Changes in the Relationship Between Plasma Fibrinogen Concentration and Functional Clot Strength After Cardiopulmonary Bypass: A Retrospective Observational Study.

Objective: To evaluate whether the relationship between plasma fibrinogen concentration (Clauss method) and functional fibrinogen activity as measured by viscoelastic hemostatic assays (VHAs)- thromboelastography-derived citrated functional fibrinogen (CFF) and Quantra-derived fibrinogen contribution to clot stiffness (FCS)-changes before and after cardiopulmonary bypass (CPB).

Design: A single-center retrospective observational study.

Setting: Cardiovascular surgery center in Japan.

Participants: 208 adult patients undergoing cardiovascular surgery with CPB.

Interventions: No intervention.

Measurements and main results: Fibrinogen function was assessed at 3 time points: before CPB (T1), immediately after protamine administration (T2), and 1 hour later (T3). CFF (n = 170) and FCS (n = 79) values, along with plasma fibrinogen concentrations, were collected. For CFF, the regression slope against Clauss fibrinogen increased from 6.12 at T1 to 8.69 at T2 (p < 0.05), then returned to 6.58 at T3. The intercept decreased significantly at T2 (from 0.29 to -8.39), indicating enhanced clot strength per unit of fibrinogen. For FCS, the slope decreased from 1.66 at T1 to 0.61 at T2 and 0.72 at T3, and the intercept increased from -3.55 to -0.32, suggesting persistently reduced fibrinogen contribution post-CPB. Conventional tests showed prolonged prothrombin time/activated partial thromboplastin time, decreased hemoglobin and platelet counts, and elevated thrombin antithrombin complex, fibrin/fibrinogen degradation products, and D-dimer levels, indicating coagulation factor consumption and thrombin generation.

Conclusions: The association between fibrinogen concentration and functional clot strength changes significantly after CPB, with contrasting trends in TEG and Quantra. These findings highlight qualitative fibrinogen alterations post-CPB, suggesting that concentration alone might not reflect true coagulative function.