Transcript Neonatal and Paediatric Anatomy and Physiology

Neonatal and Paediatric
Anatomy and Physiology
Dr Alison Chalmers
Consultant Anaesthetist
Queen Victoria Hospital
What you need to know
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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
Fetal circulation
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Ductus venosus
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Foramen ovale
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Ductus arteriosus
Changes at birth
Changes at birth
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First breath generates negative pressure
↑ FRC ↓ PVR
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↑ SVR with clamping of umbilical vessels
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Blood flows from right ventricle through lungs
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
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2 ά chains and 2 λ chains
Binds 2,3-DPG less avidly than HbA
Shifts ODC to left (P50 2.4KPa)
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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
Neonatal physiology
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CVS
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RV=LV at birth
↑ ratio of connective to
contractile tissue
Flat Starling curve
Fixed SV
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Lungs
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Bronchial tree fully
developed
Alveoli develop fully after
birth
Compliant chest wall
Diaphragmatic breathing
Less ventilatory responses
to PaO2 and PaCO2
Neonatal physiology
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Kidneys
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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
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Immature enzymes
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CNS
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Pathways complete at
birth
Temp control
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High SA to body
weight ratio
Less SC fat
Non shivering
thermogenesis
Paediatric anatomy and physiology
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Airway
Lungs
CVS
BMR
CNS
Temp regulation
Fluid balance
Pharmacology
Paediatric Airway
Paediatric respiratory system
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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 cardiovascular system
AGE
SYSTOLIC
BP (mmHg)
Preterm
45
Birth
60
Neonate
70-80
3-6 months 80-90
1 year
90-100
5 years
95-100
12 years
110-120
DIASTOLIC
BP (mmHg)
25
35
40-50
50-60
60-80
50-80
60-70
HEART
RATE
>120
>120
120-150
120-140
110-130
90-100
80-100
Paediatric nervous system
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Spinal cord ends L3; recedes by
adolescence
Immature BBB
Pronounced vagal reflexes
Fluid balance
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Blood volumes
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Birth: 90ml/kg
Child: 80ml/kg
Teenager: 70ml/kg
Maintenance fluid requirements
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4ml/kg/h for first 10kg
2ml/kg/h for next 10kg
1ml/kg/h for each kg after
Pharmacokinetics/dynamics
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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
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Hb
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WCC
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Birth: 14-22g/l, 3-6 months: 11-14, 6-12 years: 11.515.5
Birth: 10-26 x109/l, 3-6 months: 6-18, 6-12: years 513
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
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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
Any questions?
Summary
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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