Thrombosis is the formation of blood clots within vessels. Blood does not normally clot within vessels and the development of such clots may lead to problems. Thrombosis can potentially occur in any blood vessel and may have fatal consequences if it obstructs the flow of blood to a vital organ. In the context of air travel, we are concerned with thrombosis occurring in the deep veins of the lower legs.
The deep veins of the lower legs are situated in the muscles of the calf. Compression of the veins by muscular contraction, cause a pumping effect (the muscle pump) aiding the return of blood to the heart. If the muscle pump is not working (e.g. due to immobilization), the blood flow in the veins may decrease (known as venous stasis) to the point where small clots may form. Most of these are too small to cause problems. However, they may sometimes enlarge significantly or link up to produce a large obstructive thrombus.
Immobility in a seated position is an obvious predisposition to DVT as the veins of the legs can get compressed and cause stasis. DVT is known to occur in passengers on long-distance road or rail journeys as well as those by air. The common factor in all of these is immobility rather than the environment. Pressurized cabins and high altitude of aircraft have no impact on the risk of developing a DVT.
The term "Economy Class Syndrome" was first used in 1977 in a paper entitled "Pulmonary thromboembolism after travel". It is, in fact, an inaccurate term as there is no firm link between air travel in any class per se and the development of DVT. Long periods of immobility in trains, buses and automobiles carry similar risks. The House of Lords report recommends the use of the more appropriate term "traveler’s thrombosis".
The normal rate of occurrence in the general population in the UK is 1 per 1,000 to 1 per 10,000 people every year, depending on age. According to the Wright Study 1 in 6,000 passengers develop DVT after periods of immobility of 4 hours or more.
There are certain predisposing factors that are well known to contribute to the risk of having a DVT. These are:
Obviously, if more than one of the above applies, the risk of having a DVT is further increased. If this is the case, or you have any one of the conditions marked '*', we suggest you seek the advice of your doctor before flying.
As the major cause is immobility, you can do quite a lot to reduce this, and hence minimize your risk of getting DVT. Some suggestions are:
Our inflight magazine, Discovery, and inflight safety video also includes tips and exercises to do inflight to help prevent DVT.
The most common features of a DVT are:
If you experience any of these after your flight; we suggest you consult a doctor to exclude DVT.
For more information you may consult the following useful Links:
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