A Cochrane review included ten trials (n=826) comparing unfractionated heparin with control, and five trials (n=373) comparing low molecular weight (LMW) heparin with control for prevention of deep venous thrombosis (DVT) and pulmonary embolism (PE) after surgery for hip fracture in the elderly. The trials showed a reduction in the incidence of lower limb DVT (124/474 (26%) versus 219/519 (42%); relative risk (RR) 0.60; 95% confidence interval (CI) 0.50 to 0.71). There were insufficient data to confirm the efficacy of either agent in the prevention of pulmonary embolism. There was no statistically significant difference in overall mortality (42/356 (12%) versus 38/374 (10%); RR 1.16; 95%CI 0.77 to 1.74). Data were inadequate for all other outcomes including wound complications. There is insufficient evidence from five trials, involving 644 patients, to establish if LMW heparin was superior to unfractionated heparin. Most trials evaluating heparins had methodological defects.
Another systematic review including 20 RCTs with a total of 6,900 subjects was abstracted in DARE. The mean probabilities to develop deep venous thrombosis (DVT), pulmonary embolism (PE) and major and minor bleeding using unfractionated heparin (UHF) were 0.21 (95% CI 0.18 to 0.24), 0.01 (0.00 to 0.02), 0.05 (0.03 to 0.07) and 0.19 (0.17 to 0.22), respectively. The risk ratio of DVT for low molecular weight heparin (LMWH) versus UFH was 0.76 (95% CI 0.60 to 0.91) using the fixed effects model, and for LMWH versus warfarin 0.78 (0.69 to 0.87). The risk ratio of major bleeding for LMWH versus UFH was 1.72 (95% CI 1.00 to 2.88) using the fixed effects model. The RR for major bleeding for LMWH versus warfarin was 1.75 (0.92 to 3.07). The RR of minor bleeding for LMWH versus UFH was 0.76 (0.64 to 0.92). The RR for minor bleeding for LMWH versus warfarin was 3.28 (2.21 to 4.70). The RR for PE for LMWH versus UFH was 0.50 (95% CI 0.03 to 2.34). The RR for PE for LMWH versus warfarin was 1.00 (0.10 to 9.94).
A third meta-analysis abstracted in DARE assessed LMWH after total knee arthroplasty. 10 trials with a total of 1,599 patients in the treatment group and 1,480 patients in the control group were included. LMWH was effective in preventing DVT compared to the placebo group (RR 0.42, 95% CI 0.26 to 0.67) and patients in the active control groups who received either adjusted dose unfractionated heparin or warfarin (RR 0.73, 95 CI 0.66 to 0.80), NNT=7. The rate of pulmonary emboli was low both in the LMWH and control groups, RR 0.55, 95% CI 0.20 to 1.57, NS). Major bleeding complications did not differ between the groups. The mortality rate was not significantly different between the groups (0 deaths in the treatment group, 3 deaths in the control group).
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