Evidence of surfactant deficiency in persistence of the fetal circulation.

The phospholipids of tracheal aspirates in persistence of the fetal circulation (PFC) were compared to those in the respiratory distress syndrome (RDS) and those in other severe diseases of the newborn. The infants with PFC were hypoxemic despite 80 to 100% inspiratory oxygen. There were small, if any, pulmonary parenchymal changes in radiographs. Echocardiograms demonstrated evidence of increased pulmonary arterial pressure. Mechanical ventilation increased arterial oxygen tension in each case. However, five of the eight patients required ventilation at a high frequency (57-65 min) and long inspiratory time (0.6--0.7 s). The phospholipids in tracheal aspirates in PFC were quite similar to those in RDS, namely there was a small amount, if any, phosphatidylglycerol (PG), and the lecithin/sphingomyelin (L/S) ratio was low. However, phosphatidylinositol was higher in PFC than in RDS. In the other diseases studied, the phospholipid composition resembled that of the normal newborn, namely PG was present and the L/S ratio was high. Surfactant deficiency seems to be important in the pathogenesis of some cases of PFC. The favorable effect of mechanical ventilation may be partly due to the stabilization of peripheral airways.