In neonates with meconium aspiration syndrome (MAS) and pneumonia, there is increasing evidence that abnormalities of pulmonary surfactant contribute to lung dysfunction. We examined surfactant status in ventilated neonates with MAS (n=9) and bacterial pneumonia (n=8) in comparison with a control group of infants with no lung disease (n=16, median age 1.5 mths). Lung lavage fluid was collected by tracheal aspirate (TA, 4 × 0.5 ml saline), and by bronchoalveolar lavage (BAL, 3 × 1 ml/kg saline). Sequential samples were taken in the neonates with lung disease, and the sample taken closest to the height of the illness (indicated by highest alveolar-arterial oxygen difference, AaDO2) was used in this analysis. In the lavage fluid we assayed disaturated phosphatidylcholine (DSPC) and surfactant protein A (SP-A) and expressed their concentration relative to the calculated volume of epithelial lining fluid (ELF). Geometric mean values for [DSPC]ELF and[SP-A]ELF obtained in the MAS and pneumonia groups were each compared with controls by performing a t-test for independent samples on log transformed data. RESULTS: At the time of sampling, mean AaDO2 was 386 mm Hg for MAS and 372 mm Hg for pneumonia; no infant was receiving ECMO. In the MAS group, SP-A concentration in both TA and BAL specimens was deficient compared to controls, but DSPC levels appeared to be normal (seetable). For infants with pneumonia, both DSPC and SP-A in BAL samples were markedly lower than controls; these abnormalities were not clearly seen in TA specimens. CONCLUSIONS: At the height of illness, infants with MAS exhibit SP-A deficiency but normal DSPC levels, whereas in pneumonia, both surfactant indices are depressed. These findings may reflect different pathophysiological mechanisms leading to surfactant deficiency in the two diseases.
