Health Centres - Deep vein thrombosis
What is it?
Thrombosis occurs when the blood changes from a liquid to a solid state thereby producing a clot.
If the blood clot occurs within a major vein, the condition is known as deep vein thrombosis (DVT).
The most common veins affected by DVT are those of the legs or within the pelvis (lower abdomen).
Why is it dangerous?
First of all, DVT is not always dangerous - it is perfectly possible to have a small DVT without even being aware of it.
The condition only becomes dangerous, or even fatal, if the blood clot becomes big enough to cause obstruction within the most important of the body's large veins - particularly those that take blood from the heart to the lungs.
The deep veins of the legs and pelvis are large, so clots forming within these veins can be of a considerable size, making them potentially hazardous if they move.
What happens in a danger situation?
A blood clot will form in the veins of an individual's thigh or calf muscles during long periods of inactivity.
When the person suddenly stands up it increases blood flow within the vein, and the clot (or part of it) can break off and head up towards the heart, from which it can be pumped into the lungs, becoming a pulmonary embolism.
This may obstruct the flow of blood through the lungs so much that death follows very quickly.
Why is DVT at greater risk of occurring on long-haul flights?
For two main reasons: firstly, it is very dry in planes and there is a likelihood of passengers becoming dehydrated. With dehydration, the blood becomes thicker than usual and, therefore, more prone to clotting.
Alcoholic drinks are readily available on planes, but they make you go to the toilet more. Unless you drink enough non-alcoholic drinks to compensate, this will increase the tendency to dehydration.
Secondly, because there are limited opportunities to move around on planes, circulation becomes sluggish. Cramped seating may cause pressure points on the legs that slow blood flow locally, and this can increase the tendency for a clot to form.
There appear to be other factors involved, which are not yet fully understood, because DVT has also been observed among Business Class and First Class passengers, who have more leg room. DVT is also observed in other types of long journeys, not just with air travel.
What are the risks of it happening to me?
Factors that may contribute to a higher chance of DVT are:
- being a smoker
- being over 40
- taking the Pill
- being overweight
- having had the condition before
- having undergone major surgery recently.
There are also some medical and inherited conditions that are associated with an increased tendency of the blood to clot, but these are rare.
What are the symptoms?
Localised pain or tenderness within a calf or thigh muscle is a possible symptom of DVT, and more serious symptoms are the onset of a cough, increased heart rate, breathlessness, chest pain or palpitations.
Can aspirin help?
But such benefits may be outweighed by its potential to irritate the stomach lining or an existing stomach ulcer.
It is not yet proven whether aspirin, or any other blood-thinning drug, will reduce the occurrence of DVT.
Swollen ankles, particularly if one ankle is far more swollen than the other. However, swollen ankles are very common on long flights, because of the lack of 'muscle pumping' that helps drain away tissue fluid normally. This is not due to DVT.
Aspirin
makes the blood less 'sticky' and reduces its tendency to clot. 
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