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Neonatal Considerations Principles-II Juan E. Gonzalez, CRNA, MS, ARNP Clinical Assistant Professor based on prior lectu

Neonatal Considerations Principles-II Juan E. Gonzalez, CRNA, MS, ARNP Clinical Assistant Professor based on prior lecture by: John P. McDonough, CRNA, Ed.D., ARNP Professor & Director Anesthesiology Nursing Classifications Neonate Less than 30 days of age Infant 1-12 months of age

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Neonatal Considerations Principles-II Juan E. Gonzalez, CRNA, MS, ARNP Clinical Assistant Professor based on prior lectu

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  1. Neonatal ConsiderationsPrinciples-IIJuan E. Gonzalez, CRNA, MS, ARNPClinical Assistant Professorbased on prior lecture by: John P. McDonough, CRNA, Ed.D., ARNP Professor & Director Anesthesiology Nursing

  2. Classifications • Neonate • Less than 30 days of age • Infant • 1-12 months of age • Children • 1-12 yrs of age

  3. What makes them different? • Physiologic (compared to adults) • CO is heart rate dependent (CO=SVxHR), ↑ HR, ↓ BP, ↑ RR, ↓ lung compliance, ↑chest wall compliance, ↑BSA/wt ratio, ↑ total body water content • Fetus 90%Body Water • Preterm 80% Body Water • Full-term 70% Body Water • 6-12 mo 60% Body Water (similar to adults) • ↑ECF • At birth 45% of body wt is ECF • At 2mo 30% of body wt is ECF • At 6 y/o 20% of body wt is ECF • Adults: 16-18% of body wt is ECF

  4. What makes them different? • Anatomic: • ↓ LV compliance, residual fetal circulation, difficult A&V cannulation, large head & tongue, narrow nasal passages, anterior & cephalad larynx, long epiglottis, short trachea & neck (obligate nasal breathers until 5 months of age) • prominent adenoids & tonsils, ↑ resistance to airflow

  5. What makes them different? • Pharmacologic: • Immature hepatic biotransformation • Immature renal function • ↓protein binding (higher free drug in plama-> reduced drug metabolism/delayed elimination) • ↑Vd for (H2O soluble drugs) -> higher loading dose required to achieve desired clinical response • Immature NMJ (infants less than 6mo have ½ pseudocholinesterase activity than older kids. However redistribution of SUX from small muscle mass to ↑ ECF volume appears to terminate SUX quickly). • require ↑ SUX (pedi IV dose is 2mg/kg) • smaller proportion of fat & muscle stores

  6. Cardiovascular • Bradycardia →↓ CO (↓ B/P, death) • Parasympathetic activation, anesthetic overdose, hypoxia • Sympathetic NS & baroreceptors not fully developed • ↓ catecholamine stores • ↓ circulating volume → ↓ B/P w/o ↓ HR • Problems with B/P monitoring

  7. Fetal Circulation • Ductus arteriosus • Rt radial artery for monitoring • Foramen ovale • Ductus venosus

  8. Fetal Circulation • Placenta (gets ½ CO) does resp gas exchange Lungs get low blood flow (pulm & Syst circulations are parallel) 2 cardiac shunts: -Foramen ovale -Ductus Arteriosus

  9. Fetal Circulation in Motion • Well O2-blood from placenta (80% O2 sat) mixes with venous blood returning from lower body (25% O2 sat) & flow via IVC into RA • RA anatomy preferentially directs blood from IVC (67% O2 sat) thru FO into LA (right-to-left shunt) • LA blood goes to LV & it is pumped to upper body (mainly heart/brain) • Poor O2-blood from upper body returns via SVC to RA

  10. Fetal Circulation in Motion • RA anatomy preferentially directs flow from SVC into RV • RV blood is pumped into PA • Because of high PVR, 95% of blood ejected from RV (60% O2 sat) is shunted across the Ductus Arteriosus into the descending Aorta and back to the placenta & lower body

  11. Fetal Circulation in Motion • Parallel circulation results in unequal ventricular flows • RV ejects 2/3 of combined ventricular outputs • LV ejects only 1/3 • ½ of Well O2-blood in the umbilical vein can pass directly to the heart via the Ductus Venosus, bypassing the Liver • The remainder of of blood from placenta mixes with blood from the Portal vein and goes to the liver first (important in allowing rapid hepatic degradation of drugs/toxins from maternal circulation)

