Err
or
Cap
nogr
aphy
Infrar
ed a
bso
rptio
n is
the
most
Tw
o a
nal
yzer
typ
es p
lace
d b
etw
een
(Fig
ure
6–1)
com
mon m
easu
ring
met
hod
ET t
ube
and b
reat
hin
g ci
rcuit:
to d
eter
min
e CO
2in
exp
ired
1. Si
des
trea
m—
aspira
tes
gase
s in
toga
ses.
ETC
O2
repre
sents
an
alyz
er v
ia t
ubin
g (5
0–250 m
l/al
veola
r CO
2, w
hic
h
min
), r
esulti
ng
in lag
tim
e.eq
uili
bra
tes
with
PaC
O2,
2. M
ainst
ream
—m
easu
res
CO
2
refle
ctin
g ve
ntil
atory
effi
cien
cy.
dire
ctly
in a
irway
, no lag
tim
e.N
orm
al c
apnogr
am r
equire
s Er
ror: E
TCO
2under
estim
ates
PaC
O2
met
abolis
m, ci
rcula
tion, an
d
by
appro
xim
atel
y 5 m
mH
gve
ntil
atio
n a
nd it
thus
(up t
o 1
4 in h
ors
es)
due
tom
onito
rs m
ulti
ple
vita
l al
veola
r dea
d s
pac
e. Idea
lly,
funct
ions.
it
is a
good idea
to a
sses
s ac
tual
PaC
O2 p
erio
dic
ally
durin
g use
.
Puls
e oxi
met
ry
Estim
ates
oxy
genat
ed h
emo-
Two p
robe
types
:(S
aO2
or
globin
(H
gb)
as a
per
cent
of
1. Tr
ansm
ittan
ce—
sends
and
SpO
2)
tota
l hem
ogl
obin
. Bas
ed o
n
rece
ives
lig
ht
acro
ss t
issu
e:(F
igure
6–2)
prin
ciple
that
oxy
genat
ed a
nd
tongu
e, t
oe
web
, ea
r, vu
lva.
(contin
ues
)
Monitoring Anesthesia 121
Tab
le 6
–2
(Continued)
Eq
uip
men
tP
rin
cip
les
of
Op
era
tio
nP
rob
e S
ite(s
)/So
urc
e o
f Err
or
deo
xyge
nat
ed H
gb a
bso
rb
2. Ref
lect
ance
—se
nds
and r
ecei
ves
light
diff
eren
tly a
t diff
eren
t lig
ht
on t
he
sam
e pla
ne:
wav
elen
gths,
660 n
m (
red)
esophag
us,
rec
tum
, m
uco
us
and 9
40 n
m (
infrar
ed).
m
embra
nes
.Req
uire
s puls
atile
blo
od.
Erro
r:H
emogl
obin
sat
ura
tion
1. Lo
w p
uls
e pre
ssure
.re
flect
s blo
od o
xyge
nat
ion
2. In
crea
sed v
enous
puls
atio
ns
(PaO
2)
as r
epre
sente
d b
y th
e (e
.g.,
right-hea
rt f
ailu
re,
oxy
hem
ogl
obin
dis
soci
atio
n
tourn
iquet
).cu
rve
(Fig
ure
6–2).
3. C
ardia
c ar
rhyt
hm
ias.
4. M
ove
men
t.5. D
yshem
ogl
obin
s (e
.g.,
met
he-
mogl
obin
, ca
rboxy
hem
ogl
obin
).6. D
yes
(e.g
., m
ethyl
ene
blu
e).
7. A
nem
ia (
<5 g
m/d
l).
8. Ex
tern
al lig
ht.
9. El
ectroca
ute
ry u
nits
.10. Po
or
pro
be
posi
tionin
g
122 Monitoring Anesthesia
123
Figure 6–1 Diagram of normal expired CO2 waveform. Thethree phases of the normal waveform include apparatus andanatomical series dead space (phase I), mixture of anatomicalseries and alveolar parallel gas (phase II), and the alveolar plateau(phase III), a mixture of gases from well-perfused alveoli and alve-olar dead space (unperfused alveoli). (Reprinted with permissionfrom KK Tremper, Interpretation of noninvasive oxygen and carbondioxide data. Can J Anaesth 1990;37(4):Slxxxi.)
124
Figure 6–2 (A) The oxyhemoglobin dissociation curve illus-trates the relationship between blood oxygen tension (PO2) andhemoglobin saturation (SaO2). A simple guide summarizing therelationship between PaO2 and SaO2 follows for interpretation ofpulse oximeter readings obtained during clinical monitoring.
PaO2 (mmHg) SaO2 (%) Interpretation
>80 >95 Normal
<60 <90 Significant hypoxemia
<40 <75 Serious life-threatening hypoxemia
(B) A combination pulse oximeter and electrocardiograph. (Courtesy of SurgiVet Inc., Waukesha, WI.)
Plateau Phase
Arterial
Blood
Steep
Phase
Venous
Blood
Oxygen Tension (PO2)
He
mo
glo
bin
Sa
tura
tio
n (
SO
2)
20
0 20 30 40 60 80 120
40
60
80
100
(A)
(B)
Tab
le 6
–3
“Norm
al”
Val
ues
for
Sele
cted M
eas
ure
d P
aram
ete
rs in a
Var
iety
of
Speci
es
Para
mete
rD
og
Cat
Ho
rse
Cow
Go
at/
Sh
eep
Pig
Rab
bit
Tem
per
ature
37–40
37–40
37–38
37–39
37–40
38–40
38–40
(core
°C
)
Hea
rt
70–140
100–200
25–50
60–80
60–90
60–90
200–325
rate
/min
*
Res
pira
tory
10–30
12–40
8–15
12–30
15–30
10–30
30–60
rate
/min
Min
ute
170–350
200–350
NA
NA
100–130
300–400
190–240
ventil
atio
n(m
l/kg
/min
)
Blo
od v
olu
me
75–90
45–65
70–100
57–60
60–70
50–70
55–65
(ml/
kg)
Note
s: T
he
follo
win
g va
lues
are
com
mon to a
ll sp
ecie
s:
ET C
O2
(mm
Hg)
30–40
SpO
2(%
)>
95%
Arter
ial p
H7.
35–7.
45
PaCO
2(m
mH
g)35–45
*Rat
es ten
d to b
e hig
her
in n
eonat
es.
Monitoring Anesthesia 125
PaO
2(m
mH
g)80–100 (
room
air:
FIO
2=
.21)
>300 (
100%
oxy
gen: F IO
2=
1.0
)
Bic
arbonat
e (m
Eq/L
)17–25 (
smal
l anim
als)
25–31 (
larg
e an
imal
s)Bas
e ex
cess
(m
Eq/L
)–4–
+4
Tab
le 6
–4
Trouble
shooting
Identified P
roble
ms
During
Anest
hetic
Monitoring
Co
mp
lica
tio
nP
ote
nti
al
Cau
ses
Man
agem
en
t
Tach
ypnea
Too lig
ht
or
too d
eeply
Ass
ess
anes
thet
ic d
epth
anes
thet
ized
Hyp
oxe
mia
, hyp
erca
rbia
, Ass
ess
arte
rial pH
and b
lood g
asac
idosi
sH
yper
ther
mia
Ass
ess
tem
per
ature
Dru
g in
duce
d (
opio
ids,
Ass
ess
com
plia
nce
, dep
thhal
oth
ane)
Ate
lect
asis
, pneu
moth
ora
x,
Asp
irate
ple
ura
l sp
ace
if in
dic
ated
ple
ura
l ef
fusi
on
Dec
reas
ed
Too d
eeply
anes
thet
ized
Ass
ess
anes
thet
ic d
epth
resp
irato
ry r
ate,
apnea
, ch
ange
in c
har
acte
r
Pre
ssuriz
atio
n in b
reat
hin
g C
hec
k an
esth
esia
mac
hin
eci
rcuit
Tube
occ
lusi
on
Ass
ure
pat
ent
ET t
ube
Effe
ct o
f in
ject
ed a
nes
thet
ic
Pro
vide
ventil
atory
support
until
agen
tssp
onta
neo
us
bre
athin
g re
sum
es
126 Monitoring Anesthesia
Hyp
oth
erm
iaAss
ess
tem
per
ature
, dec
reas
e dep
th, pro
vide
hea
t
Iatroge
nic
hyp
erve
ntil
atio
nAllo
w C
O2
to incr
ease
to t
rigge
r sp
onta
neo
us
ventil
atio
n
Sinu
s br
adyc
ardi
a:*
Dru
g-in
duce
d (
alpha 2
Adm
inis
ter
antic
holin
ergi
cD
ogs
: <
60–
agonis
ts, opio
ids)
agen
t (A
ppen
dix
1)
70/m
inEx
cess
ive
anes
thet
ic d
epth
, Ass
ess
tem
per
ature
, pro
vide
hea
t,C
ats:
<90–
hyp
oth
erm
ia**
dec
reas
e an
esth
etic
dep
th,
100/m
in
adm
inis
ter
antic
holin
ergi
c ag
ent
Hors
es: <
20–
25/m
inC
attle
: <
40–
50/m
in
Sm. R
um
inan
ts:
Hyp
erte
nsi
on, in
crea
sed IC
P<
50/m
inSu
rgic
ally
induce
d v
agal
O
cula
r an
d v
isce
ral m
anip
ula
tion:
stim
ula
tion
stop m
anip
ula
tion
Hyp
ote
nsi
on, m
yoca
rdia
l Ass
ess
AB
P, o
xyge
nat
ion s
tatu
sis
chem
ia
Hyp
erka
lem
iaRev
iew
his
tory
; as
sess
ser
um
[K
+]
(contin
ues
)
Monitoring Anesthesia 127
Tab
le 6
–4
(Continued)
Co
mp
lica
tio
nP
ote
nti
al
Cau
ses
Man
agem
en
t
Sinus
tach
ycar
dia
Too lig
htly
anes
thet
ized
(pai
n)
Ass
ess
anes
thet
ic d
epth
Hyp
ote
nsi
on
Ass
ess
puls
e qual
ity/A
BP
Pro
vide
inotropic
support
Hyp
erca
pnia
, hyp
oxe
mia
Ass
ess
arte
rial blo
od g
ases
Dru
g in
duce
d (
antic
holin
ergi
c,
dis
soci
ativ
e ag
ents
; th
iobar
bitu
rate
s, c
atec
hola
-m
ines
)
Hyp
ote
nsi
on
Too d
eeply
anes
thet
ized
Ass
ess/
reduce
anes
thes
ia d
epth
†
Blo
od o
r flu
id loss
Incr
ease
flu
id a
dm
inis
trat
ion r
ate
Pro
vide
blo
od/c
ollo
id s
upport
Endoto
xem
ia, se
psi
sRev
iew
his
tory
, pro
vide
inotropic
su
pport: dobuta
min
e (2
–10 m
cgor
µg/
kg/m
in);
dopam
ine
(5–10
mcg
or
µg/
kg/m
in);
ephed
rine
(0.0
3–0.1
mg/
kg IV b
olu
s, low
erdose
ran
ge f
or
larg
e an
imal
s)
128 Monitoring Anesthesia
Ventric
ula
r Prim
ary
myo
card
ial dis
ease
/Rev
iew
his
tory
; trea
t w
hen
PVC
sar
rhyt
hm
ias
trau
ma
mee
t lis
ted c
riter
ia(P
VCs)
Hyp
ovo
lem
ia, hyp
ote
nsi
on
Ass
ess
fluid
req
uire
men
ts; AB
PH
yper
capnia
, hyp
oxe
mia
Ass
ess
arte
rial blo
od g
as, pro
vide
ventil
atio
n a
s in
dic
ated
Inad
equat
e an
esth
etic
dep
th
Ass
ess
dep
th; su
pple
men
t an
esth
esia
(pai
n)
as n
eeded
Elec
troly
te im
bal
ance
sRev
iew
his
tory
; as
sess
ser
um
el
ectroly
te c
once
ntrat
ions
Crit
eria
for
PVC
tre
atm
ent:
Lidoca
ine
ther
apy:
1–2 m
g/kg
>
15–20/m
in, m
ulti
foca
l,(0
.2–0.5
mg/
kg f
or
cats
, hors
es):
occ
urren
ce in r
uns,
bolu
s IV
2–4 t
imes
ove
r 20 m
in.
acco
mpan
ied b
y poor
For
repea
ted r
eturn
of
PVC
s: S
tart
puls
e qual
ityin
fusi
on a
t 50–100 m
cg o
r µg/
kg/m
in (
add 1
mg/
ml to
cr
ysta
lloid
flu
id; gi
ve a
t 0.0
5–0.1
m
l/kg
/min
)
ICP =
intrac
rania
l pre
ssure
AB
P =
arter
ial b
lood p
ress
ure
(contin
ues
)
Monitoring Anesthesia 129
Tab
le 6
–4
(Continued)
*G
uid
elin
es for
hea
rt r
ate
are
for
adults
. A h
igher
val
ue
should
be
consi
der
ed a
s “m
inim
um
” hea
rt r
ate
in n
eonat
es.
Neo
nat
es a
re m
ore
dep
enden
t on h
eart r
ate
for
adeq
uat
e ca
rdia
c outp
ut,
and in
gen
eral
, bra
dyc
ardia
should
be
trea
ted
more
agg
ress
ivel
y w
ith a
ntic
holin
ergi
c ag
ent su
pport.
**Anim
als
with
pro
found h
ypoth
erm
ia m
ay n
ot re
spond e
ffect
ivel
y to
antic
holin
ergi
c ag
ents
. Dec
reas
ing
anes
thes
iadep
th a
nd a
ttem
pts
to r
ewar
m a
re im
portan
t as
pec
ts o
f m
anag
emen
t.† A
dm
inis
trat
ion o
f in
trao
per
ativ
e opio
ids
may
hel
p to s
par
e ge
ner
al a
nes
thet
ic r
equire
men
ts w
ith m
inim
al e
ffect
on
myo
card
ial c
ontrac
tility
.130 Monitoring Anesthesia
7Supportive Care During Anesthesia
Supportive care during general anesthesia contributessignificantly to a successful outcome. Many factors, suchas increased patient risk and prolonged, complex, andinvasive procedures, increase the critical need for sup-portive measures that will assure patient homeostasisduring the anesthetic period. Supportive care beginspreoperatively with a thorough patient evaluation,including physical examination and appropriate diag-nostic evaluation and correction of any abnormalitiesidentified, especially fluid and electrolyte deficits and pHabnormalities. Intraoperative support includes appropri-ate fluid administration, assurance of acid-base balance,ventilatory support (Chapter 5), administration ofadjunct drugs as indicated, provision of external heat,
131
and positioning considerations. The most critical factorguiding supportive care during the anesthetic period isadequate monitoring (Chapter 6). Monitoring is the linkbetween recognition of developing problems and rapidcorrection before the problem becomes life threatening.
Fluid Therapy
Fluid therapy usually is unnecessary for short proceduresin healthy patients, although it is always advisable to haveintravenous access established for any anesthetizedpatient, in case of unexpected blood loss, the need forcardiorespiratory supportive drugs, or additionalinjectable anesthetic agents. For high-risk patientsundergoing invasive, prolonged procedures, fluidadministration provides replacement for intraoperativeevaporative losses and third space losses associated withsurgical trauma or the existing primary disease process,and it helps maintain cardiovascular stability and organperfusion, which are altered by anesthetic agents.
Most commonly and for most species, a balancedcrystalloid fluid similar in composition to extracellularfluid (e.g., LRS or Normosol-R) is administered at a rateof 10 ml/kg/hr. After the initial two hours of anesthesia, ifblood loss is minimal and arterial pressure stable,decreasing the fluid rate to 4–8 ml/kg/hr is recom-mended to avoid excessive dilution of packed cell vol-ume (PCV) and total protein, especially duringprolonged procedures. These fluid rate guidelines must
132 Supportive Care During Anesthesia
be adjusted, based on the individual patient, blood orother body fluid loss (e.g., third space loss), and bloodpressure monitoring, to assure adequate tissue perfu-sion. Normal body water percentage and distributionand electrolyte composition of body water and severalcommercially available fluids are listed in Table 7–1.
The following guidelines are for fluid therapy in theperioperative period:
1. Abnormalities identified on preoperative evaluation,including dehydration and acid-base and electrolyteimbalances, should be corrected prior to inductionof anesthesia, whenever possible. Table 7–2 providesa general guide for clinical and laboratory assess-ment of dehydration.
2. Fluids that do not contain an alkalinizing agent (i.e.,0.9% saline, 5% dextrose, Ringer’s) tend to promotemetabolic acidosis (by dilution) if used for pro-longed periods.
3. Blood loss may be replaced with crystalloid fluids atthree times the estimated blood volume as long asPCV remains above 20%. This guideline is based onthe fact that crystalloid fluids distribute to the entireextracellular fluid volume (ECF), which is approxi-mately three times the blood volume.
4. Fluids to which glucose has been added (for 2.5%,add 25 mg/ml; for 5%, add 50 mg/ml) should beadministered to neonates, small patients (<2 kg),
Supportive Care During Anesthesia 133
134 Supportive Care During Anesthesia
Tab
le 7
–1
Body
Wat
er
Com
par
tment
Perc
enta
ges,
the E
lect
roly
te C
om
posi
tion o
fB
ody
Wat
er,
and C
om
monly
Use
d P
arente
ral Fl
uid
s Ele
ctro
lyte
Co
mp
osi
tio
n (
mEq
/L)
Perc
en
tage (
% �
Na
Cl
KH
CO
3*
Ca
+2
MG
+2
Osm
**B
W i
n k
g y
ield
s L)
Body
wate
r sp
ace
Tota
l body
wat
er60%
(60–75%
: hig
her
in n
eo-
nat
es; lo
wer
w
ith o
bes
ity)
ECF
(ext
race
llula
r20–30%
fluid
)
Pla
sma
volu
me
5%
142
106
524
52
282
Blo
od v
olu
me
8–10%
(dep
ends
on h
emat
ocr
it)
Inte
rstit
ial flu
id15–25%
145
115
430
32
(EC
F—pla
sma
volu
me)
ICF
(intrac
ellu
lar flu
id)
30–40%
13
2155
10
22
35
Supportive Care During Anesthesia 135
Com
mer
cial flu
ids
LRS
130
109
428
30
272
Rin
ger’s
147
156
40
50
312
Norm
oso
l-R
148
98
527(a
)5
0296
23(g
)
Multi
sol-R
140
98
527(a
)3
3294
23(g
)
5%
dex
trose
(5 g
m0
00
00
0252
/dl gl
uco
se)
0.9
% s
alin
e154
154
00
00
308
Hyp
erto
nic
sal
ine
1200
1200
00
00
2400
(7%
)
1.3
% N
aHCO
3156
00
156
00
312
5%
NaH
CO
3600
00
600
00
1200
8.4
% N
aHCO
31000
00
1000
00
2000
(1 m
Eq/L
)
*O
r bic
arbonat
e-lik
e pre
curs
or:
LRS
(lac
tate
); N
orm
oso
l-R, o
r M
ulti
sol-R
(ac
etat
e [a
] or
gluco
nat
e [g
]).
**m
Osm
ol/
L.
136 Supportive Care During Anesthesia
Tab
le 7
–2
Clin
ical
and L
abora
tory
Ass
ess
ment
of
Dehyd
ration
Sk
in
TP
**%
Deh
yd
rati
on
*Te
nt
MM
Mo
istu
reEye
CR
TP
CV
**(%
)(g
m/d
l)
5–6%
2–3 s
ecM
ois
t but
Brig
ht,
slig
htly
<3 s
ec40–60
7.0–8.0
stic
kysu
nke
n
7–9%
3–5 s
ecSt
icky
to d
ryD
ull,
sunke
n3–4 s
ec60–65
8.0
–9.0
>9%
>5 s
ecD
ry, cy
anotic
Corn
ea d
ry>
4 s
ec>
65%
>9.0
Note
: Fl
uid
req
uire
men
ts for
deh
ydra
tion a
re c
alcu
late
d b
y th
e eq
uat
ion
Fluid
to a
dm
inis
ter
(L)
= %
deh
ydra
tion �
body
wei
ght (k
g)
When
tim
e per
mits
, it is
bes
t to
rep
lace
flu
id d
efic
it sl
ow
ly, o
ver
12–24 h
r to
allo
w w
hole
body
redis
trib
utio
n.
MM
= m
uco
us
mem
bra
ne
CRT
= c
apill
ary
refil
l tim
e
PC
V =
pac
ked c
ell v
olu
me
TP =
tota
l pro
tein
*≤
5%
deh
ydra
tion is
not cl
inic
ally
det
ecta
ble
.
**N
orm
al P
CV a
nd T
P v
alues
var
y am
ong
spec
ies
(Tab
le 1
–3)
and w
ill b
e af
fect
ed b
y under
lyin
g
conditi
ons
that
affe
ct n
orm
al v
alues
, such
as
anem
ia a
nd h
ypopro
tein
emia
.
avian patients, and animals at risk for hypoglycemia(e.g., those with insulinoma, diabetes mellitus, por-tal caval shunt) to avoid a hypoglycemic crisis. It isadvisable to monitor blood glucose levels duringprolonged anesthetic periods.
5. Administration of large quantities of fluids at roomtemperature can contribute significantly to hypother-mia. Efforts should be taken to warm fluids (cocoon-ing the administration line in hot water bottles,warming the fluids, using commercially availableinfusion warmers during prolonged administration;Figure 7–1), especially in small patients.
6. Administration of large quantities of fluids can con-tribute to the development of cerebral and pul-monary edema (this depends on many factors,including fluid administration rate, patient’s serumprotein concentration, and cardiac function). In at-risk patients, consider administration of a colloid, ifnecessary, to maintain adequate circulating volumeand blood pressure.
7. Animals that may not handle volume overload (e.g.,those with mitral insufficiency) should receive fluidsat 50% or less the standard rate.
8. Maximum rate of fluid administration is 90 ml/kg/hr for most domestic species; cats should notreceive greater than 50 ml/kg/hr. Higher rates (upto 360 ml/kg/hr) probably will be tolerated inrelatively healthy patients; administer fluids as rap-
Supportive Care During Anesthesia 137
138
Figure 7–1 Infusion warmers are available in two sizes toaccommodate fluid and blood administration sets. These devicesare especially useful for administering blood products or large vol-umes of fluid during prolonged procedures to help minimizehypothermia. (Reprinted with permission from Thurmon et al.,eds., Lumb and Jones’ Veterinary Anesthesia, 3rd ed., Baltimore:Williams & Wilkins, 1996, page 579.)
idly as necessary to achieve hemodynamic stabilityand decrease the rate as soon as this occurs.
9. For hypokalemic animals, it is best to correct thedeficit prior to anesthesia; K+-supplemented fluidsadministered during anesthesia could result in car-diac conduction disturbances, if fluid administrationwere suddenly increased. Potassium supplementa-tion is common (adding 10–30 mEq/L) duringsupportive care of patients with a variety of abnor-malities, such as anorexia, diarrhea, or vomiting.Intravenous potassium administration must notexceed 0.5 mEq/kg/hr.
10. Intraoperative serial assessment of packed cell vol-ume and total protein is advisable in prolonged pro-cedures and necessary when significant blood lossoccurs. While numbers vary in the literature, bloodloss greater than 20% of total blood volume (i.e.,8–10% of body weight; Table 6–3) in healthy patientsand greater than 10% loss in critical patients shouldbe replaced with whole blood, packed red cells, or anartificial blood solution, depending on availability.Colloids should be administered when hypopro-teinemia is present or when crystalloid fluids fail tomaintain adequate blood pressure (i.e., minimum of60 mmHg, mean arterial pressure). Table 7–3 listssome available blood and colloid products and basicindications and guidelines for use.
Supportive Care During Anesthesia 139
140 Supportive Care During Anesthesia
Tab
le 7
–3
Adju
nct
s to
Flu
id T
hera
py
During
Anest
hesi
a: I
ndic
atio
ns,
Sid
e E
ffect
s,an
d G
enera
l G
uid
elin
es
for
Use
Pro
du
ctIn
dic
ati
on
sSid
e E
ffect
sD
osa
ge/C
om
men
ts
Blo
od r
epla
cem
ents
Whole
blo
od*
Anem
ia,
Imm
une
reac
tion
1. Bas
ed o
n e
stim
ated
loss
hem
orrhag
ecr
oss
-mat
ch is
2. Bas
ed o
n e
quat
ion:
reco
mm
ended
es
pec
ially
with
re
pea
t tran
s-fu
sions
3. Em
piri
cal:
10–40 m
l/kg
(d
og)
and 5
–20 m
l/kg
(cat
s), freq
uen
t re
asse
ss-
men
tPa
cked
red
cel
ls**
Anem
ia,
Sam
e as
pre
vious
Sam
e as
pre
vious.
Dilu
te
hem
orrhag
ew
ith s
alin
e to
adm
inis
ter.
Blo
od s
ubst
itute
†Anem
ia,
Urin
e/tis
sue
15–30 m
l/kg
: ra
te <
10 m
l/hem
orrhag
edis
colo
ratio
n,
kg/h
r vo
lum
e ove
r-lo
ad, ar
ryth
mia
s,
renal to
xici
ty
Amou
nt =
desi
red
PCV
– ac
tual
PC
V
dono
r PC
V
�re
cipi
ent b
lood
vol
ume
Supportive Care During Anesthesia 141
Collo
ids
Pla
sma*
Hyp
opro
tein
emia
,Alle
rgic
rea
ctio
n,
10–20 m
l/kg
, in
itial
em
piri
cal
volu
me
volu
me
ove
r-dose
. C
alcu
latio
n m
ay b
eex
pan
sion
load
bas
ed o
n t
he
equat
ion:
End p
oin
t dire
cted
by
seria
l TP
ass
essm
ent.
Intrav
ascu
lar
life-
span
: 4–15
day
s
Dex
tran
(40 a
nd 7
0)
Sam
e as
for
Sam
e as
for
5–20 m
l/kg
ove
r 24 h
rpla
sma
pla
sma,
(m
ore
rap
id f
or
shock
)co
agulo
pat
hy
End p
oin
t is
dire
cted
by
stab
iliza
tion o
f AB
P.In
trav
ascu
lar lif
e-sp
an: 2–24 h
r
Het
asta
rch
Sam
e as
for
Sam
e as
for
5–20 m
l/kg
ove
r 24 h
rpla
sma
pla
sma,
(m
ore
rap
id f
or
shock
)co
agulo
pat
hy
End p
oin
t is
dire
cted
by
stab
iliza
tion o
f AB
P.(c
ontin
ues
)
Amou
nt =
desi
red
TP –
act
ual T
P
dono
r pl
asm
a TP
�re
cipi
ent p
lasm
a vo
lum
e
142 Supportive Care During Anesthesia
Tab
le 7
–3
(Continued)
Pro
du
ctIn
dic
ati
on
sSid
e E
ffect
sD
osa
ge/C
om
men
ts
Intrav
ascu
lar
life-
span
: 6 h
r (l
onge
r fo
r Pe
nta
star
ch)
Alk
alin
izin
g a
gen
ts
Bic
arbonat
eM
etab
olic
In
trac
ellu
lar
1. Adm
inis
ter
if pH
<7.
2 o
rac
idosi
sac
idosi
sbas
e def
icit
is >
—10 m
Eq/L
. Avo
id in t
he
pre
sence
of
hyp
ove
ntil
atio
n b
ecau
se
hyp
erca
pnia
is
exac
erbat
ed
and p
H f
urt
her
dec
reas
ed
by
incr
ease
d f
orm
atio
n o
f C
O2
when
HCO
3co
mbin
es
with
H+
ions.
Do n
ot
coad
-m
inis
ter
with
Ca+
+or
blo
od p
roduct
s.2. Q
uan
tity
to a
dm
inis
ter
is
bas
ed o
n b
ase
def
icit.
Q
uan
tity
(mEq
/L)
= B
ase
def
icit
�0.3
�body
Supportive Care During Anesthesia 143
wei
ght
(kg)
. G
ive
1/4
–1/2
of
calc
ula
ted d
efic
it ove
r 30 m
in a
nd r
eass
ess.
Trom
etham
ine
Met
abolic
O
smotic
diu
resi
s,1. D
osa
ge (
ml)
= b
ase
def
icit
org
anic
am
ine
acid
osi
shyp
ogl
ycem
ia�
1.1
�body
wei
ght
(kg)
buffer
(0.3
M)
incr
ease
s 2. Adm
inis
ter
slow
ly; ra
pid
coag
ula
tion
infu
sion c
an c
ause
ECG
tim
esch
ange
s si
mila
r to
hyp
er-
kale
mia
.
3. Adm
inis
trat
ion is
contrai
n-
dic
ated
with
ure
mia
and
anuria
.
Car
diov
ascu
lar
drug
s
Lidoca
ine
Ventric
ula
r Se
e cr
iteria
in t
ext
Dosa
ges
liste
d in T
able
6–4.
arrh
ythm
ias,
Avo
id w
hen
hea
rt r
ate
isve
ntric
ula
r lo
w (
<120–140/m
in f
or
tach
ycar
dia
dogs
); it
may
induce
pro
-fo
und b
radyc
ardia
and
hav
e si
gnifi
cant
neg
ativ
e ef
fect
on c
ardia
c outp
ut.
(contin
ues
)
144 Supportive Care During Anesthesia
Tab
le 7
–3
(Continued)
Pro
du
ctIn
dic
ati
on
sSid
e E
ffect
sD
osa
ge/C
om
men
ts
Dobuta
min
eH
ypote
nsi
on
Sinus
tach
ycar
dia
,2–10 µ
g/kg
/min
ute
arrh
ythm
ias
Dopam
ine
Hyp
ote
nsi
on,
Sinus
tach
ycar
dia
,5–10 µ
g/kg
/min
: lo
w d
ose
dec
reas
ed
arrh
ythm
ias
(2–5 µ
g/kg
/min
) is
urin
e re
com
men
ded
for
pro
duct
ion
incr
easi
ng
renal
per
fusi
on to
impro
ve u
rine
form
atio
n.
