Bronchoalveolar lavage in an animal model of acute lung injury. Relationship between enhanced membrane permeability and transvascular neutrophil flux.

Results of studies utilizing bronchoalveolar lavage (BAL) have led workers to propose that the neutrophil serves as the pivotal cellular element responsible for promoting enhanced alveolar capillary membrane (ACM) permeability in certain forms of acute lung injury. The authors performed BAL on anesthetized, intubated, instrumented sheep before and after the administration of 15 mg/kg ethchlorvynol, a known pulmonary edemagenic agent. Bronchoalveolar lavage fluid (BALF) protein content increased from 0.62 +/- 0.05 to 1.5 +/- 0.15 mg/ml, and the percentage of neutrophils recovered from 2% +/- 1% at baseline to 35% +/- 7% (P less than 0.01) 60 minutes after infusion of ethchlorvynol. After ethchlorvynol infusion into neutropenic sheep (less than 500 cells/microliter), BALF protein content increased from 0.35 +/- 0.08 to 1.5 +/- 0.69 mg/ml (P less than 0.01) with no increase in BALF neutrophil count. In 3 non-neutropenic sheep BAL was performed at 15 and 30 minutes after ethchlorvynol infusion. BALF protein content increased significantly within 15 minutes, whereas the percentage of neutrophils did not change. These findings suggest coexistent ACM injury as reflected by increases in BALF protein content and increased number of neutrophils in BALF does not necessarily imply a cause-and-effect relationship in certain forms of acute lung injury.