Differential clearance of colloid and crystalloid solutions from the lung

The hypothesis that alveolar fluid clearance depends on factors other than the alveolar-capillary oncotic gradient was tested by comparing lung clearance rates of three different colloid solutions and isotonic saline. The solutions (4 mL/kg) were instilled into the lower lobes of New Zealand rabbits. Colloid solutions were diluted to produce a fixed gradient of 8 mm Hg for each experiment. Fluid clearance was calculated at 3 hours, using lung gravimetrics. Surface tension, as a measure of surfactant inhibition, was measured in separate experiments using bubble surfactometry. Airway inflammatory reaction was assessed by determining leukocyte counts in bronchoalveolar lavage (BAL). Data were analyzed using ANOVA with Tukey's test for multiple comparisons. Alveolar fluid clearance rates were significantly different (p < 0.01) between groups, and varied between 2.0 +/- 0.12 mL/kg (saline), and -0.04 +/- 1.7 (plasma). Clearance rates for saline and dextran 70 were similar despite an increased plasma-alveolar osmotic gradient. Surface tension, reflecting surfactant inhibition, was greater with the plasma (3.9 +/- 3.7 mN/m) compared with the other groups (range, 0.23-0.48 mN/m) (p < 0.01). Neutrophil migration was greater with the protein group, but there were no differences in total WBC counts between groups. These data suggest that fluid clearance from the airspaces is primarily dependent on factors other than simple colloid-capillary osmotic gradient. Alveolar PMN migration was not a major determinant of fluid clearance. The association between surfactant inhibition and decreased fluid clearance rate observed with homologous plasma suggests that protein interference with the surfactant monolayer may play a role in reducing alveolar fluid clearance.(ABSTRACT TRUNCATED AT 250 WORDS)