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Deep vein
thrombosis is the formation of blood clots (thrombi) in the deep
veins.
Blood clots (thrombi) can occur in the deep veins, termed deep vein thrombosis, or in the superficial veins, termed superficial thrombophlebitis (see Venous Disorders: Superficial Thrombophlebitis). Deep vein thrombosis occurs most often in the legs or pelvis but may also occasionally develop in the arms.
Pulmonary Embolism:
A blood clot in a deep vein sometimes will break loose, becoming an embolus. The embolus can travel through the bloodstream, through the heart, and into the lungs, where it lodges in a blood vessel in the lung, blocking blood flow. This blockage is called pulmonary embolism (see Pulmonary Embolism (PE): Pulmonary Embolism) and can be fatal. The small blood clots that occur in superficial thrombophlebitis usually do not become emboli. Thus, only thrombi in the deep veins are potentially dangerous. Blood clots in the legs or pelvis are more likely to become emboli than blood clots in the arms, perhaps because the squeezing action of the calf muscles can dislodge a blood clot in a deep vein, especially when a convalescing person becomes more active.
The consequences of pulmonary embolism depend on the size and number of emboli. A small embolus may block a small artery in the lungs, causing the death of a small piece of lung tissue (called pulmonary infarction). However, a large pulmonary embolus can block all or nearly all of the blood traveling from the right side of the heart to the lungs, quickly causing death. Such massive emboli are not common, but no one can predict which case of deep vein thrombosis, if untreated, will lead to a massive embolus. Thus, doctors are greatly concerned about every person who has deep vein thrombosis.
Sometimes, people have an abnormal opening, called a patent foramen ovale, between the right and left sides of the heart (see Birth Defects: Heart Defects). If this opening is present, an embolus can pass into the arterial circulation and block a blood vessel in another part of the body, such as the brain where it will cause a stroke.
Causes
Three main factors (known as Virchow's triad) can contribute to deep vein thrombosis:
Veins may be injured during surgery, by the injection of irritating substances, or by certain disorders, such as thromboangiitis obliterans (Buerger's disease). They may also be injured by a clot, making formation of a second clot more likely.
Some disorders, such as cancer and certain inherited disorders, cause blood to clot when it should not. Some drugs, including oral contraceptives, estrogen therapy, or drugs that act like estrogen (such as tamoxifen and raloxifene ), can cause blood to clot more readily. Smoking is also a risk factor. Sometimes blood clots more readily after childbirth or surgery. Among older people, dehydration commonly causes the blood to clot more readily and can therefore contribute to deep vein thrombosis.
During prolonged bed rest and other occasions when the legs are not moving normally (such as after a leg injury), blood flow slows, because the calf muscles are not contracting and squeezing the blood toward the heart. For example, deep vein thrombosis may develop in people who have had a heart attack and lie in a hospital bed for several days without sufficiently moving their legs or in people whose legs and lower body are paralyzed (paraplegics). Deep vein thrombosis can develop after pelvic, hip, or knee surgery. Thrombosis can even occur in healthy people who sit for long periods, for example, during long drives or airplane flights, but thrombosis is extremely uncommon in this circumstance and usually occurs in people with other risk factors.
Symptoms
About half of the people with deep vein thrombosis have no symptoms at all. In these people, chest pain or shortness of breath caused by pulmonary embolism may be the first indication that something is wrong. In other people, if a deep leg vein is involved, the calf swells and may be painful, tender to the touch, and warm. The ankle, foot, or thigh may also swell, depending on which veins are involved. Similarly, if an arm vein is involved, the arm may swell.
Chronic Deep Vein Insufficiency:
Some blood clots heal by being converted to scar tissue, which may damage the valves in the veins. Because the damaged valves prevent the veins from functioning normally, fluid accumulates (a condition called edema) and the ankle swells. The edema can extend up the leg and even affect the thigh if the blockage is high enough in the vein. Edema is worse toward the end of the day, because blood must flow upward, against gravity, to reach the heart when a person is standing or sitting. Overnight, edema subsides because the veins empty well when the legs are horizontal.
Sometimes, the affected veins are obliterated (destroyed). In people whose veins are obliterated, leg edema is always present, generally worsening at the end of the day. The skin on the inside of the ankle becomes scaly and itchy and may turn a reddish brown. The discoloration is caused by red blood cells that escape from swollen (distended) veins into the skin. The discolored skin is vulnerable, and even a minor injury, such as that from scratching or a bump, can break it open, resulting in an ulcer. Varicose veins may be present. In addition to ulcer pain, there may be throbbing pain when standing or walking.
If edema is severe and persistent, scar tissue develops and traps fluid in the tissues. As a result, the calf permanently enlarges and feels hard. In such cases, ulcers are more likely to develop, and they heal less easily.
Diagnosis
Deep vein thrombosis may be difficult for doctors to detect, especially when pain and swelling are absent or very slight. When this disorder is suspected, Doppler ultrasonography (see Symptoms and Diagnosis of Heart and Blood Vessel Disorders: Echocardiography and Other Ultrasound Procedures) can confirm the diagnosis. Sometimes doctors do a blood test to measure a substance called d-dimer that is released from blood clots. If the level of d-dimer in the blood is not increased, the person probably does not have a deep vein thrombosis.
If the person has symptoms of pulmonary embolism, a computed tomography (CT) scan or chest scanning using a radioactive marker (see Symptoms and Diagnosis of Lung Disorders: Chest Imaging) is done to detect pulmonary embolism, and Doppler ultrasonography is done to check the legs for clots. These procedures are done except when a person collapses. Collapse suggests massive pulmonary embolism and requires immediate treatment.
