Low Plasma Fibrinogen Levels with the Clauss Method during Anticoagulation with Bivalirudin

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Abstract
Bivalirudin is a bivalent direct thrombin inhibitor (DTI) with a plasma half-life of approximately 25 min. It is increasingly used as a heparin alternative in percutaneous coronary intervention procedures,1 and in cardiac surgical patients with heparin-induced thrombocytopenia.2,3 The anticoagulant effect of bivalirudin usually is monitored with activated clotting time, but the utility of viscoelastic monitors, including Thrombelastograph® or thromboelastometry (e.g. , ROTEM®; Pentapharm, Munich, Germany), has been recently demonstrated by us and the other group.4,5 We herein describe a case in which bivalirudin monitoring with ROTEM® was found useful. A 68-yr-old, 110-kg female was diagnosed with acute myocardial infarction. The cardiac catheterization showed ostial occlusion of left anterior descending artery, 90% stenosis of right coronary artery, and 40% stenosis of circumflex artery. Past medical history was notable for hypertension, hypercholesterolemia, type II diabetes, chronic anemia, and mild cirrhosis. Given her previous history of heparin-induced thrombocytopenia and persistent antibody titer on admission, she was treated with argatroban infusion at 0.5 μg · kg · min until 4 h before the scheduled off-pump coronary bypass graft surgery. Baseline laboratory results showed hematocrit 33.3%, platelet 111 × 103/mm3, fibrinogen 432 mg/dl, partial thromboplastin time 73.8 s, and celite-activated clotting time 188 s. For anticoagulation, bivalirudin was given at 0.75 mg/kg, followed by infusion at 0.75 mg · kg · h, according to her ideal body weight (70 kg). This regimen maintained activated clotting time above 400 s, and delayed tissue factor induced thrombus formation on ROTEM® (fig. 1A). Bivalirudin infusion was stopped at the beginning of proximal anastomoses, and laboratory values were hematocrit 21%, platelet 103 × 103/mm3, and activated clotting time 278 s at the end of three-vessel bypass procedure. Two units of packed red blood cells were administered, and infusion of tranexamic acid 2 mg · kg · h was started. Notably, the plasma fibrinogen level using the modified Clauss method (BCS®, Dade Behring, Deerfield, IL) was reported at that time as less than 60 mg/dl, but the ROTEM®-based fibrinogen assay (maximal clot formation of FibTEM®[Pentapharm, Munich, Germany]) indicated functional fibrinogen level6 throughout the bivalirudin infusion (fig. 1A). The postoperative chest tube drainage was 180 ml over 12 h.

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