  12. Fetal Circulation

  13. Transition to Normal Circulation • At term, fetal lungs are developed but contain 90mL of plasma ultrafiltrate • This fluid is squeezed out during birth by forces of pelvic muscles and the vagina • Remaining fluid absorbed by pulm capillaries & lymphatics • Small (preterm) neonates & fullterms via C/S do not benefit from the vaginal squeeze & may have Transient Tachypnea of the Newborn

  14. Transition to Normal Circulation • Mild hypoxia, acidosis and sensory stimulation (cord clamping, pain, touch, noise) help initiate & sustain respirations • Outward recoil of of the chest at delivery aids in filling the lungs with air • Lung expansion increases PAO2 & PaO2 & decrease PVR • ↑PaO2  PA vasodilation↑Pulm blood flow ↑blood to Left heart ↑press LAfunctional closure FO (may take months) • ↑PaO2  Closure DA (other chemical mediators Ach, bradykinin, prostaglandins) (not closed until 2-3 wks) • Overall result  elimination of right-to-left shunt • First few days of life, hypoxia or acidosis can prevent or reverse these changes  persistence of (or return to) fetal circulation • Positive feedback (more of the same thing) vicious cycle is established  R-to-L shunt promotes hypoxemia & acidosis  more R-to-L shunt (via FO, DA or both). If cycle is not broken soon  fetal demise

  15. Transition to Normal Circulation

  16. Respiratory • Vt (6-8mL/kg), and dead space/Vt (0.3mL/kg) are same as adults • Small/limited number of alveoli (↓lung compliance) • Cartilaginous rib cage (↑chest wall compliance) Chest wall collapse during inspiration & low residual lung volume @ expiration (diaphragmatic breathing) ↓FRC (↓O2 reserve during apnea & predisposition to atelectasis/hypoxemia) • Hypoxic & hypercapnic drives not well developed • High Alveolar Ventilation & Low FRC ↑VE/FRC & high blood flow to VRG organs  rapid rise in alveolar anesthetic concentration (rapid induction & recovery from GA) rapid rise in FA/FI (fractional [alveolar]/fractional [inspired]) • MAC is higher in infants than in neonates for VAA

  17. Respiratory (con’t) • During spontaneous breathing resistance is an issue • Unidirectional valves, tubes, absorber • Some use Mapleson-D or Bain system • Semi-closed circle OK if ventilation is controlled • Circuit pressure monitoring required • End-tidal CO2 monitoring required • Use ventilators with caution • Circuit (length & compliance) can be an issue

  18. Respiratory System • Head & tongue problems • Obligate nasal breathers • Larynx at C-4 level • Cricoid cartilage narrowest point • small amount of edema = big problems • Right size ETT indicated by easy passage and gas leak at 10-25 cm H2O pressure (age/4)+4 = ETT size in mm

  19. pre-term to 1 year: range 2.5-4.0 uncuffed Over 1 year: age/4 + 4 is tube size. Have +/- 1/2 size ready. Depth = 3x tube size 123-789 rule:  1 kg, depth is 7 cm, etc ETT Placement

  20. PEDI “OMEGA”-SHAPED ADULT EPIGLOTISEPIGLOTIS

  21. ADULT PEDIATRIC

  22. Effect of 1mm edema

  23. Age related changes in VS(range varies 25-50%) • Neonate • RR=40, HR=140, B/P=65/40 • 12 months • RR=30, HR=120, B/P=95/60 • 3 years • RR=25, HR=100, B/P=100/70 • 12 years • RR=20, HR=80, B/P=110/60

  24. Metabolism & Temp Regulation • Metabolism & its associated parameters (O2 consumption, CO2 production, alveolar ventilation) correlate better with BSA rather than weight • Thin skin, low fat, ↑BSA = ↑heat loss (made worse with cold OR, wound exposure, IV fluids, dry anesthetic gases, & direct effect of anesthesia on temp regulation) • Hypothermia is a serious problem • delayed awakening, cardiac irritability, ↓ resp, ↑pulmonary VR, altered drug responses • Nonshivering thermogenesis (major mechanism of heat production) • metabolism of brown fat (VAA inhibits this!!)