Ephed
rine
Hyp
ote
nsi
on
Sinus
tach
ycar
dia
0.0
3–0.1
mg/
kg IV b
olu
s:
low
er d
ose
ran
ge f
or
larg
ean
imal
s. R
eported
to s
par
eute
rine
blo
od f
low
, w
hic
hm
ay b
e par
ticula
rly b
enef
i-ci
al f
or
pre
gnan
t pat
ients
.
Epin
ephrin
eRef
ract
ory
Arr
hyt
hm
ias
0.0
1–0.0
3 µ
g/kg
/min
hyp
ote
nsi
on
Sinus
tach
ycar
dia
Contrai
ndic
ated
durin
g hal
oth
ane
anes
thes
ia
Supportive Care During Anesthesia 145
Isopro
tere
nol
Bra
dyc
ardia
Arrhyt
hm
ias,
0.0
1–0.1
µg/
kg/m
inhyp
ote
nsi
on
(B2 e
ffec
t)
Note
: Blo
od a
nd p
lasm
a m
ust
be
adm
inis
tere
d thro
ugh
in-li
ne
filte
r to
rem
ove
clo
ts a
nd c
ellu
lar
deb
ris. B
lood s
hould
not be
mixed
with
cal
cium
- or
bic
arbonat
e-co
nta
inin
g flu
ids.
*Fre
sh w
hole
blo
od a
nd fre
sh fro
zen
pla
sma
also
are
effe
ctiv
e in
tre
atin
g co
agulo
pat
hy, in
cludin
g vo
n W
illeb
rand’s
dis
-ea
se. T
he
form
er a
lso is
effe
ctiv
e in
tre
atm
ent of th
rom
bocy
topen
ia. T
he
latte
r al
so is
effe
ctiv
e in
tre
atin
g pla
tele
t dys
-fu
nct
ion a
nd s
pec
ific
clotti
ng
fact
or
def
icits
.
**Pa
cked
cel
ls a
re b
ette
r fo
r an
emia
notac
com
pan
ied b
y hyp
ovo
lem
ia, w
hile
whole
blo
od o
r pac
ked c
ells
plu
s co
lloid
are
bet
ter
for
acute
(si
gnifi
cant)
hem
orrhag
e.† S
ever
al p
roduct
s ex
ist,
incl
udin
g free
-hem
ogl
obin
-bas
ed, l
iposo
me-
enca
psu
late
d h
emogl
obin
and p
erflu
roro
carb
ons;
and o
ne
pro
duct
, Oxy
globin
™ (
free
-hem
ogl
obin
bas
ed), c
urren
tly is
appro
ved for
use
in v
eter
inar
y m
edic
ine.
11. Metabolic acidosis may be preexisting or developduring anesthesia due to poor perfusion orhypothermia and may require treatment in somecases. Alkalinizing agents should be considered ifthe pH is <7.2 and the acidosis is due to the meta-bolic component (i.e., PCO2 is within normal limits;see the acid-base section later).
Routes of Administration
While subcutaneous fluid replacement with isotonicfluid (preferably without dextrose or at concentrations≤2.5%) is acceptable for mild dehydration, moderate tosevere dehydration requiring relatively rapid correctionshould be treated with intravenous fluids. While venousaccess usually is no problem in most species under rela-tively normal conditions, neonates and severely volume-depleted animals can present a challenge. For very smalland very hypotensive patients or patients with throm-bosed peripheral vasculature, the intraosseous route offluid administration may provide the necessary access toreestablish fluid balance prior to and during anesthesia.This route also is effective for infusion of a variety ofanesthetic agents and cardiosupportive drugs. The mostcommon access sites in small animals include the medialsurface of the proximal tibia 1–2 cm distal to the tibialtuberosity, the tibial tuberosity, the trocanteric fossa ofthe femur, the wing of the ilium, the ischium, and thegreater tubercle of the humerus. In birds, access sites
146 Supportive Care During Anesthesia
include the distal ulna and the proximal tibiotarsus (see Figure 11–2). A spinal needle (20–22 ga) is pre-ferred if patient size will accommodate placement. Hypo-dermic needles (22–25 ga) are more appropriate forvery small patients, but these have a tendency to becomeblocked with a bone piece during entry through the cor-tex. The needles are placed aseptically, capped, and uti-lized like IV catheters; they usually are sewn or taped tothe skin using a tape butterfly and protected with a bulkywrap to prevent bending or breaking. Fluid rate is lim-ited to 11 ml/min and can be doubled using pressuriza-tion (300 mmHg). Contraindications for intraosseouscannulation include recent fractures, pneumatic bones,infection over the access site, and sepsis.
Acid-Base Balance
Normal blood pH (7.35–7.45) is maintained throughthree general mechanisms: buffer systems (bicarbonate isthe major extracellular buffer, where pH = 6.1 + logHCO3
–/H2CO3–; hemoglobin, plasma protein, and phos-
phate play a lesser role) cushion insults that alter the pH;the lungs (respiratory mechanism) alter the pH throughchanges in PCO2 (normal PaCO2 = 35–45 mmHg;hypoventilation will increase PaCO2, and hyperventila-tion will decrease PaCO2); and the kidney (metabolicmechanism) affects the pH through excretion of H+ andgeneration and resorption of HCO3
– (normal: HCO3– =
17–31 mEq/L).
Supportive Care During Anesthesia 147
The acid-base status should be assessed prior to anes-thetic induction in high-risk patients. If preexisting meta-bolic disorders are identified, anesthesia should bepostponed until the disorders are corrected, as generalanesthesia can exacerbate an acid-base imbalance. Dis-orders of the pH can affect electrolyte concentrations(the pH affects potassium concentration inversely:decreased pH ⇒ increased K+ and vice versa; pH affectsionized calcium inversely: decreased pH ⇒ increasedionized Ca++ and vice versa), cardiac contractility, vascu-lar responsiveness, and normal cellular function.
Four primary disturbances in pH balance can occur(Table 7–4), and the complexity of interpretation isincreased by compensatory responses (the opposing sys-tem responds to turn pH back toward the normal range)and the potential for a mixed disorder in some patients.
Oxygenation
Arterial oxygen tension (PaO2), included in routine arte-rial blood gas analysis, provides accurate assessment ofthe patient’s ability to oxygenate the blood and provideadequate tissue oxygenation during anesthesia. Tissueoxygenation is determined by hemoglobin concentra-tion, hemoglobin saturation (SpO2, which is determinedby PaO2; Figure 6–2A), and blood delivery (cardiacoutput as reflected by arterial blood pressure). Five factorscontribute to decreased arterial oxygen tension (PaO
2):
148 Supportive Care During Anesthesia
Supportive Care During Anesthesia 149
Tab
le 7
–4
Altera
tions
in, C
ause
s of,
and C
om
pensa
tory
Mech
anis
ms
Invo
lved in
Aci
d-B
ase B
alan
ce
Pri
mary
Dis
ord
er/
No
nco
mp
en
sate
dC
om
pen
sate
d**
Co
mp
en
sato
ry
pH
PC
O2
HC
O3*
pH
PC
O2
HC
O3
Cau
ses
Resp
on
se
Res
pira
tory
aci
dosi
s/↓
↓↑
↑↓
↑↑
↑Anes
thes
ia, obes
ity,
met
abolic
alk
alosi
sth
ora
cic
or
bra
in d
isea
se
Res
pira
tory
alk
alosi
s/↑
↑↓
↓↓
↓↓
↓Ia
troge
nic
, ex
cess
ive
met
abolic
aci
dosi
s IP
PV,
fev
er, hyp
o-
xem
ia, an
xiet
y
Met
abolic
aci
dosi
s/↓
↓Ν
↓↓
↓↓
Poor
per
fusi
on,
resp
irato
ry a
lkal
osi
ssh
ock
, re
nal
dis
-ea
se, ke
toac
ido-
sis,
dia
rrhea
Met
abolic
alk
alosi
s/
↑↑
Ν↑
↑↑
↑Acu
te v
om
iting,
re
spira
tory
aci
dosi
supper
GI o
bst
ruc-
tion (
rum
inan
ts),
hyp
oka
lem
ia
(contin
ues
)
150 Supportive Care During Anesthesia
Tab
le 7
–4
(Continued)
Note
: Tw
o a
cid-b
ase
dis
turb
ance
s ca
n o
ccur
indep
enden
tly (
e.g.
, tra
um
a re
sulti
ng
in s
hock
and s
ever
e pulm
onar
y hem
-orrhag
e re
sulti
ng
in m
etab
olic
and r
espira
tory
aci
dosi
s) w
ith in
crea
sed s
ever
ity in
the
pH
chan
ges,
or,
in the
case
of tw
oopposi
ng
indep
enden
t dis
ord
ers
(met
abolic
alk
alosi
s as
soci
ated
with
upper
GI obst
ruct
ion w
ith a
nes
thet
ic-in
duce
d r
es-
pira
tory
dep
ress
ion), c
an e
xist
with
a n
ear
norm
al p
H. K
now
ledge
of th
e ca
se h
isto
ry a
nd la
bora
tory
fin
din
gs w
ill h
elp to
dis
cern
com
pen
sato
ry r
esponse
ver
sus
two p
rimar
y dis
ord
ers.
Durin
g an
esth
esia
, correc
tion o
f re
spira
tory
-induce
d p
H c
han
ges
invo
lves
an a
ppro
pria
te c
han
ge in
ven
tilat
ory
support.
Met
abolic
aci
dosi
s is
bes
t co
rrec
ted p
rior
to a
nes
thes
ia. T
reat
men
t w
ith b
icar
bonat
e sh
ould
be
consi
der
ed if
the
bas
eex
cess
val
ue
(norm
al v
alues
are
list
ed in
Tab
le 6
–3)
is g
reat
er than
–10 m
Eq/L
and o
nly
if n
orm
al P
aCO
2va
lues
are
esta
blis
hed
. Bic
arbonat
e dosa
ge in
mEq
/L =
Bas
e ex
cess
val
ue
�BW
(kg
) �
0.3
.
Giv
e ap
pro
xim
atel
y one
fourth the
dose
and r
eass
ess
blo
od g
as a
nal
ysis
. Rep
eat until
pH
and b
ase
exce
ss r
eturn
to
norm
al li
mits
. Met
abolic
alk
alosi
s is
tre
ated
by
adm
inis
trat
ion o
f bic
arbonat
e-free
flu
ids
(e.g
., 0.9
% s
alin
e).
*H
CO
3in
crea
ses
with
res
pira
tory
aci
dosi
s an
d d
ecre
ases
with
res
pira
tory
alk
alosi
s by
appro
xim
atel
y 1–2 m
Eq/L
for
each
10 m
mH
g ch
ange
in P
CO
2ac
cord
ing
to the
equat
ion:
CO
2+
H2O
←→H
2CO
3←→
HCO
3–
+ H
+
**As
a ge
ner
al r
ule
, the
com
pen
sato
ry r
esponse
occ
urs
when
the
prim
ary
dis
turb
ance
bec
om
es c
hro
nic
and a
cts
tobrin
g th
e blo
od p
H b
ack
tow
ard
(but usu
ally
not co
mple
tely
into
) th
e norm
al r
ange
, whic
h h
elps
diff
eren
tiate
prim
ary
from
com
pen
sato
ry c
han
ges.
Com
pen
sato
ry r
espira
tory
mec
han
ism
s ar
e m
axim
al w
ithin
8–12 h
r. C
om
pen
sato
ry m
eta-
bolic
mec
han
ism
s ar
e m
axim
al w
ithin
3–5 d
ays
and m
ore
effe
ctiv
e (t
han
res
pira
tory
) in
ret
urn
ing
the
pH
to n
orm
al.
decreased inspired concentration (FIO
2), hypoventilation,
diffusion abnormality, ventilation-perfusion (VQ) mismatch,and right-to-left shunt. All but the last benefit fromenriched oxygen delivery (FIO2 = 1.0 or 100% versusroom air; FIO2 = 0.21 or 21%). Anesthetized patients aresusceptible to hypoventilation and VQ mismatch, espe-cially horses, and supplemental oxygen is recommendedin all patients, especially those at increased risk for devel-opment of hypoxemia (e.g., those with respiratoryabnormalities). Hypoxemia is defined as PaO2 <60mmHg (which corresponds approximately to SpO2 =90%). The PaO2 value should be maintained at leastabove 60 mmHg and preferably above 100 mmHgthroughout the perianesthetic period.
Intraoperative Adjunct Drugs
The use of various agents to support cardiac perform-ance during general anesthesia is guided by the moni-toring devices applied during the anesthetic period.Continuous electrocardiography detects rhythm distur-bances that might benefit from therapeutic intervention,and quantitative blood pressure monitoring (either inva-sive or noninvasive) guides the need for inotropic sup-port. Ventricular premature complexes should be treated ifthey are multiform, appear to be superimposed on theprevious T wave, occur in runs, are >15–20/min infrequency, or have a significant detrimental effect onarterial blood pressure. Lidocaine dosages are listed in
Supportive Care During Anesthesia 151
Table 6–4. Ventricular tachycardia may respond to lido-caine if a pulse is present and the rate is ≥150/minute.
Hypotension not responsive to fluid bolus anddecreasing the depth of anesthesia may benefit frominotropic agent administration. Dobutamine anddopamine must be administered as an infusion due totheir short duration of effect. Ephedrine, as an IV bolus,will provide blood pressure support by both direct andindirect effects at both alpha and beta receptors; theeffects may persist for 10–30 min. Dosages are listed inTable 6–4. An ECG should be monitored during admin-istration, as these agents can promote arrhythmias. Infu-sion of epinephrine has been suggested for hypotensionthat fails to respond to the more commonly usedinotropes. Due to its inherent arrhythmogenicity, epi-nephrine should be reserved for refractory cases andavoided during halothane anesthesia.
Prevention of Hypothermia
Hypothermia occurs commonly during general anesthe-sia, especially in small and neonatal patients, due to therelatively large body surface to mass ratio and contribut-ing factors including inhalation of dry, cold anestheticgases; contact with cold surfaces; wet skin from surgicalsite preparation; exposure of body cavities during theprocedure; anesthetic-induced vasodilation; and ther-moregulatory depression. Severe hypothermia can causebrain damage, ventilatory depression, life-threatening
152 Supportive Care During Anesthesia
cardiac arrhythmias and conduction disturbances, and acid-base and electrolyte derangements, whichcontribute significantly to delayed recoveries. Severalmethods are available to limit heat loss during anesthe-sia, including maintaining the ambient temperaturebetween 21 and 25°C, keeping the patient on a circulat-ing water blanket, applying “space” wraps or forced airblanket heaters when possible, and using warmed intra-venous crystalloid fluids when relatively large quantitiesare administered. Minimizing anesthesia time is one ofthe most critical factors in the prevention of severehypothermia. Monitoring the patient’s temperature withan esophageal probe to assess the core temperature isthe most accurate representation of the patient’s heatbalance. Small patients benefit from recovery in incuba-tors, if available. Measures to facilitate return to nor-mothermia during recovery include providing a warmambient temperature, using water-circulating blankets to“cocoon” the patient, using heat lamps, and administer-ing warm IV fluids, if therapy is continued into the post-operative period. As patients recover, shivering invariablyoccurs as part of the warming process and can increaseoxygen consumption fivefold, often at a time when res-piration still is depressed. Providing supplemental oxy-gen until the body temperature has returned to nearnormal helps prevent development of hypoxemia and isespecially important in high-risk patients, such as thosewith underlying respiratory or cardiac abnormalities.Temperature monitoring should be continued until the
Supportive Care During Anesthesia 153
temperature returns to normal. To avoid hyperthermia,it is advisable to remove heating devices once the bodytemperature reaches 98–99°F and the patient is awakeand showing spontaneous movement.
Positioning Considerations
Padding and positioning are of greater concern in largeanimal patients, but some considerations for positioningsmall animal patients deserve mention. Considerationsfor both large and small patients assume even greaterimportance during prolonged procedures. Tiltingpatients to a “head-down” position, as for ovariohysterec-tomy, has minimal adverse effects in the short term andin healthy patients but should be avoided for prolongedperiods and in high-risk patients due to respiratory com-promise. Positioning the forelimbs forward is commonand not detrimental if done loosely. However, extremeextension of the forelimbs can interfere with respiratorymovement and cause brachial neuropathy if applied forlong periods of time. The dependent lung (lateralrecumbency) becomes atelectic over time, and this effectis exacerbated with duration of anesthesia. In patientswith unilateral lung disease, it is beneficial to place themore “normal” lung up, when possible. Assure that theairway stays patent by keeping the neck and head slightlyextended and assure unrestricted respiratory movement(equipment and elbows should not be placed on thethoracic area).
154 Supportive Care During Anesthesia
Large animal patients should be placed on apadded surface to minimize the risk of postanestheticmyopathy—this is essential for equine patients during gasanesthesia. Available padding includes bags that can befilled with air once the animal is positioned (dunnagebags) and thick (4 in. minimum) foam- or water-filledpads. Laterally recumbent animals should have the lowerforelimb extended forward to minimize the risk ofentrapping the brachial plexus with resultant neuropa-thy. The upper limbs should be supported to maintainthem parallel to the table surface (see additional species-specific recommendations in species chapters). Theseconsiderations are of lesser importance in small rumi-nants and camelids, but padding (2 in. minimum)should be provided for these patients.
Supportive Care During Anesthesia 155
8
Pain Management
The definition, recognition, and management of painhas become a central issue in veterinary practice due toincreased awareness and knowledge by veterinarians andpet owners. Pain is an unpleasant sensory or emotionalexperience associated with actual or potential tissuedamage and has been described as “an experience forwhich there is no direct measure.” Pain causes distressand suffering, which contributes greatly to the stressassociated with hospitalization and anesthesia. A series ofbehavioral, physiologic, endocrine, metabolic, and cellu-lar responses accompany pain, which maintain andamplify the pain response. Except to warn that some-thing is wrong, pain rarely, if ever, has beneficial effects,and unmanaged pain interferes with normal behavior
157
patterns. Activation of the sympathetic nervous systemsecondary to pain may result in protein catabolism,abnormal renal function, electrolyte disturbances,immune suppression, and delayed healing.
Pain is difficult to quantitate because many animalsare stoic; and signs of pain vary greatly with species,breed, age, health status, behavioral patterns, and painintensity. Table 8–1 lists physiologic and behavioral signsthat may be (but are not exclusively) associated with painas well as some specific painful insults and the expecteddegree of associated pain. Because signs of pain are oftennonspecific and sometimes discrete, management ofpain in veterinary patients often is inadequate. It isimportant to maintain a liberal attitude regarding anal-gesic therapy. While overtreatment may occur, the con-sequences of unnecessary analgesia and side effects mustbe weighed against the detrimental effects of unrelievedpain. In general, any procedure known to be painful inhumans should be assumed to be painful in animals andtreated appropriately.
Physiology of Pain
Nociceptive signals are transmitted to the spinal cord byfine myelinated A-delta fibers and unmyelinated C fibers,with their cell bodies contained in the dorsal root gan-glia. Two neuron types have been identified: nociceptivespecific neurons (which respond to input from discrete
158 Pain Management
Pain Management 159
Tab
le 8
–1
Phys
iolo
gic
and B
ehav
iora
l Sig
ns
That
May
Be A
ssoci
ated w
ith P
ain a
nd
Som
e E
xam
ple
s of
Pai
nfu
l In
sults
and t
he E
xpect
ed D
egre
e o
f A
ssoci
ated P
ain
Ph
ysi
olo
gic
Sig
ns*
Beh
avio
ral
Sig
ns
Pain
ful
Insu
lt/D
egre
e o
f P
ain
**
Tach
ypnea
Voca
lizat
ion
Surg
ery† :
mild
, m
oder
ate,
sev
ere
Tach
ycar
dia
Res
tless
nes
sM
ild t
o m
oder
ate
surg
ical pain
:
Hyp
erte
nsi
on
Agi
tatio
nC
astrat
ion, ova
riohys
tere
ctom
y,
explo
rato
ry
Dila
ted p
upils
Abnorm
al p
ost
urin
gLa
par
oto
my,
onyc
hec
tom
y
Saliv
atio
nPe
rsonal
ity c
han
geSe
vere
to d
istres
sing s
urg
ical pain
:
Pale
muco
us
Anore
xia
Am
puta
tions,
orthoped
ic
mem
bra
nes
pro
cedure
s, t
hora
coto
mie
s,
Car
dia
c D
ecre
ased
gro
om
ing
Spin
al s
urg
ery,
auric
ula
r su
rger
y,
arrh
ythm
ias
per
ianal
surg
ery
Hyp
ergl
ycem
iaEx
cess
ive
licki
ng
or
chew
ing
Trau
ma—
mild
to d
istres
sing
Obliv
ious
to s
urroundin
gsPa
ncr
eatit
is—
dis
tres
sing
Perit
oniti
s—dis
tres
sing
*M
any
sign
s m
ay b
e diff
icult
to d
iffer
entia
te fro
m e
ffect
s of an
esth
etic
em
erge
nce
and d
rugs
adm
inis
tere
d d
urin
g th
ean
esth
etic
per
iod e
spec
ially
in the
imm
edia
te p
ost
oper
ativ
e per
iod.
**D
egre
e of pai
n a
ssoci
ated
with
a s
pec
ific
insu
lt va
ries
grea
tly w
ith in
div
idual
anim
al a
nd s
urg
ical
tec
hniq
ue.
†Su
rgic
al p
ain is
div
ided
into
the
thre
e ca
tego
ries,
with
more
inva
sive
pro
cedure
s an
d m
ore
ext
ensi
ve tis
sue
trau
ma
causi
ng
grea
ter
pai
n.
topographical areas) and wide dynamic range neurons(which respond to a wide range of stimuli). It is believedthat the latter type is more important in nociception andresponsible for central sensitization of receptive fieldswith long-term activation of afferent pathways, which hasbeen referred to as wind up. This mechanism is believedto be due to repeated C-fiber stimulation, which leads tocontinued release of neurotransmitters that facilitatenociception (e.g., substance P, glutamic acid, N-methyl-D-aspartate [NMDA], neurotensin, cholecystokinin).Once activated, transmission of afferent signals to higherbrain centers, including the thalamic, medullary, pon-tine, and cortical regions, occurs via the spinothalamic,spinocervical, spinomesencephalic, and spinoreticulartracts.
Pain perception is a complex process that may bemodified clinically at several sites, including reduction ofafferent input (local techniques), signal integration andtransmission (regional techniques), or integration andrecognition at higher centers (parenterally administeredagents). Analgesic administration before the onset of pain(preemptive analgesia) provides better control of pain inthe postoperative period. Combining agents that act atdifferent sites (multimodal therapy) may provide supe-rior pain management for both acute and refractorypain with fewer side effects. With these considerations inmind, the following agents and techniques provide sev-eral options for pain management.
160 Pain Management
Therapeutic Options
Agents for pain management may be administered on ascheduled basis or dictated by dynamic patient assess-ment. Available drugs for analgesia include the opioidsand alpha
2agonists, applied epidurally or parenterally;
local anesthetic agents; ketamine; and nonsteroidal anti-inflammatory agents (NSAIDs).
Opioids
Opioid agonists and agonist-antagonists are effective inthe management of acute moderate to severe pain andalso provide variable degrees of sedation. Opioids areclassified according to the specific opioid receptor thatthey modulate, vary in their analgesic and sedative prop-erties, and are scheduled according to their potential foraddiction (Appendix 2). Pure agonists, including mor-phine, oxymorphone, hydromorphone, meperidine,and fentanyl, provide analgesia with variable durations ofaction (Table 8–2). Side effects include dose-dependentrespiratory depression and a vagomimetic effect, whichpromotes bradycardia. Myocardial contractility is well-maintained with opioids.
Morphine and meperidine may cause histaminerelease, resulting in hypotension, when administeredintravenously (IV); therefore, the subcutaneous or intra-muscular routes are preferred. The short duration ofaction and low potency of meperidine makes it less
Pain Management 161
162 Pain Management
Tab
le 8
–2
Dosa
ges
of
Anal
gesi
c A
gents
in D
ogs
and C
ats
Do
se (
mg/k
g)
Do
gC
at
Ro
ute
Du
rati
on
(h
r)C
om
men
ts
Syst
emic
opio
ids
Morp
hin
e0.0
5–0.6
0.0
5–0.2
IM, SC
2–6
Use
with
tra
nquili
zer
(cat
s)SR
(su
stai
ned
-1.0
–3.0
–PO
12
rele
ase)
Oxy
morp
hone
0.0
5–0.2
0.0
5–0.1
IM, SC
, 2–6
Use
with
tra
nquili
zer
IV(c
ats)
, 4 m
g m
axdose
Hyd
rom
orp
hone
0.1
–0.2
0.0
5–0.1
IM, SC
2–4
Use
with
tra
nquili
zer
(cat
s)
Mep
erid
ine
1.0
–4.0
1.0
–3.0
IM, SC
0.5
1
Fenta
nyl
25 µ
g Tr
ans-
Up t
o 7
212–24 h
r onse
t of
(<10 k
g)der
mal
ef
fect
(an
ecdota
l50 µ
g (1
0–
reports
of
20 k
g)dys
phoria
in
75 µ
g (2
0–
both
spec
ies)
30 k
g)
Pain Management 163
100 µ
g (>
30 k
g)2–6 µ
g/kg
IV<
1 (
prio
r bolu
s to
CRI)
2–6 µ
g/IV
CRI
kg/m
in(s
am
e)2–6 µ
g/kg
/hr
Buto
rphan
ol
0.1
–0.4
0.1
–0.4
IM, SC
, 1–3
IV
Bupre
norp
hin
e0.0
05–
0.0
05–
IM, SC
, 4–8
0.0
20.0
1IV
Epid
ura
l opio
ids
Dilu
te w
ith s
alin
e (1
ml/
5 k
g)
Morp
hin
e0.1
0.1
10–20
Or
use
Bupiv
acai
ne
(1 m
l/5 k
g)
Oxy
morp
hone
0.1
0.1
10
(6 m
l m
ax. vo
lum
e has
bee
n r
ecom
-m
ended
)
(contin
ues
)
164 Pain Management
Tab
le 8
–2
(Continued) D
ose
(m
g/k
g)
Do
gC
at
Ro
ute
Du
rati
on
(h
r)C
om
men
ts
Fenta
nyl
0.0
04
0.0
04
<1
Buto
rphan
ol
0.2
50.2
52–4
Bupre
norp
hone
0.0
03–
0.0
03–
12–18
0.0
05
0.0
05
Intra-a
rtic
ula
r opio
ids
Morp
hin
e0.1
mg/
kg
–12–24
in 0
.5 m
l/kg
bupiv
a-ca
ine
Syst
emic
alp
ha
2
agonis
ts*
Xyla
zine
0.0
1–0.2
0.0
1–0.2
IM, SC
, 1–3
IV
Med
etom
idin
e0.0
02–
0.0
02–
IM, SC
, 1–4
0.0
10.0
1IV
Pain Management 165
Epid
ura
lalp
ha
2
agonis
ts
Xyla
zine
0.2
0.2
1–3
Med
etom
idin
e0.0
10.0
14
Ket
amin
e 0.2
50.2
5IV
1–2
(with
dia
zepam
, 0.2
0.2
IVeq
ual
volu
me)
Infu
sion
Load
ing
dose
0.2
5–0.5
Sam
eIV
–m
g/kg
Intrao
per
ativ
e10 µ
g/kg
/Sa
me
IV–
min
Rec
ove
ry2 µ
g/kg
/Sa
me
IV≤
24 h
rReq
uire
s co
ntin
uous
min
obse
rvat
ion
Nonst
eroid
al anti-
infla
mm
ator
ydru
gs
Car
pro
fen**
2.0
–4.0
2.0
PO
24
One
dose
only
(ca
ts)
2.0
–4.0
2.0
IV, SC
24
One
dos
e on
ly (
both
)
Etodola
c10–15
–PO
24
Ket
opro
fen
0.5
–1.0
0.5
–1.0
PO
24
One
dos
e on
ly (
both
)
(contin
ues
)
166 Pain Management
Tab
le 8
–2
(Continued) D
ose
(m
g/k
g)
Do
gC
at
Ro
ute
Du
rati
on
(h
r)C
om
men
ts
Asp
irin
10–25
10–15
PO
8–12 (
dog)
24 (
cat)
Phen
ylbuta
zone
10–25
10–15
PO
8–12
Lim
ited u
se (
both
)
Mel
oxi
cam
**0.1
–0.2
0.1
–0.3
24
0.2
SC
(or
0.3
PO
) PO
and
PO
fo
r fir
st d
ose
,SC
only
then
0.1
PO
; 4
day
s m
ax (
cats
)
Nap
roxe
n1.0
–2.0
–PO
24
Piro
xica
m0.2
–0.4
–PO
48
Flunix
in m
eglu
min
e0.5
–1.0
–IM
, IV
One
dose
only
Ace
tam
inophen
10–15
–PO
12
Note
: Se
e sp
ecie
s-sp
ecifi
c ch
apte
rs for
reco
mm
endat
ions
for
hors
es, r
um
inan
ts, s
win
e, b
irds,
rep
tiles
, and s
mal
l mam
-m
als.
CRI =
const
ant ra
te in
fusi
on
*Do n
ot use
alp
ha 2
agonis
ts in
hig
h-ris
k pat
ients
.
