Pediatric Anesthesia

Greg Gordon MD

13 Mar 09

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 Management

1. Maintenance Fluid

2. Replace Deficit

3. Replace Ongoing Losses

Perioperative Fluid ManagementChoice 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

• 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

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

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

For more cool stuff about Pediatric Anesthesia

check out the lessons and quizzes at

http://metrohealthanesthesia.com/edu/ped/peds1.htm