Table 1.

Differential diagnosis of hypoxemia in newborn infants.

	Lung Disease without PPHN	Cyanotic Congenital Heart Disease	PPHN
History	Fetal distress, PROM, chorioamnionitis	Antenatal diagnosis	Often negative other than in secondary PPHN
Respiratory distress	Present	Usually absent	Often present
Oxygen saturation on pulse oximetry	Improves with supplemental oxygen	Fixed low saturations Minimal response to supplemental oxygen	Labile saturations. Differential cyanosis
Hyperoxia test *	PaO2 often > 150 mm Hg	PaO2 often < 100 mm Hg	PaO2 often > 100 mm Hg
PaCO2	Elevated	Normal/low	Often elevated (except in idiopathic PPHN)
Hyperoxia-Hyperventilation *	PaO2 > 150 mm Hg	PaO2 often < 100 mm Hg	PaO2 improves with hyperventilation
Chest X ray	Abnormal	Abnormalities of cardiac silhouette and pulmonary vascularity	Decreased vascularity in idiopathic PPHN
Echocardiogram	Normal	Structural cardiac abnormalities	Structurally normal heart (see text for characteristic echo findings of PPHN)

* Both hyperoxia and hyperoxia hyperventilation tests are not used routinely in clinical practice due to increased availability of echocardiography in most institutions. These tests expose the infant to hyperoxia and hypocarbia with the potential to cause oxidative stress and decreased cerebral perfusion respectively.