Pulmonary surfactant, which is crucial for alveolar stability, may also be involved in endogenous defense mechanisms of the lungs. Thus, alterations in pulmonary surfactant may promote infections, including pneumonia and septicemia. Because patients who have acute respiratory failure often develop pneumonia, thus septicemia, we investigated when surfactant is altered in these patients and whether there is a specific pattern of changes in surfactant phospholipid composition associated with septicemia in these patients. To answer these questions, we determined the phospholipid content and composition in lung washings obtained from alveolar sites (by bronchoalveolar lavage) and from tracheal sites (by aspiration). Both techniques were performed serially over a period of 18 days in 30 patients who had acute respiratory failure resulting from polytrauma, 18 of whom developed septicemia caused by pneumonia. We found that in lung washings obtained from the alveolar sites from all patients, the phosphatidylglycerol content was decreased and the phosphatidylinositol content was increased as early as 6 hr after trauma and normalized during recovery of the patients. In addition, alveolar phosphatidylcholine content was decreased 24 hr after trauma. In patients who developed septicemia during the observation time, but not in patients who had uncomplicated courses of acute respiratory failure, the concentrations of alveolar phosphatidylethanolamine (normally 4.8% of total phospholipids) and alveolar phosphatidylcholine (normally 62.8%) both approached the proportions found in the trachea (phosphatidylethanolamine 33.4%, phosphatidylcholine 35.6%), suggesting that surfactant phospholipid pool size had progressively decreased. Our results indicate that in patients who have acute respiratory failure, pulmonary surfactant is altered very early, and that when septicemia complicates the course of acute respiratory failure, the surfactant phospholipid pool size decreases progressively.(ABSTRACT TRUNCATED AT 250 WORDS)