What is it?
Thrombosis occurs when a clot forms in the blood, blocking a blood vessel.
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's 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's 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 a DVT happening to me?
One in a thousand people in the UK are affected by DVT each year, the majority of which happen as a result of a number of factors, combined with admission to hospital.
Factors that may contribute to a higher chance of DVT are:
- being a smoker
- being over 40
- taking the Pillor HRT
- being pregnant
- being overweight
- having had the condition before
- having undergone major surgery recently
- being immobile on a journey for longer than six hours
- having cancer.
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?
Swollen ankles and legs are common on long flights because of the lack of 'muscle pumping', which helps drain away tissue fluid normally. This is not due to DVT.
Localised pain or tenderness within a calf or thigh muscle is a possible symptom of DVT, particularly if there is swelling in the calf below the knee or redness or warmth in that area with a heaviness or aching sensation.
More serious symptoms are the onset of a cough, increased heart rate, breathlessness, chest pain or palpitations, which may indicate a clot in the lung or pulmonary embolism. This is a medical emergency and requires urgent treatment.
Can aspirin help?
Aspirin seems very effective at reducing clots in arteries, which is why it is taken by people to prevent or treat heart attacks and strokes but does not seem very good at preventing clots in veins so is not recommended to be taken for DVT prevention.
Because of the high number of deaths related to DVT and hospital admissions, the NHS now assesses each new patient as to their risk of developing DVT.
If the risk is high, patients may be started on blood thinning treatments, such as heparin injections and given special leg compression stockings to wear.
This is a risk factor for DVT when combined with being immobile in a hospital bed for more than three days or having an operation lasting longer than 90 minutes.
If you suspect that you have a DVT, contact your GP or out of hours service. They can arrange a D-dimer blood test, which can help rule out a DVT, or arrange an appointment for a venogram or ultrasound test on your leg veins, to confirm the blockage in the vein. Patients may be started on medication known as directly acting oral anticoagulants (DOAC's) or warfarin, heparin or dalteparin injections before having a DVT confirmed as any risks of excess bleeding due to using these medications are outweighed by the risks to health of an untreated DVT.
How can I avoid a DVT when flying?
- Drink plenty of water and or fruit juice.
- Avoid alcohol, which will dehydrate you more.
- Get up and move around as often as you can.
- When you are sitting, try moving your ankles around and going up and down on your tiptoes (a bit like mini leg-raises).
- Wear elastic compression stockings to improve circulation.
- Avoid sitting with your legs crossed and do not wear socks or tights that are too restrictive.
- Some people at particularly high risk may be recommended to have a heparin injection before a long haul flight.
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