Deep Vein Thrombosis

Deep vein thrombosis (also called deep vein thrombophlebitis, or DVT) is the formation of blood clots (thrombi) in the deep veins. Deep veins are located in the muscles or deeper.

Deep vein thrombosis is common. Inactivity increases the chance of developing deep vein thrombosis. This disorder usually affects veins in the calves or thighs.

Occasionally in deep vein thrombosis, part of one or more blood clots breaks off, travels through the veins and heart (becoming an embolus), and blocks the arteries that carry blood to the lungs. This blockage is called pulmonary embolism, which can have serious consequences.

If deep vein thrombosis persists or recurs, leg veins and the valves in them can be permanently damaged. Then blood flow back to the heart is reduced. Blood pools in veins, causing fluid to leak from the veins into tissues. This disorder is called chronic venous insufficiency.

If diagnosed before much damage has occurred, deep vein thrombosis can usually be treated effectively.

Causes

Usually, deep vein thrombosis develops in the leg veins. When a person is inactive, the leg muscles do not contract and squeeze blood vessels forcefully enough to propel blood to the heart. Blood then pools in the leg veins, where it can clot easily. Any long period of inactivity can cause deep vein thrombosis. For example, paralysis of the legs, bed rest (as required for treatment of heart failure or after hip surgery), and even long airplane flights or car trips can cause deep vein thrombosis.

Deep vein thrombosis usually develops in people whose blood is otherwise normal. However, abnormalities that make blood more likely to clot (such as some cancers, clotting disorders, and dehydration) can result in deep vein thrombosis. It can also result from damage to veins, such as that due to an injury or surgery.

Symptoms

Many people with deep vein thrombosis have no symptoms or only mild symptoms. Symptoms can include deep aching pain. The calf or thigh often swells. Swelling worsens after the leg has been lower than the body (often during the day, after walking and sitting) and lessens after the leg is elevated (often at night, after lying in bed). Sometimes the skin over the affected vein (often in the calf) appears red and feels warm or tender. Deep vein thrombosis can cause varicose veins.

If pulmonary embolism occurs, people can become short of breath, develop a rapid heart rate or low blood pressure, or lose consciousness. The severity of the symptoms depends on the size and number of pulmonary emboli. Rarely, death occurs without warning.

If chronic venous insufficiency develops, the legs may become chronically swollen.

Diagnosis

Because deep vein thrombosis can lead to serious problems, tests are often done to detect the disorder even when symptoms are mild. Deep vein thrombosis can usually be diagnosed using Doppler ultrasonography.

Doctors may use a specific blood test to help them diagnose deep vein thrombosis or pulmonary embolism. This test can detect blood clots by measuring a protein called D-dimer. D-dimer is released into the bloodstream when blood clots are being formed and broken down. However, the test is not always helpful, because the level of D-dimer in the blood can be high in other disorders.

If a person is short of breath, doctors may measure the level of oxygen in the blood (oxygen saturation). Doctors may use a device called a pulse oximeter, which is attached to a finger, toe, or ear lobe for several seconds. Or the oxygen level may be measured in a sample of blood. A low oxygen level suggests pulmonary embolism. However, an imaging study is needed to confirm the diagnosis. Usually, nuclear scanning of the lungs is done. For this test, a small amount of a radioactive material is injected into a vein, and a scanner produces a picture of how the material flows through the lungs' blood vessels. Sometimes angiography is necessary. For this test, x-rays are taken while dye is injected into the pulmonary artery. Sometimes a type of computed tomography (CT) called helical (spiral) CT may be used for diagnosis.

Prevention

Preventing deep vein thrombosis is important because serious problems can develop without warning. Many preventive measures can be effective. During any period of inactivity (such as sitting or having to stay in bed for a long time), the legs should be stretched frequently. During long flights or car trips, a person should walk every 2 hours.

See the figure Umbrellas: Preventing Pulmonary Embolism.

If a person is temporarily confined to bed, pneumatic stockings effectively prevent deep vein thrombosis. These stockings are repeatedly inflated then deflated by an electric pump. Inflating them helps squeeze the calves and empty the veins. The stockings can be applied before surgery and kept on until the person can walk. Pneumatic stockings are also helpful for people permanently confined to bed.

Drugs that make blood less likely to clot (anticoagulants, sometimes called blood thinners) can be given to people who are hospitalized and who are at high risk of deep vein thrombosis. For example, these drugs may be given to people confined to bed after certain types of surgery. Usually, the anticoagulant heparin or a related drug is injected under the skin daily.

When not in bed, people with chronic venous insufficiency can wear elastic stockings. These stockings help prevent deep vein thrombosis and leg sores and reduce swelling.

Treatment and Outlook

The goal of treatment is to dissolve the clot and prevent pulmonary embolism. Hospitalization is often necessary. Usually, an anticoagulant, such as heparin or a related drug, is injected into a vein. After a few days, another anticoagulant, warfarin, taken by mouth, is started. The heparin injections are discontinued within the next several days. People may need to take an anticoagulant for several months. Because taking an anticoagulant increases the risk of excessive bleeding, blood tests must be done periodically to check whether the blood is taking too long to clot. The doctor can then increase or decrease the dose of the anticoagulant if needed.

A drug that dissolves blood clots (thrombolytic drug), such as tissue plasminogen activator, urokinase, or streptokinase, is sometimes given, particularly if symptoms are severe.

If pulmonary embolism develops, anticoagulants are given to prevent more pulmonary emboli. A thrombolytic drug may be given to dissolve a pulmonary embolus.

Sometimes doctors insert a filter (umbrella) into the vein that carries blood from the legs to the heart (inferior vena cava). The filter traps blood clots, preventing them from traveling from the legs to the lungs. The filter can be used if anticoagulants are ineffective or if a person has a condition (such as a bleeding ulcer) that makes anticoagulants particularly risky.

Unless chronic venous insufficiency or pulmonary embolism develops, the outlook for people with deep vein thrombosis is good. For people with pulmonary embolism, death is more likely if the level of oxygen in the blood has decreased, if they have lost consciousness, or if low blood pressure develops.