REGIONAL LUNG HEMATOCRIT VARIATION AND ASSESSMENT OF ACUTE LUNG INJURY

Estimating blood content in the lung remains a key step in calculating lung water volume and microvascular permeability. We studied the effe ct of regional lung hematocrit (Hct) variation on assessment of acute lung injury. Escherichia coli endotoxin was administered in guinea pig s intravenously. Lung injury was evaluated by measuring the wet-to-dry weight ratio (W/D) and transvascular I-125-labeled albumin leakage fo r 3 h [tissue-to-plasma I-125-albumin ratio (T/P)] in five tissue samp les from each animal. Residual blood content was corrected using eithe r Cr-51-red blood cells as a blood cell marker, Tc-99m-albumin as a pl asma marker, or both, injected 10 min before the guinea pigs were kill ed. Lung Hct, estimated from the marker counts of lung and peripheral blood samples, was lower than peripheral blood Hct; intraindividual va riation, represented by the standard deviation in each subject, was 0. 024 +/- 0.015 for the control group (coefficient of variation 8.0 +/- 5.1%) and 0.026 +/- 0.013 for the endotoxin group (coefficient of vari ation 8.5 +/- 4.1%). Uncorrected W/D for residual blood content was gr eater than the corrected W/D. Tc-99m-albumin correction gave values cl oser to the W/D corrected by both markers. T/P corrected by Tc-99m-alb umin showed smaller data variations than the values obtained with Cr-5 1-red blood cell correction, which was affected by variations in lung Hct. We recommend using a plasma marker to correct for blood content i n assessing acute lung injury by W/D and TP.