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Neonatal and Paediatric Anatomy and Physiology. Dr Alison Chalmers Consultant Anaesthetist Queen Victoria Hospital. What you need to know. Fetal circulation and changes at birth Anatomical differences in the airway, head and spinal cord from the adult
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Neonatal and Paediatric Anatomy and Physiology Dr Alison Chalmers Consultant Anaesthetist Queen Victoria Hospital
What you need to know • Fetal circulation and changes at birth • Anatomical differences in the airway, head and spinal cord from the adult • Physiological differences from the adult • Haematological and biochemical changes with age • Estimation of blood volume
Ductus venosus Foramen ovale Ductus arteriosus Fetal circulation
Changes at birth • First breath generates negative pressure • ↑ FRC ↓ PVR • Blood flows from right ventricle through lungs • ↑ SVR with clamping of umbilical vessels • Reversal of right to left flow through DA • Oxygen and ↓ PGE2 stimulates ductal constriction • ↑ LAP and ↑ SVR cause closure of the FO • DV closes passively as flow ceases
Fetal haemoglobin • 2 ά chains and 2 λ chains • Binds 2,3-DPG less avidly than HbA • Shifts ODC to left (P50 2.4KPa) • Favours O2 transfer from mother to fetus • Gives up more O2 to fetal tissues than HbA • 80% circulating Hb at birth • Replaced within 3-5months by HbA
CVS RV=LV at birth ↑ ratio of connective to contractile tissue Flat Starling curve Fixed SV Lungs Bronchial tree fully developed Alveoli develop fully after birth Compliant chest wall Diaphragmatic breathing Less ventilatory responses to PaO2 and PaCO2 Neonatal physiology
Kidneys No of nephrons complete by birth RBF increases from 5% CO at birth to 20% at 1 month Low GFR; adult by 2 years Liver Immature enzymes CNS Pathways complete at birth Temp control High SA to body weight ratio Less SC fat Non shivering thermogenesis Neonatal physiology
Airway Lungs CVS BMR CNS Temp regulation Fluid balance Pharmacology Paediatric anatomy and physiology
Paediatric respiratory system • Diaphragmatic • Neonates – obligate nasal breathers • Increased respiratory rate • Very compliant chest wall – horizontal ribs • CC > FRC in normal breathing • Ventilatory response to CO2 reduced • BMR/O2 consumption high
Paediatric nervous system • Spinal cord ends L3; recedes by adolescence • Immature BBB • Pronounced vagal reflexes
Fluid balance • Blood volumes • Birth: 90ml/kg • Child: 80ml/kg • Teenager: 70ml/kg • Maintenance fluid requirements • 4ml/kg/h for first 10kg • 2ml/kg/h for next 10kg • 1ml/kg/h for each kg after
Pharmacokinetics/dynamics • Lower plasma albumin levels up to 1 year • Renal and hepatic immaturity • MAC increased in neonates • Neonates sensitive to NMB; more resistant to sux
Haematological changes with age • Hb • Birth: 14-22g/l, 3-6 months: 11-14, 6-12 years: 11.5-15.5 • WCC • Birth: 10-26 x109/l, 3-6 months: 6-18, 6-12: years 5-13 • Platelets – fairly stable between 150-500 x109/l • All vit K dependant clotting factors are low at birth – reach adult values by 6 months
Biochemical changes with age • Albumin: low up to 1 year • Bilirubin: high at birth (17-170umol/l), normal adult levels by 1 month • Ca2+: low neonate (1.9-2.8mmol/l), normal adult levels by 1 year • T4: high neonate, falls to adult range steadily up to 10 years
Summary • Fetal circulation and changes at birth • Anatomical differences in the airway, head and spinal cord from the adult • Physiological differences from the adult • Haematological and biochemical changes with age • Estimation of blood volume