Descending aorta to lower body (post-ductal)
Systemic & remnants · SaO2 ~55-60% Post-ductal
Below the ductal insertion the aorta carries a mixture dominated by ductal (right ventricular) blood and supplies the abdominal viscera, kidneys and lower limbs; the common iliac arteries then give the internal iliacs from which the umbilical arteries arise.
Traced from the start
Detail
- Saturation
- ~55-60% (PO2 ~20-25 mmHg), post-ductal
- Composition
- Mostly ductus arteriosus flow plus the ~10% of combined output that crosses the isthmus from the arch
- Destinations
- Kidneys (only ~2-3% of output; urine is mainly for amniotic fluid), gut, lower limbs, and about two-thirds onward to the placenta
- Post-ductal sampling
- Foot pulse oximetry in the neonate reads this blood
When it goes wrong
Umbilical arterial catheter in the neonate
Threaded umbilical artery -> internal iliac -> aorta; tip placed high (T6-T9, above the coeliac axis) or low (L3-L4, below the renal arteries) to keep it away from mesenteric and renal origins; a dusky or blanched leg or buttock means spasm or embolus and the line comes out
Pre-ductal coarctation with the duct supplying the lower body
Post-ductal saturation below pre-ductal (differential cyanosis) until the duct closes, then absent femoral pulses, oliguria and cardiogenic shock
Practise this structure
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