Secondly, after a clot has formed in the legs it can damage the
valves in the veins or block the veins. In either case this may cause problems in the legs in the future (see
chronic
venous insufficiency ). It has been estimated that up to 90% of patients with ilio-femoral DVT will subsequently develop signs and symptoms of chronic venous insufficiency with up to 15% developing venous ulcers. As the blood clot clears from the leg and venous blood flow resumes this is abnormal with reflux or reverse flow developing and increasing with time.
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Can the economy class syndrome
(DVT) be prevented?
For the majority of people going
about their normal business there is no need to take any special precautions to
reduce the risk of DVT. Prevention is important if you are known to be at
high risk of DVT or are to undertake an activity which could put you at
increased risk.
DVT can be prevented by taking sensible precautions. The
most important preventive measure is activity. Standing up, stretching and
taking a brief walk every hour during air travel will help to reduce your risk. It is
important not to become dehydrated - so drink water or soft drinks regularly.
This will also aid mobility!
It is important
to exercise the calves of the legs when sitting. The calves can
be gently exercised when sitting by pressing the front of the feet onto the
floor and moving the heels up and down off the floor.
Graduated compression stockings
are particular types of stocking that provide maximum compression around the
ankle area. The compressive effect then becomes less further up
the leg. This improves venous flow in the deep veins. Compression
stockings are proven in hospital studies to reduce the risk of DVT. It is
important that the stockings are fitted correctly.
If you are at particular risk of DVT, then it may be sensible to take
150mgs of aspirin before
your flight. Aspirin can cause irritation of the stomach and can rarely
lead to bleeding from the stomach. It is important not to take aspirin,
unless you know you are safe to do so and have had no previous problems with
vomiting blood or peptic ulcers.
Many patients undergoing surgery
have injections of low dose (prophylactic) heparin under the skin once or twice
per day to reduce the risk of blood clots forming. These patients can also have
pneumatic cuffs fitted to the calfs or feet which intermittently inflate and
deflate throughout surgery. This encourages the flow of blood in the veins
of the legs, and helps to prevent long periods where the blood in the veins is
slow moving and may lead to thrombosis. There are detailed guidelines available in Australia and New Zealand to assist in using methods to prevent post-operative thrombosis.
A recent randomised trial
(Scurr et al 2001 ) has produced some unexpected results. Volunteers were
allocated to wearing or not wearing below knee stockings during long flights,
returning within 6 weeks. Scanning of the veins and blood tests were
performed within 48 hours of return to detect DVT. In the group not
wearing stockings a high incidence of silent DVT was detected (1 in 10).
Volunteers wearing stockings did not suffer any DVTs. This study has been
criticised on various grounds, especially the fact that DVT was so common in the
group not wearing stockings. All the DVTs detected were very small and
present in the calf veins which is an area where the ultrasound scan can have
difficulty being accurate. Despite this it is clear that this finding
requires further detailed studies to either confirm or refute the findings.
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How is Deep Venous Thrombosis
diagnosed?
The diagnosis of DVT may be
suspected by the symptoms and signs in an individual patient and the
circumstances of the patient. For instance, pain and swelling in one calf,
in a patient after major surgery or a long flight, will raise a suspicion of DVT,
which will require exclusion with further tests. The same symptoms that
develop following a game of squash are more likely to be due to a muscle injury.
Clinical diagnosis alone is unreliable and inaccurate and further tests are
required.
Duplex ultrasound scanning . This is a simple, painless test with a
high degree of accuracy. Ultrasound can demonstrate clot within the deep veins.
It is particularly accurate in the larger veins of the leg. The image on
the left is an ultrasound scan showing thrombus (the blood clot) with some blood
flowing around the clot.
In the calf veins ultrasound is
more difficult, but can be accurate in experienced hands. Unfortunately ultrasound can be time consuming and costly.
As the majority of tests will be normal, clinicians are trying to find ways to
reduce the number of normal scans performed. One way to do this is to
measure D-dimer levels.
