A Modified Bronchoalveolar Lavage Procedure That Allows Measurement of Lung Epithelial Lining Fluid Volume

We replaced the standard serial bronchoalveolar lavage technique with a new “rewash” lavage procedure to allow estimation of the volume and protein concentration of the epithelial lining fluid (ELF) in anesthetized sheep. A bronchoscope 6.0 mm in diameter wedged in an airway was used to lavage a segment of lung with four cycles of instillation and aspiration of the lavage solution containing a radioactive tracer (technetium pertechnetate, 99mTcO4 −). Errors caused by the fall in concentration of the tracer during the lavage were minimized by extrapolating the tracer concentration back to time zero when the lavage solution had mixed with the ELF, but had not had time to be affected by loss of the tracer or influx of fluid from the interstitium. In control sheep, the ELF of these lavaged segments had a mean volume of 1.6 ± 1.0 ml and a mean protein concentration that was 26 ± 19% of the protein concentration measured in the plasma. Increasing the left atrial pressure 19 ± 5 cm H2O to cause “cardiac lung edema” had no significant effect on the ELF volume, but it increased the mean protein concentration to 57 ± 30% of the plasma value (p < 0.01). Lung injury caused by intravenous oleic acid caused lung edema, increased the mean ELF volume to 6.8 ± 2.2 ml, and increased the mean ELF protein concentration to 86 ± 26% of the plasma value (p < 0.01). The ELF volume correlated well with the degree of alveolar flooding assessed histologically (r = 0.90, p < 0.01), and the ELF protein concentrations agreed well with direct sampling measurements made by other investigators. We conclude that the rewash lavage method provides accurate estimates of the volume and protein concentrations of the ELF and that the edema caused by the 19 cm H2O increase in left atrial pressure was primarily interstitial, with little or no alveolar flooding.