Risk of blood clots lengthy plane flight

If you take a prolonged flight or ground trip by car, the most important issue related to your odds of developing a blood clot is how many risk factors you have at the time.

If you’re traveling more than eight hours by car or plane, you could be at risk for blood clots.

The story begins in the underground tube stations in London at the time of the bombing of the city during World War II. People sought refuge in these stations and brought their lawn chairs for the long nights, frequently falling asleep in the sitting position with legs bent, dependent, and immobile. On numerous occasions some of these people were found dead in the morning, and their autopsies showed the presence of pulmonary emboli that had blocked the lung circulation and caused the death of the victims, presumably due to their lengthy immobilization.

Experts speculated that while the patients were sleeping, blood pooled in the leg veins and clotted due to the lack of muscle contractions that normally pump the blood out of the legs and back to the heart during walking. Once these leg clots had formed, they would grow and a portion then could break off and travel through the leg, pelvic, and abdominal veins back to the heart.

These clots would be pumped through the lung arteries where they would lodge, blocking the flow of blood to the lungs, causing death. Not all people developed these blood clots, but those who were older, had heart problems, cancer, or other serious medical illnesses were more likely to suffer these fatal pulmonary emboli.

Deep Venous Thrombosis and Pulmonary Emboli

The development of blood clots in the legs is known as deep venous thrombosis (DVT), while clots that travel to the lungs from the legs are known as pulmonary emboli (PE). Not all leg clots result in pulmonary emboli, and both conditions are collectively known as venous thromboembolism (VTE).

A possible association of VTE with prolonged flight or travel by motor car has been suspected since 1954 and was called “economy class syndrome” in 1988 (although there is currently no evidence that cabin class solely is a determinant of risk). The case was made stronger by several extended case series originating from busy airports or distant islands. In Paris, the airport’s emergency medical service at Orly and DeGaulle diagnosed pulmonary embolism in 70 incoming passengers during the 24 years to 1998, while at Heathrow 11 of 61 in-flight deaths reported to the coroner between 1979 and 1982 were caused by pulmonary embolism. The other reports are from Martinique (40 cases of flight-related venous thromboembolism in six years), Reunion (six cases in one year), and Hawaii (where 17-25% of patients with venous thromboembolism admitted to two Honolulu hospitals reported recent air travel).

Others have reported the onset of venous thromboembolism soon after prolonged travel by bus, car, truck or train. Prolonged travel of longer than 12 hours was associated with a striking increase in incidence to about 1 pulmonary embolism per 200,000 arriving passengers. Since 10 of the 11 in-flight deaths from pulmonary embolism recorded in the Heathrow report occurred during prolonged flights, it is plausible that travel duration is an important determinant for the risk of venous thromboembolism. After correcting for the fact that pulmonary embolism can occur in 2/3 of people late after arrival, the arrivals terminal data suggest that the total overall incidence of pulmonary embolism may reach about 1:70,000 arrivals from prolonged journeys. The incidence of all venous thromboembolism could be greater if all cases of deep vein thrombosis are also included.

Two widely reported deaths from pulmonary embolism soon after airline flights between Australia and the UK have provoked intense and worldwide media and community interest in the possible association between air travel and risk of venous thromboembolism, which includes deep vein thrombosis or pulmonary embolism. Approximately 2.3 million Australian residents depart on international flights per year, which, by definition, are usually long-haul flights.

Most people with travel-associated venous thromboembolism had clinical risk factors that included older age, obesity, previous venous thromboembolism, birth control pills or hormonal replacement therapy, or recent surgery, pregnancy, leg fracture, or malignancy (see below for a complete list of risk factors). This suggests that risk of venous thromboembolism may be considerably higher than 1:70,000 in these high-risk people on long-haul journeys where specific preventive measures against venous thromboembolism are more likely to be effective. Unique travel-related risk factors for venous thromboembolism have also been proposed, including seating arrangements, body habitus, duration of the flight, dehydration, air pressure and oxygen concentration, air quality, stress and climatic change. However, their role in causing venous thromboembolism remains speculative and requires further study.

The odds of developing a travel-related DVT

Recently, Scurr and his colleagues studied 200 passengers over the age of 50 (76 men, 124 women), with no past or current history of blood clots, who made long-haul journeys of greater than eight hours’ duration from London, returning to the UK within six weeks. Ultrasound was used to scan the leg veins before and after travel. Blood samples were analyzed for two common gene mutations which predispose a person to develop blood clots and 7% of the study population were found to have one of these defects. Passengers were randomly allocated to one of two groups, one wearing special elastic compression stockings, the other not.

Twelve passengers developed asymptomatic deep vein thrombosis (12%). None of these passengers was wearing elastic compression stockings. Four more passengers with varicose veins, wearing elastic compression stockings, developed superficial blood clots (3%). From this study it was concluded that the simple measure of wearing the appropriate type of elastic compression stockings provides effective protection for the prevention of deep vein thrombosis on long flights.

