(957) Anti-Xa Monitoring for Venous Thromboembolism Prophylaxis in Patients Admitted to a Burn Center

Introduction: Venous thromboembolism (VTE) is a common complication after burn injury, despite the provision of chemical prophylaxis. Data suggest that standard dosing of enoxaparin for VTE prophylaxis (30mg twice daily or 40mg twice daily if BMI >40 kg/m2) is inadequate in this patient population, and that the optimal enoxaparin dose required to achieve prophylacic anti-Xa levels is between 40 mg and 60 mg twice daily. It is suggested that anti-Xa levels be monitored and enoxaparin doses be adjusted to achieve an anti-Xa level of 0.2 to 0.4 units/mL. However, anti-Xa levels are not routinely monitored across all burn centers. We hypothesized that the standard enoxaparin dose was not sufficient to yield prophylactic anti-Xa levels.

Methods: This project was approved by our institution’s IRB. This is a retrospective study that included adult patients admitted to our burn center who had anti-Xa levels monitored as part of usual care.
Data were collected from the electronic medical record and included demographic and injury information, enoxaparin dosing information, and incidence of VTE or bleeding. Descriptive statistics were analyzed using JMP 15.2.0.

Results: One hundred seventy-five patients were included in this analysis. Their mean age was 45.5±16.4 years and burn size 14.1±16.7% of the total body surface area. With standard dosing, 73 (41.7%) achieved prophylactic anti-Xa levels, 97 (55.4%) were sub-prophylactic, and 5 (2.9%) were supra-prophylactic. Thirty-four (19.4%) did not reach prophylactic anti-Xa levels during their hospital stay.
The mean enoxaparin dose required to yield prophylactic levels was 37.6±8.5 mg. The average time to a prophylactic anti-Xa level was 8.6±9.2 days. Nine (5.1%) patients developed VTE and 4 (2.3%) patients developed a clinically significant bleed during their hospital stay.

Conclusions: The majority of patients admitted to our burn center did not achieve prophylactic anti-Xa levels with standard enoxaparin dosing, and almost 1 in 5 never did. Despite patients receiving higher doses of enoxaparin, clinically significant bleeding was rare. Our data suggest that routine monitoring of anti-Xa levels and subsequent dose adjustment of enoxaparin is warranted in this patient population. Strategies to achieve more rapid achievement of effective prophylaxis are clearly needed.