Synthetic surfactant replacement therapy decreases estimated pulmonary artery pressure in respiratory distress syndrome. 
To evaluate the effects of surfactant replacement therapy on the pulmonary artery pressure in infants with respiratory distress syndrome.  Nonrandomized, "before-after" trial.  Neonatal intensive care unit at a referral center.  Ten preterm infants with respiratory distress syndrome.  Administration of two or four doses of an exogenous synthetic surfactant at 12-hour intervals.  Systolic pulmonary artery pressure was estimated by measuring tricuspid regurgitant flow velocity with the Doppler method before and, on average, 45 minutes after administration of synthetic surfactant.  Measurable recordings were technically obtainable on 18 of 23 occasions.  Surfactant instillation decreased pulmonary artery pressure significantly on 17 of 18 occasions, but did not change the systemic blood pressure.  Twelve hours after surfactant treatment, pulmonary artery pressure measured on nine occasions returned to the pretreatment level.  No change in the velocity or magnitude of the ductal left-to-right shunting due to exogenous surfactant was found.  Synthetic surfactant replacement therapy in infants with respiratory distress syndrome induces a significant, but transient decrease in systolic pulmonary artery pressure with no effect on the ductal shunt.