Venous thromboembolism prophylaxis in bariatric patients: What is the right dose? A quality improvement project.

Taryn Hassinger, MD1, Tjasa Hranjec, MD, MS2, Peter Hallowell, MD1, Bruce Schirmer, MD1, Sara Hennessy, MD2. 1University of Virginia, 2UT Southwestern

Introduction: Morbidly obese patients undergoing bariatric surgery are at significantly increased risk of venous thromboembolic events (VTE). Standardized weight-based dosing of low molecular weight heparin (LMWH) has been demonstrated to decrease incidence of VTE events. However, it is unclear if current dosing regimens are adequate. We aimed to determine if the current LMWH regimen establishes sufficient anti-Xa activity to provide effective prophylactic anticoagulation after bariatric surgery. 

Methods and Procedures: Between October 2014 and September 2015, a quality improvement project was conducted involving patients undergoing bariatric surgery at a single institution. Sleeve gastrectomy and Roux-en-Y gastric bypass patients were divided into two groups: Light group (<300 pounds) and Heavy group (>300 pounds). All patients received weight-based prophylactic LMWH. Anti-Xa activity, with a goal of 0.2-0.4 U/mL, was measured after administration of the third dose.  Comorbidities, anti-Xa activity, and post-operative VTE events and bleeding were compared by univariate analysis.

Results: A total of 50 patients were identified, with 21 patients in the Light group and 29 patients in the Heavy group. The two groups were equivalent in demographics and comorbidities aside from gender and hypertension. There was no significant difference in type of procedure between the two groups. Twenty-four patients (48%) had a sub-therapeutic anti-Xa level, with no significant difference between groups. Within a 30-day post-operative follow up period, there were five incidents of post-operative bleeding requiring transfusion and one identified VTE event (Table 1).

Conclusions: There was no significant difference detected in anti-Xa levels between the Heavy and Light groups. However, nearly half of the patients had inadequate anti-Xa levels after prophylaxis with LMWH. Therefore, the current VTE prophylaxis algorithm in the morbidly obese undergoing bariatric surgery may be inadequate. A large prospective study will be required to establish the clinical significance of low anti-Xa levels in bariatric surgery as well as to monitor the efficacy and safety of current prophylactic anticoagulation regimens.

Table 1: Pertinent demographics & post-operative outcomes

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