Pulmonary Embolism (PE)

The sudden blocking of an artery of the lung is not only caused by blood clots. Other material can also form emboli.

• Fat can escape into the blood from the bone marrow when a long bone is fractured or during bone surgery and form an embolus. Sometimes fat can also escape during procedures such as liposuction and fat grafting.

• Amniotic fluid that is forced into the pelvic veins during a complicated childbirth can form an embolus.

• Cancer cells in clumps may break free into the circulation to form tumor emboli.

• Air bubbles may form emboli if a catheter in one of the large veins (central veins) is inadvertently opened to air. Air emboli may also form when a vein is operated on (such as when a blood clot is being removed). An additional risk is underwater diving (because nitrogen dissolved in the blood and tissues at increased concentration by high pressure forms bubbles as pressure decreases; this is known as decompression sickness).

• Infected material may also form emboli and travel to a lung. Causes include intravenous illicit use of injected drugs, certain heart valve infections, and inflammation of a vein with blood clot formation and infection (septic thrombophlebitis).

• A foreign substance can be introduced into the bloodstream, usually by intravenous injection of inorganic substances such as talc or mercury by injection drug users, where it can form emboli and travel to the lungs.

• Medical bone cement may occasionally enter the bloodstream after a procedure called vertebroplasty.

Pulmonary infarction is when some lung tissue does not receive enough blood flow and oxygen and therefore dies due to blockage of a lung blood vessel by a pulmonary embolus. The symptoms of pulmonary infarction develop over hours. If pulmonary infarction occurs, the person may cough up blood-stained sputum, have sharp chest pain when breathing in, and in some cases have a fever. Symptoms of infarction often last several days but usually become milder every day.

In those rare people who have recurring emboli, the blood pressure in the lungs' blood vessels can increase (called pulmonary hypertension) repeatedly, causing chronic thromboembolic pulmonary hypertension. This increase in blood pressure can cause symptoms, such as shortness of breath, swelling of the ankles or legs, and weakness, which tend to develop progressively over, months, or years.

Very rarely a chest x-ray may reveal subtle changes in the blood vessel patterns that occur after embolism and may reveal signs of pulmonary infarction. However, the x‑ray results are often normal, and even when they are abnormal, they do not enable doctors to establish the diagnosis with certainty.

Electrocardiography (ECG) may sometimes show abnormalities. These abnormalities can support or suggest the diagnosis of pulmonary embolism but cannot confirm it.

The level of oxygen in the blood is measured with a sensor that is attached to a fingertip (pulse oximetry). Because pulmonary embolism blocks pulmonary arteries, the level of oxygen in the blood may be low. Sometimes doctors also take a sample of blood from an artery and measure the level of oxygen and other gases in it.

Doctors first judge how likely pulmonary embolism seems to be, based on information such as the person's risk for pulmonary embolism, the severity of their symptoms, and the results of early tests (such as the chest x-ray and level of oxygen in the blood). Importantly, a pulmonary embolism is considered unlikely if risk factors are completely absent.

If pulmonary embolism seems unlikely, a blood test that measures a substance called D‑dimer is typically done. This test may be the only test needed if pulmonary embolism seem unlikely. If the D-dimer level is normal, then the probability that a pulmonary embolus has occurred is extremely low. Although a low level of D-dimer in people at low risk means that pulmonary embolism is unlikely, a high level does not necessarily mean that pulmonary embolism is likely. Other disorders, such as infection or injury, can cause the D-dimer level to be high so additional testing is needed to confirm the diagnosis.

If pulmonary embolism seems more likely or if the result of the D-dimer test is abnormal, other testing is done, usually one or more of the following:

• Computed tomography (CT) angiography

• Lung ventilation perfusion scan

• Ultrasonography of the legs

CT angiography is a type of CT scan. It is fast, noninvasive, and fairly accurate, particularly for large clots. In this test, contrast material is injected into a vein. The contrast material travels to the lungs via the pulmonary arteries, and a CT scanner generates images of blood in the arteries to determine if a pulmonary embolism is blocking blood flow. CT angiography is the imaging test most often used to diagnose pulmonary embolism. The size of the heart may also indicate how much the heart is being strained.

A lung ventilation/perfusion scan is noninvasive and fairly accurate but takes longer than a CT scan. A ventilation/perfusion scan is actually two scans, one that measures breathing (ventilation) and one that measures blood flow (perfusion). The tests are usually done together but can also be done separately.

For a lung perfusion scan, a tiny amount of radioactive substance is injected into a vein and travels through the pulmonary arteries to the lungs, where it outlines the blood supply of the lung. Completely normal perfusion results rule out a pulmonary embolism. Abnormal scan results support the possibility of pulmonary embolism but may also indicate the possibility of other disorders. Doctors sometimes use a lung perfusion scan if a person has a kidney problem that prevents the use of CT angiography because the contrast material used for the CT might further damage the kidneys.

In a lung ventilation scan, the person inhales a harmless gas containing a trace amount of radioactive material, which is distributed throughout the small air sacs of the lungs (alveoli). The areas where carbon dioxide is being released and oxygen is taken up can then be seen on a scanner.

By comparing the ventilation scan to the pattern of blood supply shown on the perfusion scan, doctors can usually determine whether a person has had a pulmonary embolism.

Ultrasonography of the legs is noninvasive and can identify clots in the legs, which are the usual sources of pulmonary embolism. The absence of clots in the veins of the leg does not rule out pulmonary embolism. However, if ultrasonography reveals blood clots, and the person has little difficulty breathing and no decrease in their blood pressure or increase in their heart rate, people are occasionally treated as they would be for pulmonary embolism without any further testing, because the treatment for both conditions is often the same.

