Lung hypoplasia:
Congenital diaphragmatic hernia, an important cause of lung hypoplasia, is often
associated with PPHN. CDH affects 1 in 3000 live births. Pulmonary hypertension
occurs in CDH because of the decreased number of blood vessels and increased
reactivity of the vessels in the hypoplastic lungs. Similarly, prolonged rupture of
membranes and renal dysplasia and agenesis are associated with lung hypoplasia and
PPHN for similar reason.
CLINICAL PRESENTATION: Respiratory symptoms occur at birth or during first day of
life. Primary symptom is respiratory distress with cyanosis (hypoxemia). Labile
oxygenation is characteristic of PPHN. Physical exam may show tachypnea and
retractions from respiratory disease. Active precordium and systolic murmur of tricuspid
insufficiency may be appreciated on cardiac exam.
MANAGEMENT OF PPHN: It is very important to differentiate idiopathic PPHN or
PPHN due to lung disease from pulmonary hypertension, which also occurs in
congenital heart disease. Use of pulmonary vasodilators, like inhaled NO are
contraindicated in congenital heart disease associated with right to left shunts (HLHS,
coarctation of the aorta) and in TAPVR. Traditionally, responses to hyperoxia or
hyperoxia +/- mechanical ventilation have been used to distinguish PPHN from cyanotic
congenital heart disease. Although these criteria are still useful, certain caveats have to
be considered to avoid errors in diagnosis. Some neonates with congenital heart
disease and right to left shunt at PDA may experience increase in saturations with