Evaluation of the newborn who has cyanosis requires prompt and logical assessment. Although entities such as polycythemia and methemoglobinemia must be considered, the diagnoses that must be addressed most urgently are primary respiratory disease, congenital heart disease (CHD), and persistent pulmonary hypertension of the newborn (PPHN). These categories of disease are not mutually exclusive, as in the case of meconium aspiration with PPHN, but their distinct pathophysiologic mechanisms account for different results in diagnostic testing.

The essence of PPHN lies in the pathologic failure of pulmonary artery pressure to decline postnatally. Although pulmonary artery pressure varies directly with pulmonary vascular resistance (PVR), pulmonary blood flow, and pulmonary capillary wedge pressure, the first of these plays the most prominent role in PPHN. Persistently elevated PVR may result from the perinatal failure to elaborate nitric oxide and/or prostaglandin I2 in addition to increased production of phosphodiesterase-3 or -5, endothelin-1, reactive oxygen...

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