  25. Temperature Control • Warm OR (> 25° C) • Warm and humidify inspired gases • Warming blanket/lights • Warming fluids

  26. Brown Fat

  27. NPO Requirements • Healthy neonates w/o risk for delayed emptying or aspiration • Formula until 6-8 hrs preinduction • Clear liquids 2-3 hrs preinduction

  28. Renal function • Healthy infants have normal renal function by age 6 months • NOT SO in premature neonates: • impaired Na+ retention, glucose excretion, HCO3 reabsorption & ↓ creatinine cl • glucose excretion problems often offset by hypoglycemia tendency • Hypoglycemia in neonates = < 30mg/dL

  29. Fluid Requirements • Neonate TBWC = 70-75% (adult=50-60%) • Maintenance (4,2,1 RULE) • 4mL/kg/hr for 1st 10 kg of wt, 2mL/kg/hr for 2nd 10kg of wt, 1mL/kg/hr for reminder kgs of wt • D5 ½ NS (with KCl 20 meq/L) • D5 ¼ NS may be better • Watch for: • prominent veins, flushed skin, ↓ Na+ , loss of eyelid folds • Deficits • Replace 50% of Deficit during1st hr, 25% 2nd hr, 25% 3rd hr • ½ NS or lactated Ringer’s

  30. Blood Loss Replacement • Blood loss • blood volume: 100ml/kg in premmies, 80-90 ml/kg at full term, Hct 55% falling to 30% at 3 months, 76% HgbF at birth, 100 HgbA by 6 months • crystalloid 3:1 replacement • colloid 1:1 replacement • continue until lower limit reached • Sick neonates and premmies Hct ~ 40-50%

  31. Third Space Loss • 2 mL/kg/hr • atraumatic surgery • 6-10 mL/kg/hr • traumatic surgery

  32. Total Fluid Replacement • Preoperative fluid deficit, plus • Maintenance fluid, plus • Blood loss, plus • Third space loss • ? other losses

  33. Recent URIs • “runny nose” • ? infectious process, ? allergic rhinitis • Viral infections within 2-4 weeks of GETA = ↑ risk wheezing, hypoxemia, atelectasis, laryngospasm

  34. Premeds • Quick estimate of weight • 50th percentile wt (kg) = (agex2) + 9 • Probably no sedation for neonates • except cardiac surgery where MS 0.1 mg/kg may be helpful • Versed (0.5-1.0mg/kg PO) • Chloral hydrate (Notec) 65-100mg/kg PO/PR • Ped PO cocktail • Versed 0.5mg/kg, Ketamine 5mg/kg, Glyco 0.02mg/kg for drying • Ped IM cocktail • Versed 0.01mg/kg, Ketamine 3mg/kg, Glyco 0.01mg/kg drying

  35. Nonvolatile Anesthetics • Barbiturates & Opioids more potent in neonates than adults • Possible easier entry across BBB • Dec metabolic capability • Inc sensitivity of Resp Center • MSO4 should be used with caution (if at all) in neonates b/c hepatic conjugation is reduced & renal clearance of MSO4 metabolites is decreased • More resistance to ketamine • Cytochrome p-450 pathway is mature at 1 month • Propofol drip higher than adults • (150-250mcg/kg/min) high Vd & inc Clearance

  36. Induction • Inhalation • Sevoflurane often preferred • Start with 70% N2O & 30% O2 • Begin VAA, ↑ by 0.5% q3-5 breaths • IV (do not attempt IV until pedi is well anesthetized via mask induction or  laryngospasm • thiopental 3 mg/kg (neonates) • Muscle relaxant if needed (more susceptible than adults to cardiac arrhythmias, hyperkalemia, rhabdomyolysis, masseter spasm & MH aftes SUX.) If cardiac arrest after SUX takes place, assume hyperkalemia and Tx as such • IM • ketamine 5-10 mg/kg

  37. Two Interesting Scenarios • Retinopathy of Prematurity (ROP) deserves special attention. ROP is a fibrovascular proliferation overlying the retina. O2 administration should be monitored with pulse Ox or transcutaneous O2 analysis (especially infants younger than 44wks postconception) • Scoliosis pt due to Muscular dystrophy are predisposed to MH, cardiac dysrhythmias, & untoward effects of SUX (↑K, myoglobinuria, sustained muscular contractures)

  38. Emergence • Spontaneous ventilation, adequate Vt & rate • Reversal of residual muscle paralysis • Deep vs. awake extubation?? to avoid laryngospasm • “Purposeful movements” (eg. reaching for ETT) is key phrase for assessing readiness for extubation on pedi since they DO NOT FOLLOW COMMANDS!! • If Pedi/Neo ICU are far away, carry emergency intubation equipment for reintubation readiness • Postintubation croup (1-4yr) is associated with repeated intubation attempts, large ETT, prolonged Sx, head/neck Sx, excessive movement of ETT

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