AWABS - Foetal Circulation

Question 1

Foetal circulation:
Include passage, foetal variants and rough oxygen sats at each point

Answer 1

Umbilical vein carries oxygenated blood
Bypasses liver via ductus venosus to go into IVC
Right atrium with right to left shunt via PFO (encouraged by eustachian valve)
Mixing of blood between pulmonary artery and aorta via Ductus arteriosus

Rough guide of O2 sats at each point are illustrated on diagram

Question 2

Extra cardiac shunts

Answer 2

Ductus venosus allows oxygenated blood to bypass the liver

Ductus arteriosus contains O2 sensitive muscle

Question 3

Foetal Hb (HbF)

Answer 3

2 alpha subunits and 2 gamma subunits
Has lower content of 2,3 DPG (diphosphoglycerate)

In adults Hb has 2 alpha and 2 beta subunits (HbA)

Question 4

Foetal Hb oxygen dissociation curve

Answer 4

Question 5

Double Bohr effect

Answer 5

In placenta:
More CO2 from foetal blood moves down concentration gradient to maternal Hb

Question 6

Transition to adult circulation

Answer 6

Transfer from placental to pulmonary oxygenation

Umbilical vessels clamped (or stretched)

Increase in SVR

Foramen ovale closes

Increased pulmonary blood flow

Ductus venosus closes passively in 3-10 days post birth due to low flow

Acidosis and hypercapnia stimulate first breath

Expansion of lungs and fall in pulmonary vascular resistance

Question 7

Ductus arteriosus in adult transition

Answer 7

Ductus arteriosus flow initially becomes bidirectional

Increase PaO2 causes direct vasoconstriction

PGE2 made by placenta rapidly falls adding to ductal vasoconstriction

Functional closure of ductus arteriosus

Question 8

Persistent foetal circulation

Answer 8

Question 9

Tetralogy of Fallot

Answer 9

Overriding aorta
Pulmonary stenosis
Right ventricular hypertrophy
VSD

Question 10

Initial issue and management of Tetralogy of Fallot

Answer 10

Duct dependence to maintain pulmonary blood flow

Managed with prostaglandin infusion to maintain patent ductus arteriosus