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 < .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 < .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.