Relation of Antifactor-Xa peak levels and venous thromboembolism after trauma.

Background: No previous studies have established the optimal antifactor Xa (anti-Xa) level to guide thromboprophylaxis (TPX) dosing with enoxaparin in trauma patients. We hypothesize that achieving 0.2-0.4 IU/ml anti-Xa will decrease venous thromboembolism (VTE) rates after trauma. Methods: This was a restrospective review of 194 intensive care unit patients sustaining blunt or penetrating trauma from 1/2015-3/2017. All received initial enoxaparin (30mg BID subcutaneous) and mechanical devices for TPX. Peak anti-Xa levels were drawn after each third dose. The enoxaparin dose was adjusted up to a maximum of 60mg BID subcutaneous until a peak level of 0.2-0.4 IU/mL was achieved. Data are expressed as mean+/-SD if parametric or median (IQR) if not. Results: The Greenfield Risk Assessment Profile score was 9 +/- 4, Injury Severity Score 23 +/- 14, and hospital length of stay 19 (11-38) days. The overall VTE rate was 7.2% (n=14), with 10 deep venous thromboses (DVT) and 5 pulmonary emboli (PE). One patient had both a DVT and PE. The median time to VTE diagnosis was 14 (7-17) days. In those diagnosed with a VTE, 50.0% (n=7) never reached 0.2-0.4 IU/mL anti-Xa and 42.8% (n=6) were diagnosed with a VTE after achieving these levels. Prophylactic levels were achieved initially in 64 (33.0%) patients, and achieved later in 38 (19.6%) additional patients, giving an overall prophylactic rate of 52.6% (n=102). There were no differences in VTE (6.9% vs. 7.6%, p=0.841), DVT (3.9% vs 6.5%, p=0.413), or PE (3.9% vs 1.1%, p=0.213) rates between those who became prophylactic and those who did not. Conclusions: There was no difference in VTE incidence between those achieving anti-Xa peak levels of 0.2-0.4 IU/ml and those that did not. Furthermore, these levels were never achieved in some trauma patients despite repeated dosing over a >10 day period. Level of Evidence: Level IV, Therapeutic Study (C) 2017 Lippincott Williams & Wilkins, Inc.

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