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 care of 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 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. I. Preop Preparation

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 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 NOT 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

Clear liquids2 hours Breast milk4 hours Infant formula6 hours Light meal6 hours Regular meal8 hours Guidelines apply to healthy patients undergoing elective proceures. They do not guarantee complete gastric emptying. Reference: Anesthesiology 90: , 1999 Anesthesiology 90: , 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 (%) ECF ICF Fat

immature function at birth:  GFR (‘til 2 years old)  concentrating capacity  Na reabsorption  HCO3 /H exchange  free H2O clearance  urinary loss of K+, Cl- Infan t 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 D10W Day D10 1/2 NS >Day D5-D10 1/4 NS Older Child: 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

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 cc/kg + EBL 1st hour Longer and Complex Procedures rule hypovolemia: 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 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)Sys/Dias mean / / / /4050 Age (months) Sys/Dias mean 1 85/ / / / /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

Normal heart rate Age (days) Rate Age (months) Rate Age (years) Rate

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) NeonateAdult Cardiac output HR dependentSV & HR dependent Starling responselimitednormal Compliancelessnormal Afterload compensation limitedeffective Ventric interdependencehighrelatively 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 cmH 2 O needed to overcome high surface forces to introduce air into liquid-filled lungs adequate surfactant essential for smooth transition Elevated P a O 2 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 VO 2 /kg = 2 x adult value => ventilatory requirement per unit lung volume is increased less reserve more rapid drop in SpO 2 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) 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 (p a O 2 < 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 CO 2 response curve

Pediatric Respiratory Physiology – Assessment of Respiratory Control Effects of anesthesia on respiratory control Shift CO 2 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 cmH 2 O 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 months increases to adult 90 ml/kg by age 5 may be only 15% of TLC in young infants under GA plus 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 and 35-45% in 6 to 18 year-olds In young infants under general anesthesia especially with muscle relaxants FRC may = only TLC FRC may be < closing capacity leading to small airway closure atelectasis V/Q mismatch declining SpO 2

Pediatric Respiratory Physiology – Lung Volumes and Mechanics of Breathing General anesthesia, FRC and PEEP Mean PEEP to resore FRC to normal infants < 6 months6 cm H 2 O children6-12 cm H 2 O 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/πr 4 where R resistance l length η viscosity For turbulent flow: R α 1/r 5 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 PhysiologyOxygen transport (Bohr effect) = 27, normal adult (19, fetus/newborn)

Pediatric Respiratory PhysiologyOxygen transport If SpO 2 = 91 then = PaO 2 = Adult 60 6 months66 6 weeks 55 6 hours 41

Pediatric Respiratory PhysiologyOxygen transport Implications for blood transfusion older infants may tolerate somewhat lower Hgb levels at which neonates ought certainly be transfused P 50 Hgb for equivalent tissue oxygen delivery Adult > 3 months < 2 months

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 cmH 2 O ) alleviates Hemoglobin oxygen affinity changes dramatically first months of life Hgb F – low P 50 (19) P 50 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

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

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 mg/kg respectively PO induction of GA: mg/kg EMLA cream Eutectic mixture of lidocaine and prilocaine For cutaneous application one hour preop IV. Induction - premedication options 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

First Warm the OR, especially for young infants Complete the pre-anesthesia checklist. pre-anesthesia checklist Two main categories of pediatric anesthetic induction: Parent(s) present - usually best Without parents - role of premedication importantpremedication Induction General methods of induction: inhalational intravenous (IV) intramuscular (IM) rectal oral

“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%N 2 O in O 2 Slowly add/increase major inhaled agent Induction Inhalational induction tips

Induction IM induction Useful back-up plan 10% ketamine 4 mg/kg in deltoid (or thigh) 22 gauge needle Onset within 4 minutes

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 V. Technical Considerations - Airway differences – infant vs adult

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

LMA and LMA-Fiberoptic Technic Sizes LMA size Patient weight (kg) ETT's (ID, mm) sizes recommended Fiberscope size (mm) 1< , , , , , , 2.7, , 4.0* 3> >706.0, >

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