Pulmonary Embolism

An embolus is usually a blood clot (thrombus), but may also be fat, amniotic fluid, bone marrow, a tumourfragment, or an airbubble that travels through the bloodstream until it blocks a blood vessel. Pulmonary embolism is the sudden blocking of an artery of the lung (pulmonary artery) by an embolus.

Usually, unobstructed arteries can send enough blood to the affected part of the lung to prevent tissue death. However, when very large vessels are blocked or the person has a preexisting lung disease, the amount of blood supplied may be insufficient to prevent tissue death. About 10 percent of people with pulmonary embolism suffer some lung tissue death, called pulmonary infarction.

If the body breaks up small clots quickly, damage is kept to a minimum. Large clots take much longer to disintegrate, so more damage is done. Large clots may cause sudden death.

Causes

The most common type of pulmonary embolus is a blood clot, usually one that begins in a leg or pelvic vein. Blood clots tend to form when the blood is flowing slowly or not at all, as may occur in the leg veins when a person stays in one position for a long time. When the person starts moving again, the clot can break loose. Far less often, clots begin in the veins of the arms or in the right side of the heart. Once a clot in a vein breaks free into the bloodstream, it usually travels to, the lungs.

Another type of embolus may form from fat that escapes into the blood from the bone marrow when a bone is fractured. An embolus also may form from amniotic fluid during childbirth. How-ever, both fat and amniotic fluid emboli are rare. They generally lodge in small vessels like arterioles and capillaries of the lung; if many of these vessels become obstructed, acute respiratory distress syndrome may develop.

Symptoms

Small emboli may not cause any symptoms, but most cause shortness of breath. This may be the only symptom, especially if infarction doesn't develop. Often, the breathing is very rapid, and the person may feel anxious or restless and appear to have an anxiety attack. Sharp pain may be felt in the chest, especially when the person breathes deeply; the pain is called pleuritic chest pain.

In some people, the first symptoms may be light-headedness, fainting, or convulsions. These symptoms usually result from a sudden decrease in the heart's ability to deliver enough well-oxygenated blood to the brain and other organs. Irregular heartbeats may also occur. People with an occlusion of one or more large vessels of the lungs may have a blue skin color (cyanosis) and can die suddenly.

Pulmonary infarction produces coughing, blood-stained sputum, sharp chest pain on breathing, and fever. The symptoms of pulmonary embolism usually develop abruptly, whereas the symptoms of pulmonary infarction develop over a period of hours. Symptoms of infarction often last several days but usually become milder every day.

In people who have recurring episodes with small pulmonary emboli, symptoms such as chronic shortness of breath, swelling of ankles or legs, and weakness tend to develop progressively over weeks, months, or years.

Diagnosis

A doctor suspects pulmonary embolism based on a person's symptoms and predisposing factors. However, certain procedures are often needed to confirm the diagnosis.

A chest x-ray may reveal subtle changes in the blood vessel patterns after embolism and signs of pulmonary infarction. However, chest x-rays often are normal, and even when they are abnormal, they rarely confirm pulmonary embolism.

An electrocardiogram may show abnormalities, but often they're transient and can only support the possibility of pulmonary embolism.

A lung perfusion scan is often performed. A small amount of radioactive substance injected into a vein travels to the lungs, where it outlines the blood supply (perfusion) of the lung. Areas without normal blood supply appear dark on the scan because no radioactive particles can reach them. Normal scan results indicate that the per-son doesn't have a significant blood vessel obstruction, but abnormal scan results may reflect causes other than pulmonary embolism.

Usually, the perfusion scan is coupled with a lung ventilation scan. The person inhales a harm-less gas containing a trace of radioactive material, which is distributed throughout the small air sacs (alveoli) in the lungs. The areas where oxygen is being exchanged can then be seen on a scanner. By comparing this scan to the pattern of blood supply shown on the perfusion scan, a doctor can usually determine whether the person has pulmonary embolism: An area of embolism shows normal ventilation but decreased perfusion.

Pulmonary arteriography is the most accurate means of diagnosing pulmonary embolism, but it poses some risk and is more uncomfortable than other tests. A dye that can be seen on x-rays is injected into an artery and flows into the arteries of the lung. On an x-ray, pulmonary embolism shows up as a blockage in an artery.

