Stephan Moll, MD writes…
Long distance travel, either by plane, car, bus or train, is a slight risk factor for DVT (deep vein thrombosis) and PE (pulmonary embolism). The risk is low. However, there are some people who are at higher risk. In these people compression stockings and/or a dose of an oral blood thinner ( Xarelto, Pradaxa) or one injection of a low-dose “blood thinner” (low molecular weight heparin, fondaparinux) may be appropriate. It is not known whether aspirin does anything in preventing travel-associated DVT and PE – it may have a small protective effect, but may be none. Everybody should use the usual precaution measures: avoid dehydration, move around every so often (details below). A recent review article summarizes the medical scientific knowledge that we have about this topic [ref 1].
How common a problem is it?
Most of what’s known about long distance associated blood clots is known from long-distance flights. The longer the flight, the higher the risk. Flights lasting longer than 8 hours lead to a 2-fold increased risk compared to short flights of less than 4 hours duration. The vast majority of clots do not cause symptoms and are of no consequence to the individual. Our body’s protective system (= fibrinolytic system) typically dissolves these clots. Thus, they never get detected unless one was to do a routine Doppler ultrasound upon arrival at the destination airport. This, of course, does not get done routinely (and shouldn’t), except in clinical studies. The risk of having a blood clot persist for may be up to 2 weeks after landing. The realistic risk of developing a blood clot that causes symptoms is in the order of 1/600 (i.e. one of out 600 people will develop a clot, 599 won’t) for flights over 4 hours, and 1/500 for flights over 12 hours in travelers over 50 years of age.
Who is at risk?
The following are established risk factors for blood clots associated with long distance travel:
- The length of the travel
- Age over 40 years
- Women who use birth control pills or hormone replacement therapy
- Varicose veins in the legs
- Obesity (body mass index of 30 kg/m2 and above).
- Genetic clotting disorder
- Other risk factors, e.g. tall stature, short stature.
Other likely risk factors:
- previous blood clot
- estrogen patch and ring
- recent major surgery or major trauma (within last 3 months)
- recent childbirth (within 3 months)
- leg cast or immobilizer
- acquired clotting disorders (antiphospholipid antibodies).
Official prophylaxis guideline
The respected American College of Chest Physician (ACCP) 2012 guidelines [ref 2] recommend for long-distance travelers :
- For long-distance travelers at increased risk of VTE (venous thromboembolism), frequent ambulation, calf muscle exercise, or sitting in an aisle seat if feasable is suggested, as well as wearing of properly fitted, below-knee graduated compression stockings (15-30 mm Hg pressure at the ankle). This includes individuals with:
- previous clots
- recent surgery or trauma
- active cancer
- estrogen use (with birth control methods or other hormonal therapy)
- advanced age
- limited mobility
- severe obesity
- or a known clotting disorder (thrombophilia)
- ACCP 2012 suggests against the use of aspirin of blood thinners to prevent clots.
Lowering risk: More detailed comments and personal approach
(a) General recommendations for all travelers:
- Avoid constrictive clothing on the legs
- Avoid sitting with legs crossed
- Move the legs frequently, at 30 minutes intervals (either while seated or by getting up):
- Extend your legs straight out in front and flex your ankles, pulling up and spreading your toes, then pushing down and curling your toes. If shoes limit toe movement, exercise anyway or take shoes off;
- If there isn’t room to extend your legs, start with your feet flat on the floor and push down and curl your toes while lifting your heels from the floor. Then, with your heels back on the floor, lift and spread your toes. Repeat this heel – toe cycle ten times;
- Exercise your thigh muscles by sitting with your feet flat on the floor and sliding feet forward a few inches, then sliding them back. Repeat ten times.
- Drink plenty of fluid (non alcoholic and caffeine-free) to avoid dehydration.
(b) Specific measures for higher-risk passengers:
It has not been examined which patients should receive a blood thinner before a long-distance flight. Therefore, no solid recommendations can be given. My personal approach:
- Person who does not need extra blood thinners during flights:
- A patient who is already on oral or injection blood thinners because of a previous history of DVT or PE does not need additional blood thinners at time of flight, as long as the INR (in the patient on warfarin) is therapeutic. Also, this person does not need additional aspirin during the flight.
- Person who has never had a blood clot and who is only heterozygous for factor V Leiden or the prothrombin 20210 mutation. These thrombophilias by themselves are low-risk thrombophilias.
- Person in whom I would consider a blood thinner before flights:
I would discuss (and probably recommend) (a) one dose of the oral blood thinner Xarelto (10 mg) or (b) an injection (such as Fragmin® 2,500 U; Enoxaparin or Lovenox® 40 mg; Arixtra® 2.5 mg) one 1-2 hours before flights lasting longer than 5-6 hours in the following person who is not already on an oral blood thinner:
- Person with previous DVT or PE
- Person with previous unprovoked (=idiopathic) DVT or PE
- Person with previous airline-associated DVT or PE
- Person with previous provoked DVT or PE (associated with surgery, trauma, pregnancy, birth control pill, patch or ring), particularly if additional risk factors for DVT and PE are present (overweight; smoking; pregnancy; recent delivery, surgery, or major trauma; a strong clotting disorder (i.e. homozygous factor V Leiden; homozygous prothrombin 20210 mutation; heterozygous factor V Leiden PLUS heterozygous II20210 mutation; antiphospholipid antibody syndrome; deficiency of antithrombin, protein S or protein C).
- Person who has never had a DVT or PE, but who has a family history of DVT or PE and who has a strong clotting disorder (i.e. homozygous factor V Leiden; homozygous prothrombin 20210 mutation; heterozygous factor V Leiden PLUS heterozygous II20210 mutation; antiphospholipid antibody syndrome; deficiency of antithrombin, protein S or protein C).
- Person with previous DVT or PE
As always, individual decisions after discussion with the patient or affected individual need to be made. The blood thinner Xarelto, even though not FDA approved for this indication, is an attractive option, as it is an oral tablet, whereas the other blood thinners (which are also not FDA approved for this indication) are injections. I discuss with my patients who are considering Xarelto before long-distance flight, to take one Xarelto test dose a few weeks before they fly, to make sure they tolerate it well and do not develop an allergic reaction. It is not known whether Nattokinase protects humans from blood clots. I would not count on it.
- Gavish I et al. Air travel and the risk of thromboembolism. Intern Emerg Med 2011;6:113-116.
- Kahn SR et al. Prevention of VTE in non-surgical patients: Antithrombotic therapy and prevention of thrombosis. 9th ed: ACCP evidence based clinical practice guidelines. Chest Feb 2012;141:2supple195S-e226S.