Anti-Factor Xa Monitoring of Enoxaparin Thromboembolism Prophylaxis in Acute Care Surgery Patients: Standard Dosing Is Inadequate

Abstract

INTRODUCTION: The rate of venous thromboembolism (VTE) remains high in acute care surgical (ACS) patients despite chemical VTE prophylaxis. Emerging literature supports anti-factor Xa (AFXa) monitoring for patients on enoxaparin, although a significant knowledge gap remains regarding the optimal dosing and monitoring in ACS patients. We hypothesize that standard-dose VTE prophylaxis regimens provide inadequate AFXa inhibition in ACS patients. METHODS: A prospective cohort study of all adult ACS patients at a single institution between August 2021 and February 2022 receiving standard-dose enoxaparin for VTE prophylaxis was performed. AFXa levels were obtained 4 hours after the third dose of enoxaparin with a target range of 0.3 to 0.5 IU/mL. Adjustment to dosing and a repeat AFXa measurement after the adjusted 3rd dose was obtained. RESULTS: A total of 81 patients underwent AFXa monitoring, the majority (75%) of whom were started on 40 mg enoxaparin daily. Initial peak AFXa measurement was low in 87.7% of patients (mean 0.16 IU/mL). Of patients who had an initial low AFXa and remained admitted to undergo dosing adjustment and AFXa reassessment (27%), the majority were adjusted to either 30 or 40 mg enoxaparin twice daily (23.7% and 55%, respectively), with 82% of patients remaining low. There was no significant difference in demographics or BMI between groups at either initial or subsequent AFXa. CONCLUSION: Standard enoxaparin dosing provides inadequate AFXa inhibition for adequate VTE prophylaxis. These findings highlight the importance of ongoing AFXa monitoring and the need to establish clinical protocols to improve VTE prophylaxis in ACS patients.