Prevention
Although the risk of deep vein thrombosis cannot be entirely eliminated, it can be reduced in several ways. People at risk of deep vein thrombosis should flex and extend their ankles about 10 times every 30 minutes. Such people include those who have just had major surgery and those taking long trips. During long flights, everyone should walk and stretch every 2 hours while awake.
Continuously wearing elastic stockings (support hose) makes the veins narrow slightly and the blood flow more rapidly. As a result, clotting is less likely. However, elastic stockings are not sufficient protection against developing deep vein thrombosis. Also, they may give a false sense of security and discourage more effective methods of prevention. If not worn correctly, they may bunch up and aggravate the problem by blocking blood flow in the legs.
Pneumatic compression stockings are an effective way to prevent clots. Usually made of plastic, these stockings are automatically pumped up and emptied by an electric pump. They repeatedly squeeze the calves and empty the veins. The stockings are put on before surgery and kept on during and after surgery, until the person can walk again.
An anticoagulant drug (see Pulmonary Embolism (PE): Anticoagulation), such as heparin, fondaparinux , or warfarin , is given to people at high risk of developing deep vein thrombosis before, during, and sometimes after surgery. Such people include those who have clotting disorders (see Bleeding and Clotting Disorders: Introduction) and those who have recently had one or more episodes of deep vein thrombosis. For certain types of surgery (such as hip replacement surgery), the risk is particularly high. People who are at particularly high risk may be given an anticoagulant when they are hospitalized even though they are not undergoing surgery. Anticoagulants reduce blood clotting much more effectively than wearing elastic stockings.
Treatment
For deep vein thrombosis, a doctor's main goal is to prevent pulmonary embolism. Hospitalization may be necessary at first, but because of the advances in treatment, most people with deep vein thrombosis can be treated at home. Bed rest is unnecessary except to help relieve symptoms.
Treatment usually consists of anticoagulant therapy with low-molecular-weight heparin or fondaparinux given by injection under the skin (subcutaneously), accompanied by warfarin taken by mouth. The injectable drug works immediately, but warfarin takes several days to be fully effective. Once the warfarin has taken effect, people stop taking the injectable drug. For some people, doctors simply use the injectable drug and do not start warfarin . How long people continue drug treatment (with warfarin or an injectable drug) varies according to the degree of risk. Patients whose deep vein thrombosis resulted from a specific cause (such as surgery or a drug they have stopped taking) should continue for 3 to 6 months. Patients in whom a specific cause is not found should take warfarin for at least 6 months. People who have had two or more episodes of deep vein thrombosis should continue warfarin indefinitely.
Use of warfarin increases the risk of bleeding, both internally and externally. To minimize the risk, people taking warfarin must have periodic blood tests to see how much their blood is anticoagulated. Doctors then use the blood test result to adjust the dose of warfarin .
Doctors are studying the use of intravenous drugs, such as tissue plasminogen activator, to dissolve blood clots. These drugs (thrombolytic, or fibrinolytic, drugs), may be given if the blood clot has been present for less than 48 hours. After 48 hours, scar tissue begins to develop in the blood clot, making it less likely to dissolve.
Very rarely, a filter (umbrella) is placed inside a large vein between the heart and the area affected by deep vein thrombosis, usually the inferior vena cava, which returns blood to the heart from the lower part of the body. A filter can trap emboli, preventing them from reaching the lungs.
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Umbrellas: One Way to Prevent Pulmonary Embolism
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In people who have deep vein thrombosis, a blood clot may break loose from an affected vein in the leg and travel through the bloodstream. A clot that breaks loose is called an embolus.
The embolus travels toward the heart and passes through the right atrium and ventricle and into one of the pulmonary arteries, which carry blood to the lungs. The clot may lodge in an artery in a lung and block blood flow, resulting in pulmonary embolism. Pulmonary embolism may be life threatening, depending on the size of the blocked artery.
To prevent pulmonary embolism, doctors usually use drugs that limit blood clotting. However, for some people, doctors may recommend that a filter, called an umbrella, be permanently placed in the inferior vena cava. The filter traps emboli before they reach the heart but allows blood to flow through freely. Emboli that are trapped sometimes dissolve on their own.
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Complications:
If pulmonary embolism occurs, treatment usually includes oxygen (usually given by a face mask or nasal prongs), analgesics to relieve pain, and the anticoagulant drug heparin followed by warfarin . If pulmonary embolism is life threatening, thrombolytic drugs are given or surgery is done to remove the embolus.
The veins never completely recover after deep vein thrombosis develops, and surgery to repair the valves of the veins is experimental. Elastic compression stockings worn below the knee may be helpful.
If painful skin ulcers develop, properly applied compression bandages can help. When these bandages are applied once or twice a week, the ulcer almost always heals because blood flow in the veins improves. The ulcers are almost always infected, and pus and a foul-smelling discharge appear on the bandage each time it is changed. The pus and discharge can be washed off the skin with soap and water. Skin creams, balms, and skin medications of any kind have little effect.
Once blood flow in the veins has improved, the ulcer heals by itself. After it has healed, wearing an elastic stocking daily can prevent a recurrence. The stocking must be replaced as soon as it becomes too loose. If possible, the person should purchase seven stockings or pairs of stockings (if both legs are involved)—one for each day of the week so that stockings remain effective considerably longer.
Rarely, ulcers that do not heal require skin grafting. After grafting, an elastic stocking must be worn to prevent ulcers from returning.
Last full review/revision February 2008 by Alexander G.G. Turpie, MD
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