incidence of false positives, but within the first week Importantly, the pulse oximetry screen for CHD does not detect nonhypoxic heart disease (e.g., coarctation of the aorta, single ventricle, or double outlet right ventricle) The American Academy of Pediatrics (AAP) and the CDC endorse screening for critical CHD for all newborns ( Fig 96.1 ) An infant who fails the initial screen should be referred for an echocardiogram Hypoxia without respiratory distress, specifically without signs of grunting, retractions, or accessory muscle use, is more common in cardiac disease than respiratory disease To better distinguish the etiology of hypoxemia, the clinician can perform the hyperoxia test To complete the test, the infant is given 100% oxygen to breathe for to 10 minutes Serial pulse oximetry or arterial blood gas measurements are obtained on room air and after the infant has breathed 100% oxygen If there is little to no increase in oxygenation, the hypoxia can be attributed to extrapulmonary causes of right-to-left shunting Extrapulmonary right-to-left shunting occurs in persistent pulmonary hypertension and in cardiac disease To distinguish between the two, the clinician can perform the hyperventilation test In this circumstance, hyperventilating to a PaCO2 of 25 to 30 mm Hg in conjunction with 100% oxygen is more likely to elicit an increase in PaO2 levels (typically >100 mm Hg) in persistent pulmonary hypertension of the newborn (PPHN) due to relaxation of the pulmonary bed Infants that continue to have low PaO2 despite hyperoxia and hyperventilation are more likely to have a fixed, intracardiac right-to-left shunting In either circumstance, an echocardiogram is the definitive study to differentiate between the two