Principal Developer: B. Bartle
Secondary Developers: M-F Scully, W. Geerts

Travellers’ thrombosis refers to the development of a deep vein thrombosis(DVT) or a pulmonary embolus(PE) after long distance travel. The association between travel and these types of blood clots has been known since the 1950’s, but recent  research  and the publication of rare fatal cases by the lay press have made this condition a  common concern among travellers. We can now give more appropriate advice than we could a few years ago.

Travellers’ thrombosis can occur as a result of  long distance travel by plane, bus, train or car. This condition was initially thought to occur only after long airplane flights, and was called “economy-class syndrome” by some medical authorities, wrongly associating it only with the cramped space of a regular airline seat . The common ‘thread’ for all these scenarios is prolonged immobility in the sitting position, which can produce significant blockage of blood flow  from the lower legs. It appears that the longer the trip the greater the risk. Air travel may be associated with additional risk factors, such as the pressurized and dry air within the cabin, and dehydration due to excessive alcohol consumption.   Symptoms of the DVT/PE do not usually develop during the flight or immediately after the flight, but tend to appear anytime from 3 days to 2 weeks after the trip.

Pulmonary emboli arise in about 1 to 4 persons per million passengers. A DVT probably occurs a little more frequently. Small clots in the veins below the knees that rarely lead to symptoms or require medical attention may occur in as many as 1 in 20 travellers.

This information tells us that for the average healthy traveller the risk of a serious blood clot that requires urgent medical attention is extremely rare. Any of the following factors, however, may increase the risk of an individual long-distance traveller developing venous thrombosis:

• Being elderly
• Previous blood clots(but not  presently on therapy to prevent them)
• A documented inherited clotting abnormality
• Pregnancy or the first few weeks after delivery
• Active Cancer
• Severe heart failure or recent heart attack
• Recent surgery, especially involving the legs
• Estrogen therapy(birth control pills or hormone replacement therapy)
• Obesity

Patients already receiving an oral anticoagulant such as warfarin, and having a therapeutic INR  before travelling, are likely protected from any risk of developing travellers’ thrombosis.

PREVENTION

A number of general measures can be taken to minimize the risk of travellers’ thrombosis. A group of internationally-recognized thrombosis experts have suggested the  following steps for persons taking trips of greater than 6 hours:

• avoidance of constrictive clothing around the lower extremities and waist
• keep well hydrated with non-alcoholic beverages
• frequent calf muscle stretching

Most travellers, including those with some of the risk factors listed above, do NOT require any additional preventive measures. For a small proportion of long-distance travellers with additional risk factors as listed above,  in addition to the general strategies mentioned, consideration may be given to using properly fitted, below-knee graduated compression stockings , or a single injection of a  anticoagulant belonging to  either the class of low molecular weight heparin or pentasaccharide. To maximixe the effectiveness of the injections , the patient should be taught to self-inject, if possible, immediately before boarding the plane, if that is the method of travel.  Any of the above mentioned class of drugs, prescribed as a pre-filled syringe of the standard prophylactic dose for that drug would be appropriate. You or your nurse should teach the patient how to inject.

ASA and other anti-platelet drugs do not appear to protect against  blood clots associated with long-distance travel.

People travelling by land should take advantage of the planned stops by buses or trains or stop their car periodically to take short stretches of walking.  

 Patients taking warfarin should have an INR blood test done within a week of a planned long-distance trip.

In summary:

• The risk of developing a blood clot related to long-distance travel is very low.
• For most people, just following the general measures mentioned above is adequate.
• If you  have special concerns about a particular patient that might have an additional risk of developing a blood clot associated with an upcoming trip, consider suggesting that the patient get a below-knee graduated pressure stocking or prescribe an injectable anticoagulant for both departures

References

1. Brenner B. Interventions to prevent venous thrombosis after air travel. Are they necessary? Yes. J.Thrombosis Haemostasis 2006;4:2302-5
2. Rosendaal FR. Interventions to prevent thrombosis after air travel: are they necessary? No   J. Thrombosis Haemostasis 2006;4:2306-7

Reviewed by B.Geerts  MD, M-F. Scully MD