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PEDIATRIC ANESTHESIA

PEDIATRIC SECRETS IN ANESTHESIA

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PEDIATRIC ANESTHESIA

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  1. PEDIATRIC ANESTHESIA HOSSAM M. ATEF ; MD

  2. Resources • Miller’s Anesthesia • Chapters 82, 83, 84 • - A Practice of Anesthesia for Infants & Children – Charles Cote • UPMC Presentation – Dr. James Cain • Stanford (pedsanesthesia.Stanford.edu) • Essentials of Pediatric Anesthesia – Alan David Kearne • Big Blue – Dr. Neils Jensen • The World Wide Web • OpenAnesthesiaKeywords

  3. Age Definitions • Neonates: 0-30 days old • Infants: 1 month to 1 year • Children: older than 1 year • Post-Conceptual Age (PCA): • Actual age – Pre-maturity (# weeks) • Used up until age 2 yo

  4. Learning Objectives • Review of Systems • Anesthetic Management Essentials • Pre-Term (PT) Neonatal Emergencies • Full-Term (FT) Neonatal Emergencies • Pediatric Issues

  5. Review Of Systems

  6. Neuro •  Skull rigidity (fontanelles) •  Cortical neurons (2 x 10^9) • Originate at 22 weeks, maximum at 29 weeks • Thalamacortical connections (until 5 yrs of life) • Sleep-wake at 32 weeks • PNS mature at 37 weeks •  Myelination • Reaches adult size at 40 kg / 11-12y •  BBB integrity

  7. Neuro • Spinal Cord & Dura

  8. Neuro •  Pain threshold •  Nerve endings / cm2 of skin •  Dorsal horn receptor fields, decrease at 42 weeks •  Dorsal horn receptor NMDA concentration • Immature inhibitory pathways • GABA depolarizes based on intracellular Cl- •  Hypersensitive until 2-6 months •  Increased stress response to pain (cortisol, glucagon, GH, aldosterone, O2 consumption/SpO2/PaO2 •  Autoregulation •  Sensitivity to respiratory depressant effect of opioids

  9. Neuro MAC  (0 months  9-12 months)  1.5x adult  (prematurity, 12 months +), ~linear • Exception: sevoflurane  NMJ maturity /  sensitivity • Shorter onset time offset by Vd • #1 utilizer of glucose

  10. Respiratory • Anatomical - Upper Airway •  Head •  Occiput •  Face and lower jaw •  Neck length •  Trachea length (~5 cm in newborns) •  Cords-to-carina length (2 cm) • Short trachea directed downwards and posteriorly • Right main bronchus less angled than left

  11. Respiratory • Anatomical - Upper Airway • Nostrils / nasal passages • Tongue size, length • Adenoids • Loose teeth or awkward dentition •  Floppy OR stiff horseshoe (U)-shaped epiglottis

  12. Respiratory • Larynx • Anterior & Cephalad • C3 preemie, C3-4 neonate, C5-6 in adult • Narrowest • Cricoid (neonate – age 10) • Edema • La Poiseuille’s law • Vocal cords (puberty) • Larynx has a gradually tapering shape

  13. Respiratory • Anatomical - Lower Airway • Alveoli increased starting 32 weeks GA, increased over 18 months, continues for 10 years •  Chest wall compliance • Stiffens ( compliance) thereafter •  Lung compliance, Compliance thereafter • Soft chest wall • Horizontal ribs • Circular chest •  Diaphragm endurance •  Type 1 muscle fibers

  14. Respiratory • Physiological Differences • Obligate nose breathers until 3-5 months • Abdominal > thoracic breathing • NO CHANGE (per / kg) • TLC (90 ml/kg) Dead space (2 ml/kg) • Vt (7-9 ml/kg) VC (90 ml/kg) • FRC •  RR • Controlled expiration (laryngeal braking) • Tonic activity of ventilatory muscles • PEEP helps during controlled ventilation

  15. Respiratory • Physiological Differences •  INCREASE • FA/FI due to •  RR  MV • Tissue/blood partition coefficients •  CO (opposite of adults due to VRG) • Closing volumes •  DECREASE • Blood: gas coefficient •  Solubility • FRC buffering capacity •  Time to desaturation • Hypoxic respiratory drive • Hypercapnic respiratory drive

  16. Cardiovascular •  Muscle fiber •  Myocyte glycogen • No change CO • Contractile elements  SV •  HR (dependent) • Vagal tone / Avoid bradycardia • Vagal stimulation with laryngoscopy • Hypoxemia • Sympathetic tone •  Baroreceptor tone and response

  17. Cardiovascular •  BP, MAP •  RR •  Incidence of hypoxemia-induced dysrhythmias (bradycardia) • Vessel-rich group as a % of CO •  PR, QRS intervals during infancy • T-wave inverted in V1-V4 until adolescence

  18. Hematologic • Hct: Preterm > Neonate > Infant • HbF breakdown, erythropoisis,  plasma volume • Erythropoesis shifts from liver to BM at 24wk GA • HbF: Leftward shift on oxyhemoglobin dissociation curve •  P50 (19 mmHg vs 26 mmHg) • Granulopoiesis occurs in BM •  Platelets over the few days but then return  to normal levels after the 1st week of life

  19. Temperature Regulation •  Body surface area : volume •  radiant heat loss) • Thin skin •  Subcutaneous body fat •  Shivering thresholds (i.e. occurs at lower temperatures) in children • Neonates do NOT shiver •  norepinephrine  brown adipose tissue metabolism • Found scapulae, mediastinum, kidneys, adrenal glands • Thermoregulatory center not well developed

