Objective: To determine the course of systolic pulmonary artery pressure (PAP) in association with ductal shunting and cardiac output (CO) in preterm neonates.
Design: During the acute phase of respiratory distress syndrome (RDS) with and without surfactant treatment, serial Doppler ultrasound examinations were performed at the ages of 2, 12, 24, 48, and 72 hours in 51 neonates with RDS and 21 healthy, preterm controls. Twenty-eight of the distressed neonates received two or four doses of synthetic exogenous surfactant at intervals of 12 hours. Measurements of hemodynamic variables in these neonates were performed before and after 8 hours following surfactant treatments. PAP was estimated by the Doppler method from the maximal tricuspid regurgitant flow velocity. Doppler ultrasound was also used to determine simultaneously CO, and the direction and magnitude of the ductal shunting.
Results: The PAP was initially at the same level, but remained significantly higher in distressed than in healthy, preterm control neonates between the ages of 12 to 48 hours. The systolic systemic arterial blood pressures did not differ between the distressed and control neonates, but increased gradually during the study period. Consequently, the ratio of systolic pulmonary and systemic pressure was also higher in neonates with RDS than in controls during the first day of life. Bidirectional ductal shunting disappeared in all neonates studied after 2 days of life. Significant left-to-right shunting through the ductus arteriosus persisted more frequently in distressed neonates, especially those with surfactant treatment, than in control neonates during the study period, and more often caused the need for medical or surgical closure. Doppler-derived CO remained stable throughout the study in the distressed neonates, being significantly higher in surfactant-treated neonates than nontreated distressed neonates or healthy controls at 72 hours of life.
Conclusions: The data of the present study confirms that the postnatal decrease in PAP is delayed in acute RDS. Further, significant patent ductus arteriosus shunting persists longer in RDS and may contribute to elevated CO during the resolution of the disease.