Foetal Circulation

Question 1

What is the main differences between adult & foetal circulation?

Answer 1

Oxygenated blood from placenta bypasses liver & lungs

Question 2

What is the maternal blood supply to the placenta?

Answer 2

Uterine arteries = oxygenated blood
Uterine veins = deoxygenated blood

Question 3

What vessels supply (de)oxygenated blood to the placenta?

Answer 3

Deoxy = 2 umbilical arteries
Oxy = Umbilical vein

Question 4

How does most of the blood in the umbilical vein bypass the liver?

Answer 4

Via ductus venosus

Question 5

How is oxygenated blood supplied to the foetal heart/brain upper circulation?

Answer 5

• Blood from IVC shunted through FO into LA
• Then enters LV & ascending aorta

Question 6

How is blood supplied to the lower foetal circulation?

Answer 6

• Blood returns to RA from upper circulation via SVC & coronary sinus
• Into RV
• Ejected into pulmonary artery - most shunted through DA

Question 7

How much blood enters the foetal pulmonary circulation?

Answer 7

10% due to high pulmonary vascular resistance
90% through DA

Question 8

Where does deoxygenated blood return to?

Answer 8

Descending aorta into umbilical arteries

Question 9

What are the pO2 sats for the UV, AA, RA Lower circulation?

Answer 9

UV: 90%
AA: 65%
RA: 40%
LC: 50%

Question 10

What happens when a baby takes its first breath?

Answer 10

• O2 exposure of pulmonary vessels causes vasoDilation
• Rapid decrease in PVR
• Inc blood flow into pulmonary circulation
• Inc flow into LA = inc LA pressure
• Closure of foramen ovale

Question 11

What happens once the cord is clamped?

Answer 11

• Placental blood flow ceases
• Inc SVR
• Reversal of flow through DA
• Exposure to high O2 tension & reduced prostaglandin E2 production
• Constriction of DA = closed within 24hours of delivery

Question 12

What factors can trigger reversal from adult back to foetal circulation?

Answer 12

• Hypothermia
• Acidosis
• Hypoxia
• Hypovolaemia

Question 13

What would happen with persistently raised pulmonary vascular resistance post-delivery?

Answer 13

R-L shunting across FO +/- DA
Can lead to death

Question 14

What factors can cause a persistently patent DA?

Answer 14

• Drugs: Phenytoin
• Maternal ETOH
• Rubella

Question 15

How does Eisenmenger Syndrome occur?

Answer 15

• Chronic exposure to high blood volume = CCF
• Inc LV load
• Inc pulmonary artery flow = pulmonary HTN
• Reverse L-R shunt