Objective: Fibrinogen and factor XIII (FXIII) have been shown to critically influence clot firmness in the intraoperative setting and thus likely influence intraoperative bleeding. We were interested to identify potential modulators of postoperative clot firmness in a tertiary care hospital surgical intensive care unit setting, independent of their clinical course during surgery. Methods: 272 day-shift consecutive patients were evaluated for whole blood clot firmness evaluated by the ROTEM® EXTEM thrombelastometric assay and various potential modulators of clot firmness upon arrival at the surgical intensive care unit (SICU). Results: Maximum clot firmness on the SICU was found to be independently influenced by the amount of colloids given during surgery as well as by platelet count, fibrinogen concentration, and FXIII activity at the time of SICU admission. In patients with lowest clot firmness, FXIII activity was the most important independent modulator of clot firmness; in patients with the highest clot firmness, platelet count and fibrinogen concentration were the most important modulators of clot firmness. Deficiencies (i.e., results below normal range) of these modulators of clot firmness were most prevalent for FXIII (activity < 70%: 45% of cases), which was significantly more frequent than thrombocytopenia (<150 × 10⁹/l: 32%) or fibrinogen deficiency (<1.5 g/l: 6%). Conclusions: Postoperative clot firmness as evaluated by whole blood thrombelastometry (ROTEM EXTEM assay) is independently and frequently modulated though FXIII activity and the platelet count, while fibrinogen concentration is also an independent but much less frequent modulator. Different modulators show different influences, depending on the clot firmness being present. Colloids infused during surgery also independently modulate postoperative clot firmness. Based on our data, strategies can be developed to improving postoperative care of patients with bleedings or at risk for bleeding.

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