P. Mismetti et al., Meta-analysis of low molecular weight heparin in the prevention of venous thromboembolism in general surgery, BR J SURG, 88(7), 2001, pp. 913-930
Background: Low molecular weight heparins (LMWHs) have become routine throm
boprophylaxis in general surgery. However, their actual clinical effect, it
s magnitude relative to that of unfractionated heparin (UFH), and the optim
al dose are still debated.
Methods: A meta-analysis was performed of all available randomized trials i
n general surgery comparing LMWH with placebo or no treatment, or with UFH.
Results: Comparison versus placebo or no treatment confirmed that the signi
ficant reduction in asymptomatic deep vein thrombosis (DVT) obtained with L
MWH (n = 513; relative risk (RR) 0.28 (95 per cent confidence interval 0.14
-0.54)) was associated with a significant reduction in clinical pulmonary e
mbolism (n = 5456; RR 0.25 (0.08-0.79)) and clinical venous thromboembolism
(VTE) (n = 4890; RR 0.29 (0.11-0.73)), and a trend towards a reduction in
overall mortality rate. Comparison versus UFH showed a trend in favour of L
MWH, with a significant reduction in clinical VTE (P = 0.049), a trend also
found for cancer surgery. LMWH at doses below 3400 anti-Xa units seemed to
be as effective as, and safer than, UFH, while higher doses yielded slight
ly superior efficacy but increased haemorrhagic risk, including that of maj
or haemorrhage.
Conclusion: Asymptomatic DVT may be regarded as a reliable surrogate endpoi
nt for clinical outcome in studies investigating thromboprophylaxis in gene
ral surgery. LMWH seems to be as effective and safe as UFH. Determination o
f the optimal dose regimen of LMWH for this indication requires further inv
estigation.