Persistent foetal circulation and hyperviscosity syndrome.

1. Big picture

This topic has two important neonatal circulation problems:

1. Persistent fetal circulation, better called persistent pulmonary hypertension of the newborn (PPHN) → the newborn fails to switch from fetal to neonatal circulation. Blood keeps shunting right-to-left, causing severe hypoxemia.

2. Hyperviscosity syndrome, usually due to neonatal polycythemia → blood is too thick, causing poor tissue perfusion, hypoglycemia, respiratory distress, neurologic symptoms, thrombosis, and sometimes worsening pulmonary hypertension.

Both present as a sick, cyanotic or poorly perfused newborn.

Core exam idea:

Newborn after birth should drop pulmonary vascular resistance.
If pulmonary pressure remains high → right-to-left shunting → hypoxemia.
If hematocrit is too high → thick blood → slow flow → hypoxia, acidosis, hypoglycemia.

---

2. Normal fetal-to-neonatal circulatory transition