Lecithin/sphingomyelin ratio in hypopharyngeal aspirate of newborn infants.

The lecithin/sphingomyelin (L/S) ratio was measured in the hypopharyngeal aspirate of 41 newborn infants. In 20 without respiratory distress the ratio within 24 hours from birth ranged from 1.5 to 5.8 with a mean value of 3.3. In 6 with 'transient tachypnoea of the newborn' the ratio ranged from 2.0 to 6.7 with a mean value of 3.2. In 15 infants with idiopathic respiratory distress syndrome (RDS) the ratio ranged from 0.9 to 2.1 with a mean value of 1.4. In 14 of these infants the ratio within 24 hours from birth was 1.7 or less. One infant with a higher ratio and severe RDS is described in detail. Serial hypopharyngeal aspirate L/S ratios were determined in the infants with RDS. There was a possible trend toward the earlier attainment of a ratio of 2.0 in infants who received continuous distending airway pressure compared with infants who did not.