Deep Vein Thrombosis
Deep vein thrombosis is the formation of blood clots (thrombi) in the deep veins.
Thrombi can occur either in the deep leg veins, causing deep vein thrombosis, or in the superficial leg veins, causing superficial thrombophlebitis (see Section 3, Chapter 36).
Thrombophlebitis is a disorder in which the formation of blood clots (thrombosis) and inflammation of the vein (phlebitis) occur together. Because thrombosis is almost always accompanied by phlebitis, some doctors use thrombosis and thrombophlebitis interchangeably. However, there is an important distinction between deep vein thrombosis and thrombophlebitis. Deep vein thrombosis causes only a little inflammation. The less inflammation around a thrombus, the less tightly the thrombus adheres to the vein wall and the more likely it will break loose (becoming an embolus), travel through the bloodstream, and lodge in an artery downstream, blocking blood flow. In addition, the squeezing action of the calf muscles can dislodge a thrombus in a deep vein, especially when a convalescing person becomes more active. Thus, only thrombi in the deep veins are potentially dangerous. Superficial thrombophlebitis is painful but comparatively harmless, because thrombi in small, superficial veins usually do not become emboli.
Because blood in the leg veins travels to the heart and then to the lungs, emboli originating in the leg veins usually pass through the heart and block one or more arteries in the lungs, a condition called pulmonary embolism (see Section 4, Chapter 46). The seriousness of pulmonary embolism depends 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 (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.
Causes
Three main factors (known as Virchow's triad) can contribute to deep vein thrombosis: injury to the vein's lining, an increased tendency for blood to clot, and slowing of blood flow.
Veins may be injured during surgery, by injection of irritating substances, or by certain disorders, such as Buerger's disease. They may also be injured by a clot, making formation of a second clot more likely.
Some disorders, such as disseminated intravascular coagulation, cause blood to clot when it should not. Some cancers and, rarely, use of oral contraceptives can cause blood to clot more readily. Sometimes blood clots more readily after childbirth or surgery. Among older people, dehydration and smoking are common causes of this tendency and can therefore contribute to deep vein thrombosis.
During prolonged bed rest, 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 hospital beds 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 hip repair or replacement. Thrombosis can even occur in healthy people who sit for long periods, for example, during long drives or airplane flights.
Symptoms
Because deep vein thrombosis usually causes little inflammation, pain and redness of the skin over the vein are usually minimal. About half of the people with deep vein thrombosis have no symptoms at all. In these people, chest pain caused by pulmonary embolism may be the first indication that something is wrong. When deep vein thrombosis blocks blood flow in a large leg vein, 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.
Some thrombi 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.
Chronic Deep Vein Insufficiency: This complication occurs late in the course of deep vein thrombosis. The valves in the deep veins and connecting veins of the legs are destroyed. Consequently, blood is not adequately returned to the heart from the legs. Eventually, the affected veins may be obliterated.
Edema in the legs 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, color Doppler ultrasonography (see Section 3, Chapter 21) can confirm the diagnosis. If the person has symptoms of pulmonary embolism, chest scanning using a radioactive marker (see Section 4, Chapter 39) is performed to confirm the diagnosis of pulmonary embolism, and color Doppler ultrasonography is performed to check the legs for clots. These procedures are performed 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 the 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.
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.
 See the figure Umbrellas: Preventing Pulmonary Embolism.
Pneumatic 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 (see Section 4, Chapter 46), such as heparin 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 Section 14, Chapter 173) 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, treatment involves prevention of pulmonary embolism. Hospitalization may be necessary at first, but because of the advances in treatment, some people with deep vein thrombosis can be treated at home. Bed rest with the foot of the bed raised 6 inches is usually required to help prevent the thrombus from enlarging, as are anticoagulants. Usually, anticoagulant therapy consists of low-molecular-weight heparin given by injection under the skin (subcutaneously), followed by warfarin taken by mouth. How long warfarin must be taken varies. Young, active people who have had only one episode of deep vein thrombosis may need to continue the drug for only 2 months. People who have had deep vein thrombosis followed by pulmonary embolism continue to be at increased risk of deep vein thrombosis. They may need to continue the drug for 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 keep this risk as low as possible, doctors periodically perform blood tests to measure clotting time and adjust the dose of warfarin on the basis of test results.
Drugs to dissolve the thrombus (thrombolytic drugs), such as tissue plasminogen activator, may also be given intravenously, particularly if the thrombus has been present for less than 48 hours. After 48 hours, scar tissue begins to develop in the thrombus, making the thrombus less likely to dissolve.
Sometimes, 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.
If pulmonary embolism occurs, treatment usually includes oxygen (usually given by a face mask or nasal prongs), analgesics to relieve pain, and heparin followed by warfarin. If pulmonary embolism is life threatening, thrombolytic drugs are given or surgery is performed to remove the embolus.
Swelling of the legs can be reduced by resting in bed and elevating the legs or by wearing compression bandages from the base of the toes to the knee. Improperly applied, the bandages may be wrapped more tightly around the upper calf than around the foot and ankle, resulting in a tourniquet effect. Therefore, only a trained doctor or nurse should apply compression bandages. During this time, walking is important. If the swelling does not completely subside, the bandages must be reapplied. The veins never completely recover after deep vein thrombosis develops, and surgery to repair the valves of the veins is experimental. After the compression bandages are removed, elastic stockings are worn every day to prevent swelling from recurring. The stockings do not have to be worn above the knee; swelling above the knee is of little concern and causes no complications. Usually, thick elastic stockings or strong elastic pantyhose is not needed.
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. This way, 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.
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