Deep Vein Thrombosis

deep vein thrombosis

A DVT is a blood clot that forms in a deep leg vein. Veins are blood vessels that take blood towards the heart. Deep leg veins are the larger veins that go through the muscles of the calf and thighs. A calf vein is the common site for a DVT. A thigh vein is less commonly affected. A DVT is part of a group of problems together known as venous thromboembolism (VTE).

What is venous thromboembolism?

A pulmonary embolism (PE) is where a thrombus has broken off from a DVT (usually in the leg) and become stuck in one of the blood vessels in the lung. Pulmonary emboli is also part of venous thromboembolism.

Why do blood clots form in leg veins?

Blood normally flows quickly through veins, and does not usually clot. Sometimes a DVT occurs for no apparent reason. However, the following increase your risk of having a DVT:

  • Immobility which causes blood flow in the veins to be slow. Slow-flowing blood is more likely to clot than normal-flowing blood.
  • A surgical operation where you are asleep for over 1-1.5 hours is the most common cause of a DVT. Blood flow in the leg veins can become very slow, making a clot more likely to occur. Certain types of surgery (particularly operations on the pelvis or legs) increase the risk of DVT even more.
  • Any illness or injury that causes immobility increases the risk. This includes having a leg in a hard plaster cast after a fracture.
  • Long journeys by plane, train or coach/car may cause a slightly increased risk.
  • Damage to the inside lining of the vein increases the risk of a blood clot forming - for example, a DVT may damage the lining of the vein. So, if you have a DVT, then you have an increased risk of having another one in the future.
  • Conditions that cause the blood to clot more easily than normal (thrombophilia) can increase the risk. Some conditions can cause the blood to clot more easily than usual. Examples include, nephrotic syndrome and antiphospholipid syndrome.
  • The contraceptive pill and hormone replacement therapy (HRT) which contain oestrogen can cause the blood to clot slightly more easily.
  • People with cancer or heart failure have an increased risk.
  • Older people (over 60 years of age) are more likely to have a DVT, particularly if you have poor mobility or have a serious illness such as cancer.
  • Pregnancy increases the risk.
  • Obesity increases the risk.
  • Being male.
  • Dehydration can make a DVT more likely to happen.

What are the deep vein thrombosis symptoms?
A DVT most commonly develops in a deep vein below the knee in the calf. Typical DVT symptoms include:

  • Pain and tenderness of the calf.
  • Swelling of the calf.
  • Colour and temperature changes of the calf. The calf may then become warm and red.

Do I need any tests?

Sometimes it is difficult for a doctor to be sure of the diagnosis from just your symptoms, as there are other causes of a painful and swollen calf.

Two commonly used tests are:

  • D-dimer blood test. This detects fragments of breakdown products of a blood clot. The higher the level, the more likely you have a blood clot in a vein.
  • A special type of ultrasound called a duplex Doppler is used to show blood flow in the leg veins, and any blockage to blood flow. Ultrasound is useful because it is an easy, non-invasive test.

Is a deep vein thrombosis serious?

It can be. When a blood clot forms in a leg vein it usually remains stuck to the vein wall. The symptoms tend to settle gradually. However, there are two main possible complications:

  • Pulmonary embolus (a blood clot that travels to the lung).
  • Post-thrombotic syndrome (persistent calf symptoms).

A small PE may not cause any symptoms. A medium-sized PE can cause breathing problems and chest pain. A large PE can cause collapse and sudden death.

Without treatment, up to 6 in 10 people who have a DVT develop long-term symptoms in the calf. This is called post-thrombotic syndrome. Symptoms occur because the increased flow and pressure of the diverted blood into other veins can affect the tissues of the calf. Symptoms can range from mild to severe and include: calf pain, discomfort, swelling, and rashes. An ulcer on the skin of the calf may develop in severe cases.

Post-thrombotic syndrome is more likely to occur if the DVT occurs in a thigh vein, or extends up into a thigh vein from a calf vein.

What are the aims of treatment for a deep vein thrombosis?

  • To prevent the clot spreading up the vein and getting larger.
  • To reduce the risk of post-thrombotic syndrome developing.
  • To reduce the risk of a further DVT in the future.

What are the treatments for a deep vein thrombosis?

Anticoagulation - preventing the clot from getting larger

Anticoagulation is often called thinning the blood.

Warfarin is the usual anticoagulant. However, it takes a few days for warfarin tablets to work fully. Therefore, heparin injections (often given just under the skin) are used alongside warfarin in the first few days (usually five days) for immediate effect.

The aim is to get the dose of warfarin just right so the blood will not clot easily, but not too much, which may cause bleeding problems.

A new drug called fondaparinux sodium can be given by injection in some circumstances, either to prevent or to treat a DVT or PE.

If you are pregnant, regular heparin injections rather than warfarin tablets may be used. This is because warfarin can potentially cause harm (birth defects) to the unborn child.

As a guide, for a DVT that happens below the knee, you will need at least six weeks' warfarin. Usually 3-6 months of warfarin treatment is given in this situation. Note: you should not travel on any long journeys or travel by plane until at least two weeks after starting anticoagulant treatment. Travel within two weeks of a DVT is not recommended without seeking advice from a specialist - not least, because you will need regular blood tests soon after starting warfarin.

Compression stockings

Most people who develop a DVT are advised to wear compression stockings. This treatment has been shown to reduce the risk of a recurrent DVT, and can also reduce the risk of developing post-thrombotic syndrome. You should wear the stockings each day, for at least two years. If you do develop post-thrombotic syndrome, you may be advised to wear the stockings for more than two years.

Walking regularly but raising your leg whilst resting

Unless your doctor advises against this, you should walk regularly after you are discharged from hospital. Walking is thought to improve circulation in the affected leg and may help to reduce your risk of further DVT.

Other treatments

Thrombolytic therapy with drugs such as streptokinase or urokinase. These drugs may help to dissolve a blood clot. However, it is sometimes used in people with a severe DVT or with a large pulmonary embolus.

Sometimes an operation (called an embolectomy) is done to remove a blood clot from the leg vein or pulmonary artery. These operations are not routine and it is not clear if they are an effective treatment in most cases.
Occasionally, an operation is done to place a filter in the large vein above the blocked leg vein. The aim is to stop any blood clots from travelling up to the lungs.

Major operations are a risk for a DVT - particularly operations to the hip, lower abdomen, and leg. You may be given an anticoagulant such as a heparin injection just before an operation to help prevent a DVT. This is called prophylaxis.

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