Calculated Plasma Volume Status Is Associated With Mortality in Acute Respiratory Distress Syndrome

The optimal method to assess fluid overload in acute respiratory distress syndrome is not known, and current techniques have limitations. Plasma volume status has emerged as a noninvasive method to assess volume status and is defined as the percentage alteration from ideal plasma volume. We hypothesized that plasma volume status would suggest the presence of significant excess volume and therefore correlate with mortality in acute respiratory distress syndrome.

This is a retrospective cohort study of subjects enrolled in four previously completed National Heart Lung and Blood Institute-sponsored acute respiratory distress syndrome trials, using data from the National Institutes of Health Biologic Specimen and Data Repository Information Coordinating Center repository.

Study subjects included 3,165 patients with acute respiratory distress syndrome previously enrolled in National Heart Lung and Blood Institute-sponsored acute respiratory distress syndrome trials.

The exposure variable of interest was plasma volume status, calculated as the percentage alteration of actual plasma volume calculated on the basis of weight and hematocrit using sex-specific constants. We performed Kaplan-Meier survival analysis and univariable and adjusted Cox proportional hazard models to determine the association of plasma volume status with 60-day mortality. The median age of subjects was 52 years (interquartile range, 40-63 yr). Median plasma volume status was 5.9% (interquartile range, -2.4% to 13.6%), and overall, 68% of subjects had positive plasma volume status suggesting plasma volume higher than ideal plasma volume. In adjusted models, plasma volume status greater than median was associated with 38% greater risk for mortality (hazard ratio, 1.38; 95% CI, 1.20-1.59; p < 0.001). Each interquartile range increase in plasma volume status was associated with greater mortality in adjusted models (hazard ratio, 1.24 per interquartile range increase; 95% CI, 1.13-1.36; p < 0.001). Plasma volume status greater than median was associated with fewer ventilator-free days (18 vs 19 d; p = 0.0026) and ICU-free days (15 vs 17 d; p = 0.0001).

Plasma volume status is independently associated with mortality, ICU-free days, and ventilator-free days among subjects with acute respiratory distress syndrome. Plasma volume status could be considered for risk-stratification and to direct therapy, particularly fluid management.