Measurement of D-dimer (a marker
of coagulation or blood clotting) in blood is gaining increasing popularity as a
rapid and inexpensive screening test. This test is especially useful for
excluding DVT if the results are normal. In a patient at low or moderate
risk, a normal D-dimer test can safely rule out DVT (Fancher
TL, 2004 ). If the D-dimer is abnormal, then
confirmation of DVT using Duplex scanning is important. This is because
other situations where blood clotting occurs can lead to an increase in D-dimer
levels. No test is foolproof, and in a patient with a high risk of DVT and
a normal D-dimer Duplex scanning should be performed.
Other tests such as venography and
plethysmography are much less commonly used today, but venography is the most
accurate test in the diagnosis of DVT.
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Can deep venous thrombosis be
treated?
Fortunately, a DVT can be
treated and the risk of immediate serious complications can be reduced.
The main treatment is
anticoagulation and compression stockings.
Anticoagulation is a treatment
that thins the blood making it less likely to clot. This is usually
started using an injection (heparin) which is continued for between 5 and 10
days. This is because heparin acts very rapidly helping reduce the risk of
further problems as soon as it is started. When heparin is started after a
clot has formed, it is started at a higher (therapeutic) dose. Most
patients today receive low molecular weight heparin (LMWH) as it can be given as
a once or twice daily dose and is as effective as the older unfractionated
heparins which require daily monitoring with blood tests.
While still having heparin, a
further treatment is started. This treatment is warfarin. Warfarin
also thins the blood, but it can be taken in a tablet form. These tablets
act more slowly and it often takes 4 or 5 days before the blood is thinned
sufficiently so that the heparin can be stopped. Warfarin is continued for
between 3-6 months and requires regular monitoring of blood clotting tests to
make sure it is working properly. If you have had more than one DVT it may
be important to remain on warfarin for the rest of your life. Warfarin is very inconvenient to take because of the regular monitoring that is required. There are newer drugs becoming available and undergoing trials which may replace warfarin over the next 10-15 years.
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Other treatments for DVT
Compression stockings -
these are graduated compression stockings and are routinely recommended as they can help with symptomatic relief of
swelling and discomfort. They also increase blood flow in the veins.
In association with elevation of the affected limb they can provide very
effective symptomatic relief.
Stockings can also be used to
reduce the risk of developing a DVT in patients at risk. Thigh or calf
length stockings are effective.
Filters - sometimes pieces
of blood clot break off from the DVT and travel to the lungs causing pulmonary
embolism. Treatment with anticoagulation is sufficient in the majority of
patients to halt this process. In some patients anticoagulation is
dangerous or fails to stop pulmonary embolism and in these circumstances a
filter can be used to protect the lungs. The filter is a metallic sieve
which is placed in the inferior vena cava (the major vein draining the legs and
trunk) and this stops clots (emboli) reaching the lungs. Filter usage
varies considerably between different centres and surprisingly a clinical trial
of filters failed to show a survival benefit (D ecousus
H et al, 1998 ).
Thrombolysis - actively
dissolving the DVT using enzymes is attractive as it could lead to rapid
resolution of symptoms and prevent damage to the venous valves and the
vein walls. It may be most useful in patients with major DVT and the most effective technique is to use a catheter (tube) placed directly into the clot and deliver the enzyme directly to the clot. The main risk of treatment relates to bleeding in
other organs such as the brain, although this occurs in only a small percentage of patients. It is not a routine treatment as yet and
major trials are required to confirm its relative benefit and safety, but it may
have an important role in treating major DVT in large veins.
Surgery - surgery is used
infrequently, but can be helpful in the presence of massive DVT especially where
the limb may be at risk. Anticoagulation is still essential.
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Are there long term complications from a DVT?
There can be long term complications from a DVT.
