Coronary, cerebral and upper-limb circulation (pre-ductal)
Systemic & remnants · SaO2 ~65% Pre-ductal
The branches proximal to the ductus deliver ~65%-saturated blood to the myocardium, brain and upper limbs, the organs the fetal circulation is arranged to protect. Their venous return comes back desaturated via the coronary sinus and SVC.
Traced from the start
- Placenta
- Umbilical vein
- Ductus venosus
- Foramen ovale to left atrium and left ventricle
- Ascending aorta and arch (pre-ductal)
- Coronary, cerebral and upper-limb circulation (pre-ductal)
Detail
- Saturation
- ~65% arterial (pre-ductal); venous return in the SVC ~40%
- Priority
- Brain and heart together take roughly a fifth of combined output and are the last beds to be vasoconstricted in hypoxia
- Brain sparing
- Hypoxaemia dilates cerebral vessels (middle cerebral artery pulsatility falls) while gut, kidney, skin and limb beds constrict
When it goes wrong
Middle cerebral artery Doppler in a growth-restricted fetus
Cerebroplacental ratio (MCA PI / umbilical artery PI) below 1 indicates redistribution and raises the risk of adverse perinatal outcome
Practise this structure
1 question in the bank tagged Coronary Circulation.