**In
ject
able
car
pro
fen is
not cu
rren
tly a
vaila
ble
in the
Unite
d S
tate
s. M
eloxica
m is
not cu
rren
tly a
vaila
ble
in the
Unite
dSt
ates
.
useful than other opioids. Fentanyl is a potent agonistwith a short duration of effect. It is available for trans-dermal application in four sizes and for IV use asrepeated bolus or constant rate infusion (see Table 8–2).The latter use requires constant patient observation butis very effective in acute, severe pain management. Opi-oid agonists can cause dysphoria in cats, but concurrentuse of a tranquilizer (a benzodiazepine or acepro-mazine) minimizes this side effect; tranquilizers are alsobeneficial in dogs when pain relief afforded by an opioidresults in increased activity or (rarely) dysphoria. Theopioid agonist-antagonist butorphanol provides moder-ate analgesia and minimal sedation in both dogs and catsand rarely causes excitement in cats. Buprenorphine is apartial opioid agonist, useful for dogs and cats, that pro-vides moderate analgesia and has a duration of action of6–12 hr. An advantage of the opioids is reversibility withopioid antagonists, including naloxone and nalmefene,should an adverse response occur. Butorphanol may beused to reverse excessive respiratory depression inducedby an opioid agonist while preserving some analgesia.
Opioids, including morphine, oxymorphone, fen-tanyl, butorphanol, and buprenorphine, have been usedepidurally to provide analgesia of variable duration (seeTable 8–2) while minimizing sedation and the adverseeffects that may accompany systemic opioid administra-tion. The technique for epidural injection of opioids isidentical to that for local anesthetic agents (described inChapter 3) and the two are often combined for a more
Pain Management 167
profound and prolonged effect. The advantage ofepidural opioids over local anesthetic agents is thatmotor and sympathetic nerve functions are preservedand duration is longer when morphine, buprenorphine,and oxymorphone are used. Normal rear limb activity ismaintained and hypotension secondary to vasodilation,seen with local anesthetics, does not occur. An epiduraltechnique is contraindicated in the presence of bleedingabnormalities, sepsis, or infected skin at the site of injec-tion; epidural administration of local anesthetics is con-traindicated for hypovolemic patients.
Alpha2
Agonists
Alpha2
agonists, including xylazine, detomidine(horses), and medetomidine, provide good short-termanalgesia and sedation. The side effects of alpha
2ago-
nists are listed in Chapter 2, and these effects are exac-erbated by concurrently used anesthetic agents. Due tothe cardiovascular effects and the relatively short dura-tion of analgesia, use of these agents for analgesia shouldbe reserved for healthy animals recovering from electiveprocedures or suffering from relatively minor trauma.Concurrent administration with opioids will enhance theanalgesic effect and allow for use of minimal effectivedosages. Alpha
2agonists are reversible with alpha
2antag-
onists, including yohimbine, atipamezole, and tolazoline(see Table 8–2). Both xylazine and medetomidine (anddetomidine in horses and swine; see Tables 3–4 and 3–5)
168 Pain Management
have been used epidurally. While of lesser concern inhorses and swine, the potential for systemic side effectsand the relatively short duration of action make themless useful than the opioids in small animals, with oneadvantage being easy accessibility (not scheduled).
Ketamine
Subanesthetic doses of ketamine have been used inhumans for relief of acute and chronic pain. Ketamineprovides somatic analgesia in animals and is not recom-mended as the sole agent for visceral pain management.Undesirable side effects, including dysphoria, seizures,and muscle rigidity, may be minimized by using ketaminein combination with a tranquilizer. Specific contraindica-tions are listed in Chapter 2. Dosages have not beendefinitively established for pain management in animals,but suggested guidelines are included in Table 8–2.
Nonsteroidal Anti-Inflammatory Agents
NSAIDs are used for the treatment of mild to moderatepain. The side effects are due to inhibition of physiologic(protective) prostaglandins and include gastrointestinalulceration and renal tubular necrosis. With developmentof more selective NSAIDs, which are more potentinhibitors of inflammation and less organ toxic, theseagents, in combination with an opioid, have beenapplied for preemptive and perioperative managementof acute surgical pain.
Pain Management 169
Carprofen is a more specific inhibitor of cyclooxyge-nase-2. It is approved for oral use in dogs in the UnitedStates, but cat dosages have been reported (see Table8–2). While side effects are less likely than from otherNSAIDs, gastrointestinal disturbances have beenreported and acute hepatopathy has been described.
Etodolac is another specific cyclooxygenase-2inhibitor with fewer side effects. It is approved for use indogs in the United States for management of osteoarthri-tis pain.
Ketoprofen is a relatively new NSAID with potent anti-inflammatory activity but greater potential for sideeffects than carprofen. It is approved for use in cats anddogs in Europe. Ketoprofen causes gastrointestinal andrenal effects at therapeutic doses and should be avoidedin high-risk patients and in the preoperative period.
Meloxicam is approved for use in dogs in Europe. It ismarketed for treatment of chronic skeletal pain but hasbeen shown to be effective in the management ofmoderate postoperative pain. Dosages are available forcats; however, data regarding its safety currently areunavailable.
Aspirin is a potent analgesic and anti-inflammatoryagent that may be used in both dogs and cats. Gastriculceration can occur at therapeutic doses with a lesserrisk when buffered preparations are used. Dosing fre-quency is less in the cat due to prolonged plasma elimi-nation.
170 Pain Management
Use of other NSAIDs, including phenylbutazone,naproxen, piroxicam, and flunixin meglumine, in dogsand cats has been reported and dosages are listed inTable 8–2. Flunixin is a potent visceral analgesic that alsomay modulate the pathophysiologic response to endo-toxin. While dosages are available, data supporting theuse of these agents are lacking and there is a greaterincidence of adverse side effects; therefore, these drugsshould not be used unless safer agents are unavailableand the need outweighs the potential for adverse effects.
Acetaminophen is an atypical NSAID with excellentanalgesic effects but limited anti-inflammatory activity.Its use in cats is contraindicated due to methemoglobinformation.
Local and Regional Techniques
Application of local anesthetic techniques has beenshown to decrease the intensity of postoperative pain.Blocking nocioceptive impulse entry into the cord prob-ably prevents development of the sustained hyperex-citable state of the central nervous system largelyresponsible for sustained postoperative pain. Severallocal techniques and their applications are described inChapter 3. Bupivacaine is the local anesthetic of choicefor pain management due to duration of effect; sug-gested dosages for the specific techniques are includedin Chapter 3.
Pain Management 171
Selection of appropriate analgesic drugs and tech-niques for pain management is influenced by many fac-tors, including the animal’s previous behavior pattern;the type, duration, and invasiveness of the procedure orextent and location of the traumatic injury; mental sta-tus; and overall patient condition. Like anesthetic man-agement, no one agent or technique is applicable forevery situation; however, every case should be assessedand treated according to the preceding considerations.
172 Pain Management
9
Introduction to Anesthetic Management in Specific Species
Chapters 10–17 provide brief overviews of anestheticmanagement for a variety of veterinary species, includ-ing considerations that might be unique to that particu-lar species, such as restraint, venous access, intubation,positioning, monitoring, and recovery, as well as sug-gested protocols for premedication, induction, and totalparenteral anesthesia. Anesthetic protocols should beformulated to produce the desired result safely, effec-tively, and economically, based on the patient’s tempera-ment, physical status, a thorough physical examination,
appropriate laboratory and diagnostic tests, and proce-dure duration and complexity, regardless of species.
173
4. Eye lubrication should be applied to all anesthetizedanimals, as general anesthesia obtunds tearing andthe ability to blink, so as to maintain a moist cornea.
5. Monitoring may be simple or complex, dependingon the length and invasiveness of the procedure.Available techniques (Chapter 6) apply to all veteri-nary species with some species-specific considera-tions.
6. As a general rule, anticholinergic agents are not con-sidered a routine part of the preanesthetic protocolin any species but can be used as such in healthysmall animals, especially when drugs known todecrease heart rate (e.g., opioids) are part of theprotocol. Anticholinergics may precipitate colic inhorses, and horses are rarely susceptible to brady-cardia during the anesthetic period; therefore,routine perioperative use is contraindicated. Anti-cholinergic administration will not eliminate rumi-nant salivation and, in fact, may increase the viscosityof secretions, making them harder to clear; there-fore, routine use is not recommended.
Introduction to Anesthetic Management in Specific Species 175
10
Anesthetic Management of Dogs
A variety of protocols are available to provide chemical
restraint/premedication, induction of anesthesia, and
total parenteral anesthesia in dogs (Table 10–1). A neu-
roleptanalgesic (tranquilizer plus opioid) combination
will minimize anxiety and struggling for catheterization,
minimize requirements for induction and maintenance
agents, and provide preemptive analgesia. Popular and
economical combinations are acepromazine with mor-
phine (moderate to severe pain), hydromorphone (mod-
erate to severe pain), or butorphanol (mild to moderate
pain).
Diazepam can be substituted for acepromazine
when the latter is contraindicated (see Chapter 2). Mida-
zolam provides a convenient (but expensive) alternative
177
178 Anesthetic Management of Dogs
Tab
le 1
0–1
Reco
mm
ended D
osa
ges
and P
roto
cols
for
Chem
ical
Rest
rain
t,
Pre
anest
hetic
Pro
toco
ls, In
duct
ion A
gents
, an
d T
ota
l Par
ente
ral A
nest
hesi
a fo
r D
ogs
Do
sages
(mg/k
g)
Pro
toco
l(I
V,
IM,
SC
)*C
om
men
ts
Chem
ical re
stra
int/
Anim
als
can b
e ar
ouse
d d
urin
g ch
emic
alpre
med
icatio
nre
stra
int.
Opio
id p
lus*
*Ace
pro
maz
ine
or
0.0
5M
ax d
ose
: 2 m
g (p
rem
ed),
4 m
g (r
estrai
nt)
.D
iaze
pam
or
0.2
Max
rec
om
men
ded
dose
: 10 m
g.M
idaz
ola
m0.1
–0.2
Max
rec
om
men
ded
dose
: 10 m
g.
Ben
zodia
zepin
es a
re p
refe
rred
for
hig
h-
risk,
neo
nat
al, an
d g
eria
tric
pat
ients
.
Morp
hin
e0.4
–1.0
Avo
id IV r
oute
, pote
ntia
l fo
r his
tam
ine
rele
ase.
Oxy
morp
hone
0.1
–0.2
Hyd
rom
orp
hone
0.1
–0.2
Buto
rphan
ol
0.2
–0.4
Hig
h e
nd d
osa
ge f
or
smal
ler
pat
ients
. Le
ss
anal
gesi
a th
an p
ure
opio
ids
(for m
ild p
ain).
Bupre
norp
hin
e0.0
2–0.0
4
Anesthetic Management of Dogs 179
Alp
ha
2agonis
tsPro
vide
pro
found s
edat
ion a
nd a
nal
gesi
a an
d g
reat
ly s
par
e (≥
50%
) an
esth
esia
nee
ded
. U
se a
lpha 2
agonis
ts o
nly
inhea
lthy
young
anim
als.
Xyla
zine
0.2
–0.4
Med
etom
idin
e0.0
1–0.0
2
Tela
zol
2 IM
Good f
or
imm
obili
zatio
n o
f ag
gres
sive
dogs
.
Induct
ion
Adm
inis
tere
d “
to e
ffec
t” t
o f
acili
tate
unco
nsc
iousn
ess
and intu
bat
ion f
or
inhal
ant
anes
thes
ia.
Thio
pen
tal
5–10 IV
Apnea
is
com
mon.
Dia
zepam
-ket
amin
e1 m
l/10 k
g IV
Can
follo
w p
rior
tran
quili
zer
adm
inis
trat
ion.
Tela
zol
0.5
–1.0
IV
Can
follo
w p
rior
tran
quili
zer
adm
inis
trat
ion.
Pro
pofo
l2–6 IV
Apnea
is
com
mon if
not
give
n s
low
ly.
Etom
idat
e0.5
–2.0
IV
Expen
sive
but
spar
ing
of
card
iore
spira
tory
fu
nct
ion.
Tota
l pare
nte
ral
Less
control ove
r an
esth
esia
dep
th a
nd
anes
thes
iadura
tion t
han
inhal
atio
n m
ainte
nan
ce.
(contin
ues
)
180 Anesthetic Management of Dogs
Tab
le 1
0–1
(Continued)
Do
sages
(mg/k
g)
Pro
toco
l(I
V,
IM,
SC
)*C
om
men
ts
Xyla
zine
0.4
Adm
inis
trat
ion o
f X/
B p
rior
to k
etam
ine
min
imiz
es p
ain o
f IM
ket
amin
e or
keta
-m
ine
can b
e ad
min
iste
red IV “
to e
ffec
t.”
Buto
rphan
ol
0.4
Ket
amin
e10
Med
etom
idin
e0.0
1–0.0
2Adm
inis
trat
ion o
f M
/B p
rior
to k
etam
ine
min
imiz
es p
ain o
f IM
ket
amin
e or
keta
-m
ine
can b
e ad
min
iste
red IV “
to e
ffec
t.”
Buto
rphan
ol
0.4
Ket
amin
e10
Buto
rphan
ol
0.4
Dia
zepam
-ket
amin
e1 m
l/10 k
g IV
Dia
zepam
-ket
amin
e is
titr
ated
to e
ffec
t. N
ot
for
seve
rely
pai
nfu
l pro
cedure
s.
Pre
med
icat
ions
as
2–6 (
induct
ion)
Intu
bat
ion a
nd o
xyge
n d
eliv
ery
isab
ove
plu
s pro
pofo
l0.4
CRI (c
onst
ant
reco
mm
ended
rate
infu
sion)
or
repea
t bolu
s of
0.5
–1.0
ml “t
o e
ffec
t”
Anesthetic Management of Dogs 181
Opio
id a
nta
gonis
ts
Nal
oxo
ne
0.0
01–0.0
15 IV
May
be
give
n IV “
to e
ffec
t” w
hen
dilu
ted
(1 m
l in
9 m
l sa
line)
. G
ive
mat
chin
g (I
V)
dose
SC
.
Nal
mef
ene
0.0
01 IV
Longe
r dura
tion o
f ac
tion t
han
nal
oxo
ne.
Alp
ha
2anta
gonis
ts
Yohim
bin
e0.0
5–0.1
IV
May
be
give
n IM
but
less
effec
tive.
Atip
amez
ole
0.0
7–0.1
5 IV,
IM
Tola
zolin
e1–2 IV
May
be
give
n IM
but
less
effec
tive.
CRI (m
g/kg
/min
).
*As
a ge
ner
al r
ule
, use
low
er d
osa
ge r
ange
for
IV a
dm
inis
trat
ion. A
ll ro
ute
s ac
cepta
ble
unle
ss o
ther
wis
e sp
ecifi
ed.
**U
se o
f an
opio
id w
ith o
ne
of th
ese
med
icat
ions
is c
alle
d n
euro
lepta
nalg
esia
. The
com
bin
atio
n h
as a
syn
ergi
stic
effe
ct, p
rovi
din
g bet
ter
sedat
ion than
eith
er a
gent al
one.
to diazepam when SC or IM administration is needed,
since diazepam causes tissue irritation and has unreliable
absorption when given by these routes. Thiopental and
diazepam-ketamine are economical and effective induc-
tion agents, but repeated bolus administration can con-
tribute to a rough, prolonged recovery and both
thiopental and ketamine have specific contraindications
(Chapter 2). Thiopental causes prolonged recovery in
sighthounds due to an inherent inability to metabolize
the drug efficiently; alternatives include diazepam-keta-
mine and propofol.
Propofol has become a popular drug in veterinary
medicine due to its rapid effect, short duration, and lack
of cumulative effect, which allows it to be used as
repeated boluses or constant rate infusion without sig-
nificantly increasing recovery time. Even though more
expensive than thiopental, propofol’s rapid recovery and
lack of arrhythmogenic effect make it an excellent alter-
native agent.
Applying local and regional anesthetic techniques
appropriate to the procedure (most conveniently follow-
ing anesthetic induction) provides preemptive and post-
operative analgesia and further decreases anesthetic
maintenance requirements.
Dogs are prone to regurgitation and aspiration.
Anesthetized patients should be intubated to assure a
patent and protected airway, especially if fasting status is
unknown or time will not permit an adequate fast (emer-
gencies). Dogs are relatively easy to intubate by direct
182 Anesthetic Management of Dogs
visualization of the larynx, which is aided by adequate
anesthetic depth and use of a laryngoscope. Intubation
provides a route for oxygen delivery with or without
inhalant administration and an effective means for pro-
viding ventilatory support. Appropriate tube sizes for
dogs cover a wide range from 3.0 to 14.0 mm internal
diameter.
An intravenous catheter should be placed in a periph-
eral vein for procedures anticipated to take longer than
30 min and when administration of additional anesthetic
agent is likely. The most common sites are the cephalic
and lateral saphenous veins. A secure access provides a
route for intraoperative fluid and supportive drug
administration and for emergency drug administration,
should cardiopulmonary arrest occur.
Recovery should occur in a warm quiet area with
external heat provided in most cases. Extubation is per-
formed with the cuff deflated when swallowing is noted.
When there is evidence of regurgitation or when blood
has collected in the pharyngeal region, the oral cavity
should be swabbed and the tube removed with the cuff
still inflated once swallowing is observed to remove any
debris that has settled around the tube within the tra-
chea. Patients with underlying airway compromise
(brachycephalic breeds, history of a collapsing trachea)
should remain intubated as long as possible and closely
observed until recovery is complete. Animals should be
observed until vital signs have returned to normal
(Chapter 1).
Anesthetic Management of Dogs 183
11
Anesthetic Management of Cats
Total parenteral anesthetic protocols seem to be morepopular and widely used in cats than dogs for a variety ofreasons, including greater resistance to handling andrestraint, more difficult venous access, more difficultintubation, and greater effectiveness with less occur-rence of side effects associated with dissociative agents.Several protocols are available for short-term injectableanesthesia (Table 11–1). However, for complicated, pro-longed procedures and high-risk cats, inhalation mainte-nance following premedication and induction is morecontrollable and safer (see Table 11–1).
For tractable patients, neuroleptanalgesic combina-tions like those used for dogs are effective. Pure opioidagonists have been reported to cause excitement in cats,
185
186 Anesthetic Management of Cats
Tab
le 1
1–1
Reco
mm
ended D
osa
ges
and P
roto
cols
for
Chem
ical
Rest
rain
t, P
re-
anest
hetic
and I
nduct
ion P
roto
cols
, an
d T
ota
l Par
ente
ral A
nest
hesi
a fo
r C
ats
Do
sages
(mg/k
g)
Pro
toco
l(I
V,
IM,
SC
)*C
om
men
ts
Chem
ical re
stra
int/
Anim
als
can b
e ar
ouse
d d
urin
g ch
emic
alpre
medic
atio
nre
stra
int.
Ace
pro
maz
ine
or
0.0
5–0.1
Dia
zepam
or
0.2
Ben
zodia
zepin
es a
re p
refe
rred
for
hig
h-ris
k,
Mid
azola
m0.1
–0.2
neo
nat
al, an
d g
eria
tric
pat
ients
.
Use
d w
ithM
orp
hin
e0.4
–1.0
Oxy
morp
hone
0.1
–0.2
Hyd
rom
orp
hone
0.1
–0.2
Buto
rphan
ol
0.4
Less
anal
gesi
a th
an p
ure
opio
ids
(for
mild
to
moder
ate
pai
n).
Induct
ion
Adm
inis
tere
d “
to e
ffec
t” t
o f
acili
tate
unco
nsc
iousn
ess
and intu
bat
ion.
Thio
pen
tal
5–10 IV
Apnea
is
com
mon.
Dia
zepam
-ket
amin
e1 m
l/10 k
g IV
Can
be
use
d e
ven w
ith p
rior
tran
quili
zer
adm
inis
trat
ion.
Anesthetic Management of Cats 187
Tela
zol
0.5
–1.0
IV
Can
be
use
d e
ven w
ith p
rior
tran
quili
zer
adm
inis
trat
ion.
Pro
pofo
l2–6 IV
Apnea
is
com
mon e
spec
ially
with
rap
id
inje
ctio
n.
Etom
idat
e0.5
–2.0
IV
Expen
sive
but
spar
ing
of
card
iore
spira
tory
fu
nct
ion.
Pare
nte
ral anest
hesi
a
Xyla
zine
0.4
Adm
inis
trat
ion o
f X/
B p
rior
to k
etam
ine
will
Buto
rphan
ol
0.4
min
imiz
e pai
n o
f IM
ket
amin
e or
keta
-Ket
amin
e10–15
min
e ca
n b
e ad
min
iste
red IV “
to e
ffec
t.”
Med
etom
idin
e0.0
1–0.0
2Adm
inis
trat
ion o
f M
/B p
rior
to k
etam
ine
will
Buto
rphan
ol
0.4
min
imiz
e pai
n o
f IM
ket
amin
e or
keta
-Ket
amin
e10–15
min
e ca
n b
e ad
min
iste
red IV “
to e
ffec
t.”
Pro
pofo
l2–6 (
induct
ion)
Ace
pro
maz
ine
or
ben
zodia
zepin
e plu
s 0.4
const
ant
rate
opio
id f
ollo
wed
by
pro
pofo
l.in
fusi
on o
r re
pea
t bolu
s of
0.2
5–0.5
“t
o e
ffec
t”
Note
: D
osa
ges
for
reve
rsal
age
nts
are
sim
ilar
to those
list
ed for
dogs
(se
e Ta
ble
10–1 o
r Appen
dix 1
).
*As
a ge
ner
al r
ule
, use
low
er d
osa
ge r
ange
for
IV a
dm
inis
trat
ion.
but risk of this side effect is minimized with concurrentuse of a tranquilizer or when an agonist-antagonist(butorphanol) is used. Adding a low dose of ketamine tothe neuroleptanalgesic combination (see Table 11–1)will provide immobilization for less tractable patients tofacilitate catheterization and will further decrease induc-tion requirements. While mask induction following pre-medication is effective in cats, induction quality isimproved and intubation facilitated by using a rapidinduction method such as thiopental, diazepam-keta-mine, telazol, or propofol. The feline respiratory centeris more susceptible to the depression associated withthiopental and propofol and transient apnea is common.Some cats will produce excessive respiratory secretionswhen the dissociative agents are used, which may becounteracted by anticholinergic agent administration.
As a rule, cats tend to resent and resist restraintmore than dogs. Various devices, such as cat bags andfeline muzzles, often are necessary to ensure the safety ofpersonnel and the animal. Always close the doors toavoid escape when working with cats. Most cats can berestrained adequately with scruffing and stretching(holding the skin behind the neck with one hand andthe rear limbs with the other and applying gentle ten-sion) for injection of premedication. For resistant ani-mals, adding ketamine or telazol in low dosage to thepremedication protocol improves the quality of thecatheterization/induction sequence. Many of the local
188 Anesthetic Management of Cats
and regional techniques, such as epidural and localnerve blocks, are effective and feasible in cats to providepreemptive and postoperative analgesia (Chapter 3).
When indicated (high-risk animal, repeat injections,prolonged procedures), an IV catheter should beinserted. Cats seem to resist the necessary restraint asmuch as the actual catheter placement so premedicationusually is required. Sites include the cephalic, medialsaphenous, and femoral veins. Laying the animal in lat-eral recumbency for placement in the medial saphenousvein seems to be less stressful for some anxious, aggres-sive patients.
Feline intubation is more challenging than in dogs.While visualization usually is good, the feline larynx isreactive and prone to laryngospasm, which makes intu-bation more difficult and increases the risk of trauma.Patience is essential, and the process is facilitated byapplication of 0.1 ml of 2% lidocaine dropped from asyringe to desensitize the area. Commercial human spraypreparations containing benzocaine (e.g., Cetacaine™)should be avoided because of reports of methemoglo-binemia associated with its use. Once visualized anddesensitized, using a guide tube (canine polyethyleneurinary catheter) will help to stiffen the ET tube andgain access between the arytenoid cartilages and into thetrachea so that the tube may be passed, rotating slightlyif needed, to allow the bevel to pass into the trachea.Stiffer stylets are available, but the risk of trauma is
Anesthetic Management of Cats 189
greater if care is not taken to maintain the stylet pointinside the ET tube. The tube is secured around the backof the neck with tie gauze.
While a standard rebreathing circle can be usedeffectively in cats, a pediatric circle or nonrebreathingsystem is more appropriate for their size. The latter willminimize resistance to breathing but is more likely tocontribute to intraoperative hypothermia. If a rebreath-ing circuit is used, ventilatory support becomes evenmore important (due to added resistance to breathing),especially during prolonged procedures.
Cats are more challenging to monitor. The smallertidal volume makes movement of the rebreathing bagmore difficult to observe. Esophageal stethoscopes arehelpful for ausculting both respiration and heart sounds.Respiratory monitors and capnometers usually are effec-tive but add to dead space. Pulse quality is more difficultto assess; the best site for pulse palpation is the femoralartery, which may not always be accessible. The dorsalpedal artery can be palpated in some cats; clipping thearea over this artery is beneficial. Pulse oximeters andoscillometric blood pressure monitors may fail to workconsistently, due to the small vessel size. The Dopplerapparatus is effective when applied to either a forelimbor hindlimb but takes time and experience to apply effi-ciently. The feline lead II electrocardiogram is small andsometimes difficult to assess.
190 Anesthetic Management of Cats
Recovery usually is rapid in cats following inhalationanesthesia, unless severe hypothermia has developed.Providing a warm environment and thermal supportfacilitate recovery. Close attention to body temperatureis important, as cats seem prone to hyperthermia as bodyactivity increases during recovery, seemingly independ-ent of the protocol used. As a general rule, once thebody temperature reaches 99°F, thermal support shouldbe removed. Cats with elevated temperature (>104°F)benefit from the application of alcohol to the pads and afan to dissipate heat; animals act seemingly normal dur-ing this period of increased temperature; thermoregula-tion returns to normal usually within 24 hr.
Anesthetic Management of Cats 191
12
Anesthetic Management of Birds
Birds frequently require general anesthesia for a veteri-narian to perform procedures normally accomplishedwith physical restraint in most other species as well ascomplicated and invasive procedures. General anesthe-sia is challenging in birds due to less familiarity withavian anatomy, greater resistance to restraint, lower mar-gin of safety for injectable agents, less experience withcatheterization and intubation techniques, more diffi-culty in monitoring, and currently, limited informationon effective analgesic agents.
Capture and restraint should be performed in a quietand safe environment and done quickly to minimize thestress of chasing. Passeriformes may be restrained withthe bird cradled in the palm of the hand and the head
193
gently restrained between the index and middle fingers.For the larger Psittaciformes, a two-hand technique isrequired (Figure 12–1). Head restraint is vital to avoidbites to the handler and accomplished by creating a ringaround the bird’s neck with one hand and applying gen-tle pressure against the base of the skull and lowermandible. The other hand is placed around the legs togently support the body. A towel can be used to protectthe hand near the head. It is essential to not restrict tho-racic movement or compromise the airway. Restrainttechniques for adult ratites cannot be described in theconfines of this reference book; for information, readersare referred to the recommended reading list.
Anesthetic induction and maintenance with isoflu-rane is the protocol of choice for pet birds and raptors.Sevoflurane also appears to be effective and currently isgaining popularity. Dosages for some injectable proto-cols are available and listed in Table 12–1; however, theseagents usually fail to produce stable and safe levels ofanesthesia and should not be used unless gas anesthesiais unavailable. Larger birds, such as ratites, will requirean injectable premedication and induction protocol (seeTable 12–1) because mask induction is prolonged anddangerous except in debilitated patients.
Intubation is relatively easy to perform in avianspecies as the glottis is readily apparent at the base of thetongue when the beak is opened. Psittaciformes have afleshy tongue, which must be pulled forward carefully toexpose the glottis. Birds >350 grams can be intubated
194 Anesthetic Management of Birds
195
Figure 12–1 Restraint technique for Psittaciformes, demon-strating hand positioning. (Reprinted with permission from TGCurro, Anesthesia of pet birds, in: Seminars in Avian and ExoticPet Medicine: Anesthesia and Analgesia, AM Fudge, ed.,1998;7(1):12.)
Table 12–1 Reported Dosages for Injectable AnestheticAgents in Pet Birds, Raptors, and Ratites (Injectable proto-cols are not recommended in birds unless inhalant anes-thesia is unavailable.)
Drug Combination Dosage (mg/kg)*
Pet birds**
Ketamine-xylazine 10–50/1.0–10
Ketamine-diazepam 10–50/0.5–2.0
Ketamine-midazolam 10–40/0.5–1.5
Ketamine-acepromazine 10–25/0.5–1.0
Telazol (tiletamine-zolazepam) 7.7–26.0
Yohimbine 1.0
Analgesic optionsButorphanol 1–4 IV, SC, IMFlunixin 1–10 IM (not critically
evaluated)Aspirin 5 gr/250 ml drinking water
(not critically evaluated)
Raptors†
Buteo Hawks350 g 0.04–0.08 ml650–1500 g 0.08–0.15 ml900–1700 g 0.1–0.3 ml
Accipiter Hawks100–250 g 0.04–0.06 ml250–500 g 0.08–0.1 ml600–1200 g 0.05–0.07 ml
(continues)
196 Anesthetic Management of Birds
Table 12–1 (Continued)
Drug Combination Dosage (mg/kg)*
Eagles3–5 kg 0.1–0.2 ml
Falcons90–250 g 0.03–0.06 ml500–950 g 0.07–0.2 ml950–1500 g 0.12–0.3 ml
Owls60–130 g 0.03–0.05150–350 g 0.05–0.1700–2500 g 0.1–0.25 (not recommended
for surgery on great hornedor snowy owls)
Osprey 0.12–0.2 ml
Turkey vulture 0.15–0.2 ml
Ratites
Xylazine 0.2–2.2 IM
Detomidine 1.5 IM
Medetomidine 0.1 IM
Butorphanol 0.05–0.5 IV, IM
Diazepam 0.1–0.3 IV0.22–1.0 IM
Midazolam 0.15 IM
Ketamine-xylazine 2.2 IV/0.25 IV2.2–3.3 IV/2.2 IM
Carfentanil-xylazine 0.03 IV/0.5 IM
(continues)
Anesthetic Management of Birds 197
Table 12–1 (Continued)
Drug Combination Dosage (mg/kg)*
Ketamine-diazepam 5.0/0.25 IV (mixed)2.2–3.3 IV/0.22–0.5 IM
(ketamine given 15–30 min after diazepam)
Telazol 2–10 IM; 1–3 IV
Antagonists:Naloxone 2 mg IV (total dose adminis-
tered to adult ostriches)Yohimbine 12.5 mg IV (total dose admin-
istered to adult ostriches)Atipamezole 5–20 mg IV (total dose admin-
istered to adult ostriches)Naltrexone 300 mg IV (total dose adminis-
tered to adult ostriches)
*Dosages are for intramuscular administration in the pectoral muscles unless other-wise indicated.
