Pulmonary haemodynamics after surfactant replacement in severe neonatal respiratory distress syndrome.

Aortopulmonary pressure difference and pulmonary blood flow velocity were studied during the first 48 hours of life in 12 premature neonates with severe respiratory distress syndrome (RDS), treated by natural surfactant, and in 25 premature neonates with mild RDS. A non-invasive Doppler ultrasound method was used to estimate aortopulmonary pressure difference and pulmonary blood flow velocity from the left pulmonary artery. Aortopulmonary pressure difference was significantly lower at 6 hours of age in the infants with severe RDS and was not increased one hour after surfactant therapy. Aortopulmonary gradient started to rise at 24 hours of age and was equal to that of neonates with mild RDS at 48 hours. Pulmonary blood flow velocity was significantly lower, initially in the severe RDS group, and was not increased one hour after surfactant therapy. Left pulmonary artery flow velocity began to rise after 24 hours and reached the values of the mild RDS group at 48 hours. These data indicate that aortopulmonary pressure difference and pulmonary blood flow are low in the acute phase of RDS and that surfactant treatment does not seem to affect these values.