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People who have low molecular weight heparin (LMWH) for between two to four weeks after abdominal or pelvic surgery, especially for cancer, have fewer blood clots in their large veins or lungs. In this review of seven trials, five per cent of people receiving extended treatment experienced a clot compared with 13% who received LMWH only while in hospital. There was no difference in bleeding complications.

The optimal duration of treatment following abdominal surgery is uncertain, balancing bleeding against clot risk. NICE recommends using LMWH (or alternative drug) for at least seven days, extending up to 28 days for people who have had major cancer surgery.

Extended treatment with LMWH may benefit a broader group of patients, but further exploration may be needed to look at whether those with non-cancer surgery might benefit to the same extent.

Why was this study needed?

Every year about 1 in 1,000 people in the UK develop a venous thromboembolism (VTE). Either a blood clot in the deep veins (deep vein thrombosis) or in the lungs (pulmonary embolism). VTE is more common in people with cancer and following major surgery. Over half of all cases follow recent hospitalisation. VTE used to be a leading cause of preventable death in hospital.

It is now routine practice to give drug treatment to prevent blood clots while people recover in hospital after abdominal or pelvic surgery. But observational studies indicate that patients may remain at increased risk for up to four or six weeks after surgery.

The Cochrane review aimed to resolve the uncertainty by combining data from recent high-quality studies to see whether there is a place for a longer course of anticoagulation after abdominal or pelvic surgery.

What did this study do?

This Cochrane review includes seven randomised controlled trials of extended LMWH treatment, given for at least 14 days after abdominal or pelvic surgery compared with shorter treatment as an inpatient only. The 1,728 patients had either open or keyhole surgery. Five trials recruited patients specifically with cancer and two included surgery for either cancer or benign conditions.

Venous thromboembolism was confirmed by an objective test (such as venography). Most studies were of LMWH for around 28 days, with only one study treating for 14 days only. Studies using other anticoagulants or mechanical measures (e.g. compression stockings) were excluded.

Overall the evidence was rated as moderate quality. Sources of bias included lack of detail about randomisation methods, whether participants and assessors were blinded to group assignment and incomplete reporting of outcomes. Nevertheless, the results were similar across studies, and this increases confidence in the conclusions.

What did it find?

  • Extended LMWH reduced the risk of VTE up to 30 days after surgery, which occurred in 5.3% of the intervention group compared with 13.2% of the control group (odds ratio [OR] 0.38, 95% confidence interval [CI] 0.26 to 0.54; seven studies, 1,728 patients).
  • The findings were similar in the subgroup of patients who received open surgery: 6% experienced VTE after extended treatment vs 13.8% of the control group (OR 0.42, 95% CI 0.29 to 0.60; six studies).
  • Extended LMWH also reduced the risk of deep vein thrombosis in general (13% vs 5%; OR 0.39, 95% CI 0.27 to 0.55), and specifically thrombosis in the upper thigh or pelvic veins (4% vs 9%; OR 0.22, 95% CI 0.10 to 0.47; seven studies).
  • Extended treatment did not affect the risk of minor or major bleeds up to three months after surgery (3.4% in the intervention group vs 2.8% in the control group; OR 1.10, 95% CI 0.67 to 1.81; seven studies).

What does current guidance say on this issue?

The NICE guideline on reducing risk of hospital-acquired venous thromboembolism (published 2018) recommends using LMWH (or an alternative drug, fondaparinux sodium) for a minimum of seven days for people undergoing abdominal surgery, taking into account individual patient factors and according to clinical judgement.

NICE recommends considering extending VTE prophylaxis to 28 days postoperatively for people who have had major cancer surgery in the abdomen.

What are the implications?

These results suggest that extended VTE prophylaxis after abdominal or pelvic surgery is beneficial, especially in cancer surgery.  This is in agreement with evidence in orthopaedic surgery and with current NICE guidance in cancer surgery.

It is difficult to be certain whether the findings apply to patients following non-cancer surgery as two trials that included these patient groups didn’t separate their results.

Newer oral anticoagulant drugs may provide similar benefits, but these were not tested in the studies included.

Citation and Funding

Felder S, Rasmussen MS, King R et al. Prolonged thromboprophylaxis with low molecular weight heparin for abdominal or pelvic surgery. Cochrane Database Syst Rev. 2018;11:CD004318.

The review was carried out by the Cochrane Colorectal Cancer Group which is funded by the Danish Government.



NICE. Venous thromboembolism in over 16s: reducing the risk of hospital-acquired deep vein thrombosis or pulmonary embolism. NG89. London National Institute for Health and Care Excellence; 2018.

Thrombosis UK. Thrombosis statistics. Llanwrda: Thrombosis UK; accessed 2019.

Produced by the University of Southampton and Bazian on behalf of NIHR through the NIHR Dissemination Centre


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