[Synthesis: certainties/uncertainties in the prevention of venous thrombosis in medical patients].

In medical patients there are numerous and variable risk factors for deep vein thrombosis. Placebo-controlled clinical trials are rare. The efficacy of standard heparin or low molecular weight heparin for the prevention of deep vein thrombosis is clearly demonstrated for patients with recent myocardial infarction, ischaemic stroke with hemiplegia or severe pulmonary sepsis with lung failure. Pharmacological prophylaxis is probably also efficient in patients with a severe acute disease and a certain history of deep vein thrombosis. For all other medical and especially for bedridden elderly patients, use of low molecular weight heparin might decrease the incidence of deep vein thrombosis but might not modify the overall mortality. In these situations, placebo-controlled clinical trials are needed for best evaluation of the benefit-risk ratio.