pediatric anesthesia greg gordon md 13 mar 09. objectives preop preparation fluids and electrolytes...
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Objectives
•Preop preparation•Fluids and electrolytes•Cardiopulmonary physiology•Induction technics•Airway management technics
Participants will be able to explain the implications for anesthesia careof selected characteristics unique to our pediatric patients in the areas of:
Ref: MetroHealthAnesthesia.com/edu/ped/peds1.htm
Pediatric anesthesia is a family affair.
Psychological preparation involves stress reduction
The two most important sources of stress are: 1. Fear of the unknown 2. Fear of separation
These stresses are best dealt with by:
1. Simple, honest communication, colored by positive suggestionmodified according to age
In other words: tell 'em just what's gonna happen, in a positive, supportive way.
2. Maintain parental presence during induction of anesthesia
in selected cases.
I. Preop Preparation
Approach depends on age of patient:
Early infancy (neonate to about 7 months of age): Parents are the primary focusComfortable separation in preop holding area
usual
Later infancy to about 3 years: Separation anxiety major Surgery ought be
outpatient Selected parental
presence3 to 6 years: Child becomes primary focus. Explain exactly what will happen; what you
will do Then do it that way. (Be trustworthy!)
6 years to adolescent: Increasing involvement of patient.
From 3 of 4 years through adolescence: Give child choicesParental presence often helpful
Useful for all of us, from infancy to old age!
SAY
GOOD, YESsleepy breezeanesthetic vaporspinchhug your armstickerswill be neat! fun!might get the gigglesmake you laughfeels funnytake a little napgood job, good boy/girlproud of youcool, refreshingnice little back rub
NOT
BAD, NOgasbad smell, stink, stenchbee stingtake blood pressure
won't hurtdon't crymake you cryfeels badput you to sleepdon't be bad
cold solutionpress on your back
Clear liquids 2 hoursBreast milk 4 hoursInfant formula 6 hoursLight meal 6 hoursRegular meal 8 hours
Guidelines apply to healthy patients undergoing elective proceures. They do not guarantee complete gastric emptying.
Reference: Anesthesiology 90:896-905, 1999
Minimum Fasting Periods:
Offer clear liquids up to 2 hours
before induction:
• reduces hunger, irritability
• preserves hydration
• risk of hypoglycemia
Preanesthesia Checklist
The only way to
definitely confirm readiness!
USE A
PREANESTHESIA CHECKLIST
II. Fluids and Electrolytes
INFANT CHILD ADULT
Total Water (%) 75 70 55-60
ECF 40 30 20
ICF 35 40 40
Fat 16 23 30
immature function at birth:
GFR (‘til 2 years old) concentrating capacity Na reabsorption HCO3 /H exchange free H2O clearance urinary loss of K+, Cl-
Infant kidneys
What it means:
Newborn kidney has limited
capacity to compensate for
volume excess or
volume depletion
Neonates:
• limited hepatic glycogen stores
risk of hypoglycemia
provide 5%-10% dextrose
maintenance
supplemental insulin prn
fluid requirement
greater BSA:mass ratio
other factors:
radiant warmers
fever
illness
injury
thin, immature skin
Hourly Maintenance Fluids
4:2:1 Rule
4 ml/kg/hr 1st 10 kg +
2 ml/kg/hr 2nd 10 kg +
1 ml/kg/hr for each kg >
20
Maintenance Fluid Therapy
Term Newborn (ml/kg/day)
Day 1 50-60 D10W
Day 2 100 D10 1/2 NS
>Day 7 100-150 D5-D10 1/4
NS
Older Child: 4-2-1 rule
Perioperative Fluid ManagementChoice of Fluids
Isotonic Crystalloids
• best replacement fluid
Hypotonic Fluids - DANGER
• can cause hyponatremia
Effects of Intraop Glucose :
• intraop hyperglycemia
• hyperosmolality
• osmotic diuresis
• worsen neurologic outcome
after cerebral ischemia
• neonates and young infants
• debilitating chronic illness
• patients on parenteral
nutrition
• neonates of diabetic mothers
• Beckwith-Wiedemann
syndrome
• nesidioblastosis
Intraop glucose exceptions: patients at risk for hypoglycemia:
Continue D10, but at
reduced rate (e.g., reduce by 50% to 5 ml/hr)
to compensate for hyperglycemic surgical stress;
Infant comes to OR with D10 infusing at 10 ml/hr.What to do intraop?
