Neonatal and Paediatric Neonatal and Paediatric Anatomy and PhysiologyAnatomy and Physiology
Dr Alison ChalmersDr Alison Chalmers
Consultant AnaesthetistConsultant Anaesthetist
Queen Victoria HospitalQueen Victoria Hospital
What you need to knowWhat you need to know
Fetal circulation and changes at birthFetal circulation and changes at birth Anatomical differences in the airway, Anatomical differences in the airway,
head and spinal cord from the adulthead and spinal cord from the adult Physiological differences from the Physiological differences from the
adultadult Haematological and biochemical Haematological and biochemical
changes with agechanges with age Estimation of blood volumeEstimation of blood volume
Fetal circulationFetal circulation
Ductus venosusDuctus venosus
Foramen ovaleForamen ovale
Ductus arteriosusDuctus arteriosus
Changes at birthChanges at birth
First breath generates negative pressureFirst breath generates negative pressure ↑ ↑ FRC ↓ FRC ↓ PVR PVR
Blood flows from right ventricle through lungsBlood flows from right ventricle through lungs ↑ ↑ SVR with clamping of umbilical vesselsSVR with clamping of umbilical vessels
Reversal of right to left flow through DAReversal of right to left flow through DA
Oxygen and ↓ PGEOxygen and ↓ PGE22 stimulates ductal constriction stimulates ductal constriction ↑ ↑ LAP and ↑ SVR cause closure of the FOLAP and ↑ SVR cause closure of the FO DV closes passively as flow ceasesDV closes passively as flow ceases
Fetal haemoglobinFetal haemoglobin
2 2 άά chains and 2 chains and 2 λλ chains chains Binds 2,3-DPG less avidly than HbABinds 2,3-DPG less avidly than HbA Shifts ODC to left (PShifts ODC to left (P5050 2.4KPa) 2.4KPa)
Favours OFavours O22 transfer from mother to fetus transfer from mother to fetus Gives up more OGives up more O22 to fetal tissues than HbA to fetal tissues than HbA
80% circulating Hb at birth80% circulating Hb at birth Replaced within 3-5months by HbAReplaced within 3-5months by HbA
Neonatal physiologyNeonatal physiology
CVSCVS RV=LV at birthRV=LV at birth ↑ ↑ ratio of connective to ratio of connective to
contractile tissuecontractile tissue Flat Starling curveFlat Starling curve Fixed SVFixed SV
LungsLungs Bronchial tree fully Bronchial tree fully
developed developed Alveoli develop fully Alveoli develop fully
after birthafter birth Compliant chest wallCompliant chest wall Diaphragmatic Diaphragmatic
breathingbreathing Less ventilatory Less ventilatory
responses to PaOresponses to PaO22 and and PaCOPaCO22
Neonatal physiologyNeonatal physiology
KidneysKidneys No of nephrons No of nephrons
complete by birthcomplete by birth RBF increases from RBF increases from
5% CO at birth to 5% CO at birth to 20% at 1 month20% at 1 month
Low GFR; adult by 2 Low GFR; adult by 2 yearsyears
LiverLiver Immature enzymesImmature enzymes
CNSCNS Pathways complete Pathways complete
at birthat birth Temp controlTemp control
High SA to body High SA to body weight ratioweight ratio
Less SC fatLess SC fat Non shivering Non shivering
thermogenesisthermogenesis
Paediatric anatomy and Paediatric anatomy and physiology physiology
AirwayAirway LungsLungs CVSCVS BMRBMR CNSCNS Temp regulationTemp regulation Fluid balanceFluid balance PharmacologyPharmacology
Paediatric respiratory Paediatric respiratory systemsystem
DiaphragmaticDiaphragmatic Neonates – obligate nasal breathersNeonates – obligate nasal breathers Increased respiratory rateIncreased respiratory rate Very compliant chest wall – horizontal Very compliant chest wall – horizontal
ribsribs CC > FRC in normal breathingCC > FRC in normal breathing Ventilatory response to COVentilatory response to CO22 reduced reduced BMR/OBMR/O22 consumption high consumption high
Paediatric cardiovascular Paediatric cardiovascular systemsystem
AGEAGE SYSTOLIC SYSTOLIC BP BP (mmHg)(mmHg)
DIASTOLIDIASTOLIC BP C BP (mmHg)(mmHg)
HEART HEART RATERATE
PretermPreterm 4545 2525 >120>120
BirthBirth 6060 3535 >120>120
NeonateNeonate 70-8070-80 40-5040-50 120-150120-150
3-6 3-6 monthsmonths
80-9080-90 50-6050-60 120-140120-140
1 year1 year 90-10090-100 60-8060-80 110-130110-130
5 years5 years 95-10095-100 50-8050-80 90-10090-100
12 years12 years 110-120110-120 60-7060-70 80-10080-100
Paediatric nervous systemPaediatric nervous system
Spinal cord ends L3; recedes by Spinal cord ends L3; recedes by adolescenceadolescence
Immature BBBImmature BBB Pronounced vagal reflexesPronounced vagal reflexes
Fluid balanceFluid balance
Blood volumesBlood volumes Birth: 90ml/kgBirth: 90ml/kg Child: 80ml/kgChild: 80ml/kg Teenager: 70ml/kgTeenager: 70ml/kg
Maintenance fluid requirementsMaintenance fluid requirements 4ml/kg/h for first 10kg4ml/kg/h for first 10kg 2ml/kg/h for next 10kg2ml/kg/h for next 10kg 1ml/kg/h for each kg after1ml/kg/h for each kg after
Pharmacokinetics/dynamicsPharmacokinetics/dynamics
Lower plasma albumin levels up to 1 Lower plasma albumin levels up to 1 yearyear
Renal and hepatic immaturityRenal and hepatic immaturity MAC increased in neonatesMAC increased in neonates Neonates sensitive to NMB; more Neonates sensitive to NMB; more
resistant to suxresistant to sux
Haematological changes with Haematological changes with ageage
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:
11.5-15.511.5-15.5 WCCWCC
Birth: 10-26 x10Birth: 10-26 x1099/l, 3-6 months: 6-18, 6-12: years /l, 3-6 months: 6-18, 6-12: years 5-135-13
Platelets – fairly stable between 150-500 Platelets – fairly stable between 150-500 x10x1099/l /l
All vit K dependant clotting factors are low at All vit K dependant clotting factors are low at birth – reach adult values by 6 monthsbirth – reach adult values by 6 months
Biochemical changes with Biochemical changes with ageage
Albumin: low up to 1 yearAlbumin: low up to 1 year Bilirubin: high at birth (17-170umol/l), Bilirubin: high at birth (17-170umol/l),
normal adult levels by 1 monthnormal adult levels by 1 month CaCa2+2+: low neonate (1.9-2.8mmol/l), : low neonate (1.9-2.8mmol/l),
normal adult levels by 1 yearnormal adult levels by 1 year TT44: high neonate, falls to adult range : high neonate, falls to adult range
steadily up to 10 yearssteadily up to 10 years
SummarySummary
Fetal circulation and changes at birthFetal circulation and changes at birth Anatomical differences in the airway, Anatomical differences in the airway,
head and spinal cord from the adulthead and spinal cord from the adult Physiological differences from the Physiological differences from the
adultadult Haematological and biochemical Haematological and biochemical
changes with agechanges with age Estimation of blood volumeEstimation of blood volume