Complement activation during cardiopulmonary bypass and association with clinical outcomes.

In this prospective, single-centre observational study of 30 patients undergoing cardiopulmonary bypass (CPB), the effect of unfractionated heparin (UFH), CPB surgery and protamine sulphate on complement and on post-operative blood loss were assessed. Although C3 and C4 levels decreased significantly immediately following the administration of UFH, C3a, C5a, Bb fragment and SC5b-9 remained unchanged. During CPB, C3 and C4 continued to fall whilst both alternative and classical pathways activation markers, Bb, C3a, C5a and SC5b-9 increased significantly. Protamine sulphate had no effect on classical pathway components or activation markers but decreased alternative pathway activation marker Bb. Over the 12-24 h post-surgery, both classical and alternative pathway activation markers returned to baseline, whilst C3 and C4 levels increased significantly but not to baseline values. Total drain volume 24 h after the surgery showed a moderate inverse correlation with post-protamine C3 ( = -0.46,  = 0.01) and C4 ( = -0.57,  = 0.0009) levels, whilst a moderate positive correlation was observed with post-protamine C3a ( = 0.46,  = 0.009), C5a ( = 0.37,  = 0.04) and SC5b-9 ( = 0.56,  = 0.001) levels but not with Bb fragment ( = 0.25,  = 0.17). Thus, inhibition of complement activation may be a therapeutic intervention to reduce post-operative blood in patients undergoing CPB.