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 (DVT), or in the superficial veins, termed superficial venous thrombosis. In cases where the superficial veins are inflammed but without clotting (or thrombosis), this is referred to as superficial phlebitis (see see Superficial Venous Thrombosis). Deep vein thrombosis occurs most often in the legs or pelvis but may also occasionally develop in the arms.
Three main factors can contribute to deep vein thrombosis:
Veins may be injured during surgery, by the injection of irritating substances, by inflammation, or by certain disorders, such as thromboangiitis obliterans. 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 of blood clotting (see Overview of Blood Clotting 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 or a stroke), 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 major surgery, particularly 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.
Although DVT is uncomfortable, the main concern is with the complications, including
A blood clot in a deep vein sometimes can 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 to a portion of the lung. This blockage is called pulmonary embolism (see Pulmonary Embolism) and can be fatal. The small blood clots that occur in superficial venous thrombosis 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. Multiple emboli may occur, that typically go to different parts of the lungs. 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 upper chambers of the heart (the atria). If this opening is present, an embolus can pass into the arterial circulation and block an artery in another part of the body, such as the brain where it will cause a stroke.
Chronic venous insufficiency:
Some blood clots heal by being converted to scar tissue, which may damage the valves in the veins. The damaged valves prevent the veins from functioning normally, a disorder called chronic venous insufficiency or postphlebitic syndrome (see see Chronic Venous Insufficiency and Postphlebitic Syndrome). In this disorder, fluid accumulates (a condition called edema) and the ankle and sometimes lower leg swells. The skin can become scaly, itchy, and reddish brown.
Rarely, a very large blood clot in a leg causes so much swelling that it blocks the blood flow through the leg. The leg becomes pale or blue and extremely painful. Gangrene can develop if the blood flow is not restored.
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.
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 see 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, computed tomography (CT) or chest scanning using a radioactive marker (see see 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.
Although the risk of deep vein thrombosis cannot be entirely eliminated, it can be reduced in several ways:
Preventive measures are selected depending on the person's risk factors and individual characteristics.
People at low risk of deep vein thrombosis, such as those who must be temporarily inactive for long periods, as during an airplane flight, and those who are undergoing minor surgery but have no other risk factors for deep vein thrombosis, can take simple measures. Such people should elevate their legs, flex and extend their ankles about 10 times every 30 minutes and walk and stretch every 2 hours while awake during long flights.
People at higher risk of deep vein thrombosis require additional preventive treatment. Such people include those undergoing minor surgery who have specific risk factors for deep vein thrombosis (for example, cancer or excessive blood clotting), those without risk factors who undergo major surgery (especially orthopedic surgery) and those who are hospitalized with a major illness (for example a heart attack or serious injury).
For such higher risk people, an anticoagulant drug (see see Anticoagulation), such as heparin, enoxaparin, fondaparinux, or warfarin, can be used. These drugs help prevent deep vein thrombosis by reducing the blood's ability to clot but have a slight risk of excessive bleeding.
Alternatively, intermittent pneumatic compression (IPC) leggings are an effective way to prevent clots in higher risk people, particularly those who are having surgery associated with a high risk of bleeding and thus should not use an anticoagulant drug. Usually made of plastic, these leggings 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.
Continuously wearing high-compression elastic stockings (support hose) makes the veins narrow slightly and the blood flow more rapidly. As a result, clotting may be 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.
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. People whose deep vein thrombosis resulted from a specific cause (such as surgery or a drug they have stopped taking) usually continue anticoagulant therapy for 3 to 6 months. When a specific cause is not found, people usually 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 alteplase, 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.
|Umbrellas: One Way to Prevent Pulmonary Embolism
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. This filter device typically is recommended when drugs that limit clotting cannot be used, for example, when a person is also having bleeding. 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.
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 carefully 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 December 2012 by James D. Douketis, MD