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Plane Facts About Stop-Clot Socks

Tight stockings may help, but problem may not be that big a problem

THURSDAY, May 10 (HealthScout) -- Tight stockings that keep blood from pooling in the legs can prevent clots from forming on long-haul plane trips, a new study shows.

But the question still is, experts say, whether those blood clots are actually a health problem for passengers.

Deep vein thrombosis (DVT) has become a source of worry for air voyagers on marathon trips, andit has been dubbed the "economy class syndrome" because it's allegedly linked to prolonged confinement in cramped quarters. Dehydration combined with altitude can also temporarily thicken blood, at least in theory, upping the risk of clotting, experts say.

In most cases, the clots are merely painful, but if they dislodge from the legs and reach the lungs, heart or brain, they can be deadly. Last year, a 28-year-old British woman, Emma Christofferson, died shortly after stepping off a plane that had just finished a 20-hour voyage from Sydney, Australia, to London. The cause of death was reported to be a blood clot in her lungs.

But studies of "economy class syndrome" have turned up mixed results. Some researchers claim to have verified the connection between long flights and clots, and others say the risk either doesn't exist or is extremely slight. Last March the World Health Organization held a meeting about the issue of deep vein thrombosis associated with air and other travel. That session led to a call for more study on the link, which experts determined was probable but small.

"We agree that such a link, although unproven, is likely, but also that available data does not permit specific recommendations" for how to prevent DVT, says Denis Chagnon a spokesman for the International Civil Aviation Organization, a Montreal, Canada-based United Nations group representing flight-regulating agencies.

Chagnon adds that "economy class syndrome" is a misnomer, since anyone in coach, business or first class who is inactive could, in theory, develop a blood clot. Regardless of where you're seated on a long flight, take a few minutes every hour or so to walk around, Chagnon says. "It's the inactivity that's the culprit."

In the latest study, reported in this week's Lancet, Dr. John Scurr, a vascular surgeon at Lister Hospital in London, and his colleagues followed 89 men and 142 women who'd taken flights out of Heathrow airport of eight hours or longer, and who came back to the city within six weeks. Half the travelers were given tight, elastic compression stockings like those worn by surgery patients in hospital to prevent blood clots. The rest had their own legwear.

Ultrasound images showed that no one who wore the elastic stockings had blood clots in their calves within two days of their return trip. But 12 of the 116, or about 10 percent, who didn't use the socks had formed symptomless clots.

"We conclude that symptomless DVT might occur in up to 10 percent of long-haul airline travelers," the researchers write. "Wearing of elastic compression stockings during long-haul air travel is associated with a reduction in symptomless DVT."

The study was funded in part by Medi UK, a British company that makes compression stockings and commiserates about the "torture of second class travel" on its Web site. Scurr is currently involved in testing a device to improve blood flow in the legs and has endorsed the product publicly.

Dr. Jack Hirsh, a clot expert at McMaster University in Hamilton, Ontario, says the stocking study merits a further look. But it has enough holes to be troubling, adds Hirsh, co-author of a commentary on the journal article.

For starters, the rate of clotting in the sock-less group was roughly 40 to 150 times higher than earlier estimates for the prevalence of DVT, implying bias in interpreting the ultrasound results, he says. What's more, Hirsh adds, the positive ultrasound tests conflict with negative findings on another, highly sensitive screening for clots called D-dimer, suggesting that the clots were either extremely small or that the ultrasound images were mistaken.

"I think the evidence, although it's not completely solid, is that there is probably a two- to three-fold increase in thrombosis associated with air travel over if you don't travel," Hirsh says. For someonebetween the ages of 15 and 25, the baseline risk of serious thrombosis is about 1 in 100,000, so the increase is almost negligible, Hirsh says. Even for a person in his 80s, whose normal clot risk is 1 in 100, the increase isn't especially strong.

Stocking makers say the British study could be a boon to their business. "There's a very large traveling public, but how many of them will take the risk seriously remains to be seen," says Stephen Cardoza, vice president for sales and marketing at Venosan.

The Asheboro, N.C., firm, which sells its compression stockings to surgical supply houses, is a subsidiary of the Swiss company Salzmann Medico.

What To Do

So should you fret about flying? Not if you're healthy. "The only people who should be concerned about it are people who have a strong baseline risk to start with," says Hirsh. These include people with a history of clotting, or relatives with a history of bleeding disorders.

But even these patients don't have to avoid air travel, says Hirsh. He prescribes a regimen of isometric exercises, plenty of water and no alcohol or caffeine to minimize the risk of clotting during flight. In extreme cases, some people can even administer shots of blood thinner before they fly.

For more on "economy class syndrome", try this site at Wright State University, or the World Health Organization.

For more on deep vein thrombosis, check out the American Heart Association.

Or, take a look at these previous HealthScout stories on blood clots

SOURCES: Interviews with Jack Hirsh, M.D., director, Hamilton Civic Hospitals Research Center, McMaster University, Hamilton, Ontario; Denis Chagnon, spokesman, International Civil Aviation Organization, Montreal, Canada; Stephen Cardoza, vice president, sales and marketing, Venosan, Asheboro, N.C.; May 12, 2001 The Lancet
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