Prolonged thromboprophylaxis with low molecular weight heparin for abdominal or pelvic surgery.

BACKGROUND: Major abdominal and pelvic surgery carries a high risk of venous thromboembolism (VTE). The efficacy of thromboprophylaxis with low-molecular weight heparin (LMWH) administered during the in-hospital period is well documented, but the optimal duration of thromboprophylaxis after surgery remains controversial. Some studies suggest that patients undergoing major abdominal surgery benefit from prolongation of the thromboprophylaxis to 1 month after surgery. No systematic review on prolonged thromboprophylaxis after major abdominal or pelvic surgery has been published.

OBJECTIVES: To evaluate the efficacy and safety of prolonged thromboprophylaxis with LMWH for at least 1 month after abdominal or pelvic surgery with thromboprophylaxis administered during the in-hospital period only in preventing late VTE.

SEARCH STRATEGY: Electronic searches were performed January 2008 in the Medline, Embase, Lilacs, and the Cochrane Central Register of Controlled Trials. Abstract books from major congresses addressing thromboembolism were hand searched, as were reference lists from studies of relevance.

SELECTION CRITERIA: We assessed both randomised and non-randomised controlled clinical trials comparing prolonged thromboprophylaxis with any anti-thrombotic agent with placebo and/or thromboprophylaxis during the admission period only. The patient population in the trials were patients undergoing abdominal or pelvic surgery. The outcome measures included VTE (deep venous thrombosis (DVT) or pulmonary embolism (PE)) as assessed by objective means (ascending bilateral venography, ultrasonography, pulmonary ventilation/perfusion scintigraphy, spiral CT scan or autopsy). Studies exclusively reporting on clinical diagnosis of VTE, without objective confirmation were excluded.

DATA COLLECTION AND ANALYSIS: The identification of studies and data extraction were performed by the authors. Outcomes were VTE (DVT or PE) assessed by objective means. Safety outcome were defined as bleeding complications and mortality within 3 months after surgery.

MAIN RESULTS: The search exclusively detected trials evaluating prolonged thromboprophylaxis with LMWH as compared to control or placebo. 133 studies were found in the searches, of which only 4 were found eligible for inclusion, and 129 were excluded. The incidence of overall VTE after major abdominal or pelvic surgery was 14.3% (95% confidence interval 11.2% - 17.8%) in the control group as compared to 6.1% (95% CI 4.0% - 8.7%) in the patients receiving out-of-hospital LMWH. This difference was statistically significant, Peto Odds Ratio 0.41 (95% CI 0.26 -0.63), P < 0.0005. Prolonged thromboprophylaxis with LMWH was also associated with a statistically significant reduction of even the incidence of symptomatic VTE from 1.7% (95% CI 0.8% - 3.4%) in the control group to 0.2 % (95% CI 0.0% - 1.2%) in patients receiving prolonged thromboprophylaxis, Peto Odds ratio 0.22 (95% CI 0.06 -0.80), P = 0.02. The respective incidence of bleeding in the control and LMWH group were 3.7% (95% CI 2.4% -5.5%) and 4.1% (95% CI 2.7% - 6.0%), Peto Odds ratio 1.11 (95% CI 0.62 - 1.97), P = 0.73. There was no significant heterogeneity detected as regards to outcome parameters reported in the included trials.

AUTHORS' CONCLUSIONS: Prolonged thromboprophylaxis with LMWH significantly reduces the risk of VTE compared to thromboprophylaxis during hospital admittance only, without increasing bleeding complications after major abdominal or pelvic surgery.