Accurate reference measurement for postmortem lung water.

To test the hypothesis that dry blood-free lung weight is increased during pulmonary edema, thereby leading to an underestimation of the ratio of extravascular lung water-to-dry lung weight, we measured postmortem lung water, dry mass, and hydroxyproline content in 33 sheep with normal lungs (n = 10), high-pressure edema (n = 9), or increased permeability edema (n = 14). Residual blood in the lung, measured using hemoglobin as the intravascular marker in all sheep, and also using 51Cr-tagged red blood cells in 24 sheep, was not different between the two methods or among the three groups of sheep. Extravascular lung water increased 64% in sheep with high-pressure edema and 82% in those with increased permeability edema compared with control values. Dry blood-free lung weight was significantly greater (33% more than control values) in sheep with increased permeability edema, causing the ratio of extravascular lung water-to-dry blood-free lung weight to underestimate accumulated lung water by about 50%. Because hydroxyproline content of the lung was not affected by edema, the ratio of extravascular lung water-to-lung hydroxyproline content was more accurate than the ratio of extravascular lung water-to-dry blood-free lung weight in the quantification of pulmonary edema.