C3a and adult respiratory distress syndrome after massive transfusion.

We compared the degree of complement activation in 15 patients receiving massive blood transfusions and 21 patients with the septic syndrome and examined its association with other risk factors for adult respiratory distress syndrome (ARDS). Patients with massive transfusion (n = 8) as their only risk factor for ARDS had lower C3a levels (250 +/- 80 ng/ml) and a lower incidence of ARDS (0%) than patients with massive transfusion plus other risk factors (n = 7; C3a, 600 +/- 120 ng/ml; ARDS, 55%) or patients with the septic syndrome (n = 21; C3a, 540 +/- 80 ng/ml; ARDS, 19%). In our patients, the degree of complement activation appeared to reflect the presence of complicating clinical conditions.