A prospective cohort study on the effectiveness of 3500 IU versus 5000 IU bemiparin in the prophylaxis of postoperative thrombotic events in obese patients undergoing orthopedic surgery

BACKGROUND: Postoperative thromboses are among the most feared complications in orthopedic surgery as they may cause life-threatening conditions in otherwise highly successful procedures such as total joint replacement. Body weight is an important risk factor for thromboses and is used in algorithms to determine dosages in prophylaxis. However, weight patterns among orthopedic populations have changed considerably since the introduction of these algorithms, essentially shifting towards obesity. This study asks whether present-day obese patients would benefit from higher than usual dosages of bemiparin in the prophylaxis of postoperative thrombosis. PATIENTS AND METHODS: To detect at least a 5% difference in the incidence of clinically symptomatic thrombotic events with sufficient power, 750 patients were enrolled in the study and treated with 3,500 IU or 5,000 IU bemiparin. Differences in rates were modelled in a Poisson regression including as covariates the potential confounders severity of immobilization, sex, exact weight and age. RESULTS: Overall, 723 patients were followed for a total of 66.8 person-years and analyzed by intention-to-treat. The ratio of incidence rates in the two groups of patients was 0.35 (95% CI: 0.03-2.91), thus there was no evidence for a difference in rates between groups. There was, however, a borderline significant association between incidence rates and body weight. There were no complications resulting from the higher dosages of bemiparin. CONCLUSION: Both groups of treated patients showed low incidence rates of thromboses and we did not see a significant reduction of incidence rates with higher dosages of bemiparin in this population. However, there was weak evidence that higher dosages might prove beneficial if populations gain weight even further.