In conclusion, the studies done so far do not agree on the odds of developing a travel-related DVT; is it rare or common? Further studies are required to answer this question. The fact remains that if you take a prolonged flight or ground trip by car, the most important issue related to your odds of developing a blood clot is how many risk factors you have at the time. People with one or two factors do not have very much chance to develop the problem, whereas those with five or more risk factors are much more likely to have a problem. We feel that it is important for everyone to take the risk factor test before you travel and, depending on your risk factor score, consult the risk level chart for more specific information as seen below.

General measures for all travelers

It is important to do the following:

  • Drink plenty of fluids.
  • Stretch legs and change position frequently.
  • Breathe deeply frequently.
  • Be careful about leg rests that compress the calf or behind the knee.
  • Avoid excessive alcohol intake.

The following schema is arbitrary and based on the best available literature. Further research studies are necessary to refine and document this schema. As always, consult a physician experienced in these disorders and familiar with travel-related thrombosis, to determine which measures are most appropriate for you.

LOW RISK: 0-1 Factors

Passengers need NOT use prophylaxis (stockings, etc.) but should:

  • Drink plenty of fluids.
  • Stretch legs and change position frequently.
  • Breathe deeply frequently.
  • Be careful about leg rests that compress the calf or behind the knee.
  • Avoid excessive alcohol intake.

MODERATE RISK: 2 Factors

Passengers in this category should:

  • Drink plenty of fluids.
  • Stretch legs and change position frequently.
  • Breathe deeply frequently.
  • Be careful about leg rests that compress the calf or behind the knee.
  • Avoid excessive alcohol intake.
  • Walk around the cabin every 2 hours.
  • Use calf-length anti-embolism graduated hose at 20-30 mmHg.

HIGH RISK: 3-4 Factors

Passengers in this category should:

  • Drink plenty of fluids.
  • Stretch legs and change position frequently.
  • Breathe deeply frequently.
  • Be careful about leg rests that compress the calf or behind the knee.
  • Avoid excessive alcohol intake.
  • Walk around the cabin every 2 hours.
  • Request exit rows or bulkhead seats to increase leg room.
  • Use calf-length anti-embolism graduated hose at 30-40 mmHg (Physician Rx).

HIGHEST RISK: 5 + Factors

Passengers in this category should:

  • Drink plenty of fluids.
  • Stretch legs and change position frequently.
  • Breathe deeply frequently.
  • Be careful about leg rests that compress the calf or behind the knee.
  • Avoid excessive alcohol intake.
  • Walk around the cabin every 2 hours.
  • Request exit rows or bulkhead seats to increase leg room.
  • Use calf-length anti-embolism graduated hose at 30-40 mmHg (Physician Rx).
  • Consider use of low molecular weight heparin (Physician Rx).
  • Foot or calf pneumatic compression device (portable) (Physician Rx).
  • Manual exercise foot pillow.

Frequently asked questions about travel-related thrombosis

Q. Are leg spider veins or flat bluish veins a risk for developing a blood clot during travel?

No, these are skin blemishes not related to blood clots or normal veins draining the leg. If, on the other hand, one has bulging, prominent veins, these can be a risk factor despite the fact that they may not be causing pain or discomfort.

Q. What should I do if I have aching, tired, or swollen legs?

First you should consult a physician familiar with the diagnosis and treatment of these conditions. You should also wear special prescription stockings during travel as advised by the physician (the over-the-counter variety of travel hose are not sufficient).

Q. What should I do if I have a history of cancer, heart disease, stroke, or other serious disease?

Do not fly without seeking the advice of a physician familiar with the risks and preventive measures for those travelers with these conditions. Beware of advice that you will be fine following the normal preventive measures listed above only! (Seek another opinion.)

Q. If I have a history of a blood clot, or anyone in the family has experienced a blood clot, what is my level of risk?

You are in the highest risk group, and should consult with a physician who knows about the diagnosis, treatment, and prevention of these clots. You need to take special precautions before you fly.

Q. How long after major surgery can I take an eight-hour flight?

Since the risk of developing a blood clot after surgery is highest during the first month, many authorities advise not traveling since, in itself, an eight-hour car or plane ride can cause a blood clot.

Q. Are any support stockings adequate to prevent travel-related blood clots?

Beware of most over-the-counter products. Ask a physician knowledgeable about the stocking types and research that has proven the effectiveness of certain products. Separating facts from advertising claims can be difficult, even for experts in the field.

Q. If I drive from Chicago to Florida or Arizona for the winter, is this a risk factor for blood clots?

Organized research studies in such individuals have not yet been done, but scattered reports would indicate that long auto or bus trips may be a risk factor for blood clots. We further speculate that some long-haul truck drivers are very much at risk for developing travel-related thrombosis.

Q. If my personal physician is not knowledgeable in these matters, where can I find the right specialist?

Start by asking your own physician; next, consult the website for members of the American Venous Forum in your area. You may also call a medical facility to find specialists who deal with blood clotting problems.

Q. If I am under the age of 40, can I assume that I am at minimal risk for developing travel-related thrombosis?

Absolutely not; if you are overweight, taking birth control pills or hormones, have inflammatory bowel disease, or have a family or personal history of a blood clot, to mention a few, you may be at considerable risk.