And add by piggy-back or second IV line
an infusion of isotonic crystalloid (LR or NS)
Fluids - Summary
Brief Procedures ( myringotomy, PET)
replacement may be unnecessary
1-2 hr Procedures
IV placement after inhalation
induction
replace 10-20 cc/kg + EBL 1st hour
Longer and Complex Procedures
4-2-1 rule
hypovolemia: 10-20 cc/kg LR / NS
Glucose IF hypoglycemic risk
III. Pediatric cardiopulmonary physiology
In utero circulation placenta -> umbilical vein (UV)-> ductus venosus (50%) -> IVC -> RA -> foramen ovale (FO) -> LA -> Ascending Ao -> SVC -> RA -> tricuspid valve -> RV (2/3rds of CO) -> main pulmonary artery (MPA) -> ductus arteriosus (DA) (90%) -> descending Ao -> umbilical arteries (UAs)->
Transitional circulation
Placenta Out and Lungs In
PVR drops dramatically
(endothelial-derived NO and prostacyclin)
FO closes
DA closes
10-12 hours to 3 days to few weeks
prematures: closes in 4-12 months
PFO potential route for systemic emboli
DA and PFO routes for R -> L shunt in PPHN
III. Pediatric cardiopulmonary physiology
III. Pediatric cardiopulmonary physiology
Neonatal myocardial function
Contractile elements comprise 30% (vs 60% adult) of newborn myocardiumAlpha isoform of tropomyosin predominates
more efficient binding for faster relaxation at faster heart ratesRelatively disorganized myocytes and myofibrilsMost of postnatal increase in myocardial mass due to
hypertrophy of existing myocytesDiminished role of relatively disorganized sarcomplasmic reticulum (SR)
and greater role of Na-Ca channels in Ca flux sogreater dependence on extracellular Camay explain:
Increased sensitivity to calcium channel blockers (e.g. verapamil)hypocalcemiadigitalis
III. Pediatric cardiopulmonary physiology
Normal aortic pressures
Wt (Gm) Sys/Dias mean1000 50/25 352000 55/30 403000 60/35 504000 70/40 50
Age (months) Sys/Dias mean 1 85/65 50 3 90/65 50 6 90/65 50 9 90/65 55 12 90/65 55
Adrenergic receptors
Sympathetic receptor system
Tachycardic response to isoproterenol and epinephrine
by 6 weeks gestation
Myocyte β-adrenergic receptor density
peaks at birth then
decreases postnatally
but coupling mechanism is immature
Parasympathetic, vagally-mediated responses are mature at birth
(e.g. to hypoxia)
Babies are vagotonic
III. Pediatric cardiopulmonary physiology
III. Pediatric cardiopulmonary physiology
Normal heart rate
Age (days) Rate 1-3 100-140 4-7 80-145 8-15 110-165
Age (months) Rate 0-1 100-180 1-3 110-180 3-12 100-180
Age (years) Rate 1-3 100-180 3-5 60-150 5-9 60-130 9-12 50-11012-16 50-100
The Newborn Heart
•Near peak of Starling curve
•Stroke volume relatively fixed
•C.O. relatively heart rate dependent
III. Pediatric cardiopulmonary physiology
Newborn myocardial physiology
Type I collagen (relatively rigid) predominates (vs type III in adult)
Neonate AdultCardiac output HR dependent SV & HR dependentStarling response limited normalCompliance less normalAfterload compensation limited effectiveVentric interdependence high relatively low
So:
Avoid (excessive) vasoconstrictionMaintain heart rateAvoid rapid (excessive) fluid administration
Pediatric Respiratory Physiology
Perinatal adaptation
First breath(s)
up to 40 to 80 cmH2O needed
to overcome high surface forces
to introduce air into liquid-filled lungs
adequate surfactant essential for smooth transition
Elevated PaO2
Markedly increased pulmonary blood flow ->
increased left atrial pressure with
closure of foramen ovale
Pediatric Respiratory Physiology
Infant lung volume small in relation to body size
VO2/kg = 2 x adult value
=> ventilatory requirement per unit lung volume is increased
less reserve
more rapid drop in SpO2 with hypoventilation
Pediatric Respiratory Physiology
Infant and toddler
more prone to severe obstruction of upper and lower airways
absolute airway diameter much smaller that adult
relatively mild inflammation, edema, secretions
lead to greater degrees of obstruction
Pediatric Respiratory Physiology
Central apnea
apnea > 15 seconds or
briefer but associated with
bradycardia (HR<100)
cyanosis or
pallor
rare in full term
majority of prematures
Pediatric Respiratory Physiology
Postop apnea in preterms
Preterms < 44 weeks postconceptional age (PCA): risk of apnea = 20-40%most within 12 hours postop (Liu, 1983)
Postop apnea is reported in prematures as old as 56 weeks PCA (Kurth, 1987)
Associated factorsextent of surgeryanesthesia techniqueanemiapostop hypoxia
(Wellborn, 1991)
44-60 weeks PCA: risk of postop apnea < 5% (Cote, 1995)Except: Hct < 30: risk remains HIGH independent of PCA
Role for caffeine (10 mg/kg IV) in prevention of postop apnea in prematures? (Wellborn, 1988)
Pediatric Respiratory Physiology – Pulmonary and Thoracic Receptors
Laryngospasm
Sustained tight closure of vocal cords by contraction of adductor (cricothyroid) musclespersisting after removal of initial stimulus
More likely (decreased threshold) withlight anesthesiahyperventilation with hypocapnia
Less likely (increased threshold) withhypoventilation with hypercapniapositive intrathoracic pressuredeep anesthesiamaybe positive upper airway pressure
Hypoxia (paO2 < 50) increases threshold (fail-safe mechanism?)
