Dear Doctor Column, November 14, 2005

Blood Clots and Long-distance Travel

Question:

I'm taking a 14-hour flight to Australia to visit family. I've heard long plane flights can cause dangerous blood clots in the legs. I can't shorten the flying time; what can I do to prevent these clots?

Answer:

Sitting still for hours, especially in cramped conditions, is one factor that can contribute to formation of a blood clot in a deep vein, called deep venous thrombosis, or DVT. However, experts stress that long flights almost never lead to DVT in individuals without pre-existing risk factors.

When clots do form, they usually occur in the deep veins of the legs, often in the calf or thigh, but can also affect arm or neck veins. Movement and the massaging action of contracting muscles normally keep blood flowing, but during prolonged periods of immobility blood can pool in the legs, forming a clot.

DVT often has no symptoms, though people sometimes notice redness, swelling, and tenderness in the affected area. Most clots that form in deep veins are small and are gradually broken down by the body. Larger clots can shed pieces of themselves called emboli that float through the blood stream. Once loose in the circulatory system, emboli can travel to major arteries in the lung, blocking blood flow, a serious condition called pulmonary embolism. Pulmonary embolism can cause chest pain, shortness of breath, and in cases involving large clots, sudden death.

Hours of inactivity are a common feature of long-distance travel, whether by air, car, or train, and people with one or more risk factors for DVT should talk with their physicians or visit a travel medicine clinic before embarking on trips longer than 6 hours, especially if they also smoke, are obese, or are older than 60. Factors that increase risk include:

• previous DVT or pulmonary embolism
• history of DVT or pulmonary embolism in a close family member
• use of birth control pills or hormone therapy
• dehydration
• pregnancy
• recent surgery or trauma, particularly to the stomach, pelvic region, or legs
• previous or current cancer
• some uncommon conditions that increase the blood's tendency to clot

Sources: World Health Organization (WHO), American Heart Association

For at-risk patients, there are some preventive medical interventions for DVT, such as preflight subcutaneous injections of heparin, an anticoagulant that decreases the blood's ability to clot, but individuals should always discuss these measures with health care professionals at an experienced travel medicine clinic. There is no evidence aspirin is of benefit, and it is not recommended for preventing DVT.

Travelers without any risk factors can take a few simple precautions to reduce their already very low risk of DVT and make long trips more comfortable:

• Move around. Getting up every 2 or 3 hours to walk through the cabin gets blood flowing.
• If turbulence is keeping you in your seat, try some simple leg exercises, such as bending toes toward the knees and then relaxing them, or lifting the heels and pressing down through the toes — any exercise that contracts leg muscles will help keep blood from pooling. Some airlines provide pamphlets illustrating exercises you can do while seated.
• Wear loose-fitting clothing, avoiding anything that binds or restricts movement.
• Wait until you arrive at your destination to take sleep aids. They may help you nap during lengthy flights, but can also result in prolonged periods of immobility.
• Drink lots of water. The low humidity in airplane cabins can contribute to dehydration. Staying hydrated can also help limit jet leg. Alcohol and caffeine can also dry you out, so limit consumption.
• Try wearing graduated compression stockings, which may also help prevent swollen ankles — a common side effect of long-distance flights. You can purchase compression stockings at medical supply stores, but they must fit properly to be effective, so ask your doctor which type is best for you.

Symptoms of DVT or pulmonary embolism can appear hours or days after your trip, so it's important to seek medical attention if you experience symptoms a week to 10 days after traveling. Be sure to tell your doctor you've recently been on a trip so you can be accurately diagnosed. Although DVT caused by long flights is practically unheard of in individuals without risk factors, people with certain hereditary coagulation defects that put them at risk are often not aware of their condition until DVT occurs. For more information on keeping healthy while traveling, visit WHO's internet center for international travel and health.