Venous Thromboembolism Prevention in the Bariatric Surgical Patient: Are we doing enough?

Bariatric surgery has become an accepted, safe and durable method of weight loss for the obese patient. Despite this success, venous thromboembolism (VTE) continues to be one of the top two causes of mortality in bariatric surgery. Most bariatric surgeons today use a combination of non-invasive and pharmacologic techniques, including sequential compression devices, anti-embolic stockings, anticoagulation, and early ambulation, to prevent VTE. Despite these interventions, the incidence of VTE after bariatric surgery has been reported to be widely variable ranging from 0.3 to 3.8%. (1-11) The most recent study published to date reported an incidence of pulmonary emboli (PE) of 0.9%, deep venous thrombosis (DVT) without PE to be 1.3% and VTE (DVT + PE) to be 2.2% within the perioperative period. (12) Little data has been collected to evaluate the long term risk (greater than 30 days post-op) of VTE following bariatric surgery. Furthermore, the prevalence of asymptomatic deep venous thrombosis (DVT) in this population is unknown and is sure to be higher. Our main goal for this thesis was to study the effectiveness of current and future practices of venous thromboembolism prophylaxis in the bariatric surgical population. To do so, we first completed a narrative summary of the current agents and techniques used to prevent VTE in this population (Chapter one). We then analyzed a large administrative database to determine the long term risk and predictors for VTE in patients undergoing bariatric surgery using current VTE prophylaxis (Chapter two). We identified a history of previous VTE events as being the strongest predictor of development of a VTE post-surgery. This high rate of recurrence has led to the recommendation that patients with prior VTE or other high risk groups should be considered for prophylactic vena cava filter insertion before surgery. This finding motivated us to specifically assess the efficacy and risks of IVC filters in the bariatric surgery population. We completed a retrospective analysis of a large administrative database to determine these risks and benefits (Chapter three). The body habitus of a bariatric surgical patient presents technical challenges in the detection of VTE, especially asymptomatic DVT in the pelvis and lower limbs. Because of the limited sensitivity and specificity of ultrasound in the detection of DVT in the obese patient, we performed a systematic review and meta-analysis to determine the diagnostic accuracy of magnetic resonance venography in the detection of DVT in the obese (Chapter four). Based on these results above, we then designed a randomized double blinded controlled trial (RCT) to study the incidence of asymptomatic deep venous thrombosis in this special population. We compared two different anticoagulation regimens in the prevention of VTE in bariatric surgical patients:enoxaparin 40 mg subcutaneously twice daily (our standard regimen), and fondaparinux 5 mg subcutaneously once daily (a non-standard dose in the obese population, used under an IND obtained by Dr. Steele). We used MRV as a novel non-invasive diagnostic tool to detect asymptomatic DVT in our patient population (Chapter five). In the final chapter, Chapter six, we discuss public health-based approaches and future work in the prevention of VTE in this special population.