Deep Vein Thrombosis

A deep vein thrombosis (DVT) is a blood clot (thrombus) that develops in a deep vein, usually in the leg. This can happen if the vein is damaged or if the flow of blood slows down or stops. About 500,000 people in the US develops a DVT each year.

Deep vein thrombosis can cause pain in the leg, and can lead to complications if it breaks off and travels in the bloodstream to the lungs.

Where do DVTs happen?

The are two types of veins in the legs: deep and superficial (see diagram). The deep veins pass through the centre of the leg, surrounded by the muscles. It’s here that DVTs most often develop. Less commonly DVTs occur in the deep veins of the arm or pelvis.

Who gets a DVT?

Certain factors make a DVT more likely to occur. They are more common in people aged over 40 and in people who are obese, or who have already had a DVT. Several inherited conditions make the blood more likely to clot than usual, increasing the risk. Other factors include:

• prolonged bed rest, (immobility)

• major injuries, or paralysis

• surgery, especially if it lasts more than 30 minutes, or involves the leg joints or pelvis

• cancer and its treatments, which can cause the blood to clot more easily

• long-distance travel, because of prolonged immobility. It is unclear whether or not air travel is more risky than other long journeys - for example by car or coach

• pregnancy and childbirth - related to hormone changes that make the blood clot more easily and because the fetus puts added pressure on the veins of the pelvis. There is also risk of injury to veins during delivery or a caesarean. The risk is at its highest just after childbirth

• taking a contraceptive pill that contains oestrogen. Most modern pills contain a low dose, which increases the risk by an amount that is acceptable for most women

• hormone replacement therapy (HRT). For many women, the benefits outweigh the increase in risk.

• other circulation or heart problems

Problems caused by a DVT

A DVT below the knee is unlikely to cause complications and may only need to be monitored. But when a clot forms in or above the knee, there is a risk that it will break away and travel up the vein to block a blood vessel in the lung. This is called a pulmonary embolism (PE). Depending on the size of the clot, it can be a life-threatening condition. But with appropriate treatment, it is rare for a DVT to lead to a pulmonary embolism.

A DVT can damage the valves in the vein, so that instead of flowing upwards, the blood pools in the lower leg. This is called post-thrombotic syndrome, and can result in pain, swelling, discolouration and sores on the leg.

Symptoms of a DVT

When a clot forms, it can either partially or totally block the blood flow in that vein. Symptoms of a DVT can include:

• swelling of the leg

• warmth and redness of the leg

• pain that is noticeable, or worse when standing or walking

These are not always a sign of a DVT, but anyone who experiences them should contact a doctor immediately.

Diagnosing a DVT

If a DVT is suspected, the doctor will take a full medical history and carry out a physical examination. Tests that also may be required include:

• the clotting properties of the blood

• an ultrasound scan

• venography – using X-rays to show the flow of blood when special dye is injected into the veins.

Treating a DVT

Treatment aims to prevent:

• the clot becoming larger

• the blood clot breaking loose and travelling to the lungs

• new clots from forming

• post-thrombotic syndrome

Medicines

The most common treatment is anticoagulant (blood thinning) medicines, which reduce the blood's tendency to clot. These are usually taken for three to six months. Regular blood tests are needed to check the levels of the drug in the blood.

Anticoagulants can stop new blood clots from forming and old ones growing. They can’t dissolve existing clots. The body does this itself over time.

The anticoagulants used are heparin (given through a vein as a "drip" or injected just under the skin twice each day) or warfarin (taken as tablets). Anyone taking these medicines should avoid activities that could increase the risk of injury. This is because one of the main ways a wound heals is through clotting, and anticoagulants interfere with this process.

Less commonly, clot dissolving drugs called thrombolytics are used to dissolve a DVT. They carry a high risk of bleeding, so are only used in severe cases, where a life or limb is threatened.

Compression stockings

To relieve pain and swelling, and to prevent post-thrombotic syndrome, some doctors recommend wearing graduated compression stockings (also called TED or thrombo-embolic deterrent stockings), which are tighter at the foot than higher up the leg. These may need to be worn for several months or more.

Putting your feet up

Most people with a DVT are advised to place a cushion under their feet while resting or sleeping, so that the feet are raised higher than the hips. This helps to reduce the pressure in the veins of the calves.

Preventing a DVT around surgery

Surgery and some medical treatments can increase the risk of having a DVT. So, hospitals often do a pre-operative risk assessment for DVT, which takes into account your personal risk factors and the type of surgery you are having. Various measures can then be used to keep the risk as low as possible. These include anticoagulant medicines, compression stockings, and an intermittent compression pump. This is a mechanical device that automatically squeezes the feet and lower legs. This helps the circulation of blood from the legs in the first few days after surgery.

General preventive advice

Anyone who feels they are at high risk of developing a DVT should seek medical advice. There are measures anybody can take to help prevent a DVT:

• exercise the legs regularly – take a brisk 30-minute walk every day

• maintain a weight that's appropriate for your height

• avoid sitting or lying in bed for long periods of time without moving the legs

• women, particularly those over the age of 35, should consider the risks and benefits of taking the contraceptive pill

Preventive measures for travelers

Although the added risk of developing a DVT caused by traveling appears to be low, it can be reduced even further by exercising the legs at least once every hour during long-distance travel. This means taking regular breaks if driving, or walking up and down the aisle of a coach, train or plane.

The muscles of the lower legs (which act as a pump for the blood in the veins) can be exercised while sitting by pulling the toes towards the knees then relaxing, or by pressing the balls of the feet down while raising the heel.

Other preventive measures:

• don't take sleeping pills. These cause immobility, increasing the risk of DVT

• wear loose-fitting clothing

• keep the legs uncrossed

• keep hydrated by drinking normally (urine should be no darker than a pale yellow). Avoid alcohol to prevent dehydration

• wear graduated compression stockings. This is particularly important for travelers who have other risk factors for DVT

Some doctors recommend taking aspirin before traveling because of its blood thinning effects. But it is not suitable for children and can have side-effects. If in doubt, seek advice from a pharmacist or doctor.

People who have one or more of the risk factors mentioned earlier should seek medical advice before traveling.

Anyone who develops swelling or pain in the leg, or breathing problems after traveling should seek medical advice urgently.