Extravascular lung water indexed to predicted body weight is a novel predictor of intensive care unit mortality in patients with acute lung injury*

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Abstract
Acute lung injury and the acute respiratory distress syndrome are characterized by noncardiogenic pulmonary edema, which can be assessed by measurement of extravascular lung water. Traditionally, extravascular lung water has been indexed to actual body weight (mL/kg). Because lung size is dependent on height rather than weight, we hypothesized indexing to predicted body weight may be a better predictor of mortality in acute lung injury/acute respiratory distress syndrome. Prospective observational cohort study. A tertiary referral intensive care unit. Patients were recruited within 48 hrs of fulfilling the American European Consensus Conference definition of acute lung injury/acute respiratory distress syndrome. None. Demographics, severity of illness scores, and respiratory parameters were collected. Extravascular lung water was measured using the PiCCO system. This was indexed to actual and predicted body weight. Statistically significant predictors of mortality identified using single regressor logistic regression and additional variables known to be associated with outcome were entered into a multiple logistic regression analysis. Receiver operator characteristic curves were generated. Forty-four patients were recruited (septic 34%). Using single regressor logistic regression, six variables were statistically significantly related to mortality: Acute Physiology and Chronic Health Evaluation II, PaO2, PaO2/Fio2 ratio, oxygenation index, actual extravascular lung water, and predicted extravascular lung water. In multiple logistic regression analysis, predicted extravascular lung water but not actual extravascular lung water was a predictor of mortality with an odds ratio of 4.3 (95% confidence interval, 1.5–12.9) per sd. Although the area under the curve for predicted extravascular lung water (0.8; confidence interval, 0.65–0.94) was larger than for actual extravascular lung water (0.72; confidence interval, 0.53–0.91), this was not statistically significant (p = .12). A baseline predicted extravascular lung water value of 16 mL/kg predicted intensive care unit mortality with a sensitivity of 0.75 (confidence interval, 0.47–0.91) and specificity of 0.78 (confidence interval, 0.61–0.89). Early measurement of predicted extravascular lung water is a better predictor than actual extravascular lung water to identify patients at risk for death in acute lung injury/acute respiratory distress syndrome.

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