Treatment of persistent pulmonary hypertension of the newborn: update.

Persistent pulmonary hypertension of the newborn is pfimarily characterised by persistence of, or return to, the suprasystemic pulmonary vascular resistance and pressure normally found in the fetus. The increased pulmonary pressure causes right to left shunting through the ductus arteriosus or the foramen ovale, or both. The resulting hypoxaemia and acidosis may produce further pulmonary vasoconstriction and lead to a vicious cycle of shunting, hypoxia, and acidosis.