So: suction before extubation while
patient relatively deep and
inflate lungs and maybe a bit of PEEP at time of extubation
Pediatric Respiratory Physiology – Assessment of Respiratory Control
Effects of anesthesia on respiratory control
Shift CO2 response curve to right
Depress genioglossus, geniohyoid, other phayrngeal dilator muscles ->
upper airway obstruction (infants > adults)
work of breathing decreased with
jaw lift
CPAP 5 cmH2O
oropharyngeal airway
LMA
Active expiration (halothane)
Pediatric Respiratory Physiology – Lung Volumes and Mechanics of Breathing
50% of TLC =
= 25% TLC
= 60 ml/kg infant
after 18 monthsincreases to adult 90 ml/kgby age 5
may be only 15% of TLC in young infants under GAplus muscle relaxants
Pediatric Respiratory Physiology – Lung Volumes and Mechanics of Breathing
Under general anesthesia, FRC declines by
10-25% in healthy adults with or without muscle relaxants and35-45% in 6 to 18 year-olds
In young infants under general anesthesia
especially with muscle relaxants
FRC may = only 0.1 - 0.15 TLC
FRC may be < closing capacity leading to
small airway closure
atelectasis
V/Q mismatch
declining SpO2
Pediatric Respiratory Physiology – Lung Volumes and Mechanics of Breathing
General anesthesia, FRC and PEEP
Mean PEEP to resore FRC to normalinfants < 6 months 6 cm H2O
children 6-12 cm H2O
PEEP
important in children < 3 years
essential in infants < 9 months
under GA + muscle relaxants
(increases total compliance by 75%)
(Motoyama)
Pediatric Respiratory Physiology – Dynamic Properties
Poiseuille’s law for laminar flow:
R = 8lη/πr4where R resistance
l lengthη viscosity
For turbulent flow: R α 1/r5
Upper airway resistance
adults: nasal passages: 65% of total resistance
Infants: nasal resistance 30-50% of total
upper airway: ⅔ of total resistance
NG tube increases total resistance up to 50%
Pediatric Respiratory Physiology Oxygen transport
(Bohr effect)
= 27, normal adult (19, fetus/newborn)
Pediatric Respiratory Physiology Oxygen transport
If SpO2 = 91
then = PaO2 =
Adult 606 months 666 weeks 556 hours 41
Pediatric Respiratory Physiology Oxygen transport
Implications for blood transfusion
older infants may tolerate somewhat lower Hgb levels at which
neonates ought certainly be transfused
P50 Hgb for equivalent tissue oxygen delivery
Adult 27 8 10 12
> 3 months 30 6.5 8.2 9.8
< 2 months 24 11.7 14.7 17.6
Pediatric Respiratory Physiology – Selected Summary Points
Basic postnatal adaptation lasts until 44 weeks postconception,
especially in terms of respiratory control
Postanesthetic apnea is likely in prematures, especially anemic
Formation of alveoli essentially complete by 18 months
Lung elastic and collagen fiber development continues through age 10 years
Young infant chest wall is very compliant and
incapable of sustaining FRC against lung elastic recoil when
under general anesthesia, especially with muscle relaxants
leading to airway closure and
‘progressive atalectasis of anesthesia’
Mild – moderate PEEP (5 cmH2O) alleviates
Hemoglobin oxygen affinity changes dramatically first months of life
Hgb F – low P50 (19)
P50 increases, peaks in later infancy (30)
implications for blood transfusion
Parents and Toys
• "Parents are often the best premedication." G. Gordon, MD
• "The presence of the parents during induction has virtually eliminated the need for sedative premedication." -Fred Berry, MD, 1990
• Parental presence is especially helpful for children older than 4 years who have calm parents.
