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DEEP VEIN THROMBOSIS (DVT)
Deep vein thrombosis (DVT) is a blood clot (thrombus) in a deep vein, usually in the legs.
Clots can form in superficial veins (called superficial thrombophlebitis or phlebitis) and in deep veins. While blood clots in superficial veins rarely cause serious problems, clots in deep veins (deep vein thrombosis) require immediate medical care.
These clots are dangerous because they can break loose and then travel through the bloodstream to the lungs, causing a pulmonary embolism. A pulmonary embolism is often life-threatening. DVT can also cause long-lasting problems. DVT may damage the vein and cause the leg to ache, swell, and change color. It can also cause leg sores.
Blood clots most often develop in the calf and thigh veins, and less often in the arm veins or pelvic veins. This topic focuses on blood clots in the deep veins of the legs, but diagnosis and treatment of DVT in other parts of the body are similar.
What are the symptoms of deep vein thrombosis?
Superficial thrombophlebitis
Blood clots in the superficial vein system most often occur due to trauma to the vein which causes a small blood clot to form. Inflammation of the vein and surrounding skin causes the symptoms of any other type of inflammation:
- redness,
- warmth,
- tenderness, and
- swelling.
Often the affected vein can be palpated (felt) as a firm, thickened cord. There may be inflammation that follows the course of part of the vein.
Although there is inflammation, there is no infection.
Varicosities can predispose to superficial thrombophlebitis. When the valves of the larger veins in the superficial system fail (the greater and lesser saphenous veins), blood can back up and cause the veins to swell and become distorted or tortuous. The valves fail when veins lose their elasticity and stretch. This can be due to age, prolonged standing, obesity, pregnancy, and genetic factors.
Deep Venous Thrombosis
The symptoms of deep vein thrombosis are related to obstruction of blood returning to the heart and causing a backup of blood in the leg. Classically, they symptoms include:
- pain,
- swelling,
- warmth, and
- redness.
Not all of these symptoms have to occur; one, all, or none may be present with a deep vein thrombosis. The symptoms may mimic an infection or cellulitis of the leg.
Historically, healthcare providers would try to elicit a couple of clinical findings to make a diagnosis. Dorsiflexion of the foot (pulling the toes towards the nose, or Homans' sign) and Pratt's sign (squeezing the calf to produce pain), have not been found effective in making a diagnosis.
Causes
You are more likely to get DVT if you are over 40, are very tall and/or if you are obese. If you are immobile, for example after having an operation or travelling on a long-haul flight, you also have a greater risk of getting DVT.
There are a number of other risk factors that make you more likely to have DVT - these include if you have:
- had a blood clot in a vein before
- a family history of blood clots in veins
- an inherited condition that makes your blood more likely to clot (this is called thrombophilia)
- certain blood diseases
- cancer, or have had cancer treatment
- circulation problems or heart failure
- had recent surgery or an injury, especially to your hips or knees
The risk of DVT is also increased in women who:
- take a contraceptive pill that contains oestrogen
- take hormone replacement therapy (HRT)
- are pregnant
- have recently had a baby
Risk factors
Many factors can increase your risk of developing deep vein thrombosis. One of the more talked about risks is sitting for a long time, such as when traveling in a car or on an airplane. Blood clots can form in the calves of your legs if your calf muscles aren't moving. Although sitting for long periods is a risk factor, your chance of developing deep vein thrombosis while flying or driving is relatively low.
The risk factors for developing deep vein thrombosis include:
- Sitting for long periods of time, such as when driving or flying. When your legs remain still for long periods, your calf muscles don't contract, which normally helps blood circulate. As a result, blood clots can develop.
- Inheriting a blood-clotting disorder. Some people inherit a disorder that makes their blood clot more easily. This inherited condition may not cause problems unless combined with one or more other risk factors.
- Prolonged bed rest, such as during a long hospital stay, or paralysis. When your legs remain still for long periods, your calf muscles don't contract to help blood circulate. As a result, blood clots can develop.
- Injury or surgery. Injury to your veins or surgery can slow blood flow, increasing the risk of blood clots. General anesthetics used during surgery can dilate your veins, which can increase the risk of blood pooling and then clotting.
- Pregnancy. Pregnancy increases the pressure in the veins in your pelvis and legs. Women with an inherited clotting disorder are especially at risk. The risk of blood clots from pregnancy can continue for up to six weeks after you give birth.
- Cancer. Some forms of cancer increase the amount of substances in your blood that promote clotting. In addition, some forms of cancer treatment increase the risk of blood clots.
- Heart failure. People with heart failure are at risk of DVT because a damaged heart doesn't pump blood as effectively as a normal heart does. This increases the chance that blood will pool and clot.
- Birth control pills or hormone replacement therapy. Oral contraceptives (birth control pills) and hormone replacement therapy both can increase your blood's ability to clot.
- A pacemaker or a thin, flexible tube (catheter) in a central vein. These medical treatments can irritate the blood vessel wall and decrease blood flow.
- A history of deep vein thrombosis or pulmonary embolism. If you've had DVT before, you're more likely to have DVT in the future.
- A family history of deep vein thrombosis or pulmonary embolism. If someone in your family has had DVT or a pulmonary embolism, your risk of developing DVT is increased.
- Being overweight or obese. Being overweight increases the pressure in the veins in your pelvis and legs.
- Smoking. Smoking affects blood clotting and circulation.
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