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Pediatric Anesthesia

Pediatric Anesthesia. 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

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Pediatric Anesthesia

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  1. Pediatric Anesthesia

  2. 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

  3. 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.

  4. 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

  5. Useful for all of us, from infancy to old age!

  6. Minimum Fasting Periods: Guidelines apply to healthy patients undergoing elective proceures. They do not guarantee complete gastric emptying. Reference: Anesthesiology 90:896-905, 1999

  7. Offer clear liquids up to 2 hours before induction: • reduces hunger, irritability • preserves hydration •  risk of hypoglycemia

  8. Preanesthesia Checklist The only way to definitely confirm readiness!USE A PREANESTHESIA CHECKLIST

  9. 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

  10. 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-

  11. What it means: Newborn kidney has limited capacity to compensate for volume excess or volume depletion

  12. Neonates: • limited hepatic glycogen stores risk of hypoglycemia provide 5%-10% dextrose maintenance supplemental insulin prn

  13.  fluid requirement greater BSA:mass ratio other factors: radiant warmers fever illness injury thin, immature skin

  14. 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

  15. 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

  16. Perioperative Fluid Management • Maintenance Fluid • Replace Deficit • Replace Ongoing Losses

  17. Perioperative Fluid Management Choice of Fluids Isotonic Crystalloids • best replacement fluid Hypotonic Fluids - DANGER • can cause hyponatremia

  18. Is intraoperative glucose necessary? maybe, sometimes

  19. Effects of Intraop Glucose : • intraop hyperglycemia • hyperosmolality • osmotic diuresis • worsen neurologic outcome • after cerebral ischemia

  20. 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

  21. 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)

  22. 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

  23. 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)->

  24. 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

  25. 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

  26. III. Pediatric cardiopulmonary physiology 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

  27. 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

  28. 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 50-110 12-16 50-100

  29. The Newborn Heart • Near peak of Starling curve • Stroke volume relatively fixed • C.O. relatively heart rate dependent

  30. III. Pediatric cardiopulmonary physiology 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

  31. 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

  32. 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

  33. 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

  34. 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

  35. 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)

  36. 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

  37. Pediatric Respiratory Physiology – Assessment of Respiratory Control CO2 response curve

  38. 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)

  39. 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

  40. 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

  41. 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)

  42. 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%

  43. Pediatric Respiratory Physiology Oxygen transport (Bohr effect) = 27, normal adult(19, fetus/newborn)

  44. Pediatric Respiratory Physiology Oxygen transport If SpO2 = 91 then = PaO2 = Adult 60 6 months 66 6 weeks 55 6 hours 41

  45. Pediatric Respiratory Physiology 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

  46. 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

  47. 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

  48. 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

  49. 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

  50. 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

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