• Midazolam is more effective than parental presence. - Zeev Kain, 1998
• Anxiety associated with oral midazolam administration was significantly reduced in children who had earlier received a toy to play with. - Golden et al, 2006
IV. Induction - premedication options
http://metrohealthanesthesia.com/edu/ped/pedspreop6.htm
Pharmacologic premedication options
When awake separation of child from parent
before induction is planned
midazolam (Versed)
PO: 0.5 to 1.0 mg/kg up to 10 mg max.
Peak sedation by about 30 minutes
Mix with grape concentrate or
aetaminophen syrup or
ibuprofen suspension (10 mg/kg)
Mother may administer to child
Volume should not exceed 0.5 ml/kg (NPO!)
IV. Induction - premedication options
http://metrohealthanesthesia.com/edu/ped/pedspreop6.htm#premeds
PO: 6 to 10 mg/kg IM: 3 to 4 mg/kg for sedation; 6 to 10 mg/kg for induction of GA
midazolam + ketamine : PO 0.4 + 4 mg/kg respectively PO induction of GA: 0.8 + 8 mg/kg
EMLA cream Eutectic mixture of lidocaine and prilocaine For cutaneous application one hour preop
IV. Induction - premedication options
http://metrohealthanesthesia.com/edu/ped/pedspreop6.htm#ketamine
ketamine
"Infants should preferably be anesthestized in the mother's or nurse's arms. Care should be taken in anesthestizing children to make the operation as informal as possible... Mental suggestion here plays a great part, as well as gentleness in voice and movement..."
-Gwathmey J: Anesthesia 1914
Induction
http://metrohealthanesthesia.com/edu/ped/induction1.htm
FirstWarm the OR, especially for young infantsComplete the pre-anesthesia checklist.
Two main categories of pediatric anesthetic induction:
Parent(s) present - usually best Without parents - role of premedication important
Induction
General methods of induction: inhalational intravenous (IV) intramuscular (IM) rectal oral
http://metrohealthanesthesia.com/edu/ped/induction1.htm
“Try on your mask” test
Timely praise & positive reinforcement
One monitor: YOU
Think but DON’T TALK about breathing
Talk boring soothing bedtime story talk
Slowly bring mask near patient from below
Start with 70%N2O in O2
Slowly add/increase major inhaled agent
InductionInhalational induction tips
http://metrohealthanesthesia.com/edu/ped/induction5.htm#inhalational
Induction
IM induction
Useful back-up plan
10% ketamine
4 mg/kg in deltoid (or thigh)
22 gauge needle
Onset within 4 minutes
http://metrohealthanesthesia.com/edu/ped/induction6.htm#im
epiglottis and tongue relatively largerglottis more superior, at level of C3 (vs C4 or 5)cricoid ring narrower than vocal cord aperture
until approx 8 years of age 4.5 mm in term neonate11 mm at 14 years
V. Technical Considerations - Airway differences – infant vs adult
http://metrohealthanesthesia.com/edu/ped/pedAir.htm
The appropriate uncuffed ETT size (age in years):
4 + (1/4)(age)
Subtract 0.5 for the appropriate cuffed ETT
E.g.: 4-year-old: uncuffed ETT = 4 + (1/4)4 = 5, so
cuffed ETT = 4.5
The appropriate depth of ETT insertion (cm) :
Over one year of age:
oral: 13 + (1/2)age
nasal: 15 + (1/2)age
Infants (weight in kg):
oral: 8 + (1/2)(weight)
nasal: 9 + (1/2)(weight)
Alternative Intubation Technics
Blind Nasotracheal Intubation
Digital Assisted Intubation
Fiberoptic Intubation
GlideScope Video Laryngoscope
Gum Elastic Bougie Assisted Intubation
LMA Assisted Fiberoptic Intubation
Retrograde Intubation
Wuscope Intubation
http://metrohealthanesthesia.com/edu/airway/difAir4.htm#intTechnics
LMA and LMA-Fiberoptic Technic Sizes
LMA size
Patient weight (kg)
ETT's (ID, mm) sizes recommended
Fiberscope size (mm)
1 < 6.5 3.0, 3.5 2.2, 2.7
1.5 5-10 3.5, 4.0 2.2, 2.7
2 10-20 4.0, 4.5 2.2, 2.7, 3.7
2.5 20-30 5.0 3.7, 4.0*
3 >30 6.0 4.0
4 >70 6.0, 6.5 4.0
5 >80 7.0 4.0
http://metrohealthanesthesia.com/edu/ped/lmatable.htm