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Neonatal and Paediatric Anatomy and Physiology

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Title: Neonatal and Paediatric Anatomy and Physiology


1
Neonatal and Paediatric Anatomy and Physiology
  • Dr Alison Chalmers
  • Consultant Anaesthetist
  • Queen Victoria Hospital

2
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

3
Fetal circulation
  • Ductus venosus
  • Foramen ovale
  • Ductus arteriosus

4
Changes at birth
5
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

6
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

7
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

8
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

9
Paediatric anatomy and physiology
  • Airway
  • Lungs
  • CVS
  • BMR
  • CNS
  • Temp regulation
  • Fluid balance
  • Pharmacology

10
Paediatric Airway
11
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

12
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
13
Paediatric nervous system
  • Spinal cord ends L3 recedes by adolescence
  • Immature BBB
  • Pronounced vagal reflexes

14
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

15
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

16
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

17
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

18
Any questions?
19
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
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