Pulmonary embolism

View of the pulmonary vessels, as seen behind the heart. Source: Gray's Anatomy, 1918.

Cross section lungs with vessels. Source: Gray's Anatomy, 1918.

A pulmonary embolism, or PE, is a sudden blockage of a lung artery, usually due to a blood clot that originally forms in a deep vein of the leg. The clot is dislodged and then travels in the bloodstream through the heart and into the lung, where it cuts off blood supply and prevents oxygenation to the portion of the lung supplied by the affected artery. It is a severe and dangerous condition that is fatal in up to 30% of cases from lack of oxygen, or blockage of the heart causing acute right heart failure, pulseless electrical activity (PEA) and death.

PE is commmon and can cause a range of symptoms, making it difficult to diagnose in some cases. According to recent statistics, at least 100,000 cases of PE occur each year in the U.S. It is the third most common cause of death in hospitalized patients, and most deaths occur within the first few hours of the event. For this reason, the majority of patients with hospital stays longer than three days are treated with blood thinners for anticoagulation to prevent clotting of the blood. The drugs used for anticoagulation include heparin, low molecular weight heparin, and warfarin.

A PE is usually caused by a deep vein thrombosis (DVT), which is the formation of one or more blood clots in the deep veins of the body, most often the legs. These clots can break free, travel through the bloodstream to the lungs, and block an artery. There are many risk factors for developing a DVT, many of which involve long periods of immobility -- patients in the hospital (post-surgical patients), people who are bed bound, and people who have taken long flights. Other risk factors include pregnancy, and medical conditions in which the patient's blood has a tendency to form clots.

Signs and Symptoms

Signs and symptoms of PE include unexplained shortness of breath, difficulty breathing, chest pain, coughing, or coughing up blood. The chest pain is sometimes described as “pleuritic” in nature, meaning that it feels superficial and is a sharp, stabbing pain which is worse when breathing in. There may also be feelings of anxiousness, lightheadedness, difficulty breathing, sweating, or an increased heart rate. Fever may also be present. Certain types of arrhythmias (rapid or irregular heartbeats) also may indicate PE. The onset symptoms are often quite abrupt, and sudden death is one presentation. However, when PE is detected, it is often treatable. PE has symptoms similar to other serious conditions and must be differentiated from conditions such as heart attacks or pneumonia.

In some cases, the only signs and symptoms are related to the DVT. These include swelling of the leg or along the vein in the leg, pain or tenderness in the leg, a feeling of increased warmth in the area of the affected leg, and red or discolored skin on the affected leg.

It is also possible to have a PE and not have any signs or symptoms of either PE or DVT.^[1]

Causes

In 9 out of 10 cases, pulmonary embolism (PE) begins as a blood clot in the deep veins of the leg (a condition known as deep vein thrombosis). The clot breaks free from the vein and travels through the bloodstream to the lungs, where it can block blood flow through an artery.

• Immobility: Clots in the leg can form when blood flow is restricted and slows down.
  • After some types of surgeries
  • During a long trip in a car or on an airplane
  • If a person must stay in bed for an extended time
• Trauma (especially to the legs)
• Irregular heart beat
• Obesity
• Burns
• Conditions that increase clotting:
  • pregnancy
  • estrogen therapy
  • cancer
  • some protein or enzyme deficiencies
• Rarely, an air bubble, a portion of a tumor, or after a fracture, tissue travels to the lungs and causes PE. Also, when a large bone in the body (such as the thigh bone) breaks, fat from the marrow inside the bone can travel through the blood to the lungs and cause a PE.

Diagnosis

Medical history and physical exam

History from the patient and the physical exam are very important in diagnosing a pulmonary embolus, and if there is an increased suspicion that the cause may be a PE, the history will focus on:

• Identifying risk factors for DVT and PE
• Assessing the likelihood that the complaint is due to a PE rather than another condition
• Ruling out other possible causes for the symptoms

During the physical exam, the physician will check vital signs, including pulse rate and blood oxygen level, which are often deranged after PE. It is important to assess for DVT by examining the legs for swelling, as well as listening to the lungs to rule out other causes of the symptoms. PE does not have any signs that by themselves confirm the diagnosis of PE, so often physical exam involves ruling out other causes.

Diagnostic tests

A systematic approach must be taken to the diagnosis of a pulmonary embolism since there are a lot of possible tests that can be performed. Which test is selected depends on the likelihood of PE, the presence of other medical problems, for example kidney disease or lung disease, and the availability of certain tests.

Blood tests

Certain blood tests may help the doctor determine whether a PE is present.

