Background: In 2016 70% of venous thromboembolism events at the University of Pittsburgh Medical Center Presbyterian Hospital occurred in patients with BMI>=25. The American College of Chest Physicians recommend weight base dosing for VTE prophylaxis in obese patients (grade 2C) as the standard dosing regimen may not be adequate for these patients. The anti-Xa range of 0.2-0.44 is considered effective prophylaxis. Currently at UPMC obese patients do not consistently receive weight based dosing or anti-Xa monitoring to ensure adequate prophylaxis.

Methods: From June 2017-August 2018 all patients with BMI>=25 admitted to the ortho-medical-trauma service at Presbyterian Hospital who were prescribed enoxaparin for prophylaxis were originally monitored for steady state anti-Xa peak levels and later we also monitored trough levels. Designated study team members reviewed anti-Xa monitoring on a daily basis for all patients. A descriptive analysis of demographics, BMI, enoxaparin dose, adverse events, and adequacy of standard dosing regimens were collected.

Results: 555 patients on the OMT service with BMI 25 or greater were prescribed enoxaparin prophylaxis and had anti-Xa peak levels measured. 390 patients also had anti-Xa trough level measured.
Among patient cohort (N=555): 284 (51%) were female patients, age 17-98 (median 68 years), and median BMI 31.2. 494 patients received enoxaparin 30mg BID and 61 patients 40mg BID or higher. 86 patients had BMI>=40.

34% of these patients (n=86, BMI>=40), 42% (n=245, BMI 30-39), and 57% (n=224, BMI 25-29) achieved peak anti-Xa levels in the prophylactic range.

Among 390 patients who had trough anti-Xa levels measured, 349 received 30 mg BID enoxaparin and 41 received 40 mg BID or higher dosing. The goal trough levels were achieved with 30 mg BID enoxaparin dosing in 8% of patients (n=40, BMI>=40), 7.3% (n=158, BMI 30-39), and 10.2% (n=151, BMI 25-29). 16.4% of patients (n=41) receiving enoxaparin 40mg BID dosing achieved goal trough levels.

There were 17 VTEs (11 pulmonary embolisms and 6 deep venous thrombosis); 5 (5/62, 8%) in patients with BMI>=40, 5 (5/245, 2%) in patients with BMI 30-39, and 7 (7/224, 3.1%) in BMI 25-59. None of the VTE patients had attained prophylactic range anti-Xa trough levels, and only 2 patients had peak levels in range.

Conclusions: Majority of study patients failed to achieve adequate prophylaxis at prescribed enoxaparin doses. VTE incidence was higher in obese patients with BMI>=40 compared to patients with BMI<40. Morbidly obese patients should be considered for weight based enoxaparin dosing with anti-Xa monitoring.