Frequency and prevention of symptomless deep-vein thrombosis in long-haul flights: a randomised trial

Background The true frequency of deep-vein thrombosis (DVT) during long-hau l air travel is unknown. We sought to determine the frequency of DVT in the lower limb during long-haul economy-class air travel and the efficacy of g raduated elastic compression stockings in its prevention. Methods We recruited 89 male and 142 female passengers over 50 years of age with no history of thromboembolic problems. Passengers were randomly alloc ated to one of two groups: one group wore class-I below-knee graduated elas tic compression stockings, the other group did not. All the passengers made journeys lasting more than 8 h per flight (median total duration 24 h), re turning to the UK within 6 weeks. Duplex ultrasonography was used to assess the deep veins before and after travel. Blood samples were analysed for tw o specific common gene mutations, factor V Leiden (NL) and prothrombin G202 10A (PGM), which predispose to venous thromboembolism. A sensitive D-dimer assay was used to screen for the development of recent thrombosis. Findings 12/116 passengers (10%; 95% CI 4.8-16.0%) developed symptomless DV T in the calf (five men. seven women). None of these passengers wore elasti c compression stockings, and two were heterozygous for FVL. Four further pa tients who wore elastic compression stockings, had varicose veins and devel oped superficial thrombophlebitis. One of these passengers was heterozygous for both FVL and PGM. None of the passengers who wore class-I compression stockings developed DVT (95% CI 0-3.2%). Interpretation We conclude that symptomless DVT might occur in up to 10% of long-haul airline travellers. Wearing of elastic compression stockings dur ing long-haul air travel is associated with a reduction in symptomless DVT.