The Cyanotic Infant — Heart Disease or Lung Disease

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Abstract
To determine whether differential diagnosis in infants with cyanosis of uncertain etiology may be facilitated without requiring cardiac catheterization, the Pao2, Paco2, pH and bicarbonate of aortic blood were measured in 28 cyanotic infants. Measurements were made 10 to 15 minutes after the infant has breathed oxygen at a concentration of 0.9 to 1.0 at atmospheric pressure, and again 10 to 15 minutes after breathing the same concentration of oxygen under a positive end-expiratory pressure of 8 to 10 cm of water. In seven with subsequently proved cardiac disease, Pao2 fell 33 mm Hg on the average, whereas Paco2 rose 9 mm Hg. In 21 infants with subsequently proved lung disease, Pao2 rose an average of 141 mm Hg, whereas Paco2 did not change. Thus, a simple procedure is available to help differentiate cyanosis of cardiac from that of pulmonary causation; it permits earlier diagnosis of the former and avoids the risks of cardiac catheterization in the latter.