**Lower dosage range is for larger birds (>250 g) and sedation in smaller birds;higher dosage range is for smaller birds (<250 g) and for a “surgical plane” ofanesthesia in larger birds.†Dosage in mls of a mixture of 1 ml ketamine (100 mg/ml) and xylazine (20mg/ml). Low-end range represents minimal effective dose, high-end range repre-sents surgical anesthesia. As with pet birds, injectable anesthesia is not recom-mended for raptors. A dosage range for the xylazine-ketamine mixture (100 mg/20mg) has been published and dosages in ml are summarized. For details on anes-thetic management of raptors and other species, see PT Redig, Recommendationsfor anesthesia in raptors with comments on trumpeter swans, in: Seminars in Avianand Exotic Pet Medicine: Anesthesia and Analgesia, AM Fudge, ed.,1998;7(1):22–29.
198 Anesthetic Management of Birds
with a cuffed tube (smallest: 3.0–5.0 mm ID). Larger rap-tors may require slightly larger tubes, and the adult ratitetrachea accommodates tube sizes up to 18 mm ID. Birds100–350 g require uncuffed tubes (2.0–3.0 mm ID), Coletubes (uncuffed tubes with a tapered end), or largegauge IV catheters (14–18 ga). Birds smaller than 100 gare best maintained by mask with the head gentlyextended because there is an increased likelihood oftube occlusion and significant impedance to air move-ment associated with the small diameter cathetersrequired in this size bird. Endotracheal tubes with a sideopening near the bevel (Murphy tubes) help minimizethe risk of mucus occlusion. Once in place, the tube iseffectively secured with a thin piece of tape around thetube, which then is encircled around the closed beak.
For cases with airway obstruction or to perform pro-cedures in the oral cavity, inhalant anesthesia can bedelivered into the air sacs. Percutaneous catheters(14–18 ga; 2–3 cm) may be placed in the caudal thoracicor abdominal air sacs using sterile technique. A smallskin incision is required to expose the air sac membrane.The catheter is inserted and the skin secured around thecatheter; the catheter is connected to an endotrachealtube adaptor for delivery of the anesthetic agent. Theapproximate site of entry is at the last intercostal space.Apnea is common when this technique is used, makingmonitoring of cardiovascular parameters critical.
Anesthetic Management of Birds 199
For prolonged procedures or debilitated patientsand when significant hemorrhage is anticipated, intra-operative fluids should be administered. Intravenousaccess is possible in birds weighing ≥250 grams; sitesinclude the jugular, cutaneous ulnar, and medialmetatarsal veins. When fluid administration is essentialand IV access unsuccessful, the intraosseous route also iseffective. Sites of entry include the distal ulna and theproximal tibiotarsus (Figure 12–2). Spinal or hypoder-mic needles are used, depending on the size of the bird;the former minimizes the risk of needle occlusion by abone core during placement. Once placed, the needle iscapped and secured as for an IV catheter. Subcutaneousfluid administration sites include the propatagium (wingweb), intrascapular, and inguinal regions. Dextrose-con-taining fluids (LRS or Normosol with 2.5–5.0% dextrose,half strength LRS, or saline with 2.5% dextrose) are rec-ommended. Fluids administered SC should contain≤2.5% dextrose.
Sensitivity to anesthesia is variable among avianspecies and individual birds can develop complicationsrapidly; therefore, monitoring heart and respiratoryrates is essential. Effective aids to anesthetic monitoringinclude direct or esophageal auscultation, a lead II elec-trocardiogram (Figure 12–3), and respiratory (apnea)monitor; the last may not function effectively in verysmall patients, adds dead space to the breathing circuit,and usually is ineffective during mask delivery. Place-ment of ECG leads include the skin of the propatagium
200 Anesthetic Management of Birds
201
Figure 12–2 Sites for intraosseous catheterization of birds forintraoperative fluid administration: (A) site for placing spinal orhypodermic needle via the distal ulna; (B) site for placing spinal orhypodermic needle via the proximal tibiotarsus. (Reprinted withpermission from DJ Harris, Therapeutic avian techniques, in: Semi-nars in Avian and Exotic Pet Medicine: Clinical Techniques, AMFudge, ed., 1997;6(2):61.)
(A)
(B)
(LA and RA) and the skin of the stifle (LL). Alligatorclips should be padded with alcohol-soaked gauze toavoid skin damage or, alternatively and effective, snap-onsticky ECG pads can be applied. Heart rates shouldremain between 200 and 400 beats/min depending onthe size of the bird (less for large ratites: 60–120beats/min). During surgical anesthesia, birds should berelaxed and unresponsive to painful stimulation; cornealand pedal reflexes are slow and the palpebral reflex islost. Respiration should be slow, regular, and deep, withrates usually ranging from 12–30 breaths/min. Temper-ature should be monitored, especially during long pro-cedures, to avoid development of hypothermia. Externalheat sources should be provided; maintaining a bodytemperature of 101–103°F is recommended.
Recovery usually occurs within 5–15 min afterinhalant delivery is discontinued and should occur in awarm, quiet, and dimly lit environment. Birds should bewrapped loosely in a towel and gently restrained untilextubated and able to stand. For prolonged recovery,birds may be left in a padded enclosure with close obser-vation, once extubated. For extubation, the oral cavityshould be checked for regurgitation or excessive secre-tions and swabbed if needed. Extubation should be per-formed when the bird resists its presence. Informationon analgesic agent dosages for birds is limited but shouldbe considered for painful invasive procedures andadministered either intraoperatively or just prior torecovery. Dosages for butorphanol have been reported
202 Anesthetic Management of Birds
203
Figu
re 1
2–3
Norm
al E
CG
(w
ith a
sim
ultan
eous
arte
rial
pre
ssure
wav
e)
from
a 2
60 g
His
pan
iola
n A
maz
on p
arro
t. H
ear
t ra
te w
as a
bout
400 b
eat
s/m
in.
for pet birds and probably can be extrapolated toraptors. Flunixin meglumate and aspirin also have beenrecommended but not critically evaluated. Dosages arelisted in Table 12–1. Birds should be offered food andwater when able to perch.
204 Anesthetic Management of Birds
13
Anesthetic Management of Small Mammals
This chapter primarily addresses anesthetic managementof rabbits and ferrets with additional comments on man-agement and analgesic options for other small mammals.
Ferrets
Ferrets are effectively restrained (and often resent it less)by techniques established for use in cats; namely, “scruff-ing” the skin of the neck and gently stretching the ani-mal by grasping the rear limbs. Premedication isrecommended in all but extremely debilitated animals;protocols are listed in Table 13–1. Most ferrets can be
205
catheterized for IV induction following a neuroleptanal-gesic combination, although healthy, uncooperativepatients will benefit from the addition of ketamine to thepreanesthetic protocol. Induction may be accomplishedby inhalant anesthetic, preferably isoflurane, deliveredby mask, or with an IV protocol such as thiopental,diazepam-ketamine, or propofol; IV induction will pro-vide more reliable access and increased duration of timefor intubation.
Sites for intravenous catheterization in ferretsinclude the cephalic, lateral saphenous, and (last) thejugular veins. Skin is tough, so making an “introductionhole” through the skin over the vein with a hypodermicneedle to facilitate entry of the catheter (22 or 24 ga) isbeneficial. Placing a tourniquet above the site will helpmaximally raise the vessel, which is very difficult to visu-alize due to its small size and the usual presence of alarge amount of SC fat. Catheterization is recommendedfor prolonged procedures and high-risk patients to pro-vide access for administration of intraoperative fluidsand anticipated supportive measures.
Intubation is relatively easy in ferrets. Visualization issimilar to cats and the ferret larynx usually will accom-modate a 2.5–3.0 mm ID tube. The larynx is less reactivethan cats, making local anesthetic desensitization unnec-essary; visualization is facilitated by a laryngoscope. Thetube should be secured around the back of the head withtie gauze as it is in cats.
206 Anesthetic Management of Small Mammals
Anesthetic Management of Small Mammals 207
Tab
le 1
3–1
Dosa
ges
of
Pre
medic
atio
n P
roto
cols
and I
nduct
ion A
gents
for
Ferr
ets
and R
abbits
Pro
toco
lD
osa
ge (
mg/k
g)
Co
mm
en
ts
Ferr
ets
Prem
edic
atio
n/
chem
ical re
stra
int
Atropin
e0.0
5 S
C, IV
, IM
Routin
e use
not
reco
mm
ended
.
Gly
copyr
rola
te0.0
1 S
C, IV
, IM
Routin
e use
not
reco
mm
ended
.
Ace
pro
maz
ine/
0.1
/0.4
SC
Avo
id a
cepro
maz
ine
in d
ebili
tate
d p
atie
nts
.buto
rphan
ol
Add k
etam
ine
(5–10 m
g/kg
IM
) to
pro
-vi
de
imm
obili
zatio
n t
o f
acili
tate
cat
het
eri-
zatio
n, in
duct
ion, an
d m
inor
pro
cedure
s.
Mid
azola
m/
0.2
–0.4
/0.4
SC
Good f
or
deb
ilita
ted p
atie
nts
. D
iaze
pam
buto
rphan
ol
(0.2
–2.0
mg/
kg)
may
be
use
d in p
lace
of
mid
azola
m b
ut
is les
s w
ell ab
sorb
ed a
nd
cause
s pai
n o
n inje
ctio
n. Add k
etam
ine
(5–10 m
g/kg
IM
) to
pro
vide
imm
obili
za-
tion t
o f
acili
tate
cat
het
eriz
atio
n, in
duct
ion,
and m
inor
pro
cedure
s.
(contin
ues
)
208 Anesthetic Management of Small Mammals
Tab
le 1
3–1
(Continued)
Pro
toco
lD
osa
ge (
mg/k
g)
Co
mm
en
ts
Xyla
zine
0.5
–1.0
SC
For
hea
lthy
pat
ients
only
. N
ot
reco
mm
ended
as
a p
rem
edic
atio
n f
or
inhal
ant
anes
thet
icm
ainte
nan
ce.
Med
etom
idin
e0.0
8 S
CFo
r hea
lthy
pat
ients
only
. N
ot
reco
mm
ended
as
a p
rem
edic
atio
n f
or
inhal
ant
anes
thet
icm
ainte
nan
ce.
Tela
zol
6–12 IM
Rec
ove
ry m
ay b
e pro
longe
d (
>4 h
r).
Rep
orted
sid
e ef
fect
s in
clude
snee
zing
and
pad
dlin
g durin
g in
duct
ion a
nd rec
ove
ry.
Faci
litat
es m
inor nonin
vasi
ve p
roce
dure
s.
Induct
ion*
Thio
pen
tal
8–12 IV
Giv
e sl
ow
ly “
to e
ffec
t.”
Ket
amin
e plu
s 0.1
ml/
kg IV
Dru
g m
ixtu
re is
mad
e by
com
bin
ing
equal
dia
zepam
or
volu
mes
of ke
tam
ine
and b
enzo
dia
zepin
e.m
idaz
ola
mG
ive
“to e
ffec
t.”
Pro
pofo
l2–5 IV
Giv
e sl
ow
ly “
to e
ffec
t.”
Inje
ctable
mix
ture
s**
Ace
pro
maz
ine/
0.2
–0.3
/20–30 IM
keta
min
e
Anesthetic Management of Small Mammals 209
Xyla
zine/
keta
min
e2.0
/25 IM
Anec
dota
l re
ports
of
dea
th in a
ppar
ently
norm
al a
nim
als
hav
e bee
n a
ssoci
ated
with
xyl
azin
e-ke
tam
ine.
Ace
pro
maz
ine/
0.0
5/1
–2/2
0–30 IM
xyla
zine/
keta
min
e
Med
etom
idin
e/0.0
8/0
.1/1
0 IM
Giv
ing
oth
er a
gents
SC
prio
r to
IM
ket
amin
ebuto
rphan
ol/
will
hel
p m
inim
ize
the
pai
n o
f IM
ke
tam
ine
inje
ctio
n.
Rab
bit
s†
Prem
edic
atio
n/
chem
ical re
stra
int
Atropin
e0.0
4–0.5
SC
, IV
, IM
Routin
e use
not
reco
mm
ended
.
Gly
copyr
rola
te0.0
1 S
C, IV
, IM
Routin
e use
not
reco
mm
ended
.
Ace
pro
maz
ine/
0.1
SC
/0.0
4 S
C/
Giv
e ke
tam
ine
10–15 m
inute
s af
ter
oth
er
bupre
norp
hin
e/5–10 IM
agen
ts o
r gi
ve a
ll IM
; ke
tam
ine
may
not
keta
min
e be
nec
essa
ry in t
ract
able
pat
ients
. Fa
cili-
tate
s ca
thet
eriz
atio
n, in
duct
ion, an
d m
inor
nonin
vasi
ve p
roce
dure
s.
(conntin
ues
)
210 Anesthetic Management of Small Mammals
Tab
le 1
3–1
(Continued)
Pro
toco
lD
osa
ge (
mg/k
g)
Co
mm
en
ts
Mid
azola
m o
r 0.2
SC
(IM
for
Mid
azola
m p
rovi
des
more
rel
iable
abso
rptio
ndia
zepam
/dia
zepam
)/0.4
and les
s pai
n o
n inje
ctio
n. Ket
amin
e m
aybuto
rphan
ol/
SC/5
–10 IM
not
be
nee
ded
for
trac
table
or
dep
ress
edke
tam
ine
pat
ients
. G
ood a
ltern
ativ
e fo
r deb
ilita
ted
pat
ients
. Fa
cilit
ates
cat
het
eriz
atio
n, in
duc-
tion, an
d m
inor
nonin
vasi
ve p
roce
dure
s.
Tela
zol
5–11 IM
Faci
litat
es c
athet
eriz
atio
n, in
duct
ion, an
d
min
or
nonin
vasi
ve p
roce
dure
s. R
ecove
ries
may
be
pro
longe
d. N
ephro
toxi
city
has
bee
n r
eport
ed b
ut
unlik
ely
at t
hes
e dose
s.
Induct
ion*
Dia
zepam
/ket
amin
e1 m
l/5–10 k
g IV
A 1
:1 (
volu
me)
mix
ture
giv
en t
o e
ffec
t.
Pro
pofo
l4–10 IV
Adm
inis
ter
slow
lyto
avo
id a
pnea
.
Inje
ctable
mix
ture
s**
Xyla
zine/
keta
min
e5/3
5Fo
r hea
lthy
anim
als
only
. Pro
vides
≤30 m
in-
ute
s of
surg
ical
anes
thes
ia. Res
ponse
is
varia
ble
and inef
fect
ive
in s
om
e pat
ients
.
Anesthetic Management of Small Mammals 211
Pro
found h
ypoxe
mia
is
report
ed w
ith t
his
com
bin
atio
n; su
pple
men
tal oxy
gen is
reco
mm
ended
.
*Mas
k in
duct
ion is
effe
ctiv
e in
fer
rets
and r
abbits
follo
win
g pre
med
icat
ion a
nd r
ecom
men
ded
in d
ebili
tate
d p
atie
nts
.M
ask
induct
ion is
par
ticula
rly a
ppro
pria
te in
rab
bits
bec
ause
mai
nte
nan
ce o
f an
esth
esia
via
mas
k is
ver
y co
mm
on d
ue
to d
iffic
ult
intu
bat
ion. R
apid
act
ing
IV a
gents
pro
vide
super
ior
rela
xatio
n a
nd v
isual
izat
ion o
f th
e la
rynx
and m
ore
tim
e to
succ
essf
ully
com
ple
te in
tubat
ion. T
elaz
ol a
nd c
om
bin
atio
ns
incl
udin
g ke
tam
ine
may
allo
w in
tubat
ion w
ithout m
aski
ng
or
additi
onal
inje
ctab
le a
gents
.
**In
ject
able
com
bin
atio
ns
pro
vide
short d
ura
tion a
nes
thes
ia for
min
or
pro
cedure
s an
d the
dosa
ges
liste
d a
re n
ot th
ose
reco
mm
ended
for
adm
inis
trat
ion p
rior
to in
hal
ant m
ainte
nan
ce. P
atie
nts
should
be
close
ly m
onito
red w
hen
com
bin
a-tio
ns
that
incl
ude
alpha 2
agonis
ts a
re u
sed a
nd a
lpha 2
agonis
t-co
nta
inin
g co
mbin
atio
ns
are
not re
com
men
ded
prio
r to
inhal
ant m
ainte
nan
ce.
† Effe
ctiv
enes
s of in
tran
asal
adm
inis
trat
ion o
f se
vera
l anes
thet
ic p
roto
cols
has
bee
n r
eported
in r
abbits
and p
rovi
des
an
alte
rnat
ive
route
for
pre
med
icat
ion a
dm
inis
trat
ion. E
ffect
ive
(and r
elat
ivel
y sa
fe)
pro
toco
ls (
mg/
kg)
incl
ude
xyla
zine
(3)/
keta
min
e (1
0);
mid
azola
m (
2);
ket
amin
e (2
5);
mid
azola
m (
1)/
keta
min
e (2
5);
tel
azol (
10). O
nse
t tim
e w
as w
ithin
3 m
in. N
one
of th
e pro
toco
ls p
rovi
ded
consi
sten
t ev
iden
ce o
f ad
equat
e an
esth
esia
for
inva
sive
pro
cedure
s.
Effective monitoring devices include an esophagealstethoscope, ECG, respiratory monitor, capnometer, andpulse oximeter.
Ferrets lose body heat rapidly, and external heatmust be provided. Recovery should occur in a warm,quiet environment; an incubator is ideal, especially whensignificant hypothermia has developed, which is com-mon during abdominal procedures. Options for postop-erative analgesia are listed in Table 13–2.
Rabbits
Rabbits are easily stressed by handling, which can have anegative impact on the anesthetic period. When fright-ened, they may hold deceptively still then struggle toescape, which can predispose them to traumatic frac-tures of the vertebral column (due to the massive rearlimb muscles and low-density skeletal system) or exhibita rapid ventilatory rate (200 breaths/min), which mightbe misinterpreted as a respiratory abnormality. Safe
restraint is essential to avoid injury, performed by gentlygrasping the skin of the neck and supporting the bodyon the forearm or a nonslip table. Loosely wrapping therabbit in a towel or restraint bag also helps minimizeinjury. The immobility reflex (“hypnosis”) has beendescribed for rabbits and can facilitate minor proce-dures, such as physical examination and blood collec-tion. Briefly, the rabbit is placed in dorsal recumbencyand gentle traction applied to the neck while rubbing
212 Anesthetic Management of Small Mammals
Anesthetic Management of Small Mammals 213
Tab
le 1
3–2
Dosa
ges
of
Sele
cted A
nal
gesi
c A
gents
for
a Var
iety
of
Sm
all M
amm
alSpeci
es
Rat,
Ham
ster,
Gu
inea P
ig,
Dru
gFe
rret
Rab
bit
Gerb
ilC
hin
chil
laM
ou
se
Opio
ids
Bupre
norp
hin
e0.0
1–0.0
3/
0.0
1–0.0
5/
0.0
1–0.0
5/
0.1
–0.2
5/
0.0
5–0.1
/8–12 IV,
SC
8–12 S
C, IV
8–12 S
C, IV
8–12 P
O12 S
C0.0
5/
8–12 S
C
Buto
rphan
ol
0.4
/4–6 S
C0.1
–0.5
/2.0
/4 S
C1.0
–2.0
/4 S
C1.0
–5.0
/SC
2–4 S
C
Morp
hin
e0.5
–5.0
/2.0
–5.0
/2.0
–5.0
/2.0
–5.0
/2.0
–5.0
/6 S
C2–4 S
C2–4 S
C2–4 S
C2–4 S
C
NSA
IDs
Asp
irin
200/*
PO
100/*
PO
100/*
PO
87/
* PO
120/*
PO
Car
pro
fen**
2.0
–4.0
/1.5
/12 P
O5.0
/24 S
CN
A5.0
/ * S
C24 S
C
Flunix
in
0.5
–2.0
/1.1
/12 S
C2.5
/12 S
C1–2/*
SC
2.5
/12 S
Cm
eglu
mat
e12–24 S
C
(contin
ues
)
214 Anesthetic Management of Small Mammals
Tab
le 1
3–2
(Continued)
Rat,
Ham
ster,
Gu
inea P
ig,
Dru
gFe
rret
Rab
bit
Gerb
ilC
hin
chil
laM
ou
se
Ket
opro
fen
NA
3.0
/* IM
, SC
5.0
/* S
CN
AN
A
Note
: N
um
ber
s re
pre
sent dosa
ge in
mg/
kg /
inte
rval
(in
hr)
for
each
spec
ies
cate
gory
. Consi
der
able
indiv
idual
var
iatio
nin
res
ponse
exist
s in
thes
e sp
ecie
s an
d fre
quen
t as
sess
men
t of ef
ficac
y is
crit
ical
.
*Rel
iable
dat
a re
gard
ing
dosa
ge in
terv
al is
unav
aila
ble
. Conse
rvat
ive
dosi
ng
at 1
2–24 h
r in
terv
al is
rec
om
men
ded
. In
gener
al, N
SAID
s sh
ould
not be
use
d for
more
than
1–3 d
ays,
due
to the
pote
ntia
l adve
rse
side
effe
cts
and p
auci
ty o
fin
form
atio
n r
egar
din
g sa
fety
in thes
e sp
ecie
s.
**C
arpro
fen c
urren
tly is
not av
aila
ble
in the
inje
ctab
le form
in the
Unite
d S
tate
s.
Route
s of ad
min
istrat
ion:
IV =
intrav
enous
SC =
subcu
taneo
us
IM =
intram
usc
ula
r
PO
= o
ral
NA =
not av
aila
ble
Dosa
ges
are
adap
ted fro
m P
A F
leck
nel
l, Anal
gesi
a in
sm
all m
amm
als,
in: Se
min
ars
in A
vian a
nd E
xotic
Pet
Med
icin
e:Anes
thes
ia a
nd A
nalg
esia
, AM
Fudge
, ed.,
1998;7
(1):
41–47.
(D
osa
ges
for
ham
ster
s, g
erbils
, and c
hin
chill
as a
re b
ased
on e
xtra
pola
tion fro
m o
ther
spec
ies
and in
itial
dose
s sh
ould
util
ize
the
low
er d
osa
ge r
ange
.)
the abdomen. The hypnotized rabbit usually stays still fora short period of time, unless aroused by loud noises orrough handling.
Premedication usually is required to facilitatesmooth induction of anesthesia, and protocols are listedin Table 13–1. Most of the agents may be administeredsubcutaneously (over the skin of the back), and this ispreferred, due to occasional occurrence of lameness andtissue necrosis associated with IM administration. Disso-ciative agents should be administered IM, and the mostcommon sites include the anterior and posterior thigh.A significant percentage of rabbits (30–50%) possessatropinesterase, which results in rapid metabolism andabbreviated effective duration of atropine. Because ofthis, a wide range of dosages has been recommended inthe literature; however, routine use is unnecessary andanticholinergic agent administration in rabbits is bestreserved for treatment of intraoperative bradycardia(HR <70–80/min or an abrupt, marked decrease[≥20%] in HR). Dosages for atropine and glycopyrrolateare listed in Table 13–1.
Intravenous catheterization following premedica-tion usually is possible in rabbits over 2 kg and recom-mended for prolonged procedures, debilitated patients,and to facilitate IV induction of anesthesia. Sites includethe cephalic, lateral saphenous, and marginal ear veins,using a 22–24 ga catheter. The ear vein is particularlyfragile and more difficult to catheterize than the othertwo sites.
Anesthetic Management of Small Mammals 215
Mask induction, preferably with isoflurane, is aneffective method when the rabbit is adequatelyrestrained and sedated; and it is particularly applicablewhen intubation is not planned. For prolonged proce-dures, intubation is recommended; and a rapid-actinginduction agent, such as diazepam-ketamine, propofol,or thiopental, will facilitate the process. Intranasaladministration of anesthetic agents for sedation or toinduce anesthesia also has been reported for rabbits andmay provide an alternative route for some agents in spe-cific individuals (Table 13–1).
Rabbits are difficult to intubate and it takes practiceand anatomical knowledge to master the technique. Theendotracheal tube size for rabbits ranges 2.0–4.0 mm ID.The oral cavity is small but long, with limited ability forthe animal to open its mouth. The tongue tends toobscure the larynx. The epiglottis is long and pliable,often remaining dorsal to the soft palate. The pharynx islocated at a right angle to the larynx, and the larynx issusceptible to laryngospasm and trauma.
Adequate anesthetic depth is essential to facilitateatraumatic intubation, and several methods and animalpositions (with sternal recumbency being most com-mon) have been described. The head and neck shouldbe kept in full extension; a length of roll gauze placedbehind the upper incisors will help hold the mouthopen; and retraction of the tongue lateral to the lowerincisors will minimize risk of laceration during the pro-cedure. Techniques include blind (passing the tube to
216 Anesthetic Management of Small Mammals
the point of maximum intensity of breath sounds eitherwith the ear or with stethoscope earpieces attached tothe end of the tube, then passing the tube during inspi-ration when the larynx is maximally abducted) and direct
visualization (with a small lighted laryngoscope or oto-scope to guide the tube into place). Use of an introduc-tory tube, such as a small urinary catheter, placed visuallyinto the larynx may facilitate the process. A drop of 1%or 2% lidocaine on the glottis will help minimize laryn-gospasm. Evidence of proper placement includes acough reflex with passage and those signs previouslynoted in Chapter 9. Roll gauze tied around the tube andaround the back of the head will secure the tube inplace.
Once induction is complete, epidural administrationof local anesthetic agents, with or without an opioid, iseffective and relatively easy to perform in rabbits to pro-vide preemptive analgesia for procedures involving theabdomen and hind limbs. Dosages and technique aresimilar to those described for dogs and cats (Chapter 3).
Monitoring tools, to enhance observation of breath-ing rate (>15 breaths/min) and pattern and ausculta-tion/palpation of pulse rate (auricular, femoral, ordorsal pedal), include the ECG and, in larger rabbits,noninvasive blood pressure monitors placed over aperipheral artery. Pulse oximetry has limited use (due tofrequent use of a mask for maintenance and limitedexposure of the tongue for probe placement), but maywork on the ear in light-skinned rabbits. Respiratory
Anesthetic Management of Small Mammals 217
devices and the esophageal stethoscope require intuba-tion and, so, often are not applicable. Respiratory dys-function probably is the most common anestheticcomplication in rabbits and close observation of thebreathing rate and pattern is essential. A sudden changein these parameters should prompt assessment of ETtube patency (if in place) or the oropharynx for exces-sive secretions (if a mask is used), and anesthetic deliveryshould be decreased or stopped. Reflexes used to assessanesthetic depth include the pinna (“ear pinch”) andpedal reflexes with the former considered to be mostreliable. The palpebral reflex has been reported to beunreliable in rabbits; loss of the corneal reflex, as inother species, indicates excessive anesthetic depth.
Monitoring should continue into the recoveryperiod, until the animal is extubated and vital signs arestable, and should proceed in a warm environment (withincubator or heat lamp support) until the animal’s tem-perature returns to normal (Chapter 1). Analgesic agentdosages have been reported (see Table 13–2) and shouldbe applied to rabbits subjected to painful procedures tohelp minimize stress and suffering.
Other Small Mammals
A variety of “pocket pets” may be presented with the needfor general anesthesia. Some general statements regard-ing management in clinical situations can be made:
218 Anesthetic Management of Small Mammals
1. For small mammals, anesthetic management is bestaccomplished by mask or chamber induction(depending on tractability) with isoflurane orsevoflurane. Designing a mask to work effectivelymay require some innovative modification of stan-dard feline or canine masks or syringe cases. Intuba-tion may be attempted if the necessary tube sizes andadjunct equipment are available.
2. When dealing with species for which anestheticdosage and technique information is limited, effortsto minimize anesthesia time is essential.
3. Established monitoring tools often are effective; it isalways worthwhile to apply available equipment,especially during prolonged procedures.
4. Venous access is not always possible with small mam-mals, but when fluid therapy is indicated, alternativeroutes, including SC and intraosseous, should beconsidered.
5. Analgesic therapy should be considered for any ani-mal undergoing a painful procedure; when specificdosages are not readily available, extrapolation orscrutiny of the literature may provide safe, effectiveguidelines. Table 13–2 provides dosages of analgesicagents in a variety of small mammal species.
Anesthetic Management of Small Mammals 219
14
Anesthetic Management of Reptiles
A variety of reptilian species may be presented with theneed for chemical restraint and general anesthesia, andthis represents a unique challenge, including limitedsites for parenteral agent injection and IV access, a majortendency to become apneic during anesthesia (whichoften prevents use of mask induction), difficulty in car-diac auscultation, and limited usefulness of availablemonitoring tools.
Restraint techniques are relatively simple for most rep-tiles but may become more challenging in infrequentlyencountered aggressive patients. Lizards are restrainedby enclosing in the hand if small or securing on a flat sur-face then applying gentle pressure to the neck and cau-dal body. For snakes, a hand should secure the head and
221
the remainder of the body supported with the otherhand or on a flat surface. Turtles require minimalrestraint but present a unique problem in that the headusually is inaccessible for physical examination. To viewthe head, applying a gentle pinch to a front limb usuallywill cause it to emerge from the shell. Two preanestheticconsiderations are important for reptiles. Allow at least24 hr of hospitalization prior to anesthesia for acclima-tion. The optimal temperature for most species is86–88°F. Second, an accurate weight is important to cal-culate dosages for premedication, which is necessary forinduction in most reptile patients. Fasting in reptilesgenerally is not recommended; the exception is snakes,for which a large meal ingested just prior to anesthesiacould impede cardiovascular function; therefore, a 24-hr(minimum) fast is recommended.
