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Air travel and venous thrombosis

Explains 'economy-class syndrome' and the risks of thrombosis for air travelers.

Who is at risk of thrombosis?
Does air travel increase the risk of thrombosis?
How can I reduce my risk?
What are the warning signs of thrombosis?

Venous thrombosis in airplane passengers, or 'economy-class syndrome' as it is sometimes known, has received a lot of attention in newspapers and on television. Should venous thrombosis be thought of as a serious health risk to travelers? Here, we help you to separate the facts about thrombosis and air travel from the myths.

Venous thrombosis is a blood clot that develops in a vein. It usually occurs in the veins deep within the muscles of the leg or in the pelvis, causing a condition called deep-vein thrombosis or DVT for short. Deep-vein thrombosis itself is not life-threatening but can sometimes lead to a serious condition known as pulmonary embolism. Pulmonary embolism occurs when the blood clot breaks up and moves to the lungs, where it can stop the blood from flowing normally.

Who is at risk of thrombosis?
Venous thrombosis is a fairly common medical problem. Many different risk factors affect your chances of developing thrombosis at a given time. The most important of these risk factors are:

  • major operations
  • trauma (fractures)
  • medical conditions
  • cancer and its treatment
  • stroke or paralysis
  • previous deep-vein thrombosis
  • immobility/lack of movement
  • severe varicose veins
  • increasing age
  • pregnancy
  • some oral contraceptives
  • being very overweight
  • thrombophilia
  • long journeys
As you can see, a long journey is just one of many risk factors for thrombosis. During long journeys by bus, car or airplane, you may sit still for a long time. This lack of movement can slow down the flow of blood through your veins, making blood clots more likely to form.


Does air travel increase the risk of thrombosis?
A long journey may increase your risk of thrombosis, simply because you are sitting still for a long time. There are also certain conditions related to air travel that may play a part in the development of blood clots.

For example:
  • cabin pressure is lower than normal air pressure and this makes blood more likely to clot use of alcohol,
  • sedatives or sleeping pills during air travel can lead to even less movement than normal, so that your blood moves more slowly and can clot more easily
  • drinks containing alcohol and caffeine can cause dehydration, making the blood thicker, move more slowly, and more likely to clot

If passengers already have risk factors for thrombosis, then air travel may increase their risk still further. However, the results of a study carried out in France showed that, over 7 years, there were only 56 cases of pulmonary embolism found in over 135 million people who traveled by air.

Experts do not yet agree on how real the risk of thrombosis is for air travelers and are still researching and discussing this matter. For example, one study reported that, for people who already had deep-vein thrombosis, there was no difference between the risk of thrombosis in air travelers and non-travelers. The term 'economy-class syndrome' may even be misleading. There is little proof that the class you travel in (i.e. the amount of leg room you have) affects your chances of developing thrombosis. Business-class and first-class passengers actually seem to have the same risk of developing thrombosis as passengers in economy class.

Experts do agree that the risk of developing thrombosis increases as the length of the flight increases. The risk seems to become most relevant for flights lasting longer than about 8 hours. If you already have several risk factors, you are more likely to develop thrombosis. You should consult your doctor before a long flight if:

  • you have a history of thrombosis and are not being treated with anticoagulants (sometimes called blood-thinner pills)
  • you are pregnant (especially if you have a history of thrombosis)
  • you are wearing a plaster cast for a broken or fractured leg
  • you have severe varicose veins or swelling in your legs
  • you have thrombophilia
  • you have had a recent major operation


How can I reduce my risk?
The best way to avoid thrombosis during long flights has not yet been agreed, but it is recommended that all passengers:

  • exercise their lower legs every half hour or so to keep blood flowing normally. Your doctor or airline can provide suitable exercises that can be done in your seat.
  • drink plenty of noncaffeinated, nonalcoholic fluids, such as water and fruit juices.
  • avoid taking alcohol, sedatives or sleeping pills.

If you are at increased risk of thrombosis, your doctor may recommend that you wear knee-high elastic compression stockings during long flights. Compression stockings put pressure on the veins in your lower legs and this helps blood to flow back up to the upper leg. If you have severe varicose veins or have had a previous thrombosis, your doctor may recommend that you wear compression stockings that put even more pressure on your lower leg. There is some evidence that compression stockings help to prevent blood clots in air travelers, they are safe and affordable and are already used to help prevent thrombosis in patients who have had major surgery.

If you have a history of thrombosis and are not being treated with anticoagulant medications; are pregnant and also have other risk factors for thrombosis; or if you have thrombophilia, your doctor may recommend that you take anticoagulants before a long flight. Although aspirin may help to lower the risk of thrombosis, anticoagulant medications called low-molecular-weight heparins seem to be more effective; these medications have to be injected under the skin. If you are pregnant, your doctor may recommend that you are given low-molecular-weight heparin and the chances of this are higher if you also have other risk factors, such as a history of venous thrombosis.


What are the warning signs of thrombosis?
Only a small percentage of passengers who travel on flights longer than 8 hours may develop blood clots in a deep vein of the leg. However, many of these clots do not cause any signs of thrombosis and are cleared from the body naturally. If symptoms do occur, it is often a few days after a long flight rather than during the flight itself, and they usually include swelling, tenderness, pain and redness in the leg. Symptoms of pulmonary embolism include:
  • shortness of breath
  • sharp chest pain that is worse during deep breathing
  • coughing up of blood
  • a rapid heart beat
It is important to realize that such symptoms may also be signs of conditions other than thrombosis or pulmonary embolism. If you are worried, consult your doctor as soon as possible so that tests can be done to check what is causing your symptoms.


On long flights, some air travelers may be at risk of developing venous thrombosis, especially if they already have one or more risk factors for thrombosis. All travelers should move their legs as often as possible, drink plenty of noncaffeinated, nonalcoholic fluids and avoid drugs that reduce movement. If you are at high risk, your doctor may also recommend that you wear elastic compression stockings or receive anticoagulant medication or both.


Ansell JE. Air travel and venous thromboembolism - Is the evidence in? New England Journal of Medicine 2001; volume 345: pages 828-9.

Belcaro GV et al. Prevention of flight venous thrombosis in high-risk subjects with stockings or one-dose enoxaparine. Oral presentation given at the meeting of the American Heart Association 2002; Abstract 3556.

Cesarone MR et al. Venous thrombosis from air travel: the LONFLIT3 study. Angiology 2002; volume 53: pages 1-6.

Clagett GP et al. Prevention of venous thromboembolism. Chest 2001; volume 119(1 Suppl): pages 132S-75S.

Gallus AS & Goghlan DC. Travel and venous thrombosis. Current Opinions in Pulmonary Medicine 2002; volume 8: pages 372-8.

Kraaijenhagen RA et al. Travel and risk of venous thromboembolism. The Lancet 2000: volume 356; pages 1492-3.

Lapostolle F et al. Severe pulmonary embolism associated with air travel. New England Journal of Medicine 2001; volume 345: pages 779-83.

Scientific Advisory Committee of the Royal College of Obstetricians and Gynaecologists. Advice on preventing deep vein thrombosis for pregnant women travelling by air. Opinion Paper 1, October 2001.

Scurr JH et al. Frequency and prevention of symptomless deep-vein thrombosis in long-haul flights: a randomised trial. The Lancet 2001; volume 357, pages 1485-9.


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