Increased hypoxemia in neonates secondary to the use of continuous positive airway pressure.

Five neonates are presented who, while receiving continuous transpulmonary pressure, developed increased systemic arterial hypoxemia, which was relieved when this therapeutic modality was decreased or discontinued. Three of the five had chest radiographs consistent with hyaline membrane disease: the other two had atypical radiographs. None had evidence of air leaks. Levels of positive airway pressure utilized when the hypoxemia was noted ranged from 5 to 15 cm H2O. Calculated shunt fractions (Qs/Qt) improved from a mean of 73% to 37% when the continuous positive airway pressure was lowered. The site of shunting in these infants could have been in the lung or through anatomic extrapulmonary shunts. Improvement in total cardiac output may also have contributed to the improved oxygenation. This paradoxical effect of continuous transpulmonary pressure appears to be mediated through changes in the pulmonary vascular resistance brought about by the continuous transpulmonary pressure.