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Logo of bmjThis ArticleThe BMJ
BMJ. 2007 June 30; 334(7608): 1343.
PMCID: PMC1906644

Long haul flights double the risk of thrombosis related to air travel

Epidemiological studies show that the risk of venous thromboembolism doubles after long haul air travel of more than four hours' duration, a World Health Organization report says.

The final report of phase I of the WHO research into global hazards of travel (WRIGHT) project concludes that the absolute risk of venous thromboembolism among healthy individuals for a flight of more than four hours was 1 in 6000. Pathophysiological studies, it says, support these findings.

The studies were carried out by an international collaboration of researchers from the universities of Leiden (Netherlands), Leicester, Newcastle, Aberdeen, and Lausanne (Switzerland).

The studies indicate that the risk of venous thromboembolism “increases with the duration of the travel and with multiple flights within a short period,” says the report.

Furthermore, the risk of venous thromboembolism increases significantly in the presence of other known risk factors for venous thromboembolism, such as obesity, extremes of height, use of oral contraceptives, and the presence of prothrombotic blood abnormalities.

The report notes that manifestations of venous thromboembolism associated with long haul flights include pulmonary embolism, deep vein thrombosis, subclavian vein thrombosis, cerebral vein thrombosis, stroke caused by paradoxical cerebral embolism through a patent foramen ovale, and peripheral arterial thrombosis.

Most studies, it adds, have shown that lower limb deep vein thrombosis and pulmonary embolism “are the most common manifestations of VTE [venous thromboembolism].”

On the basis of the findings WHO says that “there is a need for travellers to be given appropriate information regarding risks and for further studies to identify preventive measures, which will comprise phase II of the WRIGHT project.”

WHO officials recommend that air passengers exercise their legs and ankle joints, avoid sitting cross legged, and avoid tight clothing.

Phase I of the WRIGHT project was conducted under the auspices of WHO and the International Civil Aviation Organization, was supported by an independent scientific committee, and had the collaboration of airline companies in the International Air Transport Association.

The project was launched after a WHO meeting in March 2001 on air travel and venous thrombosis, which was attended by experts on venous thromboembolism and representatives of the airline industry. It was triggered by the death in 2000 from pulmonary embolism of a young English woman who had returned on a long haul flight from Australia.

The objectives of the WRIGHT project, says the report, are to confirm that the risk of venous thromboembolism is increased by air travel and to determine the magnitude of the risk and the effects of other factors and to examine the effect of preventive measures.

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