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http://www.nytimes.com/2002/12/17/health/17BROD.html?tntemail0

On the Long Flights, Take Steps, Lots of Them

By JANE E. BRODY

word to the wise for anyone planning a winter vacation or business trip to distant lands: a few simple steps can go a long way to keep you free from an admittedly rare but sometimes deadly complication of long trips, especially those taken by air.

That complication is a blood clot called deep vein thrombosis, or D.V.T., which can result in a dangerous or even deadly pulmonary embolism in about 10 percent of cases.

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It has been variously called "coach class thrombosis" or "economy class syndrome," because confinement in narrow coach seats limits opportunities for protective movement. But in fact the problem can afflict those traveling in roomier seats, as well.

The problem is not limited to planes. Those who sat for hours in cramped air raid shelters in London in the blitz in World War II had a sixfold increase in sudden death from pulmonary embolism.

Although experts continue to debate the extent of the risk, particularly the risks linked to long plane trips, others have documented that the clots occur rather frequently, even though they do not often cause symptoms that require medical care. Also not in question is that some people are especially susceptible to the complications.

No one, however, is truly immune. A case in point was the death two years ago of a healthy 27-year-old from a pulmonary embolism immediately after debarking in London from a flight from Australia. Former Vice President Dan Quayle developed pulmonary embolisms twice after long flights. Indeed, business travelers who fly frequently are among the most vulnerable.

A major problem in documenting the frequency of deep vein thrombosis related to air travel is that patients disperse rapidly after flights, and complications can occur days or even weeks later, with neither patients nor doctors necessarily linking it to earlier trips.

How Clots Can Occur

Deep vein thrombosis is different from thrombophlebitis, a swelling in a superficial vein, often with an accompanying clot. Although painful and needing prompt medical attention, thrombophlebitis is usually not life threatening.

D.V.T., in which a clot blocks a major vein, causes death in 1 percent of patients. It usually starts in the lower leg but sometimes can begin in the thigh or pelvis. If the clot breaks loose and travels to an artery that feeds the lungs, a resulting pulmonary embolism can shut off the blood supply to the lungs. Although most such clots begin to dissolve immediately, large ones can cause death in minutes or hours.

In a recent article in The Cleveland Clinic Journal of Medicine, Dr. Daniel J. Brotman and Dr. Amir Jaffer noted that long plane trips clearly set the stage for the development of deep vein blood clots. Passengers are typically sitting immobile for long periods, when blood can pool in the veins of the legs.

Pooled blood moves slowly, increasing the risk of clot formation. Pressure from the seat against the back of the legs, particularly a problem for short people and those who are obese, may irritate the lining of the popliteal vein, which runs behind the knee and can be a factor in clot formation.

The problems can arise from long trips by car, train or bus. But in a plane, other factors kick in to make matters worse, said Dr. George Geroulakos, a vascular surgeon at Charing Cross Hospital in London.

The decreased air pressure in the cabin reduces the anticlotting ability of blood and may also relax the walls of the veins, further enhancing the pooling of blood, Dr. Geroulakos wrote last year in BMJ, a British medical journal.

In the low-pressure environment of airliners, factors that activate blood clotting may increase twofold to eightfold, he stated.

Dehydration, a chronic problem on long flights, adds to the problem. The dry air on planes; consuming alcohol, caffeine and salty snacks; and inadequate intake of hydrating fluids thicken the blood and increase its tendency to clot.

The chance of venous thrombosis is greater than average in people who are obese, as well as those who have recently had major surgery or trauma, especially hip or knee surgery; people with heart failure, poor circulation or a personal or family history of venous thrombosis; patients with current cancer; and women who are pregnant, recently had a baby or take oral contraceptives, estrogen or a modified estrogen like raloxifene (Evista) or tamoxifen.

Age also has a role. People over 50 face a greater risk than younger people. On long flights, as many as 10 percent of people with one or more such risk factors develop venous clots that can be detected in X-rays, the Cleveland doctors reported.

Clearly, the length of a trip is a big factor. Dr. Frederic Lapostolle of Bobigny, France, and colleagues studied all cases of pulmonary embolism that occurred on arrival at Charles de Gaulle Airport from November 1993 to December 2000. Fifty-six patients who required medical attention within an hour of a flight were identified among 135.3 million passengers.

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The study most likely underestimated the risk of D.V.T., because those who died on flights or developed it after leaving the airport were not included.

All who developed pulmonary embolisms had traveled at least 2,480 miles, about the distance between New York and Los Angeles.

One was a passenger who had traveled less than 3,107 miles. Four had flown 3,107 to 4,660 miles, and 51 had flown at least 4,660 miles. The risk of severe pulmonary embolism after flights longer than 6,214 miles was 400 times as great as it was for flights less than 3,107 miles.
Reducing Risk

 

Much can be done to minimize the risk of deep vein thrombosis resulting from long trips or prolonged confinement anywhere.

When making a reservation, request an aisle seat, which will allow you to get up easily and move about. Try to walk around as much as possible, preferably at least once a hour. If walking is not permitted, at least flex and stretch your leg muscles periodically.

Avoid dehydration by limiting the intake of alcohol, caffeine and extremely salty or sugary drinks and snacks.

Drink lots of plain water often. Eight ounces an hour is ideal (and that will probably force you to get up periodically to use the lavatory). The wise traveler will take along a large bottle of water.

If you have one or more risk factors for clot formation, consider wearing medically prescribed compression stockings on long trips. In at least one study, they protected fully against thrombosis, though they did cause a few cases of superficial phlebitis.

High-risk people may also be given a low-dose anticoagulant like low-molecular-weight heparin, although that has not been shown to be more effective than compression stockings.

Aspirin, however, is not recommended, because in one good study it provided no protection.

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