Air Travel and Venous Thrombosis: How Much Help Might Aspirin Be?

Yoon K Loke, MBBS; Sheena Derry, MA

In This Article


We accept that there are significant limitations to our analysis. First, we need to consider whether the risk estimates (0-40 per 100,000) used in our calculations are likely to be representative of the true figure. A study of passengers arriving at a Paris airport suggested that the rate of symptomatic pulmonary emboli was about 5 in a million for those passengers who had traveled more than 10,000 km.[5] The authors of this airport study concede that this is almost certainly a significant underestimate, as they had data only on those presenting with symptomatic pulmonary disease soon after arrival. This indicates that our estimate of 20 per 100,000 is a reasonable ballpark figure to use. Nonetheless, in view of the considerable uncertainty of the level of risk, we have specifically chosen to use methods that will allow any new data to be incorporated easily into the calculations. The NNTs at different risk levels for DVT can be easily estimated if more reliable risk data becomes available in the future -- for example, travelers with a 5 times higher risk than above would have an NNT 5 times lower (better).

There are also substantial difficulties with extrapolating the findings in hip fracture patients to long-distance travelers. The patients with hip fractures were treated with 160 mg of aspirin for 35 days. Would a single dose of aspirin offer any protection at all, or would it be more sensible to recommend that travelers take the treatment for a longer period? Similarly, the optimal dose of aspirin therapy remains uncertain -- will a low dose such as 81 mg offer equivalent protection to160 mg, or even 325 mg? These questions may not be answered easily or quickly, as clear data on aspirin in travel thromboprophylaxis are unlikely to become available in the near future.

Nonetheless, this is currently an area of immense public interest, and doctors need to answer enquiries from members of the public as to whether they should take aspirin before embarking on long journeys. We felt, therefore, that even a rough estimate would be useful in guiding the decisions of both doctors and patients.

Finally we must consider, given the magnitude of the NNT, the possibility of harm from adverse effects of aspirin, such as hypersensitivity and bleeding, even with low doses and short treatment periods. All of these factors will need to be carefully weighed in a benefit-harm assessment before deciding on treatment. We also need to consider other therapeutic options such as compression stockings, which have the potential for therapeutic benefit without the hindrance of drug-related adverse effects.[6] There is a clear need for a study directly comparing the benefit and harm of aspirin, or heparin, and compression stockings, in preventing DVT in long-distance travelers.


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