Interventions to prevent venous thrombosis after air travel: are they necessary? No

Travel was first associated with venous thrombosis in the 1930s, when cases were reported after long trips by car. From the mid1950s on, there has been a steady stream of reports associating long-haul air travel with venous thrombosis [1]. The phrase economy class syndrome was coined in 1977 [2], and the fi rst controlled study stems from 1986 [3]. Seen in that light, the recent clamor for aggressive therapy may be slightly surprising. Has anything changed? Has the mass travel that followed the postwar industrial boom led to an epidemic of venous thrombosis in front of our very eyes which we have completely missed? We recently showed that the risk of venous thrombosis is mildly elevated after travel (of more than 4 h) not only by air, but also by bus, train or car, and is of the same magnitude as the risk conferred by the use of oral contraception [4]. One may wonder whether those who advocate medicinal thromboprophylaxis for air travel also take the logical step of prescribing this for all women who use oral contraceptives, and all holiday-makers who travel by car or bus. The relevance of the risk increase lies not in the risk for the individual traveler, which is low, but in the overall burden of thrombosis caused by traveling, which is high because of the enormous number of travelers. This should lead not to unfounded advice to travelers, but to large randomized trials into interventions that can safely be used by large numbers of travelers. The survey that we carried out among attendants of the ISTH Congress in Sydney in 2005, which is published in this issue, shows that a substantial proportion (80%) of them felt that, for themselves, preventive measures were in order. Whereas a large proportion only did exercise during the flight, no less than 17% wore elastic stockings, and 28% used some form of chemoprophylaxis (aspirin, heparin, vitamin K antagonists). A lack of consensus is apparent from the wide variation in use of thromboprophylaxis by nationality and professional background. Although there may be a difference between what doctors prescribe to themselves and what they prescribe to their patients, it seems likely that this variation reflects differences in how experts advise air travelers. These different policies stem from the absence of evidence showing a beneficial, or detrimental, effect of any form of preventive action. The old adage in the absence of clear proof of benefit is not to intervene: in dubio abstine. In modern medicine, this is usually interpreted as meaning that we need evidence from randomized trials on clinical endpoints before we succumb to our drive for action. Obviously, there are exceptions; few would insist on randomized trial evidence that parachute use may be helpful to prevent death related to gravitational challenge [5]. The behavior of the attendants of the ISTH Congress, whom