The OAT-RCT study: the obesity anticoagulation thromboprophylaxis randomized controlled trial protocol.

BACKGROUND: Venous thromboembolism (VTE) is a recognized and serious complication following bariatric surgery, with the majority of events occurring after hospital discharge. Low-molecular-weight heparin is the most commonly used thromboprophylactic agent in this population. Both enoxaparin and tinzaparin are widely used, but existing evidence suggests a significant proportion of patients with obesity fails to achieve prophylactic anti-Xa levels with either agent. No adequately powered, prospective, head-to-head randomized trial comparing these agents has been conducted in a bariatric surgery population.

METHODS/DESIGN: The OAT-RCT is a single-center, prospective, open-label, parallel-group randomized controlled trial at St Vincent's University Hospital, Dublin. Adult patients undergoing laparoscopic sleeve gastrectomy or gastric bypass will be randomly allocated in a 1:1 ratio to receive either weight-based tinzaparin (Arm A) or weight-stratified enoxaparin (Arm B) for 21 days post-operatively. The primary endpoint is the proportion of patients achieving prophylactic anti-Xa levels (0.2-0.4 IU/mL) at 3-5 hours after the third dose, measured on post-operative day 2. Secondary endpoints include 30-day bleeding events, VTE incidence, sub- and supra-prophylactic anti-Xa proportions, correlations between anti-Xa and body habitus, adverse drug reactions, and patient-reported treatment satisfaction using the validated TSQM-9 questionnaire at 6 weeks. A total of 180 participants (90 per arm) are required based on a formal power calculation.

DISCUSSION: The OAT-RCT is the first adequately powered head-to-head randomized controlled trial comparing anti-Xa levels of tinzaparin and enoxaparin for VTE prophylaxis in bariatric surgery. The results will provide high-quality class I evidence to inform evidence-based prescribing guidelines for this rapidly growing surgical population.