Pediatric Anesthesia - PowerPoint PPT Presentation

Presentation Transcript

Pediatric Anesthesia

GregGordon 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!

Minimum Fasting Periods:

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 CHILD ADULT

Total Water (%) 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 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

Maintenance Fluid
Replace Deficit
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)->

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

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

Normal aortic pressures

Wt (Gm) Sys/Dias mean

1000 50/25 35

2000 55/30 40

3000 60/35 50

4000 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

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 50-110

12-16 50-100

The Newborn Heart

Near peak of Starling curve
Stroke volume relatively fixed
C.O. relatively heart rate dependent

Newborn myocardial physiology

Type I collagen (relatively rigid) predominates (vs type III in adult)

Neonate Adult

Cardiac output HR dependent SV & HR dependent

Starling response limited normal

Compliance less normal

Afterload compensation limited effective

Ventric interdependence high 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

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

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

Central apnea

apnea > 15 seconds or

briefer but associated with

bradycardia (HR<100)

cyanosis or

pallor

rare in full term

majority of prematures

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 CO2response 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

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

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 resistance

l length

η viscosity

R = 8lη/πr4

For turbulent flow: Rα1/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%

Oxygen transport

(Bohr effect)

= 27, normal adult(19, fetus/newborn)

Oxygen transport

If SpO2 = 91

then = PaO2 =

Adult 60

6 months 66

6 weeks 55

6 hours 41

Oxygen transport

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

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

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

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