Comparison of pulmonary and inflammatory effects of lipid- and water-soluble components in meconium in newborn piglets.

To understand the pathogenesis of meconium aspiration syndrome, we compared the pulmonary and inflammatory effects of the water and lipid extracts of human meconium instilled into the lungs of newborn piglets. The piglets were artificially ventilated, made hypoxemic, and randomized into three groups. At start of reoxygenation, 3 ml/kg of one of the following mixtures was instilled intratracheally: (1) meconium (n = 12); (2) water extract of meconium (n = 12), and (3) lipid extract of meconium (n = 12). During 8 h of reoxygenation, hemodynamics, pulmonary gas exchange, lung mechanics, and interleukin-8 concentrations in tracheobronchial aspirates were monitored. Oxygenation index (p = 0.04) and mean airway pressure (p = 0.04) increased more in the lipid extract group than in the water extract group. Dynamic compliance and mean arterial blood pressure decreased (p < 0.05) in the meconium and lipid extract groups, but not in the water extract group. At 8 h of reoxygenation, the interleukin-8 concentration in the tracheobronchial aspirates was three times higher in the lipid extract group as compared with the water extract group (110 +/- 102 vs. 37 +/- 27 pg/ml; p = 0.02). In conclusion, pulmonary dysfunction in meconium aspiration syndrome is caused by both the water- and lipid-soluble fractions of meconium, with stronger inflammatory and more detrimental effects promoted by the lipid extract than the water extract.