Conventional ultrafiltration increases viscoelastic clot firmness during cardiopulmonary bypass: a prospective observational study.

PURPOSE: Ultrafiltration (UF) reduces dilution of all blood components during cardiopulmonary bypass (CPB), but its impact on coagulation performance remains unclear. We examined whether conventional UF mitigates the CPB-induced decline in extrinsic-pathway clot firmness (MCF-EXTEM; reference range 50-72 mm) measured by rotational thromboelastometry (ROTEM), a marker of coagulopathic bleeding risk in cardiac surgery. METHODS: In a prospective observational study, we recruited adult cardiac surgery patients who received UF near the end of CPB (n=39) and included patients with Pre-UF MCF EXTEM ≤50 mm (n=27). Pre-UF versus Post-UF ROTEM parameters, including MCF-EXTEM, fibrin- and platelet-based clot firmness (MCF-FIBTEM and MCF-PLTEM, respectively), were compared (Wilcoxon signed-rank tests). Changes in MCF-EXTEM and their correlation with the volume of filtered free water (UF volume) were analyzed. RESULTS: UF volume ranging 500-1200 mL increased hematocrit from 21.0% to 25.0% by 4.0% (median, P < 0.001, effect size r = 0.811). As the primary outcome, UF increased MCF-EXTEM from 45.0 mm to 49.0 mm by 4.0 mm (median, 95% confidence interval 2.5‒6.0 mm, P = 0.001, r = 0.755). UF also increased MCF-FIBTEM by 2.0 mm (median, P < 0.001, r = 0.824), but it did not affect MCF-PLTEM (P = 0.060). A moderate positive correlation between UF volume and MCF-EXTEM change was observed (Spearman's ρ = 0.41, P = 0.033). CONCLUSIONS: Conventional UF during CPB is associated with an attenuation of the CPB‑induced decline in MCF‑EXTEM, and the pattern of changes in FIBTEM and PLTEM is consistent with predominantly fibrin‑related contributions rather than platelet‑related contribution, with an apparent dependence on UF volume.