Physiologic factors affecting pulmonary artery pressure in infants with persistent pulmonary hypertension.

Indwelling pulmonary artery catheters were used for continuous monitoring of pulmonary artery pressure in ten infants with severe persistent pulmonary hypertention of the newborn. The labile nature of pulmonary artery pressure, with changes up to 50 mm Hg, was documented. Pulmonary artery pressure in the eight infants with suprasystemic pulmonary hypertension was analyzed at the time of maximum decrease in pressure (mean 36.1 mm Hg) and physiologic measurements were compared over an eight-hour period. During the study period when the infants were hyperventilated, as the Paco2 decreased from 48.9 to 28.3 mm Hg (P less than 0.02) the mean pulmonary artery pressure decreased by 36 mm Hg (P less than 0.001) to subsystemic pressure levels, and the mean AadeltaO2 decreased by 146 mm Hg (P less than 0.001). After the decrease in pulmonary artery pressure, patients were mechanically ventilated to maintain Paco2 in the range of 25 to 30 mm Hg until pulmonary hypertension gradually resolved in the six survivors.