Rapid activation of the alternative pathway of complement by extracorporeal membrane oxygenation

Extracorporeal membrane oxygenation (ECMO) is an effective therapy for pati ents with severe respiratory distress syndromes. However, an inflammatory r esponse has been observed with the use of this therapy. We measured complem ent activation in vivo in two adults receiving ECMO for acute respiratory d istress syndrome (ARDS). Production of complement activation fragments C4d, Bb, iC3b, and SC5b-9 was determined using commercial ELISA kits. In both p atients there was intense activation of complement that peaked 1 hour (mean SC5b-9 increase to 1135% of baseline) after the start of ECMO and occurred predominantly via the alternative pathway (Bb production). Early and acute complement activation may be responsible for the initiation of the inflamm atory response that has been observed in patients treated with ECMO.