Various sites for blood collection have beenreported—lizards (toenail, ventral tail vein); snakes (ven-tral tail vein, heart, palatine vein); turtles (toenail,brachial plexus)—and may be required for the workupof complicated cases.
Induction and intubation for maintenance withinhalant anesthesia (preferably isoflurane) is facilitatedby IM administration of ketamine. Dosages for ketamineand other adjunct drugs are listed in Table 14–1. Noneof the agents listed provides adequate analgesia aloneand inhalant supplementation is necessary for painfulprocedures. Because many species of reptiles can convertto anaerobic metabolism and become apneic, mask
222 Anesthetic Management of Reptiles
induction is prolonged without the benefit of aninjectable agent. Like birds, reptiles have a renal portalsystem and the caudal half of the body should be avoidedfor IM drug administration. Sites for IM injectioninclude the front legs (lizards, chelonians) and the par-avertebral muscles (lizards, snakes). A nonrebreathingsystem for inhalant delivery is recommended for reptilesweighing <5 kg.
Intubation is important in anesthetic managementof reptiles to provide ventilatory support during theanesthetic period and maintain an adequate depth ofanesthesia. Intubation is relatively easy to perform andcan be accomplished in some awake reptiles, includingsnakes and some iguanas. The glottis is located rostrallyand hence easy to view. However, the glottis is closed atrest and patience is required to wait for an inspiration toallow passage of the tube. The tube may be passedthrough the closed glottis if extreme care is taken and maybe facilitated by passage of a soft stylet (urinary catheter)to guide the entry of the endotracheal tube. Tube sizesfor reptiles range from 2.0–4.0 mm ID, but smallerpatients may require other options, such as IV catheters.Short tubes should be used in turtles, due to their rela-tively short trachea. Chelonians have complete trachealrings, making them susceptible to mucosal damage dueto an overinflated cuff; snakes and lizards have incom-plete tracheal rings. When a cuffed tube is used in anyreptile, care should be taken to not overinflate the cuff.
Anesthetic Management of Reptiles 223
224 Anesthetic Management of Reptiles
Tab
le 1
4–1
Dosa
ges
for
Inje
ctab
le A
nest
hetic
Age
nts
in R
eptile
s
Agen
tD
osa
ge (
mg/k
g)*
Co
mm
en
ts
Atropin
e0.0
1–0.0
4Routin
e use
is
not
reco
mm
ended
.
Gly
copyr
rola
te0.0
1Routin
e use
is
not
reco
mm
ended
.
Tranquili
zers
/alp
ha
2D
osa
ge a
nd e
ffic
acy
info
rmat
ion is
limite
d.
agonis
ts/a
nta
gonis
ts
Ace
pro
maz
ine
0.1
–0.5
Dia
zepam
0.2
–1.0
Mid
azola
m0.2
–2.0
Xyla
zine
0.1
–1.2
5
Med
etom
idin
e0.1
–0.1
5
Atip
amez
ole
0.5
–0.7
5
Neu
role
pta
nalg
esia
Buto
rphan
ol/
mid
azola
m0.4
/2.0
Dis
soci
ativ
e agen
ts
Ket
amin
eKet
amin
e is
the
most
com
mon a
nes
thet
ic
adju
nct
util
ized
.Li
zard
s30–50
Snak
es20–40
Anesthetic Management of Reptiles 225
Turtle
s30
Tela
zol
5–10
May
contrib
ute
sig
nifi
cantly
to a
pro
longe
d
reco
very
.
Oth
er a
gen
ts
Pro
pofo
lLi
zard
s10 IO
Snak
es10 IV,
IC
Turtle
s5–10 IV
Analg
esic
agen
ts
Buto
rphan
ol
0.4
IM
, IV
, SC
Bupre
norp
hin
e0.0
1
Car
pro
fen
2.0
–4.0
PO
once
ev
ery
1–3 d
ays
Flunix
in0.1
–0.5
IM
once
dai
ly (
max
imum
of
3 d
ays)
IO =
intrao
sseo
us
IC =
intrac
ardia
c
*Adm
inis
trat
ion is
IM
unle
ss o
ther
wis
e note
d.
Intraoperative fluid administration is not routine,unless the procedure is prolonged or the animal debili-tated. Intravenous access is a daunting task in reptiles,requiring a cutdown in most cases. The exception islarge snakes, in which the palatine vein can be easily visu-alized and catheterized with a 24 ga catheter followinginduction and intubation. When needed, the intra-osseous route is feasible. Intraosseous catheter sites inlizards include the humerus and tibia. In chelonians, thejugular vein may be catheterized in some patients (some-times without a cutdown); the long bones lack a distinctmedullary canal, limiting IO sites to the bridge betweenthe plastron (bottom of shell) and carapace (top ofshell), which may be difficult to enter without penetrat-ing the coelomic cavity.
Ventilatory support at a rate of 6–12 breaths/minshould be provided for all reptiles, regardless of the indi-vidual’s spontaneous rate, to help maintain an adequateplane of anesthesia.
Monitoring anesthetized reptiles is the ultimate chal-lenge. Apnea is common, making respiratory monitor-ing undependable. Heart sounds are extremely difficultto auscultate, and peripheral pulses rarely are palpable.Useful tools include the ECG (Figure 14–1) and theDoppler blood flow probe (apparatus), which providesan audible signal of cardiac function. The crystal isplaced over the heart in snakes and lizards and at thethoracic inlet in chelonians. Reptiles relax in a cranial tocaudal direction during anesthesia, and function returns
226 Anesthetic Management of Reptiles
in the opposite direction during recovery. The rightingreflex is lost first, followed by the tail- and toe-pinchwhen a surgical plane of anesthesia is reached. Whileconsiderable variation exists, loss of the vent reflex (tailor toe movement when the vent is squeezed), thecorneal reflex, and tongue withdrawal all may indicateexcessive depth of anesthesia, which should prompt crit-ical patient assessment.
Recovery from inhalation anesthesia often is pro-longed in reptiles compared to mammals, commonlytaking 1 hr or more, especially following prolonged pro-cedures. Animals should recover in a quiet environment,ideally with the ambient temperature near the species’optimal range. Ventilatory support should be continuedto aid in elimination of the anesthetic agent; animals thatdo not resume spontaneous ventilation within 15 min ofdiscontinuation of anesthetic delivery may benefit fromdoxapram (5 mg/kg IM). Voluntary movement andincreased muscle tone usually are the first signs to indi-cate extubation, which should be delayed, if possible,until the righting reflex returns. While information islimited, analgesia should be provided for painful proce-dures. Suggested agents and dosages are listed in Table14–1.
Anesthetic Management of Reptiles 227
228
Figu
re 1
4–1
Lead
II
ele
ctro
card
iogra
m f
rom
an igu
ana
during
isoflura
ne a
nest
hesi
a. L
ead
s w
ere
pla
ced o
n t
he f
ore
limbs
and left
rear
lim
b.
15
Anesthetic Management of Horses
Horses are an anesthetic challenge due to their size, widerange of temperaments, tendency to react explosively tofear and stress, increased risk of trauma associated withinduction and recovery (which can both be rough andunpredictable), susceptibility to hypotension, andincreased risk for development of postoperative myopa-thy and neuropathy following inhalant anesthesia. Mostshort procedures (<60 min) in horses are performedwith total parenteral anesthesia, using the same agentsthat provide induction for inhalant anesthesia; recom-mended protocols are listed in Table 15–1.
Fasting is controversial in horses. Horses cannotvomit, so risk of regurgitation and aspiration is negligi-ble; however, a minimum of 6 hr is recommended. It is
229
230 Anesthetic Management of Horses
Tab
le 1
5–1
Pro
toco
ls f
or
Chem
ical R
est
rain
t, I
nduct
ion o
f A
nest
hesi
a, and
Inje
ctable
Anest
hesi
a in H
ors
es
Agen
t/P
roto
col
Do
sages
(mg/k
g)
Co
mm
en
ts
Ad
ult
s
Chem
ical re
stra
int
Ace
pro
maz
ine
0.0
2–0.0
6M
ay b
e co
mbin
ed w
ith a
lpha 2
agonis
t or
opio
id.
Xyla
zine
0.2
–1.0
May
be
com
bin
ed w
ith a
cepro
maz
ine
or
opio
id.
Det
om
idin
e0.0
1–0.0
4M
ay b
e co
mbin
ed w
ith a
cepro
maz
ine
or
opio
id.
Buto
rphan
ol
0.0
2–0.0
4U
sual
ly c
om
bin
ed w
ith a
lpha 2
agonis
t.
Morp
hin
e0.0
5D
o n
ot
use
alo
ne
due
to lik
elih
ood o
f ex
cite
-m
ent;
usu
ally
com
bin
ed w
ith a
lpha 2
agonis
t.
Induct
ion/s
hort-
term
ane
sthe
sia
Xyla
zine/
keta
min
e 1.1
*/2.2
IV
Giv
e xy
lazi
ne
first
and p
roce
ed in 5
min
or
when
sed
atio
n a
ppea
rs a
deq
uat
e. F
or
unru
lyan
imal
s, x
ylaz
ine
may
be
adm
inis
tere
d IM
(2.2
mg/
kg)
and m
ay r
equire
additi
onal
IV
xyla
zine
(0.2
–0.4
mg/
kg)
prio
r to
ket
amin
ead
min
istrat
ion. Adju
nct
dru
gs t
o im
pro
ve
Anesthetic Management of Horses 231
sedat
ion p
rior
to k
etam
ine
incl
ude
acep
ro-
maz
ine
(0.0
2 m
g/kg
IV o
r IM
) or
buto
r-phan
ol (0
.02–0.0
4 m
g/kg
IV).
Xyla
zine/
0.5
–1.1
/0.0
5–
Good f
or
deb
ilita
ted p
atie
nts
and
dia
zepam
/0.1
/2.2
neo
nat
es; xy
lazi
ne
adm
inis
trat
ion s
hould
ke
tam
ine
pre
cede
induct
ion a
nd d
ose
is
bas
ed o
npat
ient
aler
tnes
s. M
ix d
iaze
pam
and k
eta-
min
e an
d g
ive
as b
olu
s. In v
ery
dep
ress
ed,
recu
mben
t an
imal
s or
neo
nat
es, xy
lazi
ne
may
be
om
itted
. If
sedat
ion is
consi
der
ednec
essa
ry, 0.0
1–0.0
3 m
g/kg
buto
rphan
ol is
reco
mm
ended
.
Xyla
zine/
5%
0.5
–1.1
/”to
effec
t”/
Inco
rpora
ting
guai
fenes
in w
ill h
elp d
ecre
ase
guai
fenes
in/
0.7
5–2.2
xyla
zine
and k
etam
ine
require
men
ts.
keta
min
e
Xyla
zine/
5%
0.5
–0.6
/to e
ffec
t/Th
iopen
tal ca
n f
ollo
w g
uai
fenes
in a
s a
bolu
s or
guai
fenes
in/
3.0
–4.0
2 g
added
to g
uai
fenes
in a
nd g
iven
to
thio
pen
tal
recu
mben
cy.
Xyla
zine/
Tela
zol
1.1
/1.1
Rep
orted
to c
ause
a m
ore
pro
longe
d a
nd s
lightly
rough
er r
ecove
ry t
han
xyl
azin
e/ke
tam
ine.
(contin
ues
)
232 Anesthetic Management of Horses
Tab
le 1
5–1
(Continued)
Agen
t/P
roto
col
Do
sages
(mg/k
g)
Co
mm
en
ts
Inje
ctable
U
se f
ollo
win
g in
duct
ion w
ith x
ylaz
ine-
keta
min
eanes
thet
ic
(with
or
with
out
dia
zepam
, buto
rphan
ol,
main
tenance
or
acep
rom
azin
e).
Xyla
zine/
0.5
mg/
ml xy
lazi
ne
“Trip
le d
rip”:
adm
inis
tere
d a
t ap
pro
xim
atel
ygu
aife
nes
in/
and 1
mg/
ml
2.2
ml/
kg/h
our
keta
min
eke
tam
ine
added
May
be
use
d f
or
induct
ion o
f an
esth
esia
to 5
% g
uai
fenes
in(0
.5–0.6
ml/
kg)
in h
ors
es w
eigh
ing
<200 k
g.
Guai
fenes
in/
2 m
g/m
l ad
ded
C
an b
e use
d f
ollo
win
g in
duct
ion w
ith x
ylaz
ine-
thio
pen
tal
to 5
% g
uai
fenes
inke
tam
ine
or
guai
fenes
in-thio
pen
tal.
Anes
-th
etic
dep
th b
ecom
es m
ore
diff
icult
toas
sess
if
the
form
er is
use
d.
Avo
id u
sing
more
than
2 g
thio
pen
tal fo
r m
ain-
tenan
ce t
o m
inim
ize
risk
of
rough
rec
ove
ry.
Foals
Induct
ion/s
hort-
dura
tion
main
tenance
Anesthetic Management of Horses 233
Buto
rphan
ol/
0.0
6/0
.06 IV
Induce
anes
thes
ia b
y m
ask
or
nas
otrac
hea
ldia
zepam
intu
bat
ion, pre
fera
bly
with
iso
flura
ne
(or
sevo
flura
ne)
.
Buto
rphan
ol/
0.0
6/0
.1/2
.2Xy
lazi
ne
(0.2
–0.5
mg/
kg)
may
be
added
for
dia
zepam
/hea
lthy
foal
s w
hen
they
res
ist
rest
rain
t or
keta
min
ea
pai
nfu
l pro
cedure
is
to b
e per
form
ed.
Dura
tion o
f an
esth
esia
: 10–20 m
in.
Analg
esic
optio
ns
Dosa
ge inte
rval
s ar
e gu
idel
ines
to b
e ta
ilore
d t
o
indiv
idual
pat
ients
bas
ed o
n o
ngo
ing
asse
ss-
men
t.
Bupre
norp
hin
e0.0
05 IM
, SC
Inte
rval
: 6–12 h
r
Buto
rphan
ol
0.0
2 IV,
IM
Inte
rval
: 2–4 h
r
Morp
hin
e0.2
IM
Inte
rval
: 4–6 h
r
The
pre
sence
of
pai
n o
btu
nds
the
exci
tato
ry
resp
onse
that
can
occ
ur
with
morp
hin
ead
min
istrat
ion t
o h
ors
es; how
ever
, ag
itatio
nan
d e
xcite
men
t ca
n o
ccur,
whic
h a
re c
on-
trolle
d b
y xy
lazi
ne
(0.2
–0.4
mg/
kg IV).
(contin
ues
)
234 Anesthetic Management of Horses
Tab
le 1
5–1
(Continued)
Agen
t/P
roto
col
Do
sages
(mg/k
g)
Co
mm
en
ts
Morp
hin
e (c
ont.)
0.1
(ep
idura
l M
ay b
e use
d a
lone
or
com
bin
ed w
ith x
ylaz
ine
adm
inis
trat
ion)
or
det
om
idin
e (s
ee d
osa
ges
in T
able
3–4)
for
pai
n r
elie
f as
far
forw
ard a
s th
ora
x fo
r 8–24 h
r.
Avo
id f
orm
ula
tions
that
conta
in t
he
pre
serv
ativ
e fo
rmal
in (
the
pre
serv
ativ
e m
ethyl
par
aben
is
acce
pta
ble
). U
se o
f th
e pre
serv
ativ
e-free
pre
par
atio
n (
Duro
morp
h™
) is
optim
al b
ut,
due
to t
he
low
conce
ntrat
ion, ad
equat
edosa
ge m
ay b
e diff
icult
to d
eliv
er d
ue
to t
he
larg
e quan
tity
require
d.
Fenta
nyl
Tw
o 1
00 µ
g pat
ches
Dura
tion o
f ef
fect
: 48 h
r.(t
ransd
erm
al)
per
adult
hors
e(a
pplie
d o
ver
tho-
rax
beh
ind e
lbow
)
Phen
ylbuta
zone
2.2
–4.4
IV,
PO
Inte
rval
: 12 h
r
Flunix
in m
eglu
min
e1.1
IV
Inte
rval
: 8–12 h
r
Ket
opro
fen
1.1
–2.2
IV
Inte
rval
: 12–24 h
r
Note
: D
osa
ges
are
most
com
monly
adm
inis
tere
d IV.
*D
raft
bre
eds
rare
ly r
equire
more
than
600 m
g (t
ota
l IV d
ose
) xy
lazi
ne
pre
med
icat
ion for
keta
min
e in
duct
ion.
Anesthetic Management of Horses 235
advisable but unnecessary to remove shoes prior to anes-thetic induction; shoes with toe clips or devices that maycause significant body injury or excessive slipping duringrecovery should be removed. Covering shoes left in placewith padding and tape will help minimize these risks.
Adequate preanesthetic sedation is essential in adulthorses. Induction of anesthesia in an inadequatelysedated animal will increase the risk of injury to bothhorse and handler. The most commonly used drug isxylazine. Combining a second agent with xylazine, such asbutorphanol, acepromazine, or diazepam, will helpassure a smooth induction (see Table 15–1). Avoidxylazine (at least high dosages) in foals less than 1 monthof age if other agents are available (see Table 15–1). Theinduction agent most commonly used is ketamine, aloneor in combination with guaifenesin or diazepam.Thiopental also is used, largely dependent on experiencewith the drugs and the occasional contraindication asso-ciated with ketamine in individual patients (e.g., headtrauma, descemetocoele). As a general rule, protocolsusing ketamine produce a more reliable and smootherrecovery; however, some animals—such as excitable, hot-blooded breeds, donkeys, mules, and ponies—may fail torespond to ketamine induction and short-term mainte-nance, making it necessary to use other or additionalagents for induction and maintenance. Donkeys andmules appear sensitive to the effects of guaifenesin;incorporating guaifenesin into the induction protocol is
236 Anesthetic Management of Horses
effective, but care must be taken to avoid high-enddosages, which could precipitate apnea.
Because their response to anesthetics can be unpre-dictable, placing a catheter in the jugular vein, eitherbefore or after premedication, will provide easy access toadminister additional drugs when needed to smoothinduction, prolong the anesthetic period in field situa-tions, and quickly obtund voluntary movement duringinhalation anesthesia.
Intubation is performed blindly in the horse, withthe head, neck, and back extended in a straight line.Inserting a speculum, such as a short piece of PVC pipewith the edges smoothed, will facilitate passage of thetube between the cheek teeth into the larynx. Once thetube reaches the larynx, it is retracted slightly, rotated90°, and advanced again until it can pass by the arytenoidcartilages and “fall into” the trachea. This may need to berepeated, rotating in the same direction, one or severaltimes before the tube bevel can pass into the trachea.
Endotracheal tubes also can be passed nasally; thispractice is common in foals to facilitate an inhalantinduction and may be indicated in adult horses for pro-cedures of the oral cavity. Desensitizing the floor of thenasal opening with lidocaine jelly will facilitate tubeintroduction into the ventral nasal meatus. The disad-vantage of nasotracheal intubation is that a smaller tubemust be used, which will increase resistance to breathing.Orotracheal tube sizes range from 10 mm ID (newbornfoals) to 30 mm ID for draft breeds. For nasotracheal
Anesthetic Management of Horses 237
intubation, 8–12 mm ID is used in foals and 16–20 mmID can be passed in adult horses. Intubation is unneces-sary during parenteral anesthesia. However, horses areobligate nasal breathers, and some individuals maydevelop stridorous inspiration during general anesthe-sia, which may require placement of an ET tube (nasal isconvenient) to maintain airway patency. Appropriatelysized tubes always should be available for quick intuba-tion should a respiratory emergency develop.
Halothane, isoflurane, and, most recently, sevoflu-rane are used in horses. Halothane historically has beenthe agent of choice for elective procedures, due to itseffectiveness and lower cost, despite a greater negativeeffect on cardiac performance and greater likelihood ofhypotension. Isoflurane is a better choice for high-riskpatients (e.g., those with colic or needing a cesarean sec-tion) and foals. Reports have suggested a rougher recov-ery associated with isoflurane anesthesia when used inrelatively healthy horses. This potential undesirableeffect can be minimized by administration of a sedativeor tranquilizer (e.g., alpha2 agonist, butorphanol, ace-promazine) at the low-end dosage range, IV or IM, in thepostoperative period. Intramuscular administration willprovide a longer duration with less negative cardiovascu-lar effects but should be given 15–30 min prior to therecovery period. Sevoflurane has been reported to pro-duce smooth recoveries, even in healthy patients, due toits lower solubility (compared to isoflurane andhalothane) and rapid clearance.
238 Anesthetic Management of Horses
Supportive care considerations include adequatepadding and proper positioning to minimize risk of myo-pathy and neuropathy, crystalloid fluid administration tocounteract the hypotensive effects of inhalant anesthet-ics, provision of mechanical ventilation during inhalantanesthesia (especially for respiratory-compromisedpatients and during prolonged procedures), and admin-istration of inotropic agents when indicated. Minimizingdowntime is a critical factor in decreasing the risk ofmyopathy in all horses and especially important in largebreeds, such as draft horses. The most commonly usedinotrope in horses is dobutamine, administered “toeffect” at an approximate infusion rate of 2–5µg/kg/min. An easy method is to add 50 mg of dobuta-mine to a 500 ml bag of 0.9% saline or 5% dextrose andadminister at a rate of 1–2 drop/sec (10 drop/ml dripset for adults; 60 drop/ml set for foals) until the desiredblood pressure is achieved. Dobutamine may be usedintermittently as needed or the administration rate canbe adjusted to maintain a stable and adequate mean arte-rial pressure. Greater accuracy is provided by use of asyringe pump when available.
During parenteral anesthesia, the eyes should becovered to minimize external stimulation, the halterremoved to minimize risk of damage to nerves lyingsuperficially in the head, and oxygen supplemented(10–15 L/min) for procedures anticipated to exceed 60min. Demand valves, which function at 50–80 psi to
deliver 200–280 L/min of oxygen, provide supplementaland emergency ventilatory support for large animalpatients during injectable anesthesia and recovery frominhalation anesthesia when an anesthesia machine is notreadily accessible. The demand valve, connected to theendotracheal tube, is triggered by negative pressure cre-ated by the animal’s spontaneous breath or manually bythe operator. It adds resistance to breathing and shouldnot be left on the ET tube for prolonged periods of time.It can be used connected to a stomach tube with the tipplaced in the nasopharynx, but this is less efficient.
Vigilant monitoring is important in horses, as volun-tary movement, sometimes without obvious warning, iscommon. Horses may exhibit transient apnea in theimmediate postinduction period, which will delay anes-thetic uptake if ventilatory support is not provided. Res-piration is easy to observe in horses by directvisualization of the thorax and rebreathing bag. Normalrates should be 6–12 breaths/min, higher for foals(12–20 breaths/min). Horses are prone to hypoventila-tion and hypoxemia during anesthesia. Although of min-imal consequence during short field procedures, thesechanges can become significant and affect cardiac per-formance during prolonged procedures. Arterial bloodgas analysis, when available, will help guide ventilatorysupport and optimize homeostasis during the intraoper-ative period and is advised for procedures in excess of 60min and for high-risk patients.
Anesthetic Management of Horses 239
240 Anesthetic Management of Horses
The heart rate (HR) tends to remain stable in adulthorses (25–50 beats/min; performance animals mayhave even lower rates), even when anesthesia is inade-quate, so it is not an effective indicator of anestheticdepth. Foals are the exception: a marked increase in HRis likely to occur during inadequate anesthesia. Invasivearterial blood pressure monitoring is a reliable and nec-essary monitoring tool during equine inhalation anes-thesia to assure adequate perfusion pressure (minimalmean arterial pressure >60–70 mmHg, which will helpminimize the risk of myopathy), provide information oncardiac performance, and signal inadequate anestheticdepth, with a sudden and rapid increase in pressureoften (but not always) preceding voluntary movement.Both of the noninvasive arterial blood pressure monitor-ing techniques (Chapter 6) are applicable for short anes-thetic duration (<1 hr) and seem to be especiallyeffective in foals, although less reliable and accurate.
Eye signs used to assess inhalant anesthetic depth inhorses include the palpebral reflex, which shouldremain slow but present; rapid nystagmus, which oftensignals impending movement (slow nystagmus may per-sist in some individuals without accompanying voluntarymovement); and tearing, which may signal a light planeof anesthesia. These signs should be assessed in conjunc-tion with cardiopulmonary parameters whenever criticalassessment of anesthetic depth is made.
Recovery following inhalant anesthesia should occurin a dark and padded enclosure. Recovery may be assisted
with a tail rope and halter if there is adequate room in therecovery area for personnel to escape injury and amethod to secure the ropes. Assisted recovery is especiallyindicated for patients at risk of injury during recovery,such as orthopedic patients. Recovery is facilitated byplacing animals on a large pad, to maintain padding, andto discourage attempts to stand until the animal is able.Postanesthetic sedation helps to delay attempts to standuntil the animal can do so unattended or with minimalassistance. Two approaches to extubation are used,depending on personal preference and available facili-ties. The tube can be removed before swallowing isobserved and replaced with a smaller nasotracheal tube,which should be taped securely to the muzzle to assure apatent airway throughout the recovery process. Or, theanimal can be attended until swallowing is observed andthen the tube removed, assuming a patent airway can bemaintained at that time. Regardless of the preferredapproach, oxygen supplementation (15 L/min) shouldbe provided throughout recovery because a tendency tohypoxemia will persist until the horse returns to standing.
For field procedures, a safe and grassy area is pre-ferred for recovery. The eyes should remain covered andthe animal attended until it can be assisted to stand whena coordinated attempt is made.
Anesthetic Management of Horses 241
16
Anesthetic Management of Ruminants and Camelids
Ruminants are amenable to standing chemical restraintand local techniques (Chapter 3) for a variety of proce-dures due to temperament (there are exceptions) andestablished effective restraint techniques. Table 16–1 listsdosages for agents to provide chemical restraint, induc-tion, and parenteral maintenance of anesthesia. Anti-cholinergic administration is controversial and routineadministration is not recommended. Bradycardia rarelyis a complication of general anesthesia and administra-tion of atropine will not significantly decrease salivationbut will increase its viscosity and may contribute to devel-opment of bloat.
243
244 Anesthetic Management of Ruminants and Camelids
Tab
le 1
6–1
Dosa
ges
of
Inje
ctab
le A
nest
hetic
Age
nts
Use
d f
or
Chem
ical
Rest
rain
t,In
duct
ion, an
d M
ainte
nan
ce o
f A
nest
hesi
a in
Rum
inan
ts a
nd C
amelid
s
Agen
t/P
roto
col
Do
sage (
mg/k
g)*
Co
mm
en
ts
Ru
min
an
ts
Che
mic
al r
estrai
nt/
pre
med
icatio
n
Ace
pro
maz
ine
Cat
tle0.0
2–0.0
6In
effe
ctiv
e al
one
for
intrac
table
pat
ients
.G
oat
s, s
hee
p0.0
4–0.0
8M
ay incr
ease
occ
urren
ce o
f re
gurg
itatio
n.
Dia
zepam
(ca
lves
, 0.2
–0.5
Min
imal
ly e
ffec
tive
in a
dult
cattle
.sm
all ru
min
ants
)
Xyla
zine*
*C
attle
0.0
1–0.1
In g
ener
al, do n
ot
exce
ed 5
0 m
g to
tal dose
; ↑
dosa
ges
may
be
require
d f
or
intrac
table
pat
ients
.G
oat
s0.0
2–0.1
Do n
ot
exce
ed 0
.02 (
mg/
kg)
IM in k
ids.
Shee
p0.0
2–0.2
Hyp
oxe
mia
due
to p
atholo
gic
pulm
onar
y ch
ange
s has
bee
n r
eport
ed in s
hee
p; if
xyla
zine
adm
inis
trat
ion is
unav
oid
able
, use
min
imal
rec
om
men
ded
dosa
ges
and s
upple
-m
ent
oxy
gen w
hile
sed
ated
.
Anesthetic Management of Ruminants and Camelids 245
Chlo
ral hyd
rate
Cat
tle40–60 IV
80–100 P
O,
per
rec
tum
Goat
s30–50 IV
Buto
rphan
ol
Bes
t use
d in c
om
bin
atio
n w
ith a
cepro
maz
ine
or
xyla
zine.
Cat
tle0.0
1–0.0
4Sh
eep, go
ats
0.1
–0.2
Induct
ion/
main
tenance
Thio
pen
tal (s
mal
l 10–15 IV
Induct
ion o
f an
esth
esia
.ru
min
ants
)
5%
Guai
fenes
in
80–100 IV
When
use
d a
lone
for
recu
mben
cy.
(cat
tle)
50 IV
In c
om
bin
atio
n w
ith o
ther
age
nts
.
5%
Guai
fenes
in/
2–3 g
added
Adm
inis
tere
d “
to e
ffec
t”; al
so m
ay b
e use
d t
oth
iopen
tal
to 1
L 5
% G
Gm
ainta
in a
nes
thes
ia s
hort t
erm
. Add 3
g f
or
(cat
tle)
cattl
e >
1000 k
g. P
rem
edic
atio
n u
sual
ly u
nnec
-es
sary
. Intu
bat
e an
imal
durin
g m
ainte
nan
ce to
avoid
ris
k of re
gurg
itatio
n a
nd a
spira
tion.
(con
tinue
s)
246 Anesthetic Management of Ruminants and Camelids
Tab
le 1
6–1
(Continued)
Agen
t/P
roto
col
Do
sage (
mg/k
g)*
Co
mm
en
ts
5%
Guai
fenes
in/
2–3 g
added
to
Add 3
g f
or
cattle
>1000 k
g. P
rem
edic
atio
nke
tam
ine
1 L
5%
GG
usu
ally
unnec
essa
ry, but
if nee
ded
for
(cat
tle)
intrac
table
pat
ients
, xy
lazi
ne
is e
ffec
tive.
