Lecithin/sphingomyelin ratio from tracheal aspirates and compliance of the respiratory system in infants with bronchopulmonary dysplasia.

In 55 infants with respiratory distress syndrome the dynamic compliance of the respiratory system (CRS) was measured by pneumotachography during the course of the disease. Lecithin/sphingomyelin ratio (L/S) was evaluated at birth and every 10th day. Thirteen infants who developed bronchopulmonary dysplasia (BPD) had lower L/S ratios at birth than those infants without BPD (mean = 1.0 versus 3.5, p less than 0.01). During the course of disease, L/S ratios were variable and increased in all infants independently of outcome. In the first days of life CRS was low (0.30 ml/cm H2O/kg) in all infants independently of outcome. In infants with BPD who survived, CRS was significantly higher from the 30th day on than in infants who died from the disease (0.35 versus 0.23 ml/cm H2O/kg). Together with an decrease in oxygen supply at this time (less than 70%) the CRS is a reliable predictor of survival in cases of BPD.