Guidelines on travel-related venous thrombosis.

Long duration travel is a weak risk factor for the development of venous thromboembolism (VTE). The incidence of VTE after flights of >4 h is 1 in 4656 and for flights of more than 8 h in low and intermediate risk flyers is around 0.5%. Severe symptomatic pulmonary embolism in the period immediately after travel is extremely rare after flights of <8 h. In flights over 12 h the rate is 5 per million. VTE may be attributable to travel if it occurs up to 8 weeks following the journey. The risk of travel-related thrombosis is higher in individuals with pre-existing risk factors for the development of VTE. There is no evidence for an association between dehydration and travel-associated VTE and so whilst maintaining good hydration is unlikely to be harmful it cannot be strongly recommended for prevention of thrombosis (recommendation grade 2, level of evidence, B). There is indirect evidence that maintaining mobility may prevent VTE and, in view of the likely pathogenesis of travel-related VTE, maintaining mobility is a reasonable precaution for all travellers on journeys over 3 h (2B). Global use of compression stockings and anticoagulants for long distance travel is not indicated (1C). Assessment of risk should be made on an individual basis but it is likely that recent major surgery (within 1 month), active malignancy, previous unprovoked VTE, previous travel-related VTE with no associated temporary risk factor or presence of more than one risk factor identifies those travellers at highest thrombosis risk (1C). Travellers at the highest risk of travel-related thrombosis undertaking journeys of >3 h should wear well fitted below knee compression hosiery (2B). Where pharmacological prophylaxis is considered appropriate, anticoagulants as opposed to anti-platelet drugs are recommended based on the observation that, in other clinical scenarios, they provide more effective thromboprophylaxis. Usual contraindications to any form of thromboprophylaxis need to be borne in mind (2C).