111 LUNG EDEMA DECREASES THE RESPONSIVENESS TO EXOGENOUS SURFACTANT

Abstract

There is a large variability in the effect of exogenous surfactant in RDS. We have tested the hypothesis that hydrostatic lung edema decreases the responsiveness to surfactant. Respiratory failure was induced to rabbits, wt. 1-1.3 kg, by alveolar lavage (BAL, 10 ml/kg × 4). Thereafter, natural surfactant (NS, 100 mg/kg in 4 ml saline, n=10), saline carrier (n=8), or air (n=8) was administered. The animals ware paralyzed and ventilated at constant tidal volume. They received either 1 (low) or 20 ml/kg/h (high) saline i.v. during 155 min. The lung function was measured and BALs were analyzed for phosphatidylcholine (PC), concentration of PC in epithelial lining fluid (PCelf), protein, and surface activity. Saline carrier to airways decreased the gas exchange and compliance (p<0.01). In animals on low i.v. fluids, NS improved the respiratory function as compared to air-treated controls. However, in animals on high i.v. fluids, NS neither improved the gas exchange nor the compliance, despite the increase in PC (p < 0.05) and the decrease in soluble protein (p < 0.05) in BAL. The lack of surfactant responsiveness was due to low PCelf and to surfactant inhibitors. Thus, variability in surfactant responsiveness may be caused by factors affecting lung liquid.