2010B13 Describe the cardiovascular changes that occur in the neonate at birth.

 

List:

·         Foetal circulation summary

·         Foetal circulation adaptations

·         Physical changes at birth

·         Circulatory changes at birth

·         Neonatal circulation: normal and reversion

 

Foetal circulation summary:

·         Placenta allows exchange of gases, nutrient, waste product

·         Lungs are dormant

·         Massive R->L shunt

·         R and L circulations mostly in parallel, not in series

 

Foetal circulation adaptations:

 

Location/path

Function

Umbilical arteries (UA) x 2

From internal iliac arteries to placenta

 

Umbilical vein (UV) x 1

From placenta to IVC and liver

 

Ductus venosus (DV)

From UV to IVC

Near confluence of UV and left portal vein

Allows 50% DV blood to bypass liver

Foramen ovale (FO)

Hole between left atrium (LA) and right atrium (RA)

60% IVC blood guided by crista terminalis across FO to LA.

Brain receives most oxygenated blood

Ductus arteriosus (DA)

Between main pulmonary artery and aortic arch

Allow 90% RV output to bypass lungs

 

Physical changes at birth:

Breathing

·  Aeration of alveoli, ↑PAO2, ↑PaO2

·  ↓HPV, ↓PVR

Cord clamping

·  Physical clamp and hypothermia-induced contraction of Wharton’s jelly

·  ↑↑SVR and loss of maternal prostaglandins

 

Circulatory changes at birth:

 

Functional closure

Permanent closure

UA

Minutes

(Clamp, WJ contract, ↑PaO2)

Days

(Fibrosis)

UV

Hours

(Clamp, WJ contract)

3-10 days

(Fibrosis)

DV

Hours

(Stasis)

3-10 days

(Fibrosis -> ligamentum teres)

FO

Minutes, when RAP = LAP

(↓PVR/RAP, ↑SVR/LAP)

4-6/52

(Fibrosis)

DA

12-24 hours

(↑PaO2, ↓PG)

2-3/52

(Fibrosis)

 

Neonatal circulation:

Normal parameters

·  HR 120-160 (cf. 60-90 in adult)

·  SV fixed

·  CO 280mL/kg/min (cf. 70 in adult)

·  SBP 70-90mmHg (cf. 120mmHg adult)

·  Physiological shunt 20% (cf. 7% in adult)

Reversion to foetal circulation

·  ↓PaO2 -> re-open DA

·  ↓PaO2, ↑PaCO2, ↓pH, ↓temp -> ↑PVR -> ↑RAP -> re-open FO

 

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