  20. Hepatic / Metabolism • Homeostatic metabolism •  O2 consumption (7-8 ml/kg/min FT vs • 3-4 ml/kg/min Adult ; ~ 2x of adults) • Glucose consumption (6-7 mg/kg/min PT vs • 4-5 FT vs 3 mg/kg/min Adult) • Drug metabolism until 3 months •  Hepatic size/blood flow : body weight ( with age) • CyP450 (adult at 1 mo)(Enzyme systems not induced) • Oncotic proteins (e.g. albumin)  Protein binding

  21. Hepatic / Metabolism •  bilirubin load •  Hepatic cell uptake & conjugation • reaches adult levels at 6 months. •  Pseudocholinesterase activity until 6 months •  Phase II block after succinylcholine •  Hepatic glycogen (FT 30 mg/dl vs infant 40 mg/dl) •  Gluconeogenesis (primary in muscles) •  Glycogenesis / g liver mass •  Blood glucose d/rt use •  With maternal DM (insulin Ab) • Utilizer: Brain > Heart, ~ adult use at 40kg • Fetal calcium stores (until 3mo)

  22. Renal • Volume of distribution (water-soluble drugs) •  Diluting ability •  Creatinine clearance •  GFR (67% reduction) • Reaches adult values by 1-2 years of age • Tubular function by 7th month • More decreased by hypoxia, hypothermia, and CHF

  23. Renal  Urine concentrating ability (6 months)  Glucose excretion FeNa Responsible for 10% loss of body weight over first 7-19 days Followed by  Sodium excretion  H+ excretion  Morphine metabolite excretion  HCO3- resorption threshold  TBW (70-75%) , ECF  TBW with age 1 mo: 75%, 1 yr: 70%, 10 yrs: 65%

  24. Anesthetic Management

  25. GI •  pH on DOL 1  normal on DOL 2+ • Delayed gastric emptying • Delayed absorption •  GERD • Coordination of swallowing with respiration occurs at 4-5 months

  26. Face Masks & Circuits

  27. Mapleson Circuits Adult, SV • FGF • Spont: 2 -3x / • minute ventilation • PPV: 220 ml/kg • (up to 20 kg) Adult + Pediatric, CV Pediatric, SV

  28. Pre-Operative Assessment

  29. Pediatric Pain Assessment NRS 8 yo + Wong-Baker Scale 3 yo + FLACC 2 mo – 7 yo

  30. NPO Time • Bottled milk, formula, feeds = SOLIDS • Clear liquids 2 hours before surgery: • NO CHANGE in Gastric volume & PH

  31. Estimating Weight /Height • Weight • Always have all medications calculated out for patients < 20 kg • Estimating weight • 2 x (age + 4) • (2 x age) + 8 or 9 Breslow Tape (ED)

  32. Monitors Anchor to arm to prevent hyperextension Pre-ductal vs . Post-ductal considerations

  33. Monitors Pediatric Vital Signs (VS)

  34. Venous Air Embolism • (In order of sensitivity) • TEE • Doppler (left or right parasternal, between 2nd and 3rd rib, mill wheel murmur) • ETN2, ETCO2 and/or PA pressure • Cardiac output and/or CVP • Blood pressure, EKG (RV Strain pattern, ST depression), stethoscope (least sensitive)

  35. Preventing Heat Loss

  36. Table Setup

  37. Developmental Milestones

  38. Developmental Milestones

  39. Developmental Milestones

  40. Perioperative Fluid Replacement • 1st 0-10 kg → 4 cc/kg/hr • 2nd 10-20 kg → 2 cc/kg/hr • 20 kg → 1 cc/kg/hr Calculate preoperative deficit • Replace 50% first hour • Replace 25% second hour • Replace 25% third hour • Minor surgery → additional 2 cc/kg/hr • Major surgery → up to additional 10 cc/kg/hr • Transfusion threshold: Hgb 9-10 ( O2 consumption)

  41. Estimated Allowable Blood Loss(EBL) • Blood volume • Premies → 95 ml/kg • Term neonates → 90 ml/kg • Up to 1 year → 80 ml/kg • > 1 year old → 70 ml/kg • EABL → wt kg x est blood vol x (starting Hct- allowable Hct) / aveHct

  42. Airway Management • Water volume • Laryngoscopy • Blades • – Straight most common • Miller Phillips Wis-Hipple • Curved available • Fiberoptic • Bullard Glide

  43. ETT Tube Sizing • ETT tube length • Neonates: 7 – 9cm • Other • Height (cm) / 10 • Weight (kg) / 12 • (Age / 2) + 12 • ETT tube size • < 2 yrs: • 2.5 – 3 (premature) • 3 – 3.5 (neonate – 6 month) • 3.5 – 4.0 (6 month – 1 year) • 4.0 – 5.0 (1 – 2 year) • > 2 yrs: • (Age / 4) • +4 (cuffed) • +4.5 (uncuffed)

  44. Laryngoscopy • Neonate to 3 months: Miller 0 • 3 months to 18 months: Miller 1 • 18 month- 3 years: Miller 1.5, Mac 1, Wisc 1.5 • 3-5 years: Miller 1.5, Mac 2, Wisc 1.5 • >5 years: Miller 2, Mac 2-3 Straight blade necessary for neonates and young infants, can be used as a Mac blade

  45. LMA Sizing iGel

  46. Medication Management • Higher doses needed for younger rather than older children • Hepatic blood flow • Decreased filtration until 3-4 months • Decreased CYP450 activity • Increased Vd • Decreased pseudocholinesterase activity

  47. Airway Management Table

  48. Medication Management

  49. Medication Management ç

  50. Medication Management

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