Additional tests may be performed to find out where the embolus originally developed.

Prognosis

The likelihood of dying from pulmonary embolism depends on the size of the embolus, the size and number of pulmonary arteries blocked, and the person's overall health. Anyone with a serious heart or lung problem is in greater peril from embolism. A person with normal heart and lung function will usually survive unless the em-bolus blocks half or more of the pulmonary vessels. Fatal pulmonary embolism usually causes death within 1 to 2 hours.

About half of all people with untreated pulmonary embolism will have another embolism in the future. As many as half of these recurrences may be fatal. Therapy with drugs that inhibit blood clotting (anticoagulants) can reduce the rate of recurrence to about 1 in 20.

Prevention

Attempts are made to prevent clots from forming in the veins of people at risk of pulmonary embolism. For postoperative patients-especially the elderly-wearing elastic stockings, doing leg exercises, getting out of bed, and becoming active as soon as possible reduce the risk of clot formation. Leg compression stockings designed to keep blood moving lower the rate of clot formation in the calf, thereby lowering the rate of pulmonary embolism.

The most widely used therapy for reducing the likelihood of clots in calf veins after surgery is heparin, an anticoagulant. Small doses are injected just under the skin immediately before the operation and for 7 days afterward. Heparin can cause bleeding and retard healing, so it's given only to people at high risk of developing clots, including those who are in heart failure or shock, have chronic lung disease, are obese, or have had clots. Heparin isn't used for operations involving the spine or brain because the danger of hemorrhage in these areas is too great. Hospitalized people at high risk of developing pulmonary embolism may be given small doses of heparin even if they're not undergoing surgery.

Dextran, which must be injected intravenously, also helps prevent clots. Like heparin, it may cause bleeding. With certain kinds of surgery that are particularly likely to cause clots, such as hip fracture repair or joint replacement, the drug warfarin may be given orally. Warfarin therapy may be continued for several weeks or months.

Treatment

Treatment of pulmonary embolism begins with the administration of oxygen and, if necessary, analgesics. Anticoagulants such as heparin are given to prevent existing blood clots from enlarging; and additional clots from forming. The heparin is given intravenously to achieve a rapid effect, and the dose must be carefully regulated. Warfarin, which also inhibits clotting but takes longer to start working, is given next.

Because warfarin can be taken orally, it's suitable for long-term use. Heparin and warfarin are given together for 5 to 7 days, until blood tests show that the warfarin is effectively preventing clotting.

The duration of anticoagulation treatment depends on the patient's situation. If pulmonary embolism is caused by a temporary predisposing factor, such as surgery, treatment continues for 2 to 3 months. If the cause is some longer-term problem, treatment usually continues for 3 to 6 months, but sometimes it must continue indefinitely. While taking warfarin, the person periodically has a blood test to determine if the dose needs to be adjusted.

People who appear to be in danger of dying of a pulmonary embolus may benefit from two other treatment approaches-thrombolytic therapy and surgery. Thrombolytics (drugs that break up the clot) such as streptokinase, urokinase, or tissue plasminogen activator may be helpful.

However, these drugs can't be given to people who have had surgery in the preceding 10 days, are pregnant, have had a recent stroke, or have a propensity to bleed excessively. Surgery may be needed to save someone with severe embolism. Pulmonary embolectomy (removal of the embolus from the pulmonary artery) may be lifesaving.

If emboli recur despite all preventive treatment or if antiocagulants cause significant bleeding , a filter can be surgically placed in the main vein from the legs and pelvis to the right side of the heart. Clots generally originate in the legs or pelvis, and this filter prevents them from being carried into the pulmonary artery.

The author is a professor Emeritus.

What Predisposes Someone to Clotting?

The cause of clotting in the veins may not be discernible, but many times predisposing conditions are obvious. These conditions include

Surgery

Prolonged bed rest or inactivity (such as sitting during a long car or plane trip)

Stroke

Heart attack

Obesity

Hip or leg fracture

Increased tendency of blood to clot (for example, in certain cancers, with oral contraceptive use, and with a hereditary deficiency of a blood clotting inhibitor)

Submitted By:
R.G. LOUDON, M.B., CH. B

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