Effect of surfactant substitution on lung effluent phospholipids in respiratory distress syndrome: evaluation of surfactant phospholipid turnover, pool size, and the relationship to severity of respiratory failure.

The turnover and pool size of surfactant has been studied in animals, but there is little similar information in humans. In the present investigation lung effluent phospholipids were studied in 29 small preterm infants with severe RDS. Thirteen were treated with mechanical ventilation, and 16 additionally received natural human surfactant. The first dose (60 mg surfactant/kg body wt) was given between 2 and 10 h of age, and the surfactant was given again if there was an insufficient response. Together 260 aspirates, recovered during routine suctioning of the airways, were analyzed for phospholipids. Phosphatidylglycerol, present only in exogenous surfactant, was used as a specific marker to estimate the apparent pool size and the half-life of surfactant phospholipid. In addition, the saturated phosphatidylcholine/sphingomyelin ratios were correlated with the ventilatory index (mean airway pressure X fractional inspiratory oxygen/arterial oxygen tension). There was a linear correlation between the ventilatory index and the saturated phosphatidylcholine/sphingomyelin (r approximately -0.70) but no consistent correlation between the ventilatory index and the amount of phospholipids in the aspirate. The saturated phosphatidylcholine/sphingomyelin ratio increased during the surfactant-induced remission of respiratory failure, decreased during the recovery. The control infants tended to have lower saturated phosphatidylcholine/sphingomyelin ratios during the first week than the surfactant-treated infants.(ABSTRACT TRUNCATED AT 250 WORDS)