Low molecular weight heparin most effective at reducing rate of venous thromboembolism in patients undergoing bariatric surgery

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Key study points:

1. Low molecular weight heparin give pre- and post-operatively is associated with the best overall reduction in venous thromboembolism rates in bariatric surgery patients.
2. There were no differences in rates of hemorrhage or serious hemorrhage within 30 days among the different treatment groups.

Primer: Obese patients are considered to be at moderate to high risk for venous thromboembolism (VTE).  To this day, pulmonary embolism (PE) is still a significant cause of preventable morbidity and mortality among hospital patients, and reducing the rates of VTE remains an effective way of reducing the PE rate.  Among bariatric surgery patients, only 3 studies have evaluated VTE prophylaxis, and no conclusive results have been achieved.  Without VTE prevention, rates of asymptomatic events have ranged from 10-80% in prior studies, and risk of fatal PE can reach as high as 7% in high-risk patients undergoing surgery.  Low molecular weight heparin and unfractionated heparin have been utilized in the peri-operative period as part of VTE prophylaxis.  The authors of this paper focus on the different combinations and their results within the bariatric surgery patient population.

Background reading:

1. Prevention of venous thromboembolic disease in surgical patients

This [retrospective, cohort] study: Utilized data from the Michigan Bariatric Surgery Collaboratic (MBSC) clinical outcomes registry to conduct reviews of all eligible patients 30 days after surgery.  Three groups were evaluated: preoperative and postoperative unfractionated heparin (UF/UF), preoperative unfractionated heparin and post-operative low molecular weight heparin (UF/LMW), and preoperative and postoperative low molecular weight heparin (LMW/LMW).  There were small, but statistically significant differences in patient demographics, including age, BMI, gender, etc.  Operating room time and type of procedure done were included in the analysis to adjust for differences in these variables in assessing the risk of VTE in each patient population. LMW/LMW (0.25%) and UF/LMW (0.29%) groups had statistically significant lowest rates of VTE, as compared with UF/UF (0.68%).  For the highest risk patients, LMW/LMW was statistically the most effective treatment regimen with the lowest rate of VTE.  No statistically significant differences were noted among the three groups in either hemorrhage or serious hemorrhage rate.

In sum: This study supports the use of LMW heparin preoperatively and postoperatively as the most effective way of reducing the rates of VTE.  Although not measured in this study, lowering the rate of VTE should ideally also lower the rate of PE by association in these bariatric surgery patients.  The data also provide reassurance that the use of LMW heparin preoperatively is no more likely than unfractionated heparin to increase the risk of hemorrhage.  Limitations in this study include the statistically significant differences in the patient demographics of each group, as well as the operating room time spent per patient.  Ideally these results would need to be reproduced in a randomized control trial to achieve higher validity, although the authors appropriately adjusted for these differences when completing their statistical analyses.

Click to read the study in JAMA (Journal of the American Medical Association) 

By [DM] and [AH]

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