Download Pediatric Anesthesia

Pediatric Anesthesia
Greg Gordon MD
13 Mar 09
Objectives
Participants will be able to
explain the implications for anesthesia care
of selected characteristics unique to our
pediatric patients in the areas of:
•Preop preparation
•Fluids and electrolytes
•Cardiopulmonary physiology
•Induction technics
•Airway management technics
Ref: MetroHealthAnesthesia.com/edu/ped/peds1.htm
I. Preop Preparation
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 suggestion
modified 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.
Approach depends on age of patient:
Early infancy (neonate to about 7 months of age):
Parents are the primary focus
Comfortable separation in preop holding area usual
Later infancy to about 3 years:
Separation anxiety major
Surgery ought be outpatient
Selected parental presence
3 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 choices
Parental presence often helpful
Useful for all of us, from infancy to old age!
SAY
NOT
GOOD, YES
sleepy breeze
anesthetic vapors
pinch
hug your arm
stickers
will be neat! fun!
might get the giggles
make you laugh
feels funny
take a little nap
good job, good boy/girl
proud of you
cool, refreshing
nice little back rub
BAD, NO
gas
bad smell, stink, stench
bee sting
take blood pressure
won't hurt
don't cry
make you cry
feels bad
put you to sleep
don't be bad
cold solution
press on your back
Minimum Fasting Periods:
Clear liquids
Breast milk
Infant formula
Light meal
Regular meal
2 hours
4 hours
6 hours
6 hours
8 hours
Guidelines apply to healthy patients undergoing elective proceures.
They do not guarantee complete gastric emptying.
Reference: Anesthesiology 90:896-905, 1999
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
Total Water (%)
CHILD
ADULT
75
70
55-60
ECF
40
30
20
ICF
35
40
40
Fat
16
23
30
Infant kidneys
immature function at birth:
 GFR (‘til 2 years old)
 concentrating capacity
 Na reabsorption
 HCO3 /H exchange
 free H2O clearance
 urinary loss of K+, Cl-
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
Day 2
100
>Day 7
100-150 D5-D10 1/4 NS
Older Child:
D10W
D10 1/2 NS
4-2-1 rule
Perioperative Fluid
Management
1. Maintenance Fluid
2. Replace Deficit
3. Replace Ongoing Losses
Perioperative Fluid Management
Choice of Fluids
Isotonic Crystalloids
• best replacement fluid
Hypotonic Fluids - DANGER
• can cause hyponatremia
Is intraoperative
glucose
necessary?
maybe, sometimes
Effects of Intraop Glucose :
•
intraop hyperglycemia
•
hyperosmolality
•
osmotic diuresis
•
worsen neurologic outcome
after cerebral ischemia
Intraop glucose exceptions:
patients at risk for hypoglycemia:
• neonates and young infants
• debilitating chronic illness
• patients on parenteral nutrition
• neonates of diabetic mothers
• Beckwith-Wiedemann syndrome
• nesidioblastosis
Infant comes to OR with D10 infusing at 10 ml/hr.
What to do intraop?
Continue D10, but at
reduced rate (e.g., reduce by 50% to 5 ml/hr)
to compensate for hyperglycemic surgical stress;
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)->
III. Pediatric cardiopulmonary physiology
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
Neonatal myocardial function
Contractile elements comprise 30% (vs 60% adult) of newborn myocardium
Alpha isoform of tropomyosin predominates
more efficient binding for faster relaxation at faster heart rates
Relatively disorganized myocytes and myofibrils
Most of postnatal increase in myocardial mass due to
hypertrophy of existing myocytes
Diminished role of relatively disorganized sarcomplasmic reticulum (SR)
and greater role of Na-Ca channels in Ca flux so
greater dependence on extracellular Ca
may explain:
Increased sensitivity to
calcium channel blockers (e.g. verapamil)
hypocalcemia
digitalis
III. Pediatric cardiopulmonary physiology
Normal aortic pressures
Wt (Gm)
1000
2000
3000
4000
Age (months)
1
3
6
9
12
Sys/Dias
50/25
55/30
60/35
70/40
mean
35
40
50
50
Sys/Dias mean
85/65
50
90/65
50
90/65
50
90/65
55
90/65
55
III. Pediatric cardiopulmonary physiology
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
Normal heart rate
Age (days)
1-3
4-7
8-15
Rate
100-140
80-145
110-165
Age (months) Rate
0-1
100-180
1-3
110-180
3-12
100-180
Age (years)
1-3
3-5
5-9
9-12
12-16
Rate
100-180
60-150
60-130
50-110
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)
Cardiac output
Starling response
Compliance
Afterload compensation
Ventric interdependence
Neonate
HR dependent
limited
less
limited
high
Adult
SV & HR dependent
normal
normal
effective
relatively low
So:
Avoid (excessive) vasoconstriction
Maintain heart rate
Avoid 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 factors
extent of surgery
anesthesia technique
anemia
postop 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) muscles
persisting after removal of initial stimulus
More likely (decreased threshold) with
light anesthesia
hyperventilation with hypocapnia
Less likely (increased threshold) with
hypoventilation with hypercapnia
positive intrathoracic pressure
deep anesthesia
maybe 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
CO2 response curve
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
= 60 ml/kg infant
after 18 months
increases to
adult 90 ml/kg
by age 5
= 50% of TLC
may be only 15% of TLC in
young infants under GA
plus muscle relaxants
= 25% TLC
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 and
35-45% 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 normal
infants < 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:
where
R = 8lη/πr4
For turbulent flow:
R resistance
l length
η viscosity
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
6 months
6 weeks
6 hours
60
66
55
41
Pediatric Respiratory Physiology
P50
Oxygen transport
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
Implications for blood transfusion
older infants may tolerate somewhat lower Hgb levels at which
neonates ought certainly be transfused
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
IV. Induction - premedication options
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
http://metrohealthanesthesia.com/edu/ped/pedspreop6.htm
IV. Induction - premedication options
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!)
http://metrohealthanesthesia.com/edu/ped/pedspreop6.htm#premeds
IV. Induction - premedication options
ketamine
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
http://metrohealthanesthesia.com/edu/ped/pedspreop6.htm#ketamine
Induction
"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
http://metrohealthanesthesia.com/edu/ped/induction1.htm
Induction
First
Warm the OR, especially for young infants
Complete the pre-anesthesia checklist.
Two main categories of pediatric anesthetic induction:
Parent(s) present - usually best
Without parents - role of premedication important
General methods of induction:
inhalational
intravenous (IV)
intramuscular (IM)
rectal
oral
http://metrohealthanesthesia.com/edu/ped/induction1.htm
Induction
Inhalational induction tips
“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
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
V. Technical Considerations - Airway differences – infant vs adult
epiglottis and tongue relatively larger
glottis 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 neonate
11 mm at 14 years
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
For more cool stuff about
Pediatric Anesthesia
check out the lessons and quizzes at
http://metrohealthanesthesia.com/edu/ped/peds1.htm