Complement-mediated neutrophil activation in sepsis- and trauma-related adult respiratory distress syndrome. Clarification with radioaerosol lung scans.

Complement-mediated neutrophil activation (CMNA) has been proposed as an important pathogenic mechanism causing acute microvascular lung injury in the adult respiratory distress syndrome (ARDS). To clarify the relationship between CMNA and evolving lung injury, we studied 26 patients with multiple trauma and sepsis within 24 hours of risk establishment for ARDS. Pulmonary alveolar-capillary permeability (PACP) was quantified as the clearance rate of a particulate radioaerosol. Seventeen patients (65%) had increased PACP (six developed ARDS) while nine (35%) had normal PACP (none developed ARDS; clearance rates of 3.4%/min and 1.5%/min, respectively). These patients, regardless of evidence of early lung injury, had elevated plasma C3adesArg levels and neutrophil chemotactic desensitization to C5a/C5adesArg. Plasma C3adesArg levels correlated weakly, but significantly, with PACP. Thus, CMNA may be a necessary, but not a sufficient, pathogenic mechanism in the evolution of ARDS.