Effects of Cardiac Surgery and Salvaged Blood Transfusion on Coagulation Function Assessed by Thromboelastometry

Objectives: Coagulation function dynamically changes during cardiac surgery and is normalized after surgery. The authors investigated changes of coagulation function during cardiac surgery and after mimicked salvaged blood transfusion (SBT), and determined background risk factors for coagulation dysfunction by thromboelastmetry including maximum clot firmness of fibrinogen assay (FIBTEM-MCF: primary variable). Design: Prospective observational study with ex vivo laboratory experiment. Setting: University hospital. Participants: Consecutive 65 adult elective cardiac surgery patients being scheduled to use cell salvage technique. Interventions: Arterial blood sampling (preoperative: after anesthesia induction, and postoperative: after reversal of heparin), and ex vivo dilution of postoperative blood with salvaged blood (7.4%: 2.5 mL + 0.2 mL and 18.5%: 2.2 mL + 0.5 mL). Measurements and Main Results: Thromboelastometry was performed for the preoperative blood sample, and postoperative blood samples mixed with different amount of the salvaged blood. Preoperative FIBTEM-MCF significantly decreased after cardiac surgery (16.5 [95% confidence interval (15.4-17.6)] mm to 9.5 [8.4-10.6] mm, p < 0.0001). In vitro 7.4% and 18.5% salvaged blood addition dose-dependently reduced FIBTEM-MCF (9.1 [95% confidence interval (8.0-10.1)] mm, 7.9 [6.8-9.0] mm, respectively, p < 0.0001). Preoperative FIBTEM-MCF and changes of FIBTEM-MCF during cardiac surgery were independent risk factors for development of the FIBTEM-MCF 8 mm or less after in vitro salvaged blood addition. Furthermore, residual heparin within salvaged blood was indicated by significant increase of intrinsic assay-clotting time/ heparin assay-clotting time after 18.5% in vitro salvaged blood addition (p < 0.0001). Conclusions: Salvaged blood transfusion of more than 18.5% whole blood volume may impair coagulation function particularly in patients with lower FIBTEM-MCF before and after cardiac surgery.