Administration of exogenous surfactant (ExS) benefits the pulmonary status of infants with respiratory distress syndrome (RDS). Metabolism of ExS is complex, with clearance and resecretion of the phospholipids (PL) and potential effects on surfactant proteins (SP). We examined metabolism of ExS and lung function in 14 ventilated neonates (mean±SE gestation, 26±1.2 weeks) with RDS treated with ExS (4 ml/kg of Survanta, Ross Labs). PL was isolated from tracheal aspirates (TA) obtained by instillation of 2-3 ml of saline followed by suctioning. Specimens were obtained just following delivery (Pre 1), two hours after an initial dose of Survanta(Post-1), and similarly, just prior to and following a second dose (Pre-2, Post-2). A final specimen was obtained at four days of age (Day 4). Physiologic assessments of lung function prior to and following ExS included measures of dynamic compliance (Cdyn) and functional residual capacity (FRC). TA were analyzed for PL (μg/ml), proportion of PL present as large aggregates (Lag), and total protein (Protein, μg/ml). Changes in SP over time were examined by immuno dot-blot analysis. The mean±SE values were: Table Compared to Pre-1 values, SP-A increased modestly Post-1 (2.2±1 fold) and was unchanged by day 4. In contrast, SP-B increased 8±4 fold Post-1 and 14±5 fold by day 4. Mechanics demonstrated contrasting results, with Cdyn decreasing from Pre-1 to Post-1(0.6±0.1 vs. 0.34±0.04) and FRC increasing (17±3 vs. 25±3, both p<0.05). This data suggests rapid clearance of ExS from the alveolar space, and that beneficial effects of ExS are unrelated to immediate or prolonged changes in alveolar PL.

Table 1
Full size table