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Deep Venous Thrombosis

Alternate Names

  • DVT
  • economy class syndrome

Definition

Deep venous thrombosis, also called DVT, refers to a blood clot that has formed in one of the large veins far below the skin.

What is going on in the body?

A deep venous thrombosis is most common in the legs, but it can occur in other parts of the body. A blood clot in a vein blocks the normal flow of blood back to the heart. It also causes the affected vein to become inflamed.

Risks

What are the causes and risks of the condition?

A deep venous thrombosis forms when a blood clot in a vein blocks the normal flow of blood back to the heart.
Circumstances that increase an individual's risk of developing DVT include:
  • immobility that lasts more than 3 days
  • increased thickness of the blood, which may be inherited or acquired
  • recent injury or trauma
  • major surgery in the past 4 weeks, especially in the pelvis or abdomen
  • obesity
  • pacemakers
  • pregnancy, particularly right before and after delivery
Diseases and conditions that increase a person's risk for DVT include:
  • blood-clotting disorders
  • cancer
  • congestive heart failure (CHF), a condition in which the weakened heart can't pump enough blood throughout the body
  • heart attack (MI)
  • a history of blood clots, such as a pulmonary embolus or even superficial blood clots
  • nephrotic syndrome, a kidney disorder
  • sepsis, an infection throughout the body
  • stroke
  • systemic lupus erythematosus (SLE), an autoimmune disorder in which the body attacks its own tissues
  • ulcerative colitis, a bowel disorder
Medicines that can increase the risk for DVT include:
  • certain medicines used to treat breast cancer and osteoporosis
  • hormone therapy (HT)
  • illegal drugs taken intravenously
  • oral birth control pills
  • injectable progesterone birth control
Injuries can also increase a person's risk for DVT. Common injuries linked to DVT include:
  • bone fractures in the legs
  • burns
  • multiple trauma, or significant injury
  • spinal cord injury
Recently, there have been conflicting research reports about the role of long airplane flights in deep venous thrombosis. Some studies showed a relationship between airline travel and an increase in the blood's tendency to form clots.
The researchers attributed the increased risk of clot formation to the low pressure, low oxygen, dehydration, and lack of activity on long flights. Another study showed that individuals hospitalized with DVT were four times more likely to have gone on a long trip recently than those treated at the hospital for other conditions.
Because of findings like this, deep venous thrombosis is often referred to as "economy class syndrome." However, other researchers have not found the same relationship. Some suggest that only people with a particular genetic abnormality are at risk for economy class syndrome. More research is needed in this area.

Prevention

What can be done to prevent the condition?

DVT cannot always be prevented. Some helpful measures include:
  • avoiding illegal drugs
  • avoiding long periods of inactivity
  • eating a healthy diet to prevent heart disease
  • exercising appropriately during pregnancy and the postpartum period
  • following sports safety guidelines for children, adolescents, and adults
  • maintaining appropriate levels of physical activity
  • practicing appropriate weight management
Although the research is still inconclusive about the effects of airplane trips and other forms of travel on DVT, people can lower their risk of DVT by taking these steps:
  • Avoid alcohol or sleeping pills before or during the flight.
  • Avoid long periods of sleep during the flight.
  • Do seat exercises, such as ankle rolls and toe pointing.
  • Drink plenty of fluids to avoid dehydration.
  • Get up and move about periodically.
  • Limit carry-on luggage so there is plenty of legroom.
  • Obtain a seat with as much legroom as possible, such as in the first class cabin, on an aisle, or in back of a bulkhead.
  • Talk with your healthcare professional about taking aspirin for its blood-thinning properties.
  • Walk around the concourse before and between flights.
  • Wear loose, comfortable clothing and avoid tight stockings.
Blood-thinning medicines can help prevent DVT in people at high risk. These include heparin, enoxaparin (i.e., Lovenox), dalteparin (i.e., Fragmin) and warfarin (i.e., Coumadin, Jantoven).
Compression stockings can also be used to improve the flow of blood through the veins back up to the heart. Intermittent pneumatic compression, or IPC, is a device used in the hospital that gently squeezes the blood out of the leg veins and back up to the heart to help prevent blood clots from forming in high risk, hospitalized patients.
One large-scale study in Canada found that statins, which are medicines used to lower cholesterol, decreased the risk of DVT by 22% in this group. While further study is recommended, the findings are encouraging.

Diagnosed

How is the condition diagnosed?

The first step in diagnosing a deep venous thrombosis is a medical history and physical examination. Blood flow studies, measured by a test called compression ultrasonography, is commonly used to diagnose DVT.
The healthcare professional may also order an MRI venogram or other imaging studies such as contrast venography, impedance plethysmography (IPG) or an 125 I-fibrinogen scan.
A blood test called a D-dimer can sometimes be used to help rule out the diagnosis of DVT if the test is normal.

Long Term Effects

What are the long-term effects of the condition?

Most patients will recover from an episode of deep venous thrombosis without long-term problems. People who have had DVT have a higher risk of getting it again.
The most serious risk of DVT is a pulmonary embolus. This occurs when a piece of the blood clot that breaks off and travels to the lung. A blood clot in the lung can cause death.
DVT may also cause chronic pain and swelling of the affected leg.

Other Risks

What are the risks to others?

A deep venous thrombosis is not contagious and poses no risk to others.

Treatments

What are the treatments for the condition?

Treatment of a deep venous thrombosis focuses on preventing a pulmonary embolus. Bed rest and elevating the leg can help reduce the swelling and pain.
The person is often given an injection of a blood-thinning medicine. The injection may be given through an IV or under the skin. These blood-thinning medicines, such as heparin, enoxaparin (i.e., Lovenox) and dalteparin (i.e., Fragmin), help prevent further growth of the blood clot.
After a few days of blood-thinning medicines by injection, the person can be switched to pills. Warfarin (i.e., Coumadin) is the most common blood-thinning pill.
In some people, blood-thinning medicines cannot be used. For example, a person may have a high risk of bleeding, a side effect of thinning the blood. In these cases, a surgical procedure can be done. This involves inserting a filter in one of the major veins of the body that leads to the heart. This filter catches any clots that break off so they cannot get into the lungs and cause death.
In some severe cases, the blood clot has to be removed by a surgery called a venous thrombectomy.

Side Effects

What are the side effects of the treatments?

Heparin can cause bleeding and lower blood platelet counts, called thrombocytopenia. Warfarin can also cause bleeding, which in rare cases is fatal. Warfarin interferes with many other medicines. Surgery can cause bleeding, infection, or allergic reaction to anesthesia.

After Treatment

What happens after treatment for the condition?

Most patients with a deep venous thrombosis will recover fully. When DVT is in the pelvis or upper leg, warfarin is usually taken for at least 3 to 6 months. DVT in the veins of the calf is usually treated with warfarin for at least 6 weeks.
In people who develop a second DVT, warfarin treatment is usually continued for life. This long-term therapy may also be used in people with underlying causes of DVT, such as cancer.

Monitor

How is the condition monitored?

People with a history of deep venous thrombosis are told to avoid prolonged periods of immobility. They also need to watch for the common symptoms of leg pain and swelling. Individuals on blood-thinning medicines will have periodic blood tests to monitor the thickness of their blood. Any new or worsening symptoms should be reported to the healthcare professional.

Sources

Harrison's Principles of Internal Medicine, 1998, Fauci et al., pp. 1403-5.

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