Anti-Factor Xa Monitoring of Enoxaparin Thromboembolism Prophylaxis in Emergency General Surgery Patients

Abstract

Background: Rates of venous thromboembolism (VTE) remain high in emergency general surgery (EGS) patients despite chemical VTE prophylaxis. Emerging literature supports anti-factor Xa (AFXa) monitoring for patients on enoxaparin (LMWH), although a significant knowledge gap remains regarding the optimal dosing and monitoring in EGS patients. We hypothesize that standard dose VTE prophylaxis regimens provide inadequate VTE prophylaxis in EGS patients.

Study design: A prospective cohort study of all adult EGS patients at a single institution between August 2021 and February 2022 receiving standard dose LMWH 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 repeat AFXa measurement after the adjusted third dose was obtained.

Results: A total of 81 patients underwent AFXa monitoring, the majority (75%) of whom were started on 40 mg LMWH 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, remained admitted, and underwent dosing adjustment and AFXa reassessment (27%), the majority were adjusted to either 30 or 40 mg of LMWH twice daily (23.7% and 55%, respectively), with 82% of patients remaining low. There were no significant differences in demographics or BMI between those with low vs adequate AFXa levels at either initial or subsequent measurement.

Conclusions: Standard LMWH 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 EGS patients.