• A D-dimer test is performed to measure a substance in the blood signifying that formed clots are breaking up. Increased levels mean there may be a clot but this is not confirmatory. Normal levels mean that a PE is most likely not the cause of the problem. This test is often used in people who are fit and healthy and have low likelihood of PE.
• Other blood tests check for inherited disorders that cause blood clots
• Arterial blood gas (ABG) measures the amount of oxygen and carbon dioxide in the blood. A clot in a blood vessel in the lung may lower the level of oxygen in the blood. This may also be detected using pulse oximetry, which is a probe placed on the finger.

Although blood tests may be useful in ruling out PE or helping the physician determine how unwell a patient is, there is no blood test which can actually confirm PE.

Radiology tests

Often the best way to diagnose PE is by imaging either the leg to find a DVT, or the vessels of the lungs themselves to directly see the clot in the lung. To rule out other possible causes of the symptoms, the doctor may use one or more of the following tests.

• Ultrasound. Doctors use this test to look for blood clots in the legs. Ultrasound uses high-frequency sound waves to check the flow of blood in the leg veins. A transducer gives off ultrasound waves and detects their echoes after they bounce off the vein walls and blood cells. A computer then turns the echoes of the ultrasound waves into a picture on a computer screen, where the doctor can see the blockage where the thrombus is causing decreased blood flow. This is a diagnosis of DVT rather than a PE, but in a patient with symptoms consistent with both a PE and a DVT, PE should be on the list of diagnoses.

• Spiral CT scan or CT pulmonary angiogram. This is the most commonly performed test to search for PE. Dye is injected into a vein which reflects the x-rays from the CT, making blood vessels easily visible. A CT scannergives a three-dimensional picture of the vessels of the lungs (pulmonary vasculature) and is very sensitive at detecting even small blood clots. This test allows doctors to detect PEs in most patients. The test only takes a few minutes. Results are available shortly after the scan is completed.

• Ventilation-perfusion lung scan (VQ scan). This is an alternative method of detecting PE. VQ scan uses a radioactive material to show how well oxygen and blood are flowing to all areas of the lungs. This test is more easy to perform and does not damage the kidneys, however it can be hard to interpret and sometimes gives uncertain results.

• Pulmonary Angiography. This is another test used to diagnose PE. It is not available at all hospitals, and a trained specialist must perform the test. A flexible tube called a catheter is threaded through the groin (upper thigh) or arm to the blood vessels in the lungs. Dye is injected into the blood vessels through the catheter. X-ray pictures are taken to show the blood flow through the blood vessels in the lungs. If a clot is discovered, the doctor may use the catheter to extract it or deliver medicine to dissolve it. Typically this is reserved for only the most severe life-threatening clots when direct intervention with a procedure such as an embolectomy is required, since it can cause complications.

• Echocardiogram. This test uses sound waves to check heart function and to detect blood clots inside the heart. Echocardiogram can also be used to study the right side of the heart, which can fail after massive PEs develop.

• Chest x-ray. X-ray provides a picture of the lungs, heart, large arteries, ribs, and diaphragm. It can be helpful by ruling out pneumonia which can mimic PE. There are certain signs that may indicate PE but these are actually quite unusual.

• Magnetic resonance imaging (MRI). This test uses radio waves and magnetic fields to make pictures of organs and structures inside the body. In many cases, an MRI can provide information that can't be seen on an x-ray. This is not routinely used in detecting PE and is experimental at the present time.

Other tests

• Electrocardiogram (ECG or EKG). This test measures the rate and regularity of the heartbeat using its electrical signals. A characteristic abnormal pattern of the waveform of the heart circuitry can suggest PE, although often all that is seen is an increased heart rate.

Treatment

The treatment of pulmonary embolism depends on whether the patient is able to maintain his or her blood pressure. In non life-threatening PE, the main goals of treating pulmonary embolism (PE) are to:

• Stop the blood clot from getting bigger (propagating)
• Prevent new clots from forming

Treatment may include medicines to thin the blood and slow its ability to clot.

In massive or life-threatening PE, death may result, therefore the goal is to remove the clot either with drug therapy or surgical intervention.

Alternative and holistic therapies

There are no alternative therapies that can be recommended for this life threatening condition.

Medications

Anticoagulants (AN-te-ko-AG-u-lants), which are blood-thinning medications, are a class of drugs designed to prevent the blood from clotting. Since the presence of clot within a blood vessel often activates blood clotting, the goal of these drugs is to stop blood clots from getting bigger and to prevent new clots from forming. They don't break up blood clots that have already formed. When a patient experiences their first episode of PE, anticoagulation therapy is usually recommended for three to six months.