Induct
ion d
ose
: 0.5
–1.0
ml/
kgM
ainte
nan
ce d
ose
: 2.2
ml/
kg/h
r (“
to e
ffec
t”)
Xyla
zine/
keta
min
eFo
r ru
min
ant ne
onat
es, u
se ≤
0.0
2 m
g/kg
xyl
azin
e.C
attle
0.0
4/2
.2 IV
Can
mix
and a
dm
inis
ter
IV.
Goat
s0.1
IM
/5 IV
Xyla
zine
should
pre
cede
keta
min
e by
15 m
in.
Shee
p0.2
IM
/5 IV
Xyla
zine
should
pre
cede
keta
min
e by
15 m
in.
Dia
zepam
/0.2
5/5
IV
Mix
and a
dm
inis
ter
IV “
to e
ffec
t.” M
ay r
equire
keta
min
ead
diti
onal
dru
gs e
spec
ially
if
pre
med
icat
ion is
not
adm
inis
tere
d.
Lla
mas
Chem
ical re
stra
int/
pre
med
icatio
n
Xyla
zine
0.2
5–0.4
IV,
IM
Low
er d
osa
ge is
for
IV a
dm
inis
trat
ion. Avo
id in
neo
nat
es; if
nec
essa
ry t
o p
erfo
rm m
inor
pro
-ce
dure
s, u
se m
inim
um
dosa
ge r
ange
and
Anesthetic Management of Ruminants and Camelids 247
only
if
accu
rate
wei
ght
is d
eter
min
ed.
Buto
rphan
ol
0.1
–0.2
IV,
IM
Enhan
ces
sedat
ion a
nd a
nal
gesi
a w
ith x
ylaz
ine.
Ef
fect
ive
sedat
ion f
or
mas
k or
nas
otrac
hea
lin
duct
ion o
r dia
zepam
-ket
amin
e in
duct
ion in
neo
nat
es a
nd juve
nile
s.
Induct
ion/
main
tenance
Xyla
zine/
keta
min
e0.2
5/2
.2 IV
Inje
ct x
ylaz
ine
first
then
ket
amin
e. F
or
unco
op-
erat
ive
anim
als,
xyl
azin
e m
ay b
e ad
min
is-
tere
d IM
(0.4
).
5%
Guai
fenes
in/
1 m
g/m
l ke
tam
ine
1.1
–1.6
ml/
kg g
iven
“to
effec
t” t
o f
acili
tate
keta
min
ein
1 L
GG
IV
intu
bat
ion. Th
is d
ose
pro
vides
15–20 m
inan
esth
esia
and m
ay b
e tit
rate
d t
o m
ainta
inan
esth
esia
(if
nec
essa
ry).
5%
Guai
fenes
in/
2 m
g/m
l th
iopen
tal
1.1
–1.6
ml/
kg g
iven
to e
ffec
t to
fac
ilita
teth
iopen
tal
in 1
L G
G IV
intu
bat
ion. Th
is d
ose
pro
vides
15–20 m
inan
esth
esia
. M
ainte
nan
ce w
ith t
his
com
bin
a-tio
n is
not
reco
mm
ended
.
(contin
ues
)
248 Anesthetic Management of Ruminants and Camelids
Tab
le 1
6–1
(Continued)
Agen
t/P
roto
col
Do
sage (
mg/k
g)*
Co
mm
en
ts
Ru
min
an
ts a
nd
ca
meli
ds
Analg
esia
Dosa
ge inte
rval
s ar
e gu
idel
ines
only
: ad
min
istra-
tion s
hould
be
bas
ed o
n o
ngo
ing
asse
ssm
ent.
Bupre
norp
hin
e 0.0
05 IM
Inte
rval
: 12 h
r.(s
mal
l ru
min
ants
)
Buto
rphan
ol
Cat
tle0.0
1–0.0
2 IV,
IM
Inte
rval
: 2–4 h
r (o
r as
indic
ated
by
pat
ient)
.Sh
eep, go
ats
0.1
IV,
IM
Morp
hin
eSh
eep, go
ats
0.1
IM
, SC
Dose
should
not
exce
ed 1
0 m
g. Inte
rval
: bas
ed
on p
atie
nt
(eve
ry 6
–8 h
r?).
Rum
inan
ts,
0.1
(ep
idura
l Pro
vides
anal
gesi
a as
far
forw
ard a
s th
ora
x fo
rca
mel
ids
adm
inis
trat
ion)
8–24 h
r. D
ue
to t
he
syst
emic
sid
e ef
fect
s of
epid
ura
l xy
lazi
ne
in r
um
inan
ts, it
is n
ot
rec-
om
men
ded
to a
dd x
ylaz
ine
to m
orp
hin
e fo
rlo
ng-
term
pai
n m
anag
emen
t, how
ever
if
Anesthetic Management of Ruminants and Camelids 249
indic
ated
for
additi
onal
anal
gesi
a, d
osa
ge f
or
cattle
and c
amel
ids
is lis
ted in T
able
3–5.
Avo
id f
orm
ula
tions
that
conta
in t
he
pre
serv
ativ
e fo
rmal
in (
the
pre
serv
ativ
e m
ethyl
par
aben
is
acce
pta
ble
). U
se o
f th
e pre
serv
ativ
e-free
pre
par
atio
n (
Duro
morp
h™
) is
optim
al, but
due
to t
he
low
conce
ntrat
ion a
nd c
ost
, ad
e-quat
e dosa
ge m
ay b
e diff
icult
to d
eliv
er d
ue
to t
he
larg
e quan
tity
require
d f
or
adult
cattle
and c
amel
ids.
Phen
ylbuta
zone
NSA
IDs
are
not
routin
ely
use
d in r
um
inan
ts;
adm
inis
trat
ion m
ay b
e bas
ed e
mpiri
cally
on
equin
e dosa
ges
and u
sed s
par
ingl
y.C
attle
2.2
IV,
PO
Shee
p, go
ats
5–10 P
O
Flunix
in0.5
–1.0
IV
*Dru
gs m
ay b
e ad
min
iste
red IM
or
IV u
nle
ss o
ther
wis
e in
dic
ated
. Low
er d
osa
ges
should
be
util
ized
for
IV a
dm
inis
tra-
tion.
**G
reat
var
iatio
n e
xist
s am
ong
bre
eds
and in
div
idual
s. B
rahm
an b
reed
s an
d H
eref
ord
s m
ay d
emonst
rate
incr
ease
d s
en-
sitiv
ity to x
ylaz
ine
effe
cts
and lo
w-e
nd d
osa
ges
should
be
util
ized
and in
crea
sed a
s nee
ded
.
Fasting is essential in ruminants and camelids (seeTable 1–4) to decrease rumen/forestomach contentsand thus decrease risk of regurgitation and aspiration,bloat, and respiratory compromise during induction andmaintenance of general anesthesia. Neonates (less than1 month of age) need only a 2–4 hr fast.
The need for premedication to facilitate catheterplacement and anesthetic induction depends largely onpatient cooperation and availability of restraint facilities(adult cattle). Agitated adult cattle will benefit from pre-medication regardless of secure restraint facilities to pro-vide maximal safety to the animal and personnel andminimize movement during catheterization. In field sit-uations, it may be necessary to cast the animal with ropesto facilitate handling following sedation. Small rumi-nants and calves can be adequately restrained by placingthem in lateral recumbency, controlling the dependentlimbs, and applying gentle pressure to the head andneck. Camelids have a unique personality and are proneto spitting, striking, biting, and butting. Placing a towelloosely over the face (hooding) will aid handling andhelp avoid being spit on. Adult camelids, like cattle, maybe restrained in a chute or head gate. Premedication isindicated in all but the most tractable or debilitatedcamelid patients.
Vascular access in adult cattle and camelids is the jugu-lar vein. Both species require cutdown via a stab incisionthrough the skin to allow entry of the stylet and smoothpassage of the catheter shaft. The jugular furrow is
250 Anesthetic Management of Ruminants and Camelids
apparent and the vein usually easy to observe whenoccluded distally in cattle. However, in camelids, there isno discernible jugular groove and the vein does notbecome readily apparent, even when distally occluded,although a fluid wave may be observed with percussion.The optimal site for catheter entry into the internal jugu-lar vein in camelids is the right side (to avoid the esoph-agus) at the junction of the cranial and middle third ofthe neck. There is greater risk of accidental penetrationof the carotid artery compared to cattle. The jugular veinis used for small ruminants, calves, and young camelidsand cutdown usually is unnecessary; additionally, thecephalic vein, similar in location to dogs, can be utilized.
Induction of anesthesia should be performed withrapid-acting agents (see Table 16–1) in adult ruminantsand camelids to facilitate quick-sequence intubation andminimize risk of regurgitation and aspiration. Maskinduction and maintenance with inhalant anesthesia isacceptable for ruminant and camelid neonates for shortprocedures (<1 hr). In adult cattle, intubation is per-formed by digitally palpating the arytenoid cartilagesand guiding the ET tube through the larynx. Whenthere is inadequate room for the hand and ET tube, pass-ing a smaller long tube (a medium-sized equine naso-gastric tube) digitally into the trachea, to guide passageof the ET tube, may be necessary. Rotation of the tube tomanipulate the bevel will facilitate passage into the tra-chea. The cuff then should be inflated quickly to protectthe airway.
Anesthetic Management of Ruminants and Camelids 251
Orotracheal intubation of small ruminants,camelids, and calves requires visualization of the larynx.A flat, long blade (180–350 mm) laryngoscope facilitatesthe procedure. Positioning of the endotracheal tube mayobstruct the view of the ET tube passing through the lar-ynx; passing a small, long, stiff piece of polyethylene tub-ing visually into the trachea to guide the ET tube may bebeneficial in these cases. Use gauze loops to hold themouth open and extend the head and neck to maximizevisualization.
Blind orotracheal intubation is possible in llamas,small ruminants, and calves but more difficult than theprocedure in horses. Nasotracheal intubation has beendescribed for llamas and calves, and it also is more diffi-cult than the procedure in horses. Llamas have a largepharyngeal diverticulum, which may complicate nasotra-cheal intubation. Head and neck extension is essentialfor both techniques. Delivering 1.0–2.0 ml of lidocainethrough the tube with the tip positioned just over thelarynx may help obtund swallowing and facilitate suc-cessful intubation.
Endotracheal tube sizes for adult cattle range from20–30 mm ID and for adult camelids, 12–14 mm ID(10–12 mm ID for nasotracheal intubation). Calves andcrias usually require size 8–12 mm ID and size 7–9 mmID, respectively. Small ruminants accommodate size8.0–12 mm ID tube, while juveniles require size 5.0–7.0mm ID tube.
252 Anesthetic Management of Ruminants and Camelids
Adult ruminants and camelids should be positionedwith support under the neck so that the head will tiltdownward to prevent accumulation of saliva in theoropharynx and encourage drainage out of the oral cav-ity. Adequate padding of the down surface, positioningof the down forelimb forward and supporting the uplimbs parallel to the table are necessary in adult cattleand camelids during prolonged procedures to minimizerisk of myopathy and neuropathy. When adequatepadding is not feasible, placing an inner tube tire aroundthe down limb will help minimize risk of neuropathy.Small ruminants and neonates should be provided anexternal heat source for prolonged invasive procedures.Intraoperative fluids are indicated for prolonged proce-dures in all ruminants to replace intraoperative fluidlosses and provide a route for administration of adjunctdrugs.
Recovery in ruminants usually is uneventful; animalsgenerally recover quietly and smoothly. Endotrachealtubes should be removed when swallowing is observed,with residual cuff inflation to remove any saliva or regur-gitation that may have collected rostral to the cuff. Adultruminants should be positioned upright in sternalrecumbency as soon as possible, to facilitate eructationof collected rumen gases. Analgesic dosages are availablefor ruminants and should be administered when indi-cated (see Table 16–1).
Anesthetic Management of Ruminants and Camelids 253
17Anesthetic Management of Swine
Swine anesthesia presents a plethora of challenges,including resistance to physical restraint, which oftenprecludes adequate physical examination and collectionof blood for preoperative assessment; lack of easily acces-sible superficial veins, which makes IV anesthetic induc-tion challenging; difficult intubation; a tendency towardintraoperative hyperthermia, including an inability todissipate heat due to low body surface to mass ratio andthe risk of malignant hyperthermia; and lack of readilypalpable peripheral pulses, which increases the chal-lenge of effective intraoperative monitoring.
Pigs usually resist restraint. Neonates and compan-ion breeds (i.e., Vietnamese potbelly) usually can berestrained by holding the animal against the body and
255
wrapping with a towel. Safe restraint is critical in com-panion breeds to avoid damage to their relatively fragileskeleton. Restraint techniques used in food animalbreeds, such as nose snares and lifting by the rear limbs,is not recommended. An effective device for restrainingpigs of all sizes is a webbed stanchion with wheels to allowtransport (Figure 17–1). Using a board or moveable gateto squeeze pigs into a small confinement usually facili-tates IM premedication injection in larger swine.
Pigs vomit and an adequate fast (see Table 1–4) isimportant to minimize risk of regurgitation, especiallywhen intubation is not planned. It is best to delay anes-thesia, when possible, if fasting status is unknown orinadequate.
Intramuscular induction is the most commonmethod of anesthesia in swine. The minimal needlelength for injection is 11/2 in. to reach the muscle, sinceswine have a large quantity of superficial fat stores. Sitesinclude the neck muscles just behind the ear and themuscles of the hind limb; the latter site should beavoided in pigs destined for human consumption. Intra-venous induction by use of the auricular vein is possiblefollowing adequate premedication and restraint (Table17–1). Pigs that can be safely restrained are amenable tomask induction with inhalation anesthetic agents. Pigsusually accept the mask and transition smoothly withminimal movement (3–5 min). The process is facilitatedby premedication (see Table 17–1).
256 Anesthetic Management of Swine
257
Figure 17–1 A web-topped mobile table for restraint andtransport of swine for physical examination and induction of anes-thesia. (Reprinted with permission from JC Thurmon and GJ Ben-son, Special anesthesia considerations of swine, in: Principles andPractice of Veterinary Anesthesia, CE Short, ed., Baltimore:Williams and Wilkins, 1987, page 311.)
258 Anesthetic Management of Swine
Tab
le 1
7–1
Anest
hetic
Age
nts
for
Pre
medic
atio
n, In
duct
ion, an
d A
nal
gesi
a in
Sw
ine
Agen
t/P
roto
col
Do
sage (
mg/k
g)*
Co
mm
en
ts
Chem
ical re
stra
int/
pre
med
icatio
n
Ace
pro
maz
ine
0.0
3–0.2
Do n
ot
exce
ed 1
5 m
g. M
inim
al t
ranquili
zatio
n.
Aza
per
one
0.4
–3.0
Low
er d
osa
ge r
ange
for
larg
er s
win
e; e
ffec
ts
may
per
sist
for
seve
ral hours
.
Dia
zepam
0.4
–1.0
Inef
fect
ive
alone.
Undep
endab
le a
bso
rptio
n.
Mid
azola
m0.1
–0.5
Quic
k onse
t. M
inor
effe
ct w
hen
use
d a
lone.
Xyla
zine
0.5
–2.0
Hig
her
dosa
ge f
or
smal
l sw
ine
and v
ice
vers
a.
Xyla
zine
is les
s ef
fect
ive
in s
win
e th
an o
ther
sp
ecie
s.
Med
etom
idin
e0.0
1–0.0
5Appea
rs t
o b
e m
ore
effec
tive
than
xyl
azin
e.
Buto
rphan
ol
0.1
–0.2
May
be
com
bin
ed w
ith t
ranquili
zer
or
alpha 2
agonis
t to
enhan
ce s
edat
ion.
Induct
ion/
main
tenance
Xyla
zine/
keta
min
e0.5
–2.0
/2.2
–4.4
Induct
ion is
often
pro
longe
d a
nd inco
mple
te.
Scal
e to
pig
siz
e: B
igge
r pig
tak
es low
er d
osa
ge.
Anesthetic Management of Swine 259
Usi
ng
med
etom
idin
e (0
.02–0.0
4)
in p
lace
of
xyla
zine
may
pro
vide
a sm
ooth
er, bet
ter
qual
ity induct
ion.
Addin
g buto
rphan
ol m
ay im
pro
ve induct
ion a
nd
qual
ity o
f an
esth
esia
.
In g
ener
al, th
is p
roto
col is
inad
equat
e fo
r su
rgi-
cal m
ainte
nan
ce; re
pea
ted d
osi
ng
is n
eces
-sa
ry if
move
men
t per
sist
s.
Ket
amin
e dose
for
PB
P is
5–10 m
g/kg
.
Xyla
zine/
keta
min
e/2.0
/2.0
/0.0
75
For
juve
nile
s an
d P
BP.
oxy
morp
hone
Good a
nal
gesi
a an
d m
usc
le r
elax
atio
n f
or
min
or
surg
ical
pro
cedure
s; d
ura
tion o
f ef
fect
is
20–30 m
in.
Rap
id s
hal
low
bre
athin
g is
a c
om
mon s
ide
effe
ct.
Xyla
zine/
tela
zol
0.5
–1.0
/2–6
Pro
vides
rap
id (
<5 m
in)
smooth
induct
ion.
Pre
ferred
induct
ion a
gent
but
expen
sive
.Rec
ove
ry m
ay t
ake
seve
ral hours
(>
4 h
r) w
hen
hig
h-e
nd d
ose
is
use
d.
(contin
ues
)
260 Anesthetic Management of Swine
Tab
le 1
7–1
(Continued)
Agen
t/P
roto
col
Do
sage (
mg/k
g)*
Co
mm
en
ts
Med
etom
idin
e (0
.02–0.0
4)
may
be
use
d in
pla
ce o
f xy
lazi
ne,
and b
uto
rphan
ol m
ay b
e ad
ded
to p
roto
col.
Pro
vides
adeq
uat
e im
mobili
zatio
n f
or
min
imal
ly
pai
nfu
l, nonin
vasi
ve p
roce
dure
s.
Ace
pro
maz
ine/
0.1
/5–10
Aza
per
one
(0.4
–2)
may
be
subst
itute
d f
or
keta
min
eac
epro
maz
ine.
Incr
ease
ket
amin
e dosa
ge t
o
15 m
g/kg
for
PB
P.Se
par
ate
inje
ctio
ns
by
30 m
in, gi
ving
tran
quili
zer
first
.U
nre
liable
; m
ay p
rovi
de
adeq
uat
e im
mobili
za-
tion t
o g
ain IV a
cces
s.
Thio
pen
tal
5–10 IV
Req
uire
s se
cure
IV a
cces
s, u
sual
ly a
uric
ula
r ve
in.
Use
2.5
–5%
solu
tion t
o m
inim
ize
tissu
e irr
itatio
n a
t in
ject
ion s
ite.
Exce
llent
rela
xatio
n f
or
intu
bat
ion.
Guai
fenes
in (
GG
)/In
duct
ion: 1.0
ml/
Add 2
g t
hio
pen
tal per
1 L
of
5%
GG
.th
iopen
tal
kg IV
Anesthetic Management of Swine 261
Mai
nte
nan
ce:
Del
iver
y (i
dea
lly)
should
not
exce
ed 1
hr
to≤4 m
l/kg
/hr
IVdec
reas
e ris
k of
rough
rec
ove
ry.
Guai
fenes
in (
GG
)/In
duct
ion: 0.5
–1.0
Add 1
mg/m
lxy
lazi
ne
and
1 m
g/m
lke
tam
ine
xyla
zine/
ml/
kg IV
to 5
% G
G.
keta
min
eM
ainte
nan
ce:
Min
imal
res
pira
tory
dep
ress
ion.
2.2
ml/
kg/h
r IV
Rec
ove
ry is
smooth
and r
elat
ivel
y ra
pid
eve
n
afte
r 2 h
r m
ainte
nan
ce.
Use
d f
or
induct
ion if
IV a
cces
s is
poss
ible
or
fol-
low
ing
IM induct
ion (
as p
revi
ousl
y outli
ned
).
Tela
zol/
keta
min
e/1.3
–2.0
mg/
kgTe
lazo
l (5
00 m
g) is
reco
nst
itute
d w
ith 2
.5 m
l xy
lazi
ne
(dis
soci
ativ
e)ea
ch o
f ke
tam
ine
and 1
0%
xyl
azin
e. (
The
liste
d(1
00 m
g/m
l dosa
ge e
quat
es t
o 1
ml/
50–75 k
g.)
dis
soci
ativ
e)Als
o e
ffec
tive
for
PB
P a
t a
dose
of
0.6
–1.2
m
g/kg
dis
soci
ativ
e, w
hic
h e
quat
es t
o 0
.006–
0.0
12 m
l/kg
.
An
tago
nis
ts
Alp
ha
2re
cepto
r
Yohim
bin
e0.0
5–0.2
IV,
IM
Tola
zolin
e1–2 IV
(contin
ues
)
262 Anesthetic Management of Swine
Tab
le 1
7–1
(Continued)
Agen
t/P
roto
col
Do
sage (
mg/k
g)*
Co
mm
en
ts
Atip
amez
ole
0.2
IM
Ben
zodia
zepin
e
Flum
azen
il0.0
2–0.1
IV
Opio
id
Nal
oxo
ne
0.0
4 IV,
IM
, SC
Analg
esia
**
Bupre
norp
hin
e0.0
05–0.0
2In
terv
al: 12 h
r.
Buto
rphan
ol
0.1
–0.4
Inte
rval
: 2–4 h
r.
Morp
hin
e0.2
IM
Inte
rval
: 4–6 h
r.0.1
(ep
idura
l In
terv
al: 12–24 h
r.ad
min
istrat
ion)
Morp
hin
e m
ay b
e gi
ven a
lone
(dilu
ted t
o a
vol-
um
e of
3–5 m
l w
ith 0
.9%
sal
ine)
or
added
to lid
oca
ine,
with
or
with
out
alpha 2
agonis
t,as
des
crib
ed in T
able
3–5.
Note
: D
osa
ges
are
also
applic
able
for
potb
ellie
d p
igs
(PB
P)
unle
ss o
ther
wis
e note
d.
*D
osa
ges
are
for
IM in
ject
ion u
nle
ss o
ther
wis
e in
dic
ated
.
**D
osa
ge in
terv
als
are
extrap
ola
ted fro
m o
ther
spec
ies.
Adm
inis
trat
ion u
ltim
atel
y sh
ould
be
bas
ed o
n o
ngo
ing
pat
ient
asse
ssm
ent.
Pigs can be effectively maintained with inhalationagents delivered with a tight-fitting mask. However, forlong and complicated procedures and in high-riskpatients, endotracheal intubation is advised. Both sternaland dorsal recumbency have been recommended forswine intubation, with sternal being better when theexperience of the anesthetist is limited. Intubation is dif-ficult in swine for several anatomical reasons: The larynxis a long way from the tip of snout, the mouth does notopen widely, there is a large middle ventricle (middlelaryngeal ventricle) on the floor of the larynx and lateralopenings near vocal folds (lateral laryngeal ventricles)that tend to trap the tip of the ET tube, and the larynx issusceptible to laryngospasm. To assist the process:
1. Use gauze strips (versus fingers) behind upper andlower canine teeth to hold the mouth open to opti-mize visualization.
2. Extend the head moderately.
3. Use a flat long-blade (180–350 mm) laryngoscope tovisualize the larynx and pull the epiglottis forward.
4. Apply 2% lidocaine (0.2–0.5 ml) to the laryngealopening to minimize risk of laryngospasm.
When the pig is positioned sternally, the tip of the tubeshould point ventral until it meets resistance as it con-tacts the floor of the larynx. The tube should be rotated180° and advanced, with minimal pressure, just into the
Anesthetic Management of Swine 263
trachea, at which time the tube should be returned tothe initial position and inserted to the appropriate level.Once proper placement is verified, the tube is securedwith gauze, around the tube and then the snout, and thecuff inflated to form an effective seal. Tube sizes rangefrom 3–4 mm ID in neonates up to 16–18 mm ID in largesows and boars, which is smaller (given comparable bodyweight) than for other species. Tube sizes for adult com-panion pigs usually are in the range of 5.0–7.0 mm ID.
For prolonged anesthetic procedures, an IV cathetershould be inserted to provide fluid therapy and a routefor administration of additional anesthetic agents whena parenteral protocol is being used. Sites include theauricular, cephalic (located on the dorsomedial aspect ofthe forelimb), femoral, and medial and lateral saphe-nous veins. Except for the auricular and femoral veins,these veins are difficult to visualize and successfullycatheterize but provide alternatives when the auricularveins are too small to visualize (many potbelly pigs havesmall ears) or have hematomas due to unsuccessfulcatheterization attempts.
Effective monitoring devices include esophagealstethoscopes and capnometers (if intubated), ECG, andpulse oximeter on the tongue (if accessible), or ear (innonpigmented individuals). Breathing rate should rangefrom 8–20/min but may be higher in neonates. Heartrate should stay above 40–50 beats/min and usually ismaintained at 70–100 when dissociative agents havebeen administered. Rates of 100–140 beats/min are
264 Anesthetic Management of Swine
common in neonates. Pulse quality can be assessed bypalpation of femoral, brachial, metatarsal, coccygeal,and auricular arteries.
Temperature should be closely monitored in swinebecause of greater tendency to develop hyperthermiaand increased susceptibility to malignant hyperthermia(MH). White breeds historically have been linked to thedisease—specifically, Pietrain, Landrace, Hampshire,and (less commonly) Duroc. While hyperthemia follow-ing isoflurane anesthesia has been reported in a potbellypig, the existence of genetically linked MH has not beendemonstrated in this breed.
Malignant hyperthermia is an inherited predisposi-tion to uncontrolled generalized muscle rigidity trig-gered by stress, all inhalant anesthetics (halothane hasbeen the most commonly incriminated), and succinyl-choline. The genetic defect is at the level of the sar-coplasmic reticulum and associated with excessivecalcium release. Clinical signs include muscle rigidity,tachycardia, hyperthermia, tachypnea, metabolic acido-sis, hypoxia, and blotchy skin. The disease can rapidlyprogress to dyspnea, apnea, arrhythmias, and death ifnot treated immediately. Treatment includes discontinua-
tion of inhalant delivery, efforts to cool the animal (alcoholbath, chilled IV fluids), continued delivery of 100% oxy-gen to meet increased metabolic demands, bicarbonateadministration (1 mEq/kg) preferably guided by bloodpH analysis, corticosteroids, and dantrolene (2–5 mg/kgIV). Dantrolene is a peripheral muscle relaxant that
Anesthetic Management of Swine 265
suppresses calcium ion release from the sarcoplasmicreticulum but has minimal effect on respiratory musclefunction. Oral dantrolene is less expensive than the IVpreparation. Administration (5 mg/kg PO) 8–10 hrbefore anesthetic induction in high-risk breeds may bebeneficial, especially when inhalant anesthetics must beused and a prolonged anesthetic period is anticipated.
Recovery in swine generally is uneventful andshould take place at a neutral ambient temperature in aquiet, safe area. Small patients may require an externalheat source, the need for which should be based on bodytemperature recorded at the end of anesthesia (seeTable 6–3). Animals should be monitored until extu-bated and able to maintain sternal recumbency unas-sisted with normal vital signs.
266 Anesthetic Management of Swine
18
Overview of Cardiopulmonary Resuscitation
Prevention of cardiopulmonary arrest through appro-priate patient preparation (minimizing risk factors) andoptimal anesthetic management and monitoring is farbetter than cardiopulmonary resuscitation (CPR).Guidelines for CPR are summarized here. Resuscitationusually is successful in relatively healthy small animals(and large animal neonates) when arrest is recognizedearly; resuscitation in horses and adult cattle often is inef-fective, making prevention through early recognition ofand intervention for potential problems critical in thesespecies.
Quickly recognizing signs of impending cardiopul-monary arrest is optimized by monitoring vital signs at
267
5-min intervals. Indications include cyanosis (which can-not occur in anemic patients if [Hgb] <5 g/dl); pro-longed capillary refill time (CRT) (>2–3 sec); irregular,absent, or sudden change in pulse or heart sounds; car-diac arrhythmias; abnormal respiratory pattern orapnea; and loss of corneal reflex. When problems arenoted, the first step is to stop delivery of anesthesia, flushthe breathing system with 100% oxygen; and supportventilation to ensure adequate oxygen delivery. The ETtube should be checked for patency and the animalintubated if a tube is not already in place. Whenreversible agents have been used, administration of theirantagonist is usually indicated.
CPR guidelines include basic (A, B, C) andadvanced (D, E) steps for life support:
Step A. Airway Establish or assure patent airway withET tube for delivery of ventilation.
Step B. Breathing Provide 100% oxygen (150ml/kg/min for small animals; 15–20ml/kg/min for large animals); ventilate simul-taneous with chest compressions at a rate of12–20/min (6–12 for large animals).
Step C. Circulation (compressions) Deliver chest compres-sions at 80–120/min (40–80/min or as rapidlyas possible for large animals) in a “coughlike”manner, meaning rapid and forceful delivery ofpressure. Chest compressions should be initiated assoon as absence of effective blood flow is identified and
268 Overview of Cardiopulmonary Resuscitation
while the airway is being assured or established.External massage promotes forward movementof blood through one of two methods. In smallpatients or those with narrow thoracic width,the cardiac pump theory best explains forwardblood flow associated with actual compressionof the myocardium during chest compressions.In larger patients, the thoracic pump theoryexplains the resulting forward blood flow as aresult of sudden and significant increases ininternal thoracic pressure (associated withcompressions) being transmitted to the heart.Therefore, for small animals (<10 kg), com-press the chest directly over the heart withhands or fingers applied to both sides of thechest. For larger patients (>10 kg), compresschest over widest portion or at the seventhintercostal space at the junction of dorsal andmiddle thirds of chest. Ventral-dorsal compres-sions may be more effective in some patients.