Pulmonary artery angiography is very rarely needed to diagnose acute pulmonary embolism.

Echocardiography may show that a blood clot is in the right atrium or right ventricle of the heart. The results of this test may help doctors determine the severity of the embolism by showing that the right side of the heart is strained by trying to push blood through the clots.

In people who have no apparent risk factors for blood clots or recurring clots, doctors may also measure proteins in the blood to determine whether a clotting disorder is the cause.

One type of heparinheparin requires frequent blood tests to monitor the effect and continued hospitalization. A different kind of heparin called low molecular weight heparin

heparin therapy (by vein or by injection under the skin) for the first few days of therapy before they can give the edoxaban or dabigatranheparinheparin and warfarin are given for the first few days of therapy, and then warfarin alone is used thereafter.

warfarin dose is frequently adjusted based on the results of the blood tests. Also, warfarin interacts with many different types of food, drugs, and supplements, which can result in blood that is too thin or too thick. If excessive anticoagulation occurs, severe bleeding in a number of body organs can develop.

Because many substances can interact with warfarin, people who take it should be sure to check with their doctor before taking any other drugs or supplements, including those that can be obtained without a prescription (over-the-counter) such as acetaminophen or aspirin, herbal preparations, and dietary supplements. Foods that are high in vitamin K (which affects blood clotting), such as broccoli, spinach, kale, and other leafy green vegetables, liver, grapefruit and grapefruit juice, and green tea, may need to be either eaten in very consistent amounts or avoided.

warfarin, these medications can be taken by mouth, but dose adjustments and tests to monitor the level of anticoagulation are not needed. Furthermore, these medications do not often interact with food or other medications and are less likely to cause severe types of bleeding when compared with warfarin. Rivaroxaban should always be taken with food.

Sometimes, if a person appears to be in danger of dying from a massive pulmonary embolism, doctors may try to break up or remove the embolus using a catheter inserted into the pulmonary artery.

Surgery may be needed in some cases of severe embolism. Removal of the embolus from the pulmonary artery may be lifesaving. Surgery is also used to remove long-standing pulmonary artery clots that cause persistent shortness of breath and high pressures in the pulmonary artery (chronic thromboembolic pulmonary hypertension [CTEPH]).

A filter can be placed via a catheter in the main vein in the abdomen that drains blood from the legs and pelvis to the right side of the heart. Such a filter can be used if emboli recur despite anticoagulant treatment or if anticoagulants cannot be used initially for some reason such as ongoing bleeding. . Because clots generally originate in the legs or pelvis, a filter usually prevents them from being carried into the pulmonary artery. Newer filters are removable (retrievable). Removal helps prevent some complications that can occur when filters are left in place permanently.

Inferior Vena Cava Filters: One Way to Prevent Pulmonary Embolism

To prevent pulmonary embolism, doctors usually use medications that limit blood clotting. However, for some people, doctors may recommend that an inferior vena cava (IVC) filter be temporarily or permanently placed in the inferior vena cava. This filter device typically is recommended when medications that limit clotting cannot be used, for example, when a person is also having bleeding. The filter can trap emboli before they reach the heart but allow blood to flow through freely. Emboli that are trapped sometimes dissolve on their own.

comes in two forms:

• Unfractionated

• Low molecular weight

Heparin is the most widely used medication for reducing the likelihood of clots forming in calf veins after any type of major surgery, especially surgery on the legs. Low molecular weight heparin is more predictable than the unfractionated form of heparin and is commonly used for prevention of clots in people undergoing surgery that has a high risk of causing clots, such as hip or knee replacement. Small doses of heparin, either unfractionated or low molecular weight heparin, are injected just under the skin, usually within 6 to 12 hours after surgery. Ideally, additional doses are given until the person is up and walking again (and sometimes longer).

People who are hospitalized and at high risk of developing pulmonary embolism (such as those with heart failure, immobility, critical illness or obesity, or who have had clots in the past) benefit from small doses of heparin even if they are not undergoing surgery. Low-dose heparin does not increase the frequency of severe bleeding complications, but heparin can increase minor oozing of blood from wounds.

an anticoagulant given by mouth, can be used for people at risk of pulmonary embolism. It is used much less commonly now because people need regular blood tests to monitor the effect of warfarin, warfarin interacts with many drugs, foods, and supplements that people may be taking, and newer medications are safer and more effective.

Direct oral anticoagulantswarfarin. Nonetheless, warfarin is still considered the best choice for some people such as those with metallic heart valves.

For people who have undergone surgery—especially older people—the risk of clot formation can be reduced by

• Using intermittent air compression devices or wearing elastic compression stockings

• Doing leg exercises

• Getting out of bed and becoming active as soon as possible

Intermittent air compression devices are inflatable devices that go over the lower legs and inflate and deflate to provide external pressure to keep blood moving in the legs. However, these devices alone are inadequate to prevent clot formation in people who have undergone certain high risk surgeries such as hip or knee replacement surgery.

Elastic compression stockings provide steady pressure on the blood vessels of the legs to keep blood flowing. They are likely less effective than intermittent compression devices but still may be helpful in reducing the risk of blood clots in the legs.

Doing leg exercises and getting out of bed also help keep blood flowing in the legs.

When people who are at high risk of developing pulmonary embolism cannot take anticoagulants due to a high risk of bleeding, a filter (called an inferior vena cava filter) may be placed inside a large vein between the heart and the inferior vena cava, which returns blood to the heart from the lower part of the body. A filter can trap emboli, preventing them from reaching the lungs.