Anti-Factor Xa measurements in acute care surgery patients to examine enoxaparin dose.

Background: The purpose of this study was to determine if fixed dose enoxaparin prophylaxis provided effective anticoagulation for acute care surgery patients and to examine whether a real-time enoxaparin dose adjustment algorithm optimized anticoagulation.

Methods: Acute care surgical patients placed on enoxaparin prophylaxis 30 mg twice daily were recruited prospectively. Peak steady state aFXa levels were drawn with a goal peak aFXa range of 0.2-0.4 IU/ml. A real time dose adjustment algorithm was implemented for patients with out-of-range levels.

Results: Fifty five patients were included. 56.4% of patients had low aFXa levels (<0.2 IU/mL). Real-time enoxaparin dose adjustment significantly increased the proportion of patients who achieved in-range peak aFXa levels, compared to standard dosing (74.5% vs 41.8%, p < 0.001). Patients with initial inadequate peak aFXa levels had a higher rate of 90-day post-operative VTE, although not statistically significant (16.1% vs. 8.3%, p = 0.50).

Conclusion: The majority of acute care surgery patients receive inadequate VTE prophylaxis with fixed enoxaparin dosing.