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.
are deep vein thrombosis (DVT) and pulmonary embolism?
There are two systems of veins in the legs - the important deep veins (which carry
most of the blood up the legs towards the heart) and the less important superficial
veins 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 well settle completely, as the thrombosis is dissolved by natural processes.
If a DVT extends up the deep veins, two things can sometimes happen:
1. The thrombosis can become dislodged from the vein, and 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.
Why does deep vein thrombosis occur?
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.
is at special risk of deep vein thrombosis?
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
• Having had a recent major operation
• The contraceptive pill or hormone replacement therapy (HRT)
• Malignant disease (cancer)
• Obesity (being overweight)
• Severe heart disease
• Some blood diseases
The risks of DVT are probably highest for people
with more than one of these risk factors.
large is the risk?
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).
There is now evidence
that wearing below knee graduated compression stockings reduces the change of
DVT for people with special risk factors. Because so few people without risk factors
ever develop DVT or pulmonary embolism as a result of long journeys, there is
no definite 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:
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.
Don’t get dehydrated.
• Drink plenty of fluid –
water is ideal.
• Avoid excessive alcohol, which tends to cause dehydration.
Wear compression stockings.
• Graduated compression stockings
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).
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.
Taking an aspirin tablet (either a 75mg “junior
aspirin” or half of a normal 300mg aspirin tablet) a few hours before a
long journey may provide a small amount of extra protection against DVT.
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.
a Deep Vein Thrombosis Information Pack
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