ObjectiveTo examine the effect of FIO2on the contents of total protein, total phospholipids, phosphatidylcholine, and phosphatidylglycerol in the bronchoalveolar lavage-accessible space in male and female rats in vivo.DesignProspective, controlled trial.SettingResearch laboratory.SubjectsAdult male and female Sprague-Dawley rats.InterventionsAfter animals were anesthetized with an intraperitoneal injection of pentobarbital (50 mg/kg), a 24-gauge catheter was placed in the femoral artery. Determinations of arterial pH and PaO2and PaCO2were performed before tracheostomy, and all animals were then ventilated for 3 mins with an FIO2of 0.21, followed by a reduction bronchoalveolar lavage. The animals were randomly divided equally by gender and given either an FIO2of 0.21, 0.50, or 1.00. All subjects were ventilated in the same manner. Sampling bronchoalveolar lavage was performed 80 and 160 mins after institution of the variable FIO2. Bronchoalveolar lavage samples were analyzed for protein and phospholipid content. Arterial blood was obtained for determination of arterial pH and the PaO2and PaCO2immediately and 40 mins after each sampling bronchoalveolar lavage.Measurements and Main ResultsAt the times of bronchoalveolar sampling lavage, the PaCO2increased and the PaO2decreased, as did the pH. In the 40-min samples obtained between sampling lavages, the arterial pH and PaCO2and PaO sub 2 returned to pretracheostomy values (animals ventilated with an FIO2of 0.21) and/or higher po2values (animals ventilated with an FIO2of 0.5 or 1.0).No differences were found between genders in amounts of total protein and phospholipid content in reduction and zero time bronchoalveolar lavage fluid. Males and females ventilated with an FIO2of 0.21 differed in the amounts of total protein, total phospholipids, phosphatidylcholine, and phosphatidylglycerol found in sampling bronchoalveolar lavage at 80 and 160 mins. Amounts of total protein and total phospholipids also demonstrated gender differences with the administration of an FIO2of 1.0, but no differences were found with the administration of an FIO2of 0.5. In terms of the phospholipids, males had greater amounts in the sampling bronchoalveolar lavage at 80 mins, and females at 160 mins. Administration of an FIO2of 0.5 or 1.0 resulted in decreased amounts of total phospholipids in both males and females when compared with an FIO2of 0.21. In males, administration of both FIO2of 0.5 and 1.0 resulted in decreased amounts of phosphatidylcholine found in the bronchoalveolar lavage-accessible space; in females, amounts of phosphatidylcholine were only decreased when an FIO2of 1.0 was administered. In males, administration of an FIO2of 1.0 also resulted in decreased amounts of phosphatidylglycerol. The decreased amount of phosphatidylglycerol occurred in females given an FIO2of 0.5. Amounts of total protein in males and females given an FIO2of 0.5 and in females given an FIO2of 1.0 were found to be increased.ConclusionsOur findings support the hypothesis that hyperoxia alters surfactant composition. Further investigation is warranted to determine the mechanisms affecting secretion of phosphatidylcholine and phosphatidylglycerol into the bronchoalveolar space and to explore the gender difference in secretion.(Crit Care Med 1996; 24:862-869)