Over the past several days, I have noticed that my left leg seems swollen and tight compared with my right.When I called my oncologist’s office and talked to the nurse, she told me to go to the emergency room immediately.What’s the problem?

Why do I have to go to the emergency room?

The nurse is concerned that you may have a deep vein thrombosis (DVT), a blood clot in a large vein. The large veins of the legs may develop long, thick clots that block the return of blood flow to the heart. This can cause pain and swelling. The most dangerous complication of DVT, however, occurs if the clot breaks away from the walls of the vein and travels to the heart. A large clot can become lodged in the heart valves, but more commonly, the clot becomes lodged in the arteries of the lung. A clot that has clogged the pulmonary arteries is called a pulmonary embolus.

A pulmonary embolus can cause sudden death. It has been estimated that up to 15% of all cancer patients die of pulmonary embolus. Although DVT does not always result in pulmonary embolus, the presence of a clot in the extremities should be taken very seriously. Doctors hospitalize patients with DVT to keep them on bed rest, to begin anticoagulant therapy, and to evaluate for further evidence of pulmonary embolus.

A DVT in the lower limbs can be detected by ultrasound, which can detect blood flow through the veins below the surface of the skin and muscle. The most dangerous clots are those in the deep veins of the thigh and pelvis because these vessels are quite large.

A pulmonary embolus does not always cause symptoms. Some clots break up gradually, releasing a shower of small clots that lodge in the pulmonary vessels. A large clot typically causes shortness of breath, chest pain, or a cough. Although a chest Xray may be normal, other tests, such as a ventilation/ perfusion scan or a chest computed tomography (CT) angiogram, may show a loss of normal blood flow to one or both lungs. Patients may require supplemental oxygen for several days because of this blockage of blood flow to the lung.

Anticoagulants (blood thinners), such as heparin, enoxaparin (Lovenox), dalteparin (Fragmin), tinzaparin (Innohep), and fondaparinux (Arixtra), prevent the development of further clots; however, these drugs are all given by injection. Many patients prefer to take an oral anticoagulant called warfarin (Coumadin). Patients taking warfarin must be closely monitored with regular blood tests because of the drug’s interactions with other medications and certain foods.

Some DVT patients, including those with recent neurosurgery, are at risk for bleeding complications from anticoagulants. Such patients may benefit from the placement of an inferior vena cava (IVC) filter, which is an internal device that is placed into the large vein below the heart to act as a screen for blood clots that may break off and travel to the heart and lungs. An inferior vena cava filter is often used in combination with an anticoagulant because DVT may still form in the limbs, causing pain and swelling (Figure 26).

It is not always possible to predict or prevent DVT. Patients who are not ambulatory, who have had recent surgery, and who have a history of DVT should discuss ways to reduce the risk of DVT and pulmonary embolus with their doctors. Some doctors always prescribe a blood thinner if the patient is expected to be immobile for a long period of time, even if the patient has not had a previous history of blood clots.