Travel and thrombosis.

The available evidence suggests an association between long distance travel and the development of venous thromboembolism. The main problem for travellers and physicians is the interpretation of the evidence and its translation into appropriate advice on the risk and the prevention of thrombosis. Most available data relate to air travel. Thrombosis risk is greater following journeys of more than 8 h and those at greatest risk are travellers with a history of venous thromboembolism or risk factors. Based on the best evidence available the risk of symptomatic venous thromboembolism after flights of more than 12 h is 0.5%. It is likely that stasis plays a major role in the aetiology of travel related thrombosis. The evidence for hypobaric hypoxia induced coagulation activation requires confirmation. There is evidence that compression stockings and low molecular weight heparin prevent asymptomatic deep vein thrombosis (DVT) but clinical DVT has been observed in long distance flyers in spite of prophylaxis with aspirin and stockings.