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 Fetal circulation and changes at birth Anatomical differences in the airway, head and spinal cord from the adult Anatomical differences in the airway, head and spinal cord from the adult Physiological differences from the adult Physiological differences from the adult Haematological and biochemical changes with age Haematological and biochemical changes with age Estimation of blood volume Estimation of blood volume

Fetal circulation Ductus venosus Ductus venosus Foramen ovale Foramen ovale Ductus arteriosus Ductus arteriosus

Changes at birth

First breath generates negative pressure First breath generates negative pressure ↑ FRC ↓ PVR ↑ FRC ↓ PVR Blood flows from right ventricle through lungs Blood flows from right ventricle through lungs ↑ SVR with clamping of umbilical vessels ↑ SVR with clamping of umbilical vessels Reversal of right to left flow through DA Reversal of right to left flow through DA Oxygen and ↓ PGE 2 stimulates ductal constriction Oxygen and ↓ PGE 2 stimulates ductal constriction ↑ LAP and ↑ SVR cause closure of the FO ↑ LAP and ↑ SVR cause closure of the FO DV closes passively as flow ceases DV closes passively as flow ceases

Fetal haemoglobin 2 ά chains and 2 λ chains 2 ά chains and 2 λ chains Binds 2,3-DPG less avidly than HbA Binds 2,3-DPG less avidly than HbA Shifts ODC to left (P KPa) Shifts ODC to left (P KPa) Favours O 2 transfer from mother to fetus Favours O 2 transfer from mother to fetus Gives up more O 2 to fetal tissues than HbA Gives up more O 2 to fetal tissues than HbA 80% circulating Hb at birth 80% circulating Hb at birth Replaced within 3-5months by HbA Replaced within 3-5months by HbA

Neonatal physiology CVS CVS RV=LV at birth RV=LV at birth ↑ ratio of connective to contractile tissue ↑ ratio of connective to contractile tissue Flat Starling curve Flat Starling curve Fixed SV Fixed SV Lungs Lungs Bronchial tree fully developed Alveoli develop fully after birth Compliant chest wall Diaphragmatic breathing Less ventilatory responses to PaO 2 and PaCO 2

Neonatal physiology Kidneys Kidneys No of nephrons complete by birth No of nephrons complete by birth RBF increases from 5% CO at birth to 20% at 1 month RBF increases from 5% CO at birth to 20% at 1 month Low GFR; adult by 2 years Low GFR; adult by 2 years Liver Liver Immature enzymes Immature enzymes CNS CNS Pathways complete at birth Temp control Temp control High SA to body weight ratio Less SC fat Non shivering thermogenesis

Paediatric anatomy and physiology Airway Airway Lungs Lungs CVS CVS BMR BMR CNS CNS Temp regulation Temp regulation Fluid balance Fluid balance Pharmacology Pharmacology

Paediatric Airway

Paediatric respiratory system Diaphragmatic Diaphragmatic Neonates – obligate nasal breathers Neonates – obligate nasal breathers Increased respiratory rate Increased respiratory rate Very compliant chest wall – horizontal ribs Very compliant chest wall – horizontal ribs CC > FRC in normal breathing CC > FRC in normal breathing Ventilatory response to CO 2 reduced Ventilatory response to CO 2 reduced BMR/O 2 consumption high BMR/O 2 consumption high

Paediatric cardiovascular system AGE SYSTOLIC BP (mmHg) DIASTOLIC BP (mmHg) HEART RATE Preterm4525>120 Birth6035>120 Neonate months year years years

Paediatric nervous system Spinal cord ends L3; recedes by adolescence Spinal cord ends L3; recedes by adolescence Immature BBB Immature BBB Pronounced vagal reflexes Pronounced vagal reflexes

Fluid balance Blood volumes Blood volumes Birth: 90ml/kg Birth: 90ml/kg Child: 80ml/kg Child: 80ml/kg Teenager: 70ml/kg Teenager: 70ml/kg Maintenance fluid requirements Maintenance fluid requirements 4ml/kg/h for first 10kg 4ml/kg/h for first 10kg 2ml/kg/h for next 10kg 2ml/kg/h for next 10kg 1ml/kg/h for each kg after 1ml/kg/h for each kg after

Pharmacokinetics/dynamics Lower plasma albumin levels up to 1 year Lower plasma albumin levels up to 1 year Renal and hepatic immaturity Renal and hepatic immaturity MAC increased in neonates MAC increased in neonates Neonates sensitive to NMB; more resistant to sux Neonates sensitive to NMB; more resistant to sux

Haematological changes with age Hb Hb Birth: 14-22g/l, 3-6 months: 11-14, 6-12 years: Birth: 14-22g/l, 3-6 months: 11-14, 6-12 years: WCC WCC Birth: x10 9 /l, 3-6 months: 6-18, 6-12: years Birth: x10 9 /l, 3-6 months: 6-18, 6-12: years Platelets – fairly stable between x10 9 /l Platelets – fairly stable between x10 9 /l All vit K dependant clotting factors are low at birth – reach adult values by 6 months 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 Albumin: low up to 1 year Bilirubin: high at birth (17-170umol/l), normal adult levels by 1 month Bilirubin: high at birth (17-170umol/l), normal adult levels by 1 month Ca 2+ : low neonate ( mmol/l), normal adult levels by 1 year Ca 2+ : low neonate ( mmol/l), normal adult levels by 1 year T 4 : high neonate, falls to adult range steadily up to 10 years T 4 : high neonate, falls to adult range steadily up to 10 years

Any questions?

Summary Fetal circulation and changes at birth Fetal circulation and changes at birth Anatomical differences in the airway, head and spinal cord from the adult Anatomical differences in the airway, head and spinal cord from the adult Physiological differences from the adult Physiological differences from the adult Haematological and biochemical changes with age Haematological and biochemical changes with age Estimation of blood volume Estimation of blood volume