In some patients as the blood clot is reabsorbed by the body the
valves lining the deep veins are damaged. This can lead to abnormal
reverse flow (reflux) in the deep veins. Over many years this can lead to high
pressures in the veins around the ankle and lower calf. In some people this may lead to the development of
leg ulcers and chronic
venous insufficiency. This is called the post-thrombotic syndrome or
post-phlebitic limb. This syndrome develops in about one third of patients
with a first time proximal (in the larger veins, above the lower leg) DVT even with standard
treatment. The post-thrombotic syndrome is likely to be much worse if blockages remain in the veins. The incidence of post-thrombotic syndrome can be reduced by
wearing below knee graduated compression stockings (Kyrle
and Eichinger, 2005 ).
Sometimes the blood clot
cannot be reabsorbed by the body and the deep veins remain permanently blocked.
In these unusual circumstances the superficial veins enlarge to form
varicose
veins , so that blood can drain from the legs. It is important that these
superficial varicose veins are not removed, because they are acting as an
important pathway for blood to drain from the leg.
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Latest news
A recent study has reported on nearly 9.5
million people who arrived in Western Australia from international flights
between 1981 and 1999.
Over the same period 246 patients were admitted with a first DVT/PE (lung clot)
within 14 days of arrival. The risk of requiring admission with a DVT/PE
in this study was 26 travellers in 1,000,000 (0.000026%) overall.
Interestingly, the risks for non-Australian citizens were greater than for
Australian citizens (33 per million for non-Australian versus 9.6 per million
for Australian). The study also found a definite increased risk of DVT/PE
in passengers on long haul flights of 12%. It is important to remember
that this is only a tiny increase in risk, as the absolute
risk is so low. In comparison the authors quote a risk of dying in a motor
vehicle accident as about 100 times greater than the risk of dying from a
pulmonary embolism/DVT after a long haul flight (Kelman
et al 2003 ).
A pooled analysis of all studies in the medical literature found an 18% higher risk of clots for each 2 hour increase in travel duration using any mode of transport. There was a 26% higher risk of clots for every 2 hours of air travel. One problem the authors noted was the variability and inconsistency in the reported literature (Chandra et al, 2009).
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References
Fancher TL, White RH, Kravitz RL.
Combined use of rapid D-dimer testing and estimation of clinical probability in
the diagnosis of deep vein thrombosis: systematic review. Brit Med J 2004; 329:
821-829. Cruickshank JM, Gorlin R, Jennett B. Air travel
and thrombotic episodes: the economy class syndrome. Lancet 1988; 11: 497-98.Homans J. Thrombosis of the deep leg veins due to
prolonged sitting. New Engl J Med 1954; 250: 148-149.
Schreijer AJM et al. Activation of coagulation system during air travel: a
crossover study. Lancet 2006; 367: 832-38.Kelman CW, Kortt MA, Becker NG
et al. Deep vein thrombosis and air travel: record linkage study. Brit Med J
2003; 327: 1072-76.Scurr JH, Machin SJ,
Bailey-King S et al. Frequency and prevention of symptomless deep vein
thrombosis in long haul flights: a randomised trial. Lancet 2001; 357:
1485-89.Fraser DGW, Moody AR,
Martel A, Morgan PS. Re-evaluation of iliac compression syndrome using
magnetic resonance imaging in patients with acute deep venous thromboses. J Vasc
Surg 2004; 40: 604-11.Fraser DGW,
Moody AR, Martel A, Morgan PS. Iliac compression syndrome and recanalization
of femoropopliteal and iliac venous thrombosis: a prospective study with
magnetic resonance venography. J Vasc Surg 2004; 40: 612-19.Blann
AD, Lip GYH. Venous thromboembolism. Brit Med J 2006; 332: 215-9.Decousus H, Leizorovicz
A, Parent F, et al . A clinical trial of vena caval filters in the prevention
of pulmonary embolism in patients with proximal deep-vein thrombosis. Prevention
du Risque d'Embolie Pulmonaire par Interruption Cave Study Group. N Engl J Med
1998 Feb 12; 338(7): 409-15.Kyrle PA, Eichinger S. Deep vein
thrombosis. Lancet 2005; 365: 1163-74.
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