What Measures Prevent Travel-Associated Thrombosis?

By Laura S. Lehman, PharmD, from Medscape

Question: The risk for thrombosis after long airplane trips is well known. What should I recommend for prophylaxis? (Women, in particular, are prone to embolisms to the lungs from long flights.)

Response from Laura S. Lehman, Doctor of Pharmacy:

The rate of venous thromboembolism (CLOTS) (VTE) increases with duration of airplane flight. For flights less than 6 hours, VTE is very rare. However, the odds progressively increase as travel time increases.

VTE associated with flight also increases with presence of underlying risk factors.

History of deep venous thrombosis or VTE, pregnancy, estrogen use (including oral contraceptives), malignancy, advanced age, obesity, immobility, recent major surgery, congestive heart failure, and thrombophilic disorders are risk factors for VTE.

Although studies have found conflicting results on risk for VTE development associated with travel, a meta-analysis of 14 studies evaluating this risk (by air, land, or sea), found an 18% higher risk for VTE for each 2-hour increase in duration of travel.

On the basis of data from 3 studies that focused on air travel, the pooled relative risk for VTE was 26% higher for each 2-hour increment of flight duration.

Several guidelines (from the United States and United Kingdom) exist for prevention of VTE with travel.

Unfortunately, there is a lack of strong evidence from well-designed clinical trials from which the various guidelines could derive sound recommendations. The following lists preventive measures extrapolated from these guidelines.

General measures for all travelers:

• Avoid dehydration;
• Avoid constrictive clothing from the waist down;
• Walk around the cabin at regular intervals if feasible (at least every 2 hours); and
• Periodically flex and extend feet and knees.

Patients with risk factors for VTE who are not chronically anticoagulated should follow the above general measures.

These measures may also be considered:

• Properly fitted below-the-knee compression stockings providing 15-30 mm Hg pressure at the ankle; and
• A single dose of low-molecular-weight heparin administered prior to departure for flights (and potentially other forms of travel) longer than 6-8 hours.

Aspirin is not recommended for VTE prevention for long-distance travel


General measures are recommended for all travelers. Measures such as graduated compression stockings or low-molecular-weight heparin (LMWH) may be considered for those patients felt by their practitioners to be at higher risk for VTE.

The role of aspirin is controversial.

Although the Aerospace Medical Association guidelines recommend aspirin as an option with or without compression stockings in moderate-risk patients, the American College of Chest Physicians (ACCP), the British Medical Association, and others recommend against aspirin for prevention of VTE with long-distance travel.

Those who advocate for the use of aspirin likely base that recommendation on data finding that aspirin 160 mg daily for 5 weeks reduced rate of pulmonary embolus by a third in hip fracture patients.

Those who advocate against routine use of aspirin note the LONFLIT3 study. This randomized trial evaluated aspirin vs low-molecular-weight heparin (LMWH) for prevention of VTE associated with air travel in high-risk patients.

Three arms were evaluated:

(1) control with no prophylaxis;

(2) aspirin 400 mg daily for 3 doses, initiated 12 hours prior to travel; and

(3) a single dose of weight-adjusted enoxaparin administered 2-4 hours prior to flight. Thrombosis occurred in 4.8% of control patients, 3.6% of aspirin patients, and no LMWH patients.

Aspirin was not significantly more effective than the control arm.

Use of LMWH for prevention of VTE associated with travel is not approved by the US Food and Drug Administration.

Therefore, practitioners should assess individual patient risk factors for VTE and determine whether the benefits of LMWH outweigh the risks. In addition, it is unclear which specific dose of LMWH should be used.

The ACCP guidelines recommend a prophylactic LMWH dose prior to departure. The British Medical Association notes that empirical regimens given the day before, the day of, and day after travel have been used.

LONFLIT3 used an enoxaparin dose equivalent to 0.1 mL per 10 kg body weight.


Dr. Pinna says:

The injection of heparin sounds ideal, but here in the USA, the FDA does not support its use.

If a patient developed uncontrollable bleeding or suffered a stroke after such an injection, there would be a lawsuit instantly.

Therefore, I recommend large quantities of water. Why? The traveler has to go to the bathroom frequently and thereby walks. The walking prevents the blood clots.

Another of my recommendations is: Break up the flight. Stop for a night on long flights (over 24 hours). When we fly to Australia, we stop at Las Vegas and then Honolulu. Costs more. So what?

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