In advanced CPR, step D includes drugs and/or defib-rillation and step E is recognition of the specific ECGabnormality. The initial drug to be administered is epi-nephrine followed by atropine and other agents (Table18–1), as indicated by the individual patient’s underlyingand identified problems and abnormalities identified onECG. Defibrillation is indicated for ventricular tachycar-dia and fibrillation and recommended dosages are listedin Table 18–1.
Overview of Cardiopulmonary Resuscitation 269
270 Overview of Cardiopulmonary Resuscitation
Tab
le 1
8–1
Dosa
ges
and I
ndic
atio
ns
for
Dru
gs U
sed D
uring
Car
dio
pulm
onar
yA
rrest
Agen
tD
osa
ge(m
g/k
g)*
Ind
icati
on
s/Eff
ect
s
Dru
g
Epin
ephrin
e (I
T)0.0
2–0.2
**
Alp
ha
agonis
t ef
fect
s in
crea
se p
erip
her
al r
esis
t-(s
mal
l an
imal
)an
ce a
nd intrat
hora
cic
blo
od f
low
to p
rom
ote
0.0
1–0.0
2
per
fusi
on w
hile
pre
fere
ntia
lly p
rese
rvin
g(l
arge
anim
al)
flow
to b
rain
and h
eart.
Bet
a ac
tivity
to im
pro
ve c
ontrac
tility
and t
o
rees
tablis
h n
orm
al c
ardia
c rh
ythm
(in
som
eca
ses)
.
Atropin
e (I
T)0.0
2–0.0
4
Incr
ease
s hea
rt r
ate.
(sm
all an
imal
)Tr
eats
bra
dyc
ardia
and a
syst
ole
.2–6 m
g to
tal dose
(l
arge
anim
als)
Lidoca
ine
(IT)
2–4 (
dogs
)Tr
eats
rec
urren
t ve
ntric
ula
r ar
rhyt
hm
ias
and
0.5
–1.0
(ca
ts,
tach
ycar
dia
.hors
es, ru
min
ants
)
Doxa
pra
m0.0
5–0.2
(bolu
s)C
entral
act
ing
resp
irato
ry s
timula
nt
indic
ated
for
5–10 µ
g/kg
/min
ap
nea
due
to a
nes
thet
ic o
verd
ose
.(i
nfu
sion)
Overview of Cardiopulmonary Resuscitation 271
Inotropes
Impro
ves
card
iac
contrac
tility
once
NSR
is
rees
tablis
hed
.
Dobuta
min
e2–10 µ
g/kg
/min
Dopam
ine
5–10 µ
g/kg
/min
Dire
ct r
enal
vas
odila
tory
effec
t (q
ues
tionab
le in
cats
).
Ephed
rine
0.0
3–0.1
IV b
olu
sLo
wer
dose
ran
ge f
or
larg
e an
imal
s.
Isopro
tere
nol
0.0
1–0.1
µg/
kg/m
inIn
crea
ses
hea
rt r
ate
in r
efra
ctory
cas
es.
Impro
ves
contrac
tility
but
may
dec
reas
e blo
od
pre
ssure
due
to b
eta 2
vaso
dila
tory
effec
ts.
Arrhyt
hm
oge
nic
: m
onito
r EC
G d
urin
g ad
min
istrat
ion.
Cal
cium
(ch
lorid
e 5–10 m
g/kg
(sm
all
Posi
tive
inotrope,
may
enhan
ce e
ffec
t of
or
gluco
nat
e)an
imal
)in
otropic
age
nts
but
can c
ause
asy
stole
2 m
g/kg
(la
rge
if ove
rdose
d.
anim
al)
Cal
cium
has
bee
n incr
imin
ated
in t
he
pat
hoge
n-
esis
of
post
resu
scita
tion s
yndro
me
(cer
ebra
lis
chem
ia)
and is
not
use
d in r
esusc
itatio
n(u
nle
ss t
he
under
lyin
g c
ause
of
arr
est
is d
ue
to h
ypoca
lcem
ia o
r hyp
erka
lem
ia). (c
ontin
ues
)
272 Overview of Cardiopulmonary Resuscitation
Tab
le 1
8–1
(Continued)
Agen
tD
osa
ge(m
g/k
g)*
Ind
icati
on
s/Eff
ect
s
Bic
arbonat
e1–2 m
Eq/k
g or
Correc
ts m
etab
olic
aci
dosi
s.dose
on c
al-
Usu
ally
unnec
essa
ry if
arre
st is
<10 m
in a
nd n
ocu
late
d d
efic
it†under
lyin
g im
bal
ance
was
pre
sent.
Adm
inis
trat
ion m
ay p
rom
ote
more
succ
essf
ul
resp
onse
to d
efib
rilla
tion.
If ad
min
iste
red w
hen
ven
tilat
ion is
inad
equat
e,
can p
rom
ote
intrac
ellu
lar
acid
osi
s (p
arad
oxi
cce
rebra
l ac
idosi
s) d
ue
to g
ener
atio
n o
f ca
r-bon d
ioxi
de.
Cortic
ost
eroid
sPro
tect
aga
inst
cer
ebra
l ed
ema
follo
win
g re
susc
itatio
n.
Solu
-med
rol™
30
Enhan
ces
ATP r
elea
se f
rom
the
mito
chondria
to
(met
hyl
pre
d-
faci
litat
e norm
al m
embra
ne
funct
ion.
nis
olo
ne
sodiu
msu
ccin
ate)
Solu
-del
ta-c
ortef
™30–60
(pre
dnis
olo
ne
sodiu
m s
ucc
inat
e)
Overview of Cardiopulmonary Resuscitation 273
Dex
amet
has
oneS
P2.0
–4.0
(sodiu
m
phosp
hat
e)
Ele
ctri
cal
(wat
t-se
c =
Joule
)Fo
r ve
ntric
ula
r ta
chyc
ardia
and f
ibril
lato
n.
defi
bri
llati
on
Exte
rnal
5–10 J
oule
/kg
Inte
rnal
0.5
–2.0
Joule
/kg
Ch
em
ical
When
ele
ctric
al d
efib
rilla
tor
is u
nav
aila
ble
.d
efi
bri
llati
on
Pota
ssiu
m
1 m
g/kg
Effic
acy
is q
ues
tionab
le.
chlo
ride
plu
sAce
tylc
holin
e6 m
g/kg
10%
Cal
cium
10 m
g/kg
Cal
cium
follo
ws
KC
l-ace
tylc
holin
e m
ixtu
re.
chlo
ride
Po
stre
susc
itati
on
th
era
py f
or
cere
bra
l p
rote
ctio
n
Cortic
ost
eroid
sAs
liste
d p
revi
ousl
yFu
rose
mid
e1 m
g/kg
More
effec
tive
in t
reat
ing
edem
a fo
llow
ing
man
nito
l.(c
ontin
ues
)
274 Overview of Cardiopulmonary Resuscitation
Tab
le 1
8–1
(Continued)
Agen
tD
osa
ge(m
g/k
g)*
Ind
icati
on
s/Eff
ect
s
Man
nito
l1 g
m/k
gC
ereb
ral ed
ema;
giv
e ove
r 20–30 m
in.
Dia
zepam
0.1
–0.2
Giv
en “
to e
ffec
t” t
o c
ontrol se
izure
s.0.5
mg/
kg/h
r in
fusi
on
Pro
pofo
l1 m
g/kg
bolu
sSe
izure
control;
anim
al u
sual
ly r
emai
ns
0.1
mg/
kg/h
r co
nsc
ious
at t
his
dosa
ge.
infu
sion
NSR
= n
orm
al s
inus
rhyt
hm
.
*Dru
gs s
hould
be
give
n in
trav
enousl
y or
intrat
rach
eally
(IT
), if
spec
ified
by
the
spec
ific
dru
g. D
osa
ges
for
the
IT r
oute
should
be
double
the
IV d
osa
ge. D
osa
ges
are
in m
g/kg
unle
ss o
ther
wis
e sp
ecifi
ed.
**Th
is d
osa
ge is
controve
rsia
l. Lo
w d
ose
sugg
ests
dilu
ting
epin
ephrin
e (1
mg/
ml) w
ith 9
ml o
f 0.9
sal
ine
and a
dm
inis
-te
ring
at 1
ml p
er 5
kg;
hig
h d
ose
sugg
ests
use
of undilu
ted e
pin
ephrin
e at
1 m
l per
5 k
g. It is
pru
den
t to
atte
mpt use
of lo
w d
ose
epin
ephrin
e fo
r one
or
two d
ose
s bef
ore
util
izin
g th
e hig
her
rec
om
men
ded
dosa
ge.
† Bic
arbonat
e re
quire
men
ts a
re c
alcu
late
d b
y th
is e
quat
ion:
Req
uire
d a
mount (m
Eq/L
) =
Def
icit
(bas
e def
icit
or
diff
eren
ce b
etw
een b
icar
bonat
e va
lue
and n
orm
al v
alue)
�BW
(kg)
�0.3
(EC
F vo
lum
e). G
ive
appro
xim
atel
y one
quar
ter
the
calc
ula
ted d
efic
it an
d r
eass
ess
blo
od p
H a
nd g
as v
alues
.
Intravenous access should be established early in theresuscitation efforts. While a central line (jugular vein) isideal, a peripheral vein usually is easier and faster toaccess (at least in small animal species). Other routes fordrug administration include intratracheal (epinephrine,atropine, lidocaine, naloxone) and intraosseous routes(also for fluid delivery). For intratracheal delivery,
1. Dose should be doubled.
2. Drug should be diluted in 3–10 ml of sterile saline orwater.
3. Drug should be deposited with a small long catheter(urinary catheter) with the tip positioned at thecarina.
4. Two or three breaths should be delivered immedi-ately following drug instillation before resumingcompressions.
Potential causes and specific treatment for electrocar-diogram traces identified during arrest are listed inTable 18–2.
Internal cardiac compression has been shown to bemore effective than external compression in promotingmyocardial and peripheral tissue perfusion during CPR.Internal compression requires a thoracotomy, althoughcardiac access may be gained through the diaphragmwhen arrest occurs during an abdominal procedure.Indications include the presence of pneumothorax or
Overview of Cardiopulmonary Resuscitation 275
Tab
le 1
8–2
Ele
ctro
card
iogra
m T
raci
ngs
Identified D
uring
Car
dio
pulm
onar
y A
rrest
,Pote
ntial
Pre
dis
posi
ng
Cau
ses,
and T
reat
ment
Ste
ps
Treatm
en
t Ste
ps
Trace
Po
ten
tial
Cau
ses
(in
ad
dit
ion
to
ste
ps
A,
B,
an
d C
)
Ventric
ula
r fib
rilla
tion
Exci
tem
ent
durin
g in
duct
ion
Early
def
ibril
latio
n (
3 c
onse
cutiv
eor
reco
very
(en
doge
nous
shock
s)ca
tech
ola
min
e re
leas
e)Rea
sses
s EC
G, re
pea
t co
unte
r-Anes
thet
ic o
verd
ose
shock
at
incr
ease
d lev
el.
Under
lyin
g m
yoca
rdia
l Adm
inis
ter ep
inep
hrin
e: lo
w d
ose
dis
ease
or
trau
ma
initi
ally
then
hig
h d
ose
if
no
Undet
ecte
d o
verp
ress
uriz
a-re
sponse
; re
pea
t sh
ock
.tio
n o
f bre
athin
g ci
rcuit
Lidoca
ine
for
refrac
tory
cas
es;
Hyp
oth
erm
ia, hyp
ovo
lem
iare
pea
t sh
ock
.Aci
dosi
s or
elec
troly
te
Iden
tify
and c
orrec
t pote
ntia
lim
bal
ance
under
lyin
g ca
use
s.
Ventric
ula
r ta
chyc
ardia
Sam
e as
for
fibril
latio
nTr
eat
like
fibril
latio
n if
no
pal
pab
le p
uls
e.If
puls
e is
pal
pab
le, lid
oca
ine
bolu
s.
Asy
stole
Anes
thet
ic o
verd
ose
Low
-dose
epin
ephrin
e, a
tropin
e.
276 Overview of Cardiopulmonary Resuscitation
Overview of Cardiopulmonary Resuscitation 277
Hyp
ote
nsi
on: sh
ock
, H
igh-d
ose
epin
ephrin
e.en
doto
xem
iaAdm
inis
ter flu
id b
olu
s (1
0–20 m
l/Va
gal st
imula
tion:
kg).
visc
eral
, ocu
lar
Dopam
ine
if rh
ythm
ret
urn
s but
puls
e w
eak.
Iden
tify
and c
orrec
t under
lyin
g ca
use
s.
Elec
trom
echan
ical
EC
G m
ay a
ppea
r norm
alSa
me
as f
or
asys
tole
.dis
soci
atio
n
or
show
idio
ventric
ula
rAdm
inis
ter
cortic
ost
eroid
ear
ly(p
uls
eles
s or
ventric
ula
r es
cape
Consi
der
bic
arbonat
e af
ter
elec
tric
al a
ctiv
ity)
rhyt
hm
with
no
asso
ciat
ed
10 m
in.
puls
ePro
gnosi
s is
poor
for
succ
essf
ul
Cau
ses:
hyp
ovo
lem
ia,
resu
scita
tion
tam
ponad
e, p
neu
moth
ora
x,
pulm
onar
y em
bolis
m,
hyp
oxi
a, a
nes
thet
ic
ove
rdose
broken ribs, inability to apply effective external com-pressions due to size and shape of the thorax, failure ofexternal compression to produce effective forwardblood flow, and absence of spontaneous rhythm after5–10 min CPR. Thoracotomy is performed, followingabbreviated aseptic preparation, by making a liberal inci-sion at the fifth intercostal space. The pleura is pene-trated with a finger or blunt tip to avoid damage tounderlying thoracic structures. Compression rate shouldbe coordinated with ventricular filling. Once sponta-neous stable rhythm is reestablished, the thorax shouldbe flushed with warm isotonic crystalloid fluid, the inci-sion closed in a routine manner, and thoracocentesisperformed to evacuate the pleural space.
Animals successfully resuscitated following CPAremain vulnerable to recurrence of myocardial instabil-ity and development of neurologic consequences associ-ated with tissue ischemia and reperfusion insult. Oxygensupplementation should be continued and the ECG andarterial blood pressure monitored for several hours fol-lowing resuscitation. Conservative fluid therapy (50ml/kg/24 hr; less for cats) should be continued to main-tain adequate perfusion and preload but minimize riskof contribution to edema formation. Glucose-containingfluids are contraindicated because glucose can exacerbateneurologic damage. Inotropic support may be necessary(see Table 18–1) and a suggested goal of therapy is tomaintain diastolic blood pressure above 60 mmHg. Mon-
278 Overview of Cardiopulmonary Resuscitation
itoring urine output provides an additional indicator ofadequate tissue perfusion. Ideally, arterial pH and bloodgas analysis should be performed to assure adequate ven-tilation and oxygenation and assess the metabolic acid-base status. When conscious, the animal’s neurologicstatus should be evaluated and findings recorded. Cere-bral edema may develop 24–48 hr following resuscitationand may be signaled by seizures, depression, coma, orblindness. Specific treatment for cerebral insult andedema are listed in Table 18–1.
Overview of Cardiopulmonary Resuscitation 279
Appendix 1
Approximate Dosages (mg/kg) ofAnesthetic Agents and Adjuncts for
Common Domestic Species
281
Dru
gD
og
Cat
Ho
rse
Cow
Sh
eep
, G
oat
Pig
Atropin
e0.0
2–0.0
40.0
2–0.0
40.0
04–0.0
10.0
1–0.0
20.0
4–0.0
60.0
4
Gly
copyr
rola
te0.0
10.0
10.0
02
0.0
02
0.0
05–0.0
10.0
03
Ace
pro
maz
ine
0.0
5–0.2
0.0
5–0.2
0.0
2–0.0
60.0
1–0.1
0.0
4–0.0
80.0
3–0.2
Aza
per
one
––
––
–0.4
–3.0
Dia
zepam
0.2
–0.4
0.2
–0.4
0.0
2–0.1
0.0
2–0.1
0.1
–0.2
0.4
–1.0
Mid
azola
m0.1
–0.4
0.1
–0.4
––
–0.1
–0.5
Flum
azen
il0.0
1–0.0
20.0
1–0.0
2–
––
0.0
1–0.0
8
Xyla
zine
0.2
–1.0
0.2
–1.0
0.2
–1.0
0.0
1–0.1
0.0
2–0.2
0.5
–2.0
Det
om
idin
e0.0
005–0.0
2–
0.0
1–0.0
40.0
1–0.0
2–
–
Med
etom
idin
e0.0
1–0.0
40.0
1–0.0
60.0
05–0.0
10.0
1–0.0
4–
0.0
1–0.0
5
Rom
ifidin
e0.0
1–0.0
4–
0.0
3–0.0
80.0
1–0.0
2–
–
Yohim
bin
e0.0
5–0.1
50.1
–0.2
0.0
7–0.1
0.2
–1.0
0.1
–0.2
0.0
5
Tola
zolin
e0.5
–2.0
1.0
–2.0
0.5
–2.0
2.0
–3.0
2.0
–3.0
1.0
–2.0
Atip
amez
ole
*0.0
7–0.2
0.2
–0.4
0.1
5–0.4
0.0
1–0.1
0.0
1–0.2
0.1
–0.2
Morp
hin
e*0.2
–0.6
0.2
–0.4
0.0
5–0.2
–0.1
–0.2
(10
0.2
mg
max
.)
Mep
erid
ine
2.0
–6.0
5.0
2.0
–4.0
2.0
2.0
(200 m
g 2.0
max
.)
Hyd
rom
orp
hone
0.2
–0.4
0.1
–0.2
––
––
282 Appendix 1
Oxy
morp
hone
0.1
–0.2
0.0
5–0.1
0.0
2–
–0.0
2
Fenta
nyl
0.0
02–0.0
06
––
––
–
Bupre
norp
hin
e0.0
05–0.0
40.0
05–0.0
10.0
05
–0.0
05
0.0
05–0.0
1
Buto
rphan
ol
0.2
–0.4
0.2
–0.4
0.0
2–0.0
40.0
1–0.0
40.1
–0.2
0.1
–0.2
Nal
buphin
e1.0
–3.0
1.0
–3.0
––
––
Penta
zoci
ne
2.0
2.0
–3.0
0.3
–0.5
––
2.0
Nal
oxo
ne
0.0
01–0.0
40.0
01–0.0
40.0
1–
0.0
05–0.0
20.0
1–0.0
5
Nal
mef
ene
0.0
01
0.0
01
––
––
Chlo
ral H
ydra
te–
–5–30**
40–60 IV
30–50 IV
–80–100 P
O
Met
hohex
ital†
3.0
–8.0
3.0
–8.0
5.0
–6.0
3.0
–6.0
2.0
–4.0
3.0
–10
Pento
bar
bita
l†30
30
3.0
–10.0
14.0
20.0
–30.0
10–30
Ket
amin
e2.0
–10.0
5–20
2.2
(IV
2.2
(IV
5.0
–15.0
2.0
–12.0
only
)only
)
Tela
zol
2.0
–8.0
2.0
–8.0
1.1
(IV
2.0
–4.0
(IV
)2.0
–6.0
(IV
)2.0
–6.0
IM
only
)
Thio
pen
tal†
10
10
4.0
–6.0
4.0
–8.0
4.0
–10.0
4.0
–8.0
Pro
pofo
l (b
olu
s)2.0
–6.0
2.0
–4.0
2.0
–4.0
––
–(i
nfu
sion m
g/0.4
0.4
0.0
5–0.1
––
–kg
/min
)
(contin
ues)
Appendix 1 283
Dru
gD
og
Cat
Ho
rse
Cow
Sh
eep
, G
oat
Pig
Etom
idat
e0.5
–2.0
0.5
–2.0
––
–0.5
–2.0
Guai
fenes
in–
–40–80
60–100
60–100
40–80
Pancu
roniu
m0.0
2–0.0
40.0
20.0
8–0.1
20.0
4–0.1
0.0
05
0.0
5–0.1
2
Vecu
roniu
m0.0
12–0.2
0.0
24–0.0
40.0
5–0.1
–0.0
05
0.1
–0.2
Atrac
uriu
m0.1
2–0.4
0.0
6–0.2
50.0
7–0.1
0.1
5
0.0
05/h
r0.5
(lla
ma)
(infu
sion)
cis–
Atrac
uriu
m0.0
50.0
5–
––
–
Edro
phoniu
m‡
1.0
1.0
0.2
5–0.5
0.5
0.5
0.5
Neo
stig
min
e‡0.0
40.0
40.0
2–0.0
40.0
2–0.0
40.2
–0.0
40.0
2–0.0
4
Pyr
idost
igm
ine‡
0.2
0.2
0.2
0.2
0.2
0.2
*Rec
om
men
ded
for
IM u
se o
nly, a
lthough
thes
e ag
ents
hav
e bee
n u
sed in
trav
enousl
y.
**Rec
om
men
dat
ions
sugg
est usi
ng
chlo
ral h
ydra
te in
incr
emen
tal l
ow
dosa
ges
to a
chie
ve d
esire
d e
ffect
, whic
h r
ange
sfrom
mild
to p
rofo
und s
edat
ion-h
ypnosi
s.† A
ll bar
bitu
rate
s sh
ould
be
titra
ted to e
ffect
. Pen
tobar
bita
l is
notre
com
men
ded
for
anes
thet
ic in
duct
ion a
nd m
ainte
-nan
ce in
clin
ical
pra
ctic
e as
rec
ove
ry is
pro
longe
d a
nd r
espira
tory
dep
ress
ion m
ay b
e si
gnifi
cant.
When
use
d, t
he
calc
u-
late
d d
ose
is g
iven
“to
effect
,” a
ppro
xim
atel
y one
quar
ter
to o
ne
hal
f is
giv
en r
elat
ivel
y ra
pid
ly a
nd the
rest
titr
ated
slow
ly to the
des
ired le
vel o
f an
esth
esia
. The
hors
e dosa
ge li
sted
for
pen
tobar
bita
l is
for
sedat
ion o
r co
ntrol o
f se
izure
s.A d
ose
of 15–30 m
g/kg
of pen
tobar
bita
l inje
cted
intrat
estic
ula
rly h
as b
een r
ecom
men
ded
for
cast
ratio
n o
f la
rge
boar
s.
284 Appendix 1
‡ Rev
ersa
l of neu
rom
usc
ula
r blo
ckad
e w
ith a
cety
lcholin
este
rase
inhib
itors
should
be
pre
ceded
by
an a
ntic
holin
ergi
cag
ent re
gard
less
of sp
ecie
s. R
esponse
to thes
e ag
ents
is h
ighly
var
iable
, dep
endin
g on the
deg
ree
of blo
ckad
e pre
sent
when
age
nts
are
giv
en; th
eref
ore
, the
dosa
ge r
ecom
men
dat
ions
should
be
consi
der
ed g
uid
elin
es a
nd e
ffect
iven
ess
of
reve
rsal
should
be
bas
ed o
n u
se o
f th
e trai
n-o
f-fo
ur
resp
onse
(sh
ould
be
retu
rned
to n
orm
al)
with
a n
erve
tw
itch s
tim-
ula
tor.
See
the
first
thre
e re
fere
nce
s in
“Rec
om
men
ded
Rea
din
g” for
det
ails
reg
ardin
g in
terp
reta
tion o
f m
onito
ring
with
the
ner
ve tw
itch s
timula
tor.
Appendix 1 285
Appendix 2
Drug Scheduling Classification andGuidelines for Storing, Dispensing,
and Administering Scheduled Agents
AgentSchedule Signification Description Examples
I C-I No accepted Heroin, marihuana,medical use. methaqualoneMajor potentialfor abuse.
II C-II Approved medical All pure opioid uses but high agonists (e.g., potential for morphine), abuse leading cocaine, to addiction. pentobarbital,
amphetamine
(continues)
287
AgentSchedule Signification Description Examples
III C-III Approved medical Thiopental, uses. High telazol™,potential for ketamine,abuse but less anabolicthan that for steroidsC-II.
IV C-IV Approved medical Diazepam, uses. Less midazolam, potential for oxazepam abuse than C-III butorphanol, but addiction pentazocine, is possible. chloral hydrate,
methohexital, phenobarbital
V C-V Approved medical Buprenorphineuses. Least potential for abuse of the scheduled agents.
1. To administer, prescribe or dispense scheduled drugs, veterinarians must be reg-istered (initial application: form DEA-224) with and approved by the DrugEnforcement Agency of the United States Department of Justice (Headquarters:1-800-882-9539).
2. To purchase Schedule II drugs for clinical use, triplicate order form DEA-222must be filled out and sent to the supplier. Upon receipt of Schedule II drugs,appropriate quantity should be verified by dating and completing the order form.
3. Schedule III-V drugs do not require the triplicate order form. However, records oftransactions should be maintained for two years by use of supplier’s invoices orlogbook, including date of receipt and quantities ordered and received.
288 Appendix 2
4. The DEA license is valid for only one office where controlled substances areadministered or dispensed. If multiple offices are used to administer and dis-pense controlled substances, each must be registered independently.
5. A record of transaction must be maintained for all controlled substances admin-istered or dispensed and should include patient name and identification, withdrug and amount used to account for all controlled substances.
6. Controlled substances stored in a clinic must be kept in a securely locked, sub-stantially constructed cabinet or safe. Ideally, stock should be kept to a minimumand maintained within a two- or three-lock system.
7. When controlled substances are dispensed, a record of each transaction isrequired.
8. For the prescription of controlled substances II-V, it is necessary to be registeredwith the DEA but it is not required to keep records of those transactions. Pre-scriptions must be signed and include the address and DEA registration number.The prescription order should be precise, legible, and alteration proof. Clearlyindicate refill authorization directions. Schedule II prescriptions may not berefilled.
Appendix 2 289
Appendix 3
Suggestions for Anesthetic Preparation and Management
of High-Risk Patients
General statements may be applied to all species. (Forspecific protocols, see species-specific chapters.)
Trauma Patients
Preparation
Treat shock
• Fluid/blood component therapy
• Corticosteroids
Assess lead II ECG throughout the anesthetic period
291
Assess thoracic/abdominal imagingEstablish baseline blood pressureCalculate lidocaine dosage
Management
Plan a rapid induction to gain control of airwayInduce with ECG if possible (small animal)Monitor arterial blood pressure throughout the anes-thetic periodBe ready to provide arrhythmia treatment and inotropicsupportManage pain appropriately
Cardiac Patients
Preparation
Identify potential problems
• Lead II ECG
• Thoracic radiographs
• Echocardiography
Plan for potential problems
• Arrhythmias
• Hypotension
292 Appendix 3
Management
Determine fluid needs (conservative with risk of volumeoverload)Premedicate to minimize anxietyOxygenate throughout anesthetic period (including pre-and postop)Assist ventilation to maintain normal PaCO2
Monitor cardiovascular parameters quantitatively ifpossible
Respiratory Patients
Preparation
Preoperative assessment
• Thoracic radiographs
• Arterial blood gas analysis
Thoracocentesis (when indicated)Preoxygenation (essential)Rapid (IV) premedication and induction
Management
Supervise entire premedication and induction processAssist ventilation throughout the procedure
Assess continuous ECG if possibleEvaluate arterial blood gases intraoperatively, if availableFacilitate a smooth and gradual recovery
Appendix 3 293
Provide oxygen supplementation throughout the recov-ery period
Neurologic Patients
Preparation
Record preoperative neurologic exam findingsTreat cerebral edema if necessary
• Solu-medrol/Solu-cortef: 20–30 mg/kg IV
• Furosemide: 1–2 mg/kg
• Mannitol: 1 g/kg over 20–30 min
Assure normal fluid balance to maintain normal MAP
Management
Provide smooth induction with minimal physicalrestraintUse conservative but adequate fluid therapy (avoid glu-cose-containing fluids)Provide IPPV to maintain PaCO2 at 30–35 mmHgMonitor ABP to assure adequate cerebral perfusionAvoid acepromazine and ketamine; isoflurane is the bestinhalant to useMonitor mentation postoperatively and assess neuro-logic status frequently
294 Appendix 3
Cesarean Section Patients
Preparation
Administer fluid bolus preoperatively (10–20 ml/kg)Prepare surgery site prior to inductionPreoxygenateAdminister premedications
• To minimize anxiety
• Choose reversible agents
Prepare to provide resuscitation for newborns
• Oxygen delivery
• Oropharynx suction
• Warmth
• Reversal agents (e.g., naloxone)
• Dopram
• Administer agents into umbilical stalk or sublin-gually
Management
Two general approaches to anesthetic management:
1. Rapid induction/intubation with propofol ordiazepam-ketamine following neuroleptanalgesiccombination; maintain on isoflurane or sevoflurane
Appendix 3 295
(halothane is acceptable but more cardiodepress-ing)
2. Neuroleptanalgesia (ruminants may not requirepremed) plus regional anesthesia: epidural, lineblock, paralumbar technique (Table 3–5)
Monitor and maintain adequate ABPEfficiency is essential to minimize time to delivery
Hepatic Disease Patients
Preparation
Assess chemistry panel for accompanying abnormalities
• Hypoproteinemia
• Hypoglycemia
• Coagulopathy (coagulation panel, bleeding time)
Assure adequate fluid balanceAvoid agents that depend on hepatic metabolism
Management
Choose reversible premedications (e.g., opioid)Benzodiazepine use is controversial and is best avoidedin the presence of hepatoencephalopathyPropofol or etomidate are good small animal inductionagents; guaifenesin-ketamine is suitable for large animals
296 Appendix 3
Isoflurane is most sparing of hepatic blood flow and isagent of choiceConsider glucose-containing fluids and colloids whenindicated
Renal Disease Patients
Preparation
Correct azotemia prior to inductionAssure normal fluid balanceAssess for accompanying disorders
• Anemia
• Hypoproteinemia
• Acid-base and electrolyte imbalances
Be prepared to minimize anesthesia time
Management
Choose a cardiac-sparing protocol: opioid-benzodi-azepine, ketamine, low-dose propofol, isoflurane main-tenanceAdminister fluids intraoperatively: (10 ml/kg/hr)Monitor ABP and urine production (normal: 1–2ml/kg/hr)Consider dopamine infusion: 2–5 µg/kg/minute
Appendix 3 297
Geriatric Patients
Preparation
Geriatric = the last 20–25% of natural lifespan
• <10 kg dogs >11 yr
• 10–25 kg dogs >10 yr
• 25–40 kg dogs >9 yr
• >40 kg dogs >7.5 yr
• cats >12 yr
Physiologic changes
• Decreased metabolic rate
• Decreased maximal cardiac output
• Decreased alveolar gas exchange
• Decreased organ reserve including liver and kidneys
• Increased fat
• Decreased anesthesia requirements
Complete physical exam, blood workup, other diagnos-tic tests as indicated by physical exam findings
Management
Select reversible premedication with minimal cardiacand respiratory effects: opioid + benzodiazepine
298 Appendix 3
PreoxygenateInduction: mask, propofol, thiopental, diazepam-keta-mineIsoflurane or sevoflurane for maintenanceConsider local/regional techniques to spare require-mentsMonitor ECG and ABPAdminister fluids at conservative rateSupport ventilation during anesthesiaProvide adequate analgesia and oxygen postoperatively
Neonates
Preparation
Considerations
• Age: ≤12 wks
• Increased metabolic demands
• Cardiac output is rate dependent
• Response to hypotension is less well-developed
• PCV and TP slightly less than adults
• More susceptible to hypothermia
increased surface area to body mass ratio
less body fat
poorly developed thermoregulatory center
Appendix 3 299
• Increased susceptibility to dehydration
greater body water content
less ability to concentrate urine
• Hepatic function not fully developed
limited ability to metabolize drugs
limited glycogen stores
Management
Select reversible premedication with minimal cardiaceffects: consider anticholinergic premedication whendrugs known to decrease HR are used (e.g., opioids)Premedication: opioid + benzodiazepineInduction: mask induction, propofol, diazepam-keta-mineMaintenance: isoflurane or sevoflurane, nonrebreathingsystemAdminister glucose-containing fluids (2.5–5%)Provide external heat sourcesPostoperative period: maintain oxygen delivery as longas possible and provide warm environment
300 Appendix 3
Recommended Reading
Altman RB, Clubb SL, Dorrestein GM, QuesenberryK, eds. Avian Medicine and Surgery. Philadelphia: WBSaunders Co.; 1997.
