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

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 AirwayPaediatric Airway

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

Any questions?Any questions?

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