Effective pulmonary blood flow in preterm and light-for-date infants.

Using a method employing low concentrations (3%) of nitrous oxide, we measured effective pulmonary capillary blood flow (Qpc eff) in 23 preterm infants, 26 light-for-date infants, and 15 infants who were both preterm and light-for-date. All infants studied had no clinical or laboratory evidence of idiopathic respiratory distress syndrome (IRDS) and were studied before the age of 48 hours. The mean Qpc eff of 175 ml/kg/min in preterm infants (a group at high risk of developing IRDS), although significantly less than the mean of 214 ml/kg/min found in light-for-date infants (a group with a low risk of developing IRDS), was similar to that reported in normal term infants. The mean result for preterm, light-for-date infants was 189 ml/kg/min. No evidence was found that preterm infants were predisposed to IRDS as a consequence of preexisting pulmonary hypoperfusion.