Recurrent blood clots need a longer period of treatment. If under treatment for another illness, such as cancer, anticoagulants will need to be taken for as long as risk factors for PE are present. Recurrent blood clots such as these without obvious risk factors may indicate a clotting disorder, or thrombophilia. In such cases, a number of tests will be performed on the blood to study for genetic conditions that may cause abnormally active clotting. If present, treatment is often different and sometimes lifelong therapy is required.

The most common side effect of anticoagulants is bleeding. This happens if the medicine thins the blood too much. This side effect can be life threatening. Sometimes, the bleeding can be internal. This is why people treated with anticoagulants usually receive regular blood tests. These tests are called PT and PTT tests, and they measure the blood's ability to clot. It is especially important to check these tests when changing diet or other medications, since warfarin levels can be widely affected by both.

Thrombin inhibitors are a newer type of anticoagulant medicine. They're used to treat some types of blood clots for patients who can't take heparin. However, these drugs are expensive and must be injected so their use is usually confined to hospitalized patients. There is a good deal of interest in developing new tablet drugs for treating PE since it is very common and to reduce the amount of blood tests performed that are needed now to monitor drug toxicity.^[2]

Emergency treatment

When PE is life threatening, doctors may use treatments that remove or break up clots in the blood vessels of the lungs. These treatments are given in the emergency room or in the hospital.

Thrombolytics are medicines given to quickly dissolve a blood clot. They're used to treat large clots that cause severe symptoms. Because thrombolytics can cause sudden bleeding, they're used only in life-threatening situations. They cannot be given to people who have recently undergone surgery or suffered a stroke.

In some cases, the doctor may use a catheter to reach the blood clot. A catheter is a flexible tube placed in a vein to allow easy access to the bloodstream for medical treatment. The catheter is inserted into the groin (upper thigh) or arm and threaded through a vein to the clot in the lung. The catheter may be used to extract the clot or deliver medicine to dissolve it.

Rarely, surgery may be needed to remove the blood clot.

Other types of treatment

In patients unable to take anticoagulants, or who develop clots while taking blood thinners, the doctor may use a device called a vena cava filter to keep clots from traveling to the lungs. The filter is inserted inside a large vein called the inferior vena cava (the vein that carries blood from the body back to the heart). The filter acts as an umbrella which catches clots before they travel to the lungs. This prevents PE, but it doesn't stop other blood clots from forming.

Graduated compression stockings can reduce the chronic (ongoing) swelling that may occur after a blood clot has developed in the leg. The leg swelling is due to damage to the valves in the leg veins. Graduated compression stockings are worn on the legs from the arch of the foot to just above or below the knee. These stockings are tight at the ankle and become looser as they go up the leg. This causes a gentle compression (or pressure) up the leg. The pressure keeps blood from pooling and clotting.

Prevention

Preventing pulmonary embolism (PE) begins with preventing DVT. In hospital it is often the job of the physician to treat a patient with preventive measures to prevent DVT. Since DVT is associated with long flights and immobility, patients can certainly help themselves with prevention. Patients at high risk of DVT are obese, smokers, or women taking hormonal therapy including oral contraceptive pills containing estrogen. People with these risk factors should take extra care. The following are suggestions for preventing DVT:

• Exercising the lower leg muscles during long car trips and airplane rides
• Taking frequent walks and moving around the cabin as much as possible on airplane flights of greater than five hours duration
• Taking rest breaks in the car at least every three hours
• Getting out of bed and moving around as soon as possible after having surgery or being ill.

For patients in hospital the following treatments may be recommended:

• Use of graduated compression stockings to increase the blood flow speed in the legs and prevent clots
• Use of mechanical squeezing devices to return stagnant blood to the heart before it clots
• Preventive (prophylactic) doses of anticoagulants which decrease risk of DVT and PE without significantly increasing the risk of bleeding

Living with Pulmonary Embolism

In the majority of cases, if the initial PE is survived by the patient, there are no long term adverse effects to the lungs. The DVT which causes the PE however may lead to long term problems with circulation, which is outlined in the DVT page. In some people there may be long lasting problems related to failure of the right heart which is strained by pumping past all of the blocked arteries in the lungs.

Treatment for PE intially takes place in the hospital. After leaving the hospital treatment is necessary for between three months and lifelong. The critical lifestyle changes induced by PE are as follows:

• Need to take prescribed medicines, often by injection, every day
• The need for frequent blood tests
• The need to talk to a doctor before taking anticoagulants with any other medicines, including over-the-counter medicines. Over-the-counter aspirin, for example, can thin the blood. Taking two medicines that thin the blood (even if one is over-the-counter) may increase the risk for bleeding additively.
• Maintain a consistent diet. Foods that contain vitamin K can affect how well warfarin works. Vitamin K is found in green leafy vegetables and some oils, such as canola and soybean oil. It's best to eat a well-balanced, healthy diet.
• With certain medications including warfarin, alcohol should be avoided.

