Neonatal and Paediatric Anatomy and Physiology

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Neonatal and Paediatric Anatomy and Physiology

• Dr Alison Chalmers
• Consultant Anaesthetist
• Queen Victoria Hospital

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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

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Fetal circulation

• Ductus venosus
• Foramen ovale
• Ductus arteriosus

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Changes at birth
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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

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Fetal haemoglobin

• 2 ? chains and 2 ? 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

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Neonatal physiology

• CVS
• RVLV 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

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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

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Paediatric anatomy and physiology

• Airway
• Lungs
• CVS
• BMR
• CNS
• Temp regulation
• Fluid balance
• Pharmacology

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Paediatric Airway
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Paediatric respiratory system

• Diaphragmatic
• Neonates obligate nasal breathers
• Increased respiratory rate
• Very compliant chest wall horizontal ribs
• CC gt FRC in normal breathing
• Ventilatory response to CO2 reduced
• BMR/O2 consumption high

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Paediatric cardiovascular system
AGE SYSTOLIC BP (mmHg) DIASTOLIC BP (mmHg) HEART RATE
Preterm 45 25 gt120
Birth 60 35 gt120
Neonate 70-80 40-50 120-150
3-6 months 80-90 50-60 120-140
1 year 90-100 60-80 110-130
5 years 95-100 50-80 90-100
12 years 110-120 60-70 80-100
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Paediatric nervous system

• Spinal cord ends L3 recedes by adolescence
• Immature BBB
• Pronounced vagal reflexes

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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

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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

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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

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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

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Any questions?
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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