Venous Thrombosis Prevention
Venous Thrombosis Prevention
Venous thrombosis prevention refers to the use of medications, other devices, or behavioral changes to prevent blood clots from forming in veins within the body.
Different preventative methods can also maintain normal blood flow and therefore enable oxygen and nutrients to reach the cells of the body. Blood clots can be painful and can cause serious damage to tissues and organs. Sometimes, they can cause rapid death. Blood clot prevention can enhance blood flow and save lives.
Blood clots can form in any vein within the body. Deep vein thrombosis (DVT) can be quite serious. DVT occurs when a blood clot (thrombus) forms in the legs or pelvis; in a few cases, DVT occurs in the arms. If the thrombus is large enough, it can block the blood flow within the vein, cutting off oxygen to the tissues. An embolus (a clot that breaks away from the wall of the blood vessel) can travel into the lung, the heart, or the brain where it can disrupt the normal functioning of these organs and become life threatening. Some blood clots distend the walls of the blood vessel, creating a sac called an aneurysm. Sometimes the aneurysm bursts, causing blood to leak out. If this occurs within the brain, the heart, or the lungs, it can be fatal.
Venous thrombosis can occur for a number of reasons. There are three large categories of factors that influence the likelihood of DVT: changes in the rate of blood flow; injuries to the tissue lining the inner walls of the veins; and changes in the thickness of the blood or its ability to coagulate. These three categories are known as Virchow’s triad, named for Rudolf Virchow (1821–1902) a German physician and pathologist.
Patients with DVT may have disease within the blood vessels such as an inflammation of the walls of the vein (phlebitis) or hereditary blood clotting disorders. The patient may also develop blood clots because of other medical conditions such as heart disease, heart failure, stroke, or cancer. Some drugs used in cancer chemotherapy increase the risk of DVT. Clots can also occur after surgery or prolonged bed rest or inactivity. People who smoke and take oral contraceptives may be more susceptible to blood clots. Pregnancy and childbirth also increase the risk of DVT, as do Crohn’s disease and ulcerative colitis. Such autoimmune disorders as systemic lupus erythematosus (SLE) increase the risk of DVT; about 9% of lupus patients develop spontaneous DVT. Last, people who have had surgery to remove or close varicose veins have an increased risk of DVT.
The classical symptoms of DVT include pain, swelling, and redness of the affected leg, and dilation of the surface veins. The doctor can examine the leg for possible DVT by measuring the circumference of both legs at the same point to see whether one is swollen, or palpate (touch with light pressure) the veins in the affected leg to see whether the area is sore or tender. The absence of these signs and symptoms, however, does not mean that the patient does not have DVT. As of 2008, there is no laboratory blood test that can definitely confirm or exclude a diagnosis of DVT.
Pulmonary embolism (PE) is one of the most common, but highly fatal, types of blood clots that patients experience. Sometimes there is little or no warning, causing sudden death. On the other hand, some doctors think that cases of DVT and PE are underdiagnosed; one researcher estimates that one of every 9 persons in the United States develops recognized DVT before the age of 80. Studies of autopsies indicate that approximately 80% of all cases of DVT and PE remain undiagnosed even when they are the immediate cause of death. About 90% of pulmonary embolisms are the result of DVT in the legs or the pelvis; the clot moves into the lung and blocks the pulmonary artery. Most often, the DVT occurs in the recovery period after surgery, though there is an alarming trend of DVT events that are the result of airline travel. In 1999, nearly 2,000 Americans, many of them young and fit, died from travel-related DVT strokes. In 2003, NBC reporter David Bloom, who was embedded with the United States Army as he covered the war in Iraq, died of a pulmonary embolism due to his riding in a cramped position for long hours over several days.
Aneurysm— A sac created by the distention of the walls of a blood vessel.
Embolus— A clot that breaks away from the wall of the blood vessel and travels throughout the body.
Phlebitis— An inflammation of the walls of a vein.
Prophylaxis— A measure designed to preserve health and/or prevent the spread of disease.
Thrombus— A clot that forms within a blood vessel and remains attached to its place of origin.
Venous thrombosis— The formation or presence of a blood clot in a vein.
Virchow’s triad— Three categories of factors that affect a patient’s risk of venous thrombosis: alterations in the rate of blood flow; injuries to the tissue lining the walls of the veins; and alterations in the blood’s ability to coagulate.
There are several methods physicians use to prevent blood clots. Some use medications, others use mechanical means, and still others require behavioral changes, or a combination of all of these.
Heparin and other blood thinners
Anticoagulants (blood thinners) such as heparin are often prescribed as prophylactics for venous thrombosis. These drugs decrease the clotting ability of the blood. A study published in 2008 indicates that anticoagulant prophylaxis prevents about 48% of cases of DVT. There has been very good success combining heparin and pneumatic compression stockings, especially for colorectal and cardiac surgery patients.
There are some precautions, however, for using this drug. People who have had an unusual reaction to the drug should not take it, as well as those with allergies to beef and pork. Women who are pregnant and nursing should only use anticoagulants with caution. In addition, certain medications should not be used with heparin. They include aspirin, hyperthyroid medication, and drugs for pain or inflammation.
Mechanical leg pumps (pneumatic compression stockings)
Mechanical stimulation of the calf muscles of the leg can help stimulate blood flow. Many hospitals require all surgery patients, especially those who have abdominal or cardiac surgery, to wear pneumatic compression stockings. These devices wrap around the lower leg from ankle to the knee, and some reach as high as the thigh. When plugged in and turned on, a pneumatic device pumps air into chambers within the stocking, which gently tighten around the legs for a few seconds and then are released. This pulsing massage keeps the blood flowing and discourages venous thrombosis.
Often physicians recommend compression stockings for patients to prevent DVT and edema, and to treat varicose veins and phlebitis. Graduated compression stockings apply more pressure at the ankle and less up the leg and closer to the knee. This pressure prevents backflow of blood and clot formation. A controlled trial to measure the effectiveness of compression stockings in preventing DVT is underway in Canada, as of the summer of 2007.
Sitting for long periods or being confined to bed after surgery or during a long illness can slow blood flow, allowing clots to form. As soon as possible after surgery, the patient should move the legs, stand, and begin taking short walks. Travelers or people who work sitting at a desk or computer for several hours at a time should take a break every hour to get up and move around. People can also do such specific exercises as ankle circles or leg lifts while sitting in the confines of an airplane or lying in bed.
It is important not to restrict fluids when recovering from surgery, traveling, or working for long periods in a seated position. Not only will the body be kept hydrated, but drinking fluids will help prevent venous thrombosis. Drinking fluids keeps the blood liquid and moving, discouraging clot formation. Travelers should drink something every hour. This may be difficult since some air carriers may not have frequent beverage service.
The most important preparation that the patient can do is discuss his or her own personal risk of developing blood clots with a physician. If medication is given, the patient should be instructed how to take it and what side effects to look for. Special exercises should be explained to the patient, and a daily walk should be encouraged.
Any of these prevention methods can help a patient avoid having a blood clot after surgery or during long periods of inactivity such as bed rest or while traveling. Travelers and sedentary workers may find moving around and drinking fluids are the best methods for them to prevent blood clots. For patients recovering from surgery, however, a combination of methods is usually necessary. Pneumatic compression pumps with or without a round of heparin may be the best option for surgery patients.
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Rebecca Frey, PhD
Ventilation seeMechanical ventilation