Medicines used to treat PE can cause bleeding in the digestive system or the brain if their levels are not monitored frequently. Signs and symptoms of bleeding in the digestive system include:

• Bright red vomit or vomit that looks like coffee grounds
• Bright red blood in the stool or black, tarry stools
• Pain in the abdomen
• A feeling of faintness or dizziness, particularly when moving from a lying to a standing position

Signs and symptoms of bleeding in the brain include:

• Severe headache
• Sudden changes in the vision or loss of vision
• Sudden loss of movement in the face, legs or arms
• Memory loss or confusion

Excessive bleeding, defined as bleeding that will not stop after application of firm pressure for more than 10 minutes, resulting from a fall or injury may also mean that PE medicines are present in excessive, or "supratherapeutic" levels. This often requires hospital treatment.

In some hereditary thrombophiliac disorders, which predispose to clotting, PE may recur after or even during initial treatment. These include Protein C deficiency, Protein S deficiency and Factor V Leiden disease. These conditions may require longer term anticoagulation and should always be communicated with physicians before surgery or hospital treatment. Even in the absence of known thrombophilia disease, having a PE once increases the likelihood that a patient will have another, so particular care should be taken to institute preventive measures both by the patient and his or her treating physician.

Chances of Developing Pulmonary Embolism

Populations affected

Pulmonary embolism occurs equally in men and women. Risk increases with age: For each 10 years after age 60, the risk of PE doubles.

Certain inherited conditions, such as factor V Leiden, increase the risk of blood clotting, and, therefore, the risk of PE.

Other risk factors

People who recently have been treated for cancer or who have a central venous catheter (a tube placed in a vein to allow easy access to the bloodstream for medical treatment) are more likely to develop DVT. The same is true for people who have been bedridden or have had surgery or suffered a broken bone in the past few weeks.

Other risk factors for DVT, which can lead to PE, include sitting for long periods of time (such as on long car or airplane rides), pregnancy and the six-week period after pregnancy, and being overweight or obese. Women who take hormone therapy or birth control pills also are at increased risk for DVT.

People with more than one risk factor are at higher risk for blood clots.

Key Points

• A pulmonary embolism (PE) is a blockage of an artery in the lung, usually due to a blood clot that traveled in the bloodstream to the lung from the leg. The clot blocks blood flow to part of the lung. PE can be life threatening.
• In most cases, PE is a complication of a condition called deep vein thrombosis (DVT). In DVT, blood clots form in the deep veins of the body—most often in the legs. These clots can break free, travel through the bloodstream to the lungs, and block an artery.
• At least 100,000 cases of PE occur each year in the United States. PE is the third most common cause of death in hospitalized patients. If left untreated, about 30% of patients with PE will die. Most of those who die do so within the first few hours of the event.
• The greatest risk for PE occurs in people who have DVT, have previously had DVT, or have previously had PE.
• PE occurs equally in men and women.
• The risk for PE doubles every 10 years after age 60.
• The most common signs and symptoms of PE are unexplained shortness of breath, difficulty breathing, chest pain, coughing, or coughing up blood. Other symptoms may be linked to DVT, such as swelling of the leg. It's possible to have PE and not have any signs or symptoms of PE or DVT.
• The doctor will take the person's medical history and do a physical exam and several diagnostic tests to decide whether a PE is present.
• The main goals in treating PE are to keep the current blood clot from getting bigger and to stop new clots from forming.
• Treatment varies depending on how severe the symptoms are.
• Treatment usually includes anticoagulant medicines (blood-thinning medicines), such as warfarin (Coumadin^®) and heparin, which help prevent clots from forming and help keep clots from getting larger.
• Preventing PE begins with preventing DVT.
• Contact a doctor at once for any signs or symptoms of DVT or PE.

Clinical Trials

• Pulmonary Embolism Clinical Trials (ClinicalTrials.gov)

References

1. ↑ The Lung Association. Pulmonary Embolism
2. ↑ The Merck Manuals Online Medical Library. Pulmonary Embolism

External Links

National Heart Lung and Blood Institute:

• Deep Vein Thrombosis (Diseases and Conditions Index)

• Study Finds Ways to Improve Detection of Blood Clots in the Lung (NIH press release, May 31, 2006)

• Low Dose Warfarin Prevents Recurrence of Blood Clots—NHLBI Stops Study (NIH press release, February 24, 2003)