Text Box: BENEFICIAL EFFECTS OF ADDING SOLUBLE POLYMERS TO PULMONARY SURFACTANTS Lu K W, Dehority W, and Taeusch H W Department of Pediatrics, University of California-San Francisco, USA Objective: Surfactant treatment of lung injuries (e.g., acute or adult respiratory distress syndrome) has been less successful than treatment of respiratory distress syndrome of premature infants because of surfactant inactivation by proteinacious alveolar edema. Our goal is to make therapeutic surfactants that are resistant to inactivation and to find whether they can also improve treatment of acute lung injuries. Methods: We added polymers, e.g., dextran or polyethylene glycol (PEG), to a variety of surfactants and studied the resistance to serum inactivation in a pulsating bubble surfactometer. In addition, we studied Survanta with or without PEG in four lung injury models: saline lavage, meconium, HCl, and lipopolysaccharide (LPS) in rats. Results: For the in vitro experiments, PEG was of most benefit when added to Survanta whereas dextran was of most benefit with Curosurf and Infasurf. Neither polymer was of significant benefit with native surfactant (which did not inactivate easily) or with Exosurf. The degree of polymer-induced aggregation correlated with improvement in surface activity. In rat experiments, Survanta + PEG significantly improved lung function when compared with Survanta alone. These effects were most evident with the meconium, endotoxin, and HCl injuries. In the lavage injury, we think beneficial effects of PEG added to Survanta were damped due to osmotic effects of PEG increasing alveolar edema. Conclusions: Results indicate that surface activity is improved when polymers are added to surfactants and that addition of polymers to surfactants provides better treatment of acute lung injuries. Polymers interact with SP-B and SP-C as well as surfactant lipids in ways that are not well understood to prevent inactivation of surfactant and to improve surface activity. 2422