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 Eustachian valve 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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