Transition phase during hyperventilation therapy for persistent pulmonary hypertension of the neonate.

It is important for the clinician who is hyperventilating infants with persistent pulmonary hypertension (PPHN) to recognize a transition phase during therapy when pulmonary hypertension is no longer the primary cause of hypoxemia, because infants who are hyperventilated develop parenchymal lung disease after 2 to 3 days. This study reports ten infants who showed PaO2 lability early in the course of PPHN, with an inverse relationship between PaO2 and PaCO2. At a mean age of 79 +/- 14 (SEM) there was a transition phase, after which PaO2 lability decreased and the infants did not require hyperventilation. The mean change in PaO2 per change in PaCO2 was significantly (p less than .05) higher pretransition (22.4 +/- 5.2) compared to during transition (5.1 +/- 1.4) or post-transition (1.9 +/- 1.2). Mean alveolar-arterial oxygen gradient was higher (p less than .05) pretransition (495 +/- 36) vs. post-transition (405 +/- 52) and was more labile relative to PaCO2 change pretransition (20.3 +/- 5.9) compared to post-transition (.3 +/- 2.4). When ventilator settings were reduced after the transition phase, PaCO2 rose by 12.2 torr.