Fudge AM, ed. Seminars in Avian and Exotic Pet Medi-
cine: Anesthesia and Analgesia. Vol 7. Philadelphia:W.B. Saunders Co.; 1998.
Johnson-Delaney CA, Harrison LR, eds. Exotic Com-
panion Medicine Handbook for Veterinarians. LakeWorth, FL: Wingers Publishing; 1996.
Muir WW, Hubbell JAE, eds. Equine Anesthesia Moni-
toring and Emergency Therapy. St. Louis: Mosby Year-Book; 1991.
Muir WW, Hubbell JAE, eds. Handbook of Veterinary
Anesthesia. 2nd ed. St. Louis: Mosby Year-Book; 1995.
301
Seymour C, Gleed R, eds. Manual of Small Animal
Anaesthesia and Analgesia. United Kingdom: BritishSmall Animal Veterinary Association; 1999.
Short CE, ed. Principles and Practice of Veterinary Anes-
thesia. Baltimore: Williams & Wilkins; 1987.
Thurmon JC, Tranquilli WJ, Benson GJ, eds. Lumb
and Jones Veterinary Anesthesia. 3rd ed. Baltimore:Williams & Wilkins; 1996.
Tully TN, Shane SM, eds. Ratite Management, Medi-
cine, and Surgery. Malabar, FL: Krieger PublishingCo.; 1996.
302 Recommended Reading
A
Acepromazinecharacteristics of, 13, 44tspecies-specific indications
birds, 196tcats, 186t, 282tcattle, 244t, 282tdogs, 178t, 282tferret, 207t, 209thorses, 230t, 282trabbits, 209treptiles, 224tsheep, 244t, 282tswine, 258t, 282t
Acetaminophen, 166t, 171Acetylcholinesterase inhibitors,
51tAcetylpromazine.
See AcepromazineAcid-base balance, 147–148Acidosis
metabolic, 149trespiratory, 149t
Aerrane. See IsofluraneAlfentanil, 14, 46tAlkalinizing agents, 142t–143t,
146Alkalosis
metabolic, 149trespiratory, 149t
Alpha2 agonists. See also specific
drug
antagonists, 181t, 261tpain management using,
164t–165t, 168–169species-specific indications
dogs, 179treptiles, 224t
Alveolar ventilation, 81t–82tAmidate. See EtomidateAnalgesics
alpha2 agonists, 164t–165t,168–169
nonsteroidal anti-inflammatory drugs,165t–166t, 169–171
opioids, 161–168species-specific indications
camelids, 248t–249thorses, 233t–234treptiles, 225truminants, 248t–249tsmall mammals, 213t, 214t,
219swine, 262t
Anectine. See Succinylcholine
303
Index
Page references with “t” denote tables; “f” denote figures.
Anesthesiadefinition of, 1monitoring during.
See Monitoringpatient preparation for, 3–7positioning during, 154–155principles of, 2–3
Anesthesia machinecommon gas outlet, 98–99malfunction assessments, 105toperating recommendations,
105toverview of, 91–92oxygen calculations, 96, 97foxygen flush valve, 96, 98pin index safety system, 92, 93fpressure regulators, 92tanks, 91–92vaporizers, 92, 94–96
Anesthetic agents. See also specific
agent
biotransformation of, 86–87elimination of, 85–86ideal properties of, 52tinhalation. See Inhalation
agentsinjectable, 13–43, 44t–51tscheduling of, 287–288selection of, 11–12types of, 13–43
Anesthetic equipmentanesthesia machine. See Anes-
thesia machinebreathing systems, 99–103ventilators. See Ventilatorswaste gas scavenging, 103–104
Anesthetic record, 9, 10f, 113Ansed. See XylazineAnticholinergics, 44t, 175Antisedan. See AtipamezoleArrhythmias, 128tArterial blood gases, 115tArterial blood pressure.
116t–117tAspirin, 166t, 170, 196t, 213tAsystole, 276t–277tAtipamezole
general characteristics of, 14,46t
species-specific indicationsbirds, 198tcats, 282tdogs, 181t, 282thorses, 282treptiles, 224tswine, 262t, 282t
Atracurium, 14–15, 50t, 284tAtropine, 15, 44t, 207t, 209t,
224t, 270t, 282tAuriculopalpebral nerve, 62t, 66tAzaperone, 15–16, 44t, 258t, 282t
B
Barbiturates, 48t–49tBenzodiazepines, 44t–45tBeuthanasia-D. See PentobarbitalBicarbonate, 142t–143t, 147,
272tBier block, 59tBiotransformation, 86–87Birds
anesthetic agents, 194,196t–198t
304 Index
body temperature, 5tcatheter placement, 199electrocardiographic monitor-
ing of, 200, 202, 203ffasting period, 8tfluid therapy, 146–147, 200heart rate/minute, 5tintubation of, 194, 199laboratory studies and find-
ings, 6tmonitoring guidelines, 200,
202recovery of, 202, 204respiratory rate, 5trestraint methods, 193–194
Blood. See also Plasmaintraoperative assessments,
139replacement of, 133replacement therapy, 140tvolume of, 125t, 134t
Blood pressure monitoring,116t–118t
Body temperaturemonitoring of, 191species-specific values, 5t, 125t,
191Body water, 134tBoiling point, 74, 76Brachial plexus block, 59t, 70fBreathing systems. See also Venti-
latorscircle, 99–102description of, 99gas flow rates, 100t–101tmalfunction assessments, 105tnonrebreathing, 102–103
Brevane. See MethohexitalBrevital. See MethohexitalBrietal. See MethohexitalBupivacaine, 16Buprenorphine
general characteristics of,16–17, 47t
pain management using,163t–164t, 167
species-specific indicationsdogs, 178t, 283thorses, 233t, 283treptiles, 225truminants, 248t, 283tsmall mammals, 212t, 283tswine, 262t, 283t
Butorphanolgeneral characteristics of, 17,
47tpain management using,
163t–164tspecies-specific indications
birds, 196tcats, 186t–187t, 283tcattle, 245t, 248t, 283tdogs, 178t, 180t, 283thorses, 230t, 233t, 283tllamas, 247treptiles, 225tsheep, 245t, 248t, 283tsmall mammals, 212tswine, 258t, 262t, 283t
C
C fibers, 158, 160Calcium, 271tCapnography, 121t, 123f
Index 305
Carbocaine-V. See MepivacaineCardiac compression, 275, 278Cardiopulmonary arrest,
267–268Cardiopulmonary resuscitation
condition-specific approaches,276t–277t
drugs used, 270t–274tfluid therapy, 278guidelines, 268–269intravenous access, 275postrecovery monitoring,
278–279Cardiovascular system
disorders of, 292–293inhalation agents effect, 84monitoring parameters,
115t–118tCarfentanil, 17–18, 46t, 197tCarprofen, 165t, 170, 213t, 225tCats
analgesic agents, 162t–167tblood pressure monitoring,
117tblood volume, 125tbody temperature, 5t, 125t,
191catheter placement, 189chemical restraint, 186t, 188epidural technique, 71ffasting period, 8tfluid administration rates, 137heart rate/minute, 5t, 125tinduction of, 186t–187tintubation of, 189–190laboratory studies and
findings, 6t
local anesthetic techniques,58t–61t
minute ventilation values, 125topioid use, 185, 188parenteral anesthesia of, 187tpremedication, 186trecovery of, 190–191respiratory rate, 5t, 125trestraint methods, 186t, 188sinus bradycardia in, 127tventilatory support for, 190
Cattleblood pressure monitoring,
118tblood volume, 125tbody temperature, 5t, 125tcatheter placement, 250–251chemical restraint of,
244t–247tfasting period, 8t, 250heart rate/minute, 5t, 125tinduction of, 251intubation of, 251–252laboratory studies and find-
ings, 6tlocal anesthetic techniques,
63t–68tminute ventilation values, 125tpremedication, 244t–247t, 250respiratory rate, 5t, 125tsinus bradycardia in, 127t
Central venous pressure, 118tCesarean section, 295–296Chinchilla, 213tChloral hydrate, 18, 48t, 245t,
283tChloroprocaine, 55t
306 Index
Circle rebreathing systems,99–102
cis-Atracurium, 18–19, 50t, 284tColloid solutions, 141t–142tCommon gas outlet, 98–99Corticosteroids, 272tCow. See CattleCurare. See Tubocurarine
D
Defibrillation, 273tDehorning procedures, 66t–67tDehydration, 136tDemerol. See MeperidineDesflurane, 19, 79t–80tDetomidine, 19–20, 45t, 197t,
230t, 282tDexamethasone, 273tDextran, 141tDiazepam
cardiopulmonary resuscitationuses, 274t
general characteristics of, 20,44t, 177, 182
species-specific indicationsbirds, 196t–197tcats, 186t, 282tcattle, 244t, 282tdogs, 177, 182, 282thorses, 231t, 282trabbits, 210treptiles, 224tswine, 258t, 282t
Digital block, 60t, 72fDiprenorphine, 20–21, 47tDissociative agents, 47t–48t,
224t–225t
Dobutamine, 144t, 152, 271tDogs
analgesic agents, 162t–167tblood pressure monitoring,
117tblood volume, 125tbody temperature, 5t, 125tcatheter placement, 183chemical restraints, 178tdiazepam administration, 177,
182epidural technique, 71ffasting period, 8theart rate/minute, 5t, 125tinduction of, 179tintubation of, 182–183laboratory studies and
findings, 6tlocal anesthetic techniques,
58t–61tminute ventilation values, 125tparenteral anesthesia of,
179t–180tpremedication of, 178trecovery of, 183respiratory rate, 5t, 125tsinus bradycardia in, 127t
Dopamine, 144t, 153, 271tDormitor. See MedetomidineDormosedan. See DetomidineDoxacurium, 50tDoxapram, 270tDuromorph. See Morphine
E
Eagles, 197tEdrophonium, 20, 51t, 284t
Index 307
Electrocardiographybird monitoring using, 200,
202, 203fdescription of, 151reptile monitoring using, 226,
228fEndotracheal intubation.
See IntubationEnd-tidal carbon dioxide,
114t–115tEnflurane, 21–22, 79t–80t, 85Ephedrine, 144t, 152, 271tEpidural anesthesia
caudal, 67t–68tcranial, 68topioids, 163t–164t, 167–168regional, 60t, 71f
Epinephrine, 144t, 270tEthrane. See EnfluraneEtodolac, 165t, 170Etomidate
for cats, 187t, 284tfor dogs, 179t, 284tgeneral characteristics of, 22,
49tEtorphine, 22–23, 46tExamination. See Physical
examinationExtracellular fluid, 134tEye lubrication, 175
F
Falcons, 197tFasting
duration of, 7species-specific recommenda-
tions, 8t, 229, 235, 250
water, 7Fentanyl
for dogs, 283tgeneral characteristics of, 23,
46tfor horses, 234tpain management using,
162t–164t, 167Ferrets
analgesic agents, 213tbody temperature, 5tcatheter placement, 206chemical restraint of,
207t–208tfasting period, 8theart rate/minute, 5tinduction of, 205–206, 208tintubation of, 206laboratory studies and
findings, 6tmonitoring of, 212premedication, 207t–208trecovery of, 212respiratory rate, 5trestraint methods, 205
Flaxedil. See GallamineFluid therapy
administration ofrates, 137, 139routes, 146–147
blood replacement, 140tbody water percentages, 134tcolloid solutions, 141t–142tcommercial fluids, 135tdescription of, 132guidelines, 133, 137, 139, 146
308 Index
infusion warmers, 137, 138fpostresuscitation, 273t–274t,
278Flumazenil, 23, 45t, 262t, 282tFlunixin meglumine, 166t, 171,
196t, 213t, 225t, 234t,249t
Fluothane. See HalothaneFoals, 233t–234t, 240Forane. See IsofluraneFurosemide, 273t
G
Gallamine, 23–24, 50tGeneral anesthesia
characteristics of, 75tdefinition of, 113monitoring parameters,
114t–119tstages of, 75t, 113
Gerbil, 213tGeriatric patients, 298–299Glycerol guaiacolate.
See GuaifenesinGlycopyrrolate, 24, 44t, 207t,
209t, 224t, 282tGoat
blood volume, 125tbody temperature, 5t, 125tfasting period, 8theart rate/minute, 5t, 125tlaboratory studies and
findings, 6tminute ventilation values, 125trespiratory rate, 5t, 125t
Guaifenesin, 24–25, 49t, 235,245t–246t, 260t–261t, 284t
Guinea pig, 213t
H
Halothanecardiovascular effects, 84description of, 88–89general characteristics of, 25for horses, 237physicochemical properties of,
79t–80trespiratory effects, 83
Hamster, 213tHawks, 196tHeart rate
monitoring of, 115tspecies-specific values, 5t, 125t
Hemoglobin saturation, 115tHepatic disease, 296–297Hetastarch, 141t–142tHorses
analgesic agents, 233t–234tanesthetic agents, 230t–233tblood pressure monitoring,
117tblood volume, 125tbody temperature, 5t, 125tcatheter placement, 236chemical restraint of, 230tdepth assessments, 240eye covering, 238–239fasting period, 8t, 229, 235fluid therapy, 238heart rate/minute, 5t, 125t,
240induction of, 230t–232tintubation of, 236
Index 309
Horses, cont.
laboratory studies and findings, 6t
local anesthetic techniques,62t
minute ventilation values, 125tmonitoring of, 239–240postanesthetic myopathy,
154–155premedication, 230t, 235–236recovery of, 240–241respiratory rate, 5t, 125t, 239sinus bradycardia in, 127tsupportive care, 238–239ventilatory support for, 239
Hydromorphonefor cats, 186t, 282tfor dogs, 178t, 282tgeneral characteristics of, 47tpain management using, 162t
Hypercapnia, 109Hyperthermia, malignant, 85,
265–266Hypnomidate. See EtomidateHypnovel. See MidazolamHypokalemia, 139Hypotension, 128t, 152Hypothermia
etiology of, 152fluid therapy and, 137prevention of, 152–154systemic effects, 152–153
Hypoxemia, 151
I
Infraorbital nerve, 58tInfusion warmers, 137, 138f
Inhalation agentsbiotransformation of, 86–87cardiovascular effects, 84description of, 73disadvantages of, 73elimination of, 85–86environmental exposure,
86t–87tfactors that affect, 81t–82thepatocellular injury caused
by, 84–85minimum alveolar concentra-
tion, 78, 79t–80t, 82physicochemical properties of,
74, 76quantity determination, 76,
77frequirements for, 83trespiratory effects, 82–83systemic effects of, 82–85
Inspiratory time, 108tInspiratory to expiratory ratio,
108tIntercostal nerve, 60tIntermittent positive pressure
ventilation, 104, 106Interpleural region, 60tIntracellular fluid, 134tIntraosseous cannulation,
146–147, 201fIntraval. See ThiopentalIntravenous regional anesthesia
in cats, 59tin cattle, 65tin dogs, 59tin ruminants, 65t
310 Index
Intubationgeneral considerations, 174species-specific indications and
guidelinesbirds, 194, 199cats, 189–190cattle, 250–251dogs, 182–183ferret, 206horses, 236reptiles, 223ruminants, 250–251sheep, 250–251swine, 263–264
tube placement, 174Isoflurane, 25–26, 79t–80t, 88,
194, 237Isoproterenol, 144t, 271t
K
Ketaminegeneral characteristics of, 26,
48tpain management using, 165t,
169species-specific indications
birds, 196tcats, 186t–187t, 283tdogs, 179t–180t, 283tferret, 208thorses, 230t–231t, 283trabbits, 210treptiles, 224t–225t
Ketaset. See KetamineKetoprofen, 165t–166t, 170,
214t, 234t
L
Lidocaine, 26–27, 55t, 142t, 270tLizards. See ReptilesLlamas
body temperature, 5tchemical restraint of,
246t–247tfasting period, 8theart rate/minute, 5tlaboratory studies and
findings, 6tpremedication, 246t–247trespiratory rate, 5t
Local anestheticsdescription of, 53–54mechanism of action, 54, 57pain management using, 171properties of, 55ttechniques for administering,
58t–68ttoxic effects of, 56t
M
M-99. See EtorphineMalignant hyperthermia, 85,
265–266Mandibular nerve, 59t, 69fMannitol, 274tMarcaine. See BupivacaineMaxillary nerve, 58t, 69fMedetomidine
general characteristics of, 26,45t
pain management using,164t–165t
species-specific indicationsbirds, 197t
Index 311
Medetomidine, cont.
cats, 187t, 282tdogs, 179t–180t, 282tferret, 208t–209tswine, 258t, 282t
Meloxicam, 166tMeloxicxam, 170Mental nerve, 58t, 69fMeperidine, 27–28, 46t, 161,
162t, 282tMepivacaine, 28, 55tMetabolic acidosis, 139, 146,
149tMetabolic alkalosis, 149tMethohexital, 28–29, 48t, 283tMethoxyflurane
general characteristics of, 29nephrotoxic effects, 85physicochemical properties of,
79t–80tMetofane. See MethoxyfluraneMidazolam
general characteristics of,29–30, 44t
species-specific indicationsbirds, 196t–197tcats, 186t, 282tdogs, 282tferret, 207trabbits, 210treptiles, 224tswine, 258t, 282t
Minimum alveolar concentra-tion, 78, 79t–80t, 82
Mivacurium, 50tMolecular weight, 76
Monitoring. See also specific species,
monitoring
capnography, 121t, 123fguidelines for, 111–113parameters assessed, 114t–119tpulse oximetry, 121t–122t,
124fMorphine
general characteristics of, 30,46t
pain management using, 161,162t–164t
species-specific indicationscats, 186t, 282tdogs, 178t, 282thorses, 230t, 233t–234t,
282truminants, 248t–249t, 282tsheep, 248t–249t, 282tsmall mammals, 213tswine, 262t, 282t
Mouse, 213t
N
Nalbuphine, 30–31, 47t, 283tNalmefene
general characteristics of, 31,47t
species-specific indications,181t, 283t
Nalorphine, 47tNaloxone
general characteristics of,31–32, 47t
species-specific indicationsbirds, 198tdogs, 181t, 283t
312 Index
swine, 262t, 283tNaltrexone, 32, 47t, 198tNaproxen, 166tNarcan. See NaloxoneNembutal. See PentobarbitalNeonates, 299–300Neostigmine, 32–33, 51t, 284tNeurologic injury, 294Neuromuscular blocking agents,
49t–51tNimbex. See cis-AtracuriumNitrous oxide
diffuse hypoxia and, 88indications, 88physicochemical properties of,
79t–80tNonrebreathing systems,
102–103Nonsteroidal anti-inflammatory
drugs, 165t–166t,169–171, 213t
Norcuron. See VecuroniumNovocaine. See ProcaineNSAIDs. See Nonsteroidal anti-
inflammatory drugsNubain. See NalbuphineNumorphan. See Oxymorphone
O
Onychectomy, 61t, 72fOpioids
agonists, 167antagonists, 181t, 262tclassification of, 161dosing of, 162t–167tepidural uses, 163t–164t,
167–168
general characteristics of,46t–47t
side effects of, 161species-specific indications
cats, 185, 188dogs, 178t, 181tferrets, 213trabbits, 213tsmall mammals, 213t
types of, 162t–167tOwls, 197tOxygen flush valve, 96, 98Oxygenation
calculations regarding, 96, 97ffactors that affect, 148, 151intraoperative assessments,
148, 151Oxyhemoglobin dissociative
curve, 124fOxymorphone
general characteristics of, 33,46t
pain management using,162t–163t
species-specific indicationscats, 186t, 283tdogs, 178t, 283t
P
Packed red blood cells, 140tPaCO
2. See Partial pressure ofcarbon dioxide
Paindefinition of, 157perception of, 160physiology of, 158, 160signs of, 158, 159t
Index 313
Pain, cont.
treatment ofalpha2 agonists, 164t–165t,
168–169local anesthesia, 171nonsteroidal anti-
inflammatory drugs,165t–166t, 169–171
opioids, 161–168regional anesthesia, 171
Pancuronium, 33–34, 50t, 284tParavertebral techniques,
63t–65tPartial pressure of carbon
dioxide, 106, 109Partial pressure of oxygen, 124fPatient preparations, 3–7Pavulon. See PancuroniumPeak inspiratory pressure, 108tPentazocine, 34, 47t, 283tPenthrane. See MethoxyfluranePentobarbital, 34–35, 48t, 283tPentothal. See ThiopentalPeterson eye block, 65tPethidine. See MeperidinePhenobarbital, 35Phenylbutazone, 166t, 234t, 249tPhysical examination
laboratory studies and findings, 6t
parameters assessed, 3, 5tpreprocedural, 3species-specific findings, 5t
Physical status, 4tPig. See SwinePin index safety system, 92, 93f
Piroxicam, 166tPlasma. See also Blood
replacement therapy, 141tvolume assessments, 134t
Pontocaine. See TetracainePositioning, 154–155Postanesthetic myopathy,
154–155Pregnancy, 295–296Premature ventricular
contractions, 128t, 151Premedication agents, 12,
44t–48tPressure regulators, 92Procaine, 36, 55tPromace. See AcepromazinePropofol
cardiopulmonary resuscitationuses, 274t
general characteristics of, 36,49t
species-specific indicationscats, 187t, 283tdogs, 179t, 182, 283tferret, 208trabbits, 210treptiles, 225t
Prostigmine. See NeostigminePulse oximetry, 121t–122t, 124fPulse rate, 115t–116tPulseless electrical activity, 277tPyridostigmine, 37, 51t, 284t
R
Rabbitsanalgesic agents, 213tblood volume, 125t
314 Index
body temperature, 5t, 125tcatheter placement, 215chemical restraint of,
209t–210tfasting period, 8theart rate/minute, 5t, 125timmobility reflex of, 212induction of, 210t, 216–217laboratory studies and
findings, 6tminute ventilation values, 125tmonitoring of, 217–218premedication, 209t–210t, 215premedication of, 209t–210trespiratory rate, 5t, 125trestraint methods, 212, 215
Rapifen. See AlfentanilRapinovet. See PropofolRat, 213tRecord keeping, 9, 10f, 113Recovery, anesthetic
birds, 202, 204cats, 190–191dog, 183ferret, 212horses, 240–241reptiles, 227ruminants, 253swine, 266
Regional anesthesiain cats, 59tin cattle, 65tin dogs, 59tpain management using, 171in ruminants, 65t
Regonol. See Pyridostigmine
Renal disease, 297Reptiles
anesthetic agents, 224t–225tfluid therapy, 226induction of, 222–223intubation of, 223monitoring of, 226–227recovery of, 227restraint methods, 221–222ventilatory support, 226
Respiratory acidosis, 149tRespiratory alkalosis, 149tRespiratory rate
decreased, 126t–127tmonitoring of, 114t–115tspecies-specific values, 5t, 125t
Respiratory systemdisorders of, 293–294inhalation agents effect, 82–83
Revex. See NalmefeneRevivon. See DiprenorphineRobinul. See GlycopyrrolateRocuronium, 50tRomazicon. See FlumazenilRomifidine, 37–38, 45t, 282tRompun. See XylazineRuminants
analgesic agents, 248t–249tblood pressure monitoring,
118tcatheter placement, 250–251cattle. See Cattlechemical restraint of,
244t–247tfasting period, 250induction of, 251
Index 315
Ruminants, cont.
intubation of, 251–252llamas. See Llamaspositioning of, 253premedication, 244t–247t, 250recovery of, 253sheep. See Sheepsinus bradycardia in, 127t
S
Scoline. See SuccinylcholineSedivet. See RomifidineSevoflurane, 38, 79t–80t, 85, 89,
194, 237Sheep
blood volume, 125tbody temperature, 5tcatheter placement, 250–251chemical restraint of,
244t–245tfasting period, 8t, 250heart rate/minute, 5t, 125tinduction of, 251intubation of, 251–252laboratory studies and find-
ings, 6tminute ventilation values, 125tpremedication, 244t–245t, 250respiratory rate, 5t, 125t
Sinus bradycardia, 127tSinus tachycardia, 128tSmall mammals
ferret. See Ferretguidelines regarding, 218–219rabbit. See Rabbit
Snakes. See ReptilesSolubility coefficient, 78
Solu-Delta-Cortef, 272tSolu-Medrol, 272tSpecific gravity, 76Stiglyn. See NeostigmineStresnil. See AzaperoneSublimaze. See FentanylSuccinylcholine, 38–39, 51tSucostrin. See SuccinylcholineSufenta. See SufentanilSufentanil, 38, 46tSupportive care
acid-base balance, 147–148,149t
adjunctive drugs, 151–152fluid therapy. See Fluid therapyintraoperative, 131–132oxygenation, 148, 151preoperative, 131
Suprane. See DesfluraneSupraorbital nerve, 62tSwine
analgesic agents, 262tblood pressure monitoring,
118tblood volume, 125tbody temperature, 5t, 125t, 265catheter placement, 264chemical restraint of, 258tfasting period, 8t, 256heart rate/minute, 5t, 125tinduction of, 256, 258t–261tintubation of, 263–264laboratory studies and
findings, 6tmalignant hyperthermia in,
265–266
316 Index
minute ventilation values, 125tmonitoring of, 264–265premedication, 258trecovery of, 266respiratory rate, 5t, 125trestraint methods, 255–256
T
Tachycardia, 128t, 151, 159t, 276tTachypnea, 126t, 159tTalwin. See PentazocineTelazol
general characteristics of, 40,48t
species-specific indicationsbirds, 196tcats, 187t, 283tdogs, 179t, 283tferret, 208thorses, 283trabbits, 210t
Temgesic. See BuprenorphineTensilon. See EdrophoniumTetracaine, 55tThiopental
characteristics of, 39–40, 48tspecies-specific indications
cats, 186t, 283tdogs, 179t, 182, 283tferret, 208truminants, 245t, 283tswine, 260t, 283t
Tidal volume, 108t, 114tTolazoline
general characteristics of,40–41, 46t
species-specific indications,181t, 261t, 282t
Torbugesic. See ButorphanolTorbutrol. See ButorphanolTotal body water, 134tTracrium. See AtracuriumTrauma, 291–292Trexonil. See NaltrexoneTrigeminal nerve, 58t, 69fTromethamine organic amine
buffer, 143tTubocurarine, 41, 50tTurtles. See Reptiles
U
Ultrane. See SevofluraneUrinary output assessments, 118t
V
Valium. See DiazepamVapor pressure, 74Vaporizers, 92, 94–96Vecuronium, 41–42, 50t, 284tVentilators
indications, 104, 106–107malfunction assessments, 106tpressure-cycled, 107settings, 108tspecies-specific support
cats, 190horses, 239reptiles, 226
volume-cycled, 107–108Ventricular arrhythmias, 128t,
151Ventricular fibrillation, 276tVersed. See Midazolam
Index 317
Vetalar. See KetamineVetergesic. See Buprenorphine
W
Waste gas exposureminimization methods, 87tscavenging systems, 103–104,
106tside effects of, 86t
Water withholding, 7Wildnil. See Carfentanil
X
Xylazinegeneral characteristics of, 42,
45tpain management using,
164t–165tspecies-specific indications
cats, 187t, 282tcattle, 244t, 246t, 282tdogs, 179t–180t, 282t
ferret, 208t–209thorses, 230t, 282tllamas, 246trabbits, 210treptiles, 224truminants, 244tsheep, 244t, 246t, 282tswine, 258t–260t, 282t
Xylocaine. See Lidocaine
Y
Yohimbine (Yobine)general characteristics of, 43,
45tspecies-specific indications
birds, 196t, 198tcats, 282tdogs, 181t, 282thorses, 282tsheep, 282tswine, 261t, 282t
318 Index
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