Higher Doses of Prophylactic Anticoagulation Is More Effective in Preventing Venous Thromboembolism in Morbidly Obese Inpatients.

Obesity increases the risk for venous thromboembolism (VTE), and the optimal dose of prophylactic anticoagulation to prevent VTE in morbidly obese inpatients is unknown.

To quantify the efficacy and safety of higher doses of prophylactic heparin or enoxaparin for VTE prevention in morbidly obese inpatients with a body mass index (BMI) ≥ 40 kg/m²and/or weight >100 kg within the BJC HealthCare system.

We analyzed 10,239 inpatients with weight > 100 kg and/or morbid obesity (BMI ≥ 40 kg/m²) discharged from the three major hospitals in the BJC HealthCare system from January 1^st, 2010 through February 29^th, 2012. We used logistic regression to calculate odds ratios (OR) and 95% confidence intervals (CI) and Wald's chi-square to compare proportions. The primary efficacy outcome was an ICD-9 diagnosis code for VTE. The primary safety outcome was an ICD-9 diagnosis codes for bleeding.

On-treatment analysis showed higher doses of prophylactic anticoagulation (heparin 7500 units three times daily instead of 5000 units two or three times daily or enoxaparin 40 mg twice daily instead of 40 mg once daily) halved the risk (OR 0.52, 95% CI 0.27–1.00; p = 0.05) of symptomatic VTE in the 3928 morbidly obese inpatients (weight > 100kg and BMI ≥ 40 kg/m²). The rate of VTE was 1.48% (35/2369) in these morbidly obese inpatients who received standard prophylactic doses of unfractionated heparin or enoxaparin, compared to 0.77% (12/1559) in those who received higher doses, with an absolute risk reduction of 0.71% and a number needed to treat (NNT) of approximately 140. Intention-to-treat analysis failed to show reduction in VTE rate due to low (< 40%) physician compliance in prescribing the higher doses. Increased doses of prophylactic anticoagulation were not associated with bleeding (OR 0.84, 95% CI 0.66–1.07, p = 0.15).

Higher doses of prophylactic anticoagulation nearly halve the rate of VTE in morbidly obese inpatients (with BMI ≥ 40 kg/m² and weight > 100 kg), but do not increase bleeding. Given their safety and ease of implementation, higher doses of prophylactic heparin or enoxaparin should be considered in morbidly obese inpatients. Clinicians' compliance and awareness need to be improved to prevent VTE in this vulnerable population.

No relevant conflicts of interest to declare.