Long Flight? Be Aware of the Risk of VTE


Cramped airline seats might be putting you at more risk than you realize. Luckily, there are evidence-based strategies for safer travels.

Cramped airline seats might be putting you at more risk than you realize. Luckily, there are evidence-based strategies for safer travels.

Many of us spend a lot of time on commercial aircraft. It is well known that this air travel is associated with an increased risk of venothromboembolic events (VTEs). This risk is unique to air travel and should be considered by all when preparing for a flight. For some, the risk is negligible. However, for others, the risk may be substantial. While there is some debate in the literature, regarding specific risk factors and prevention strategies, one should not lose sight of the fact that the risks are real and there is evidence that we can make travel safer.

Recently, a friend and colleague of mine was diagnosed with pulmonary emboli (PE). Other than his air travel, he had no risk factors for VTE. He was a healthy individual with no prior history of anything. Surprisingly, he experienced multiple, bilateral pulmonary emboli without even a twinge of calf or thigh pain. In truth, DVTs that are precipitated by air travel are asymptomatic 60% of the time. Thus, those whom experience DVT from air travel may be more likely to be diagnosed after embolization.

The same principles of Virchow’s triad (stasis, hypercoagulability and endothelial injury) still apply? But prolonged immobilization accentuates the stasis arm of the triad. Along with dehydration that is superimposed on cabin hypoxia, the risk of VTE from air travel is greater than any other form of travel. Some may argue that immobilization in a long car trip is no different. However, I suspect that gas tank and bladder capacities are an unintended DVT prophylaxis that air travel just doesn’t provide.

The risk for air travel-related DVT is 3-12%, with those at greatest risk being obese females over 40 years of age who use oral contraceptives. Varicosities and genetic thrombophilia are also substantial risk factors. Although much of the research has focused on “long haul” travel, 4 to 10 hours or greater, it should not be assumed that anything less carries no risk. The longer your flight, the more you should consider prophylaxis.

At the risk of being obvious, hydration is important. But alcohol is not the answer. It is true that many find their middle coach seats much more tolerable with a little alcohol, some authors feel that alcohol intake increases the risk for VTE This is most likely secondary to further inactivity from the sedative effect and from alcohol’s ADH suppressant effect contributing to further dehydration. Any type of sedation, through alcohol or otherwise, is probably a risky practice. Every hour of sleep increases the risk of VTE by 10%

Pick your seat wisely, and I don’t mean scratch an itch when no one is looking. The data shows that picking a bad seat actually increases your risk as well. 85% of air travel-related DVT occurs in non-aisle seats So, being land locked in a window or aisle is more than just uncomfortable, it’s a risk.

Strategies to reduce your risk of VTE, beyond seat selection, include aspirin, compression hose and low molecular weight heparin (LMWH). For standard VTE, aspirin offers virtually no protection at all. However, looking at air travel-related DVT, taking 400 mg of aspirin for three days, beginning twelve hours before the flight, reduced the DVT incidence from 4.8% to 3.6%. However, a dramatic benefit was noted from LMWH in that same study. When given within 2-4 hours prior to travel, the incidence was reduced to 0% in “long haul” flights.

If you don’t like aspirin or Lovenox and want to make a fashion statement, consider compression stockings. Although this puts shorts and mini skirts off of the fashion list for travel day, it is a mechanical alternative to pills and shots. Hirsh found that asymptomatic DVT occurred in 10% of controls older than 50 years old. Compression stockings reduced the incidence to 0%. Interestingly, those that used compression stockings experienced superficial venous thrombosis (SVT) 4% of the time, which did not occur at all in the control group.

Certainly, this data isn’t conclusive. However, it does provide enough useful information to guide some safe decision-making. When you are managing your own health and your own risk, you can take poetic license to apply the data how you see fit. This is particularly true when we are considering several common sense strategies that have no associated risk and minimal associated cost.

First, you have to decide what you feel is a long flight. Consider 4 hours as a reasonable starting point. Next, do all you can to get an aisle seat. Remember to hydrate yourself during your travels, limit your alcohol intake and get up and walk intermittently when you can or exercise your calf muscles. Avoid excessive sleep.

If you’re female, use oral contraceptives, are obese, have varicosities or have any of the aforementioned risk factors, consider taking a full aspirin and continuing aspirin for three days. Although some data refutes the benefits of aspirin alone, if there are no contraindications to its use, it may be worthwhile for the potential benefit. If you have several of the above risk factors, consider the use of compression stockings or even LMWH. Finally, if you know you are at high risk (i.e. thrombophilia or previous history of DVT or PE), you should really consider a dose of Lovenox.


(Cesarone MR,Venous thrombosis from air travel: the LONFLIT3 study–prevention with aspirin vs low-molecular-weight heparin (LMWH) in high-risk subjects: a randomized trial. Angiology. 2002.). Jan-Feb;53(1):1-6.

(Gavish I, Brenner B. Air travel and the risk of thromboembolism. International Emerg Med. 2010 Nov 6.).

(Philbrick JT, Shumate R, Siadaty MS, Becker DM (2007). “Air travel and venous thromboembolism: a systematic review”. Journal of general internal medicine: official journal of the Society for Research and Education in Primary Care Internal Medicine 22 (1): 107–14.).

Schreijer, Anja J. M.; Suzanne C. Cannegieter, Carine J. M. Doggen, Frits R. Rosendaal (Nov 25 2008). “The effect of flight-related behaviour on the risk of venous thrombosis after air travel”. British Journal of Haematology 144 (3): 425–429.).

(Cesarone. Angiology. 2002.) and passengers who sit in window seats have twice the risk of those who don’t (Schreijer, Anja J. M.; Suzanne C. Cannegieter, Carine J. M. Doggen, Frits R. Rosendaal (Nov 25 2008). “The effect of flight-related behaviour on the risk of venous thrombosis after air travel”. British Journal of Haematology 144 (3): 425–429.).

(Geerts WH, Prevention of venous thromboembolism: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition). Chest. 2008 Jun;133(6 Suppl):381S-453S.). 


  1. 85% of the DVTs might be from non-aisle seats, but what percentage of seats in cattle class are non-aisle? A quick guesstimate would be in a long haul cabin with seating config of 3-5-3 then we have 4/11 aisle so about 65% non-aisle. This makes the difference a lot less significant, possible non significant dependent on numbers.

  2. working in a ski area, our ED sends home, often via airplane, numerous patients with leg immobilization. I have seen no data on VTE prophylaxis here. If the injury is several days old (i.e., not at risk for more bleeding), the use of Lovenox SC or oral Pradaxa seems to make sense and has been used by some of our Orthos. ASA seems to puny. Does anyone have data to support?

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