Click here for more detailed information on the risks of Venous
thrombosis
People have become concerned about
the risks of deep vein thrombosis (DVT) during long air flights,
following reports in the press about occasional deaths due to
fatal pulmonary embolism. The aims of this advice are:
- to provide reassurance that the risk
for most people is miniscule
- to explain about DVT and pulmonary
embolism
- to identify people who may be at
increased risk
- to advise on possible precautions to
reduce the risk
The advice is similar for all long journeys – whether by
air, coach, car, or train.
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What are deep vein thrombosis (DVT) and pulmonary embolism?
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There are two systems of veins in the legs - the
important deep veins (the "main motorways" which carry most of the blood up the legs
towards the heart) and the less important superficial veins("A
and B roads") just
under the skin (which can form varicose veins). Deep vein
thrombosis (DVT) means thrombosis (clotting) of blood in the
deep veins of the legs. It can cause swelling and pain in the
leg, but often occurs without giving any symptoms. A DVT may
disappear completely, as the thrombosis is dissolved by
natural processes. If a DVT extends up the deep veins, two
things can sometimes happen:
- The thrombosis can become dislodged from the vein, and be carried through the main veins and heart to lodge in the
lungs. This is called a pulmonary embolism. Small pulmonary
emboli may cause chest pain, and sometimes coughing up of
blood. Multiple or larger pulmonary emboli may cause
breathlessness. A large pulmonary embolus which blocks the
main blood vessels to the lungs will be fatal.
- The thrombosis can cause chronic blockage in the deep
veins or damage to their valves, leading to long term
swelling and sometimes skin problems at the ankle. This
condition is called the Post
Thrombotic or Post
Phlebitic Syndrome. For more information about this
click on the words.
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Why does deep vein thrombosis occur?
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All the veins in the leg have valves which should
direct blood flow upwards, towards the heart. The deep veins lie
between the muscles, and muscular activity (moving the legs,
walking, or any leg exercise) helps to pump the blood up these
veins. When the legs are inactive, and particularly when sitting
or standing, blood tends to stagnate in the deep veins.
Stagnation of blood can eventually lead to thrombosis. Sitting
with the legs bent (as in an aircraft or coach seat) may also
restrict flow of blood up the veins in the calf. The longer the
period of stagnation, the more likely is thrombosis.
If the blood is unusually “thick” or “sticky” then the
risk of thrombosis is greater: this can be caused by dehydration
and some medical conditions. |
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Who is at special risk of deep vein thrombosis?
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We have no direct evidence about people at special risk of DVT
as a result of long journeys, but based on evidence about
surgical operations the following increase the risk of
thrombosis:
- Having had a DVT or pulmonary
embolism before
- Having had a recent major operation
- Pregnancy
- The contraceptive pill or hormone
replacement therapy (HRT)
- Malignant disease (cancer)
- Some blood diseases
- General ill health
- Increased age
The risks of DVT are probably highest for people with more
than one of these risk factors.
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How large is the risk?
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| For people without any of the risk factors listed
above the risk of DVT (even on a long haul flight) is miniscule
- one in hundreds at the most. For people with risk factors who
take no precautions against thrombosis, the risk of DVT
detectable on special scans is as high as one in twenty on long
haul flights (but many of these thromboses are minor and cause
no problems). |
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What can be done to reduce the risk?
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There is now evidence that wearing below knee
graduated compression stockings reduces the chance of DVT for
people with special risk factors. Few people
without risk factors ever develop DVT or pulmonary embolism as a
result of long journeys, so there is no good evidence about
other measures which reduce the risk. However, based on what is
well known about the causes of DVT and the successful methods of
prevention used in hospital, the following are sensible
precautions, particularly on long haul flights and other
journeys lasting several hours:
1. Move your legs.
• Don’t sit with your legs bent for hours on end. Stretch
your legs out from time to time, and move your feet up and down
at the ankles. Stand up to stretch the legs now and then.
Stretching and moving the legs stops blood stagnating in the
deep veins of the calf, and is the simplest and most effective
thing you can do.
• Go for a walk up and down the aisle.
2. Don’t get dehydrated.
• Drink plenty of fluid – water is ideal. Consider taking a
bottle of water to drink.
• Avoid excessive alcohol, which tends to cause dehydration.
3. Wear compression stockings.
• Graduated compression stockings may reduce the risk of DVT. They
also help to prevent the ankle swelling which many people
experience on long journeys.
• BELOW KNEE stockings are the most comfortable kind, and seem
just as effective as full length stockings.
• Medical graduated compression stockings are supplied in
three classes: Class 1 or Class 2 stockings are suitable for
most people (Class 3 are excessively strong for this purpose).
• Compression stockings can be prescribed by a doctor if there
is a medical need. They can be bought at chemists, surgical
appliance specialists, and now at some other shops, for example
in airports.
• These stockings come in a range of sizes, and your legs will
need to be measured to get the right fitting.
• People who have trouble with the arteries of their legs
should seek medical advice before using compression stockings.
If you would like to be fitted with stockings, please contact
Mr Braithwaite for a consultation.
4. Aspirin.
Taking an aspirin tablet (either a 75mg “junior aspirin” or
a normal 300mg aspirin tablet) everyday for a week before a long journey
may provide a small amount of extra protection against DVT. Take
the aspirin after a meal and stop taking it if you get tummy
ache
5. Anticoagulants.
Special anticoagulant drugs (e.g. heparin injections, or
warfarin by mouth) may be advisable for a few people who have
medical conditions with a particularly high risk for DVT. This
kind of treatment will always be on the explicit advice of a
doctor.
Reference:
Venous thromboembolism from air travel. The LONFLIT Study.
Belcaro G, Geroulakos G, Nicolaides A, Myers K A, Winford M.
Angiology 2001; 52: 369-374.
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REMEMBER – THE RISK OF DEEP VEIN THROMBOSIS
ON LONG
JOURNEYS IS VERY SMALL. THE BEST PRECAUTION IS TO STRETCH
AND MOVE YOUR LEGS REGULARLY
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