general anaesthesia
TRANSCRIPT
1
General anaesthesia
Henning Andreas Haga
Associate professor
Norwegian School of Veterinary Science
Anaesthesia
• A reversible drug induced condition of unconsciousness.
• Goals:– Unconsciousness
– Muscle relaxation
– Analgesia
2
Anaesthetics
• Injections
• Gas
Side effects
• Respiratory depression
• Cardiovascular depression
• Risk of reduced oxygen tension (hypoxia)
• Balance between moving animals and respiratory arrest.
3
Injection
• Subcutaneously (under skin)
• Intramuscullary (into muscle)
• Intraperitoneally (into abdominal cavity)
• Intravenously (into vein)
4
• Subcutaneous, intramuscular or intraperitoneal injection.
• Simple, but less control
Injection
Injection
• Subcutaneous, intramuscular or intraperitoneal injection
• Simple but less control
Time
Eff
ect
5
Intravenous anaesthesia
• Rapid effect
• Easy to administer more
• Intravenous access
TidPla
smak
onse
ntra
sjon
Intravenous induction
• Rapid
• Good control
• Can be given to effect
6
Intravenous anaesthesia
0
0
Tid
Pla
smak
ons
entras
jon
(ng/m
l)
Infusjonskons
0
0
Tid Plasm
akonse
ntras
jon (ng/m
l)
Boluskons
Plasmakons
Infusjonskons
Intravenous anaesthesia
7
Species difference
• 10 mg xylazine is a suitable dose to sedate a cow (500 kg) and a cat (5 kg)
• Diclofenac, NSAID kills vulture through residues in carcasses.
• Ketamine doses: – Horse 2.5 mg/kg– Pig 15 mg/kg– Rat 70 mg/kg
• Diazepam (Valium©), excitation in some animals
Anaesthetic gas
Anaesthetic gas
Gas anaesthesia
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Why gas?
Anaesthetic machine
• You need to convert fluid into gas
• You need to remove CO2
• You need to administer oxygen
9
Gas induction
• Possible to use only one anaesthetic
• Rapid recovery• No drug need to be
matbolised• Stressful• Sevoflurane better for
induction than isoflurane
Maintainance of gas anaesthesia
10
Maintainance of gas anaesthesia• Transition from
injection to gas, need to consider for how long the injection has effect
Tid
Gass
Injeksjon
MAC
• Minimum alveolar concentration
• The alveolar gas concentration inhibiting movement as a response to a standardised nociceptive stimulus in 50 % of animals.
• MAC differs between species, but the order between the gases within a species is similiar.
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MAC
MAC
1,89 %Mean
1,65 %11
1,85 %10
1,85 %9
2,35 %8
1,75 %7
2,05 %6
2,25 %5
1,85 %4
1,65 %2
1,65 %1
Individual isoflurane MACPig number
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Perception →←Modulation
Transduction →
Transmission →
General anaesthesia
↓↓↓↓
Analgesia
Blodtrykk, mmHg
55
60
65
70
75
0 5 10 15 20
Tid, minutter
Gje
nnom
snitt
stry
kk, m
mH
g
Bedøvelse Kastrasjon
Kontroll
Testikkel
Streng
Theta power
59
60
61
62
63
0 5 10 15 20
Tid (minutter)
The
ta p
ower
(dB
)
Streng
Kontroll
Testikkel
Injeksjon Kastrasjon
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Aims of anaesthesia
• Unconsciousness
• Muscle relaxation
• Analgesia
With one drug?
Balanced anaesthesia
• In contrast to one single anaesthetics doing all
• Combination of drugs to minimise side effects and taylor drugs to the need of the patient
• Drug combination depends upon:– Species
– Nociception to be expected
– Duration of procedure
– Equipment and expertise avaiable
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Maintainance
• Gas for unconsciousness.
• Analgesics should optimally take care of nociception.
Monitoring of anaesthesia
• Manuel:– Respiratory
movements
– Pulse rate and quality
– Mucous membrane colour
• Electronic equipment– Pulsoximetry
– Multi gas analyser
– Elektrocardiography
– Blood pressure
– etc....
15
Temperature
Recovery from anaesthesia
• Take care of the needs of the animal– Oxygen
– Temperature
– Fluids
• Analgesia!– Do not let an animal
wake up to pain.
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Take home message
• Pain and nociception induces malign physiological changes
• Combination of analgesics may be wise• Anaesthetised does not feel pain, but they respons
to nociceptive input• Anaesthesia is a balance between respiratory and
cardiovascular compromise and moving animal.• Perioperative pain management important for
postoperative pain.