June 03, 2003 Volume 39 Issue 22

ISTM: Blood clot risk not linked to airlines' economy-class seats

Study of travellers reveals increase in coagulation in various long trips

By Charlene Laino

NEW YORK – Sitting in a cramped position for long periods at a time—whether in a plane, train or automobile—can increase the risk of venous thromboembolism, test flights of travellers suggest.

The study, said to be the first to use real travel conditions to analyse the mechanism of travellers' thrombosis, showed markers of coagulation increased in passengers on both long-haul airplane flights and long-distance bus trips, said Dr. Wolfgang Schobersberger, a professor of intensive care medicine at the University of Innsbruck in Austria.

"This activated coagulation could be a risk factor for venous thromboembolism," he told a press conference at the meeting here.

Several years ago, researchers linked long airplane flights to an increased risk of deep vein thrombosis (DVT), blaming the events on high altitude, low humidity and low oxygen pressure, Dr. Schobersberger said.

But since thromboembolic events have also been reported in people sitting for long periods in cramped air raid shelters as well as after long-distance car, bus and train travel, his team postulated another factor must be the culprit.

To test the hypothesis, the researchers prospectively enrolled 40 people at low or medium risk for DVT. Twenty flew from Vienna to Washington, D.C., and back two days later. The others travelled by bus from Innsbruck to Rome and back two days later. Each trip takes about 10 hours.

Risk factors for DVT include: age 60 or older, heart disease, family history of DVT, varicose veins or chronic venous insufficiency, obesity, pregnancy, malignancy and recent surgery.

Markers measured

Molecular markers for coagulation and fibrinolysis were measured before the trip, five to eight hours into the trip, immediately after the trip, one day later and three days later. In addition, activated thromboelastography was used to gather functional measurements of coagulation.

Thromboelastography revealed activation of coagulation in all participants during and after travel, regardless of whether they travelled by plane or bus, Dr. Schobersberger reported.

Also, factor VII and factor VIII coagulant activity was increased in all patients, he said. Levels stayed elevated for at least 24 to 48 hours after the trip ended, he added.

None of the travellers developed DVT, "but we didn't expect it, with only 20 people in each group," Dr. Schobersberger said.

"Since both forms of travel increased risk, we can conclude that reduced humidity and moderate hypoxia do not play a critical role in thromboembolic formation," he said. "But sitting in a cramped position is a trigger.

"The findings should put an end to the term 'economy class syndrome,' " he added. "There is no evidence that blood clot risk is increased by sitting in the economy section on an airplane compared to business or first class, or in an airplane versus another form of transportation."

To reduce the risk of developing DVT during a trip of five hours or more, all travellers should drink plenty of non-alcoholic fluids to avoid dehydration and frequently move their legs, he said. Those at moderate risk should also wear compression stockings, sometimes called support pantyhose, Dr. Eklof said.

Travellers at high risk should be given an injection of a low molecular weight heparin, which will provide protection for about 12 hours, immediately before the trip, he said.