Hypoproteinemia as a marker of acute respiratory distress syndrome in critically ill patients with pulmonary edema

Objective: To assess the value of serum protein levels for differentiating permeability pulmonary edema in the course of acute respiratory distress syndrome (ARDS) from cardiogenic pulmonary edema (CPE). Design and setting: Observational cohort study in intensive care units of 720-bed university hospital. Patients: Twenty-four consecutive patients with clinical evidence of edema, 11 fulfilling the consensus definition of ARDS, 7 having sepsis, 5 with all ARDS consensus criteria and sepsis but a pulmonary capillary wedge pressure above 18 mmHg (mixed), and 8 with CPE. All patients except for one with CPE were mechanically ventilated. Measurements and results: Radionuclide assessments of pulmonary microvascular protein (transferrin) permeability (pulmonary leak index, PLI) were carried out and serum protein levels determined at admission and for ARDS/mixed patients, at recovery, defined by a decrease in positive end-expiratory pressure to 0 cmH₂O. At admission the PLI was higher in ARDS/mixed than in CPE patients. The total protein and transferrin levels were lower in the former. The area under the curve of the receiver operating characteristic for diagnosing ARDS (vs. CPE) was 0.98 for transferrin (cutoff value 1.5 g/l), 0.95 for total protein (cutoff value 59 g/l) and 0.80 for albumin (cutoff value 24 g/l) levels. In various clinical diagnostic groups the transferrin level approached the PLI in diagnostic value. At recovery the PLI had decreased and serum protein levels increased. Conclusions: The data suggest that hypoproteinemia is a marker of ARDS. This may partially reflect increased permeability in the lungs, systemically, or both.