Factor XIIIa and clot strength after cardiopulmonary bypass

Reduced factor XIIIA levels and decreased clot strength have been associated with increased bleeding after cardiopulmonary bypass (CPB). The purpose of this study was to evaluate the relationship between hemostatic factors, including factor XIIIA, and clot strength before, during and after CPB. Factor XIIIA antigen, platelet counts, fibrinogen, factor V activity, tissue plasminogen activator and clot strength (by thromboelastograph) were measured at baseline, after 45 min of CPB, at the end of CPB and 4 h post-operatively in 34 patients. Baseline factor XIIIA antigen was 5.2 ± 1.4 mg/l. On average, factor XIIIA levels dropped to 64% and clot strength to 77% of baseline values after 45 min on CPB and remained below baseline during the immediate post-operative period. Clot strength was significantly correlated (r = 0.81) with platelet count and fibrinogen but not plasma factor XIIIA levels. Addition of 10 mg/l recombinant factor XIII{a₂} significantly increased clot strength. Postoperative bleeding at 2 h was inversely correlated with platelet count, factor XIIIA antigen and clot strength measured at the end of CPB. Maintenance of adequate platelet counts and factor XIIIA levels at the end of CPB may play a role in maintaining clot strength and reducing blood loss.