Lecithin/sphingomyelin ratios in tracheal aspirates from newborn infants

A sensitive and rapid high-performance liquid chromatography method for determining lecithin/sphingomyelin (L/S) ratios in small volume tracheal aspirates has been evaluated in 115 infants sampled within 3 h of delivery. Respiratory distress syndrome was present in 41 infants and all had L/S ratios of less than or equal to 15 (sensitivity 100%). Respiratory distress syndrome was absent in 74 infants, 67 of whom had L/S ratios of greater than 15 (specificity 91%). Serial tracheal aspirates (n = 68) in 27 infants showed little change in nine respiratory distress syndrome infants with L/S ratio less than or equal to 15 over 3 h while 18 nonrespiratory distress syndrome infants with L/S greater than 15 were more variable. In two infants initial immature ratios rose to maturity rapidly after birth. Comparison of amniotic fluid L/S ratios obtained within 2 h of delivery correlated with the corresponding tracheal aspirate L/S in 24 infants (r = 0.81, p less than 0.001) although the latter were three times higher. This method may have potential routine application in the assessment of surfactant replacement and mechanical ventilator therapies.