Effectiveness of Body Mass Index–Based Prophylactic Enoxaparin Dosing in Bariatric Surgery Patients

Abstract

IntroductionEnoxaparin is administered for venous thromboembolic (VTE) prophylaxis in bariatric surgery patients. There is concern whether body mass index (BMI)-based enoxaparin dosing consistently achieves prophylactic targets in patients with severe obesity. MethodsThis retrospective study included patients who underwent bariatric surgery at an academic medical center from Jan 2015-May 2021 and had an anti-Xa level drawn 2.5-6 h after ≥3 doses of BMI-based prophylactic enoxaparin. The primary outcome was the percentage of patients who achieved a target anti-Xa level. Secondary outcomes were prevalence of venous thromboembolic and bleeding events within 30 d post-operatively. ResultsOverall, 137 patients were included. Mean BMI was 59.1 ± 10.4 kg/m2, mean age was 43.9 ± 13.3 y and 110 patients (80.3%) were female. Target anti-Xa levels were achieved in 116 patients (84.7%); 14 (10.2%) were above target and 7 (5.1%) were below target. Patients with above target anti-Xa levels were significantly shorter in height than those within target range (167.1 versus 159.8 cm, P = 0.003). Five patients (3.6%) had a bleeding event; no thromboembolisms occurred. Anti-Xa levels correlated more strongly with enoxaparin dose per unit estimated blood volume (EBV) than dose per unit BMI (Rho = 0.54 versus Rho = 0.33). ConclusionsTarget range anti-Xa levels were achieved in 85% of patients using BMI-based enoxaparin dosing. Patients with above target anti-Xa levels were significantly shorter by nearly 3 inches, suggesting an increased risk of overdosing enoxaparin in shorter, obese patients. An EBV-based dosing regimen may better account for patient height and is supported by a greater correlation with anti-Xa levels with dosing based on EBV than BMI.