Air travel and venous thromboembolism: Minimizing the risk

RISK FACTORS IN LONG-DISTANCE TRAVELERS

The risk of traveler’s thrombosis has recently attracted the attention of passengers and the airline industry. Airlines are now openly discussing the risk and providing reminders such as exercises that should be undertaken in-flight (see the patient information page that accompanies this article). Some airlines are recommending that all patients consult their doctor to assess their personal risk of deep vein thrombosis before flying.

The most common risk factors for VTE in travelers are well established and are additive (Table 1). The extent of the additive risk, however, is not entirely clear.

What is clear is that when VTE occurs it is a life-altering and life-threatening event. If it occurs on an outbound trip, the local resources and capabilities available at the destination may not be adequate for optimal treatment. If a traveler experiences a VTE event on an outbound trip, an emergency return trip to the continental United States or a regional center of expertise may be required. There is an additive risk with this subsequent travel event if the patient is not given immediate treatment first (Table 4). Hence, treatment prior to evacuation should be strongly considered.

The traveler must also be aware that VTE can be recognized up to 2 months after a long-haul flight, though it is especially a concern within the first 2 weeks after travel.^2,4,16,17

RECOMMENDATIONS FOR LONG-DISTANCE AIR TRAVELERS

Each person should be evaluated on a case-by-case basis for his or her need for VTE prophylaxis. Medical guidelines for airline passengers have been published by the Aerospace Medical Association and the American College of Chest Physicians (ACCP).^18,19 In general, travelers should:

• Exercise the legs by flexing and extending the ankles at regular intervals while seated (see the patient information material that accompanies this article) and frequently contracting the calf muscles.
• Walk about the cabin periodically, 5 minutes for every hour on longer-duration flights (over 4 hours) and when flight conditions permit.
• Drink adequate amounts of water and fruit juices to maintain good hydration.¹⁷
• Avoid alcohol and caffeinated beverages, which are dehydrating.
• Be careful about eating too much during the flight.
• Request an aisle seat if you are at risk
• Do not place baggage underneath the seat in front of you, because that reduces the ability to move the legs.
• Do not sleep in a cramped position, and avoid the use of any type of sleep aid.
• Avoid wearing constrictive clothing around the lower extremities or waist.

We recommend that all airplane passengers take the steps listed above to reduce venous stasis and avoid dehydration, even though these measures have not been proven effective in clinical trials.¹⁹

The ACCP further advises that decisions about pharmacologic prophylaxis of VTE for airplane passengers at high risk should be made on an individual basis, considering that there are potential adverse effects of prophylaxis and that these may outweigh the benefits. For long-distance travelers with additional risk factors for VTE, we suggest the following:

• Use of properly fitted, below-the-knee graduated compression stockings providing 15 to 30 mm Hg of pressure at the ankle (particularly when large varicosities or leg edema is present)
• For people at very high risk, a single prophylactic dose of a low-molecular-weight heparin or a factor Xa inhibitor injected just before departure (Table 5)
• Aspirin is not recommended as it is not effective for the prevention of VTE.²⁰

SUMMARY FOR THE AIR TRAVELER

All travelers on long flights should perform standard VTE prophylaxis exercises (see the patient information pages accompanying this article). Although VTE is uncommon, people with additional risk factors who travel frequently either on multiple flights in a short period of time or on very long flights should be evaluated on a case-by-case basis for a more aggressive approach to prevention (compression support hose or prophylactic administration of a low-molecular-weight heparin or a factor Xa inhibitor).

Should a VTE event occur during travel, the patient should seek medical care immediately. The standard evaluation of a patient with a suspected VTE should include an estimation of the pretest probability of disease (Table 2, Table 3), followed by duplex ultrasonography of the upper or lower extremity to detect a deep vein thrombosis. If symptoms dictate, then spiral computed tomography, ventilation-perfusion lung scan, or pulmonary angiography (where available) should be ordered to diagnose acute pulmonary embolism. A positive D-dimer blood test alone is not diagnostic and may not be available in more remote locations. A negative D-dimer test result is most helpful to exclude VTE.

Standard therapy for VTE is immediate treatment with one of the anticoagulants listed in Table 4, unless the patient has a contraindication to treatment, such as bleeding or allergy. Immediate evacuation is recommended if the patient has a life-threatening pulmonary embolism, defined as hemodynamic instability (hypotension with a blood pressure under 90 mm Hg systolic or signs of right heart failure) that cannot be treated at a local facility. An air ambulance should be used to transport these patients. If the patient has an iliofemoral deep vein thrombosis, it is also advisable that he or she be considered for evacuation if severe symptoms are present, such as pain, swelling, or cyanosis. Unless contraindicated, all patients should be given either full-dose intravenous or full-dose subcutaneous heparin or subcutaneous injection of a readily available low-molecular-weight heparin preparations or factor Xa inhibitor at once.²¹