Air Travel and Blood Clots: Is There a Link?

The formation of blood clots in the leg veins that has been linked to long distance air travel has received much attention in the national and international news media, a phenomenon called "Air-Travel Related Thromboembolism". These blood clots, or deep vein thromboses, that arise in the venous system of leg veins have the potential to break off and travel to the heart and lungs, causing a potentially fatal lung clot, or pulmonary embolism. In September 2000, news coverage of an apparently healthy 28 year old woman collapsing and dying from a pulmonary embolism after a 20 hour flight from Australia to London fueled international attention to this matter. It is also now known that both President Richard Nixon and Vice-President Dan Quayle developed leg clots after spending considerable time sitting on airplanes. The death of a television reporter during the recent war in Iraq was attributed to a DVT that occurred while riding in a cramped tank in the desert. The syndrome was once thought to be more prevalent in the more cramped space of coach class, hence the name "coach-class thrombosis." However, we know now that persons flying in any part of the airplane may be at risk.

How large is this risk?
A number of recent reports have linked blood clots with air travel, especially long flights of over 6,000 miles, but the overall risk appears to be very low. In one research study, only 1 in 200,000 persons had any signs and symptoms of serious pulmonary embolism diagnosed within 1 hour of arrival. The greatest risk for developing blood clots appear to be in persons with heart and lung disease, a previous history of venous thromboembolism, chronic venous stasis, obesity, pregnancy, and a history of cancer. Some studies show that 3 to 10% of these patients with risk factors will develop clots in the leg veins, although most do not show symptoms. Risk factors of long distance air travel include prolonged immobility, possible concentration or "thickening" of the blood due to dehydration, and increased clotting due to reduced oxygen levels in the cabin.

What are appropriate preventive measures?
For most people, the risk for clots appears to be low, so reasonable steps of prevention include drinking plenty of non-alcoholic drinks to avoid dehydration. Stretching and flexing the leg muscles, moving the feet and walking in the isles during a long flight is encouraged. Compression stockings are helpful to decrease leg swelling and help the venous circulation to return blood to the heart. For those with risk factors for known DVT (mentioned in the previous paragraph), especially with flights of more than about 3000 miles, it would be wise to consult with a physician. Your physician may recommend an injection of a dose of blood thinner before a long flight.

Medical experts and the international airlines at a recent session by the World Health Organization have recognized the need for further studies in this area. Already some airlines give written warnings to their passengers, and some airlines have a video to teach passengers how to stretch their legs. Future studies into travel-related blood clots may take years to complete, but researchers are hopeful that many of the important questions will be answered, including how travel-related DVT can be prevented.

About the Author: Alex C Spyropoulos, MD, FACP, is the Medical Director of the Clinical Thrombosis Center, Lovelace Health Systems in Albuquerque, NM. Dr. Spyropoulos is a national investigator and sits on the steering committee for research studies on thromboembolic disease.