Blood Clots: Pulmonary Embolism Diagnosis

  • Diagnosis

    Pulmonary embolism is a sudden blockage of one of the blood vessels in the lungs. It is usually caused by a blood clot from the leg that travels through the body and the heart before reaching the lungs. Figure 01 Large clots can seriously affect the lung's ability to transfer oxygen to the blood, resulting in shortness of breath, chest pain, and a rapid heart rate. These symptoms indicate an emergency situation, and cause sudden death in about one-third of the cases.

    Pulmonary emboli are a serious risk to older people, and are more likely to occur in those who have been immobilized for long periods; for example, in those recovering from leg or hip surgery.

    Pulmonary embolism can be fatal if not detected and treated quickly. Fortunately, treatment is life-saving in almost all cases. People who have sudden life-threatening symptoms of pulmonary embolism have a death rate of 30% if not treated promptly. With rapid diagnosis and treatment, mortality rates drop to only 3%.

    Click to enlarge: Pulmonary embolism

    Figure 01. Pulmonary embolism

    The vast majority of emboli are caused by blood clots that arise from veins in the legs. About 80% of emboli arise from leg veins, although they can also arise in other blood vessels. Under certain circumstances, blood tends to form clots in the deep veins, the larger veins located inside the leg (not the visible veins). This is a condition known as deep venous thrombosis. (Thrombosis is the formation of a blood clot, or thrombus. Once it has lodged in a blood vessel, it is referred to as an embolus.) Deep venous thrombosis tends to occur:

    • if circulation is slow, such as occurs with lack of activity
    • if there is an injury to the blood vessel, such as when a leg has broken, or following leg or hip surgery
    • if a blood vessel is inflamed or damaged
    • if blood tends to clot easily, as occurs with some hereditary conditions and in pregnant women and women taking birth control pills. Cancer also increases the risk of blood clots.

    Emboli can result from substances other than blood. Emboli can also arise from a piece of fat or bone marrow that has escaped from the inside of a fractured long bone. In very rare cases, a piece of a malignant tumor can break off, invade the bloodstream, and cause pulmonary embolism. Air emboli from catheters or IV drug use can also cause pulmonary embolism, as can emboli from parasite eggs (such as those in schistosomiasis), or from amniotic fluid released during labor.

    An embolus can cause part of the lung to die. An embolus can be large enough to cut off the blood supply to surrounding lung tissue. If the blood is stopped for long enough, the tissue in the area dies.The area of dead tissue is known as an infarction.

    Symptoms vary depending on the size of the blockage. Tiny emboli may cause no symptoms; however, large emboli can be life-threatening. Many people have no symptoms from a pulmonary embolus. A small blockage may not cause enough damage to affect lung function significantly.

    A large blockage, on the other hand, can cause:

    • shortness of breath
    • sharp, stabbing chest pain, which may worsen with breathing
    • rapid heart rate
    • coughing up blood or blood-streaked sputum
    • dizziness or fainting, caused by a sudden drop in blood pressure.

    Blood clots in the deep veins of the legs (deep vein thrombosis) can lead to pulmonary embolism. Therefore, it is important to recognize the symptoms of deep vein thrombosis, as treatment for this disease can prevent pulmonary embolism. Deep venous thrombosis often manifests as swelling and pain in the calf muscle. Pain increases with walking, when applying pressure to the leg muscles, or when pointing the toes and foot upward. Redness and a warm feeling may be apparent. If the thrombosis is in the thigh, a swollen leg may be the only sign. However, many patients will have no visible leg abnormalities.

    Pulmonary emboli affect approximately 5 out of 10,000 people in the US each year. Incidence increases with age and being overweight or obese.

    Prolonged inactivity is a major risk factor. Prolonged bedrest, such as occurs during hospitalization or recuperation, is a clear risk factor for pulmonary emboli. In hospital situations, patients deemed at high risk are often put on blood thinners as a precautionary measure, and patients are encouraged to walk around and increase activity as soon as possible. Inactivity, such as occurs during many hours of sitting in a car or airplane, also places individuals at risk. If you have to spend a lot of time sitting still during travel, try the following things to keep your blood moving:

    • periodically flex and relax your leg muscles
    • try to get up and walk around every half hour during long flights
    • if you are driving, make stops every hour or so to walk and stretch

    Injury or surgery to the legs or hips increases risk. People who are recovering from hip or knee replacements and those who have had a traumatic injury, such as a fracture of the hip or femur (long leg bone), are at high risk for pulmonary embolism. The long period of inactivity necessary for recuperation, as well as damage to the blood vessels, further increases the likelihood of clot formation. Doctors often place such patients on blood-thinning therapy as a precautionary measure.

    Some hereditary disorders make blood clotting more likely. Many components of the blood are involved in clot formation and breakdown. Some inherited conditions involve deficiencies or defects of such factors, making clots more likely to occur. For example, some people are resistant to a protein called activated protein C (factor V Leiden), which makes them more likely to develop blood clots and progress to pulmonary embolism.

    Some medications are associated with a risk for pulmonary embolism. Medications associated with a slightly higher-than-average risk for pulmonary embolism include:

    • oral contraceptives
    • hormone-replacement therapy
    • raloxifene (Evista), which is used for osteoporosis
    • tamoxifen (Nolvadex), which is used for cancer prevention and treatment.

    A few other conditions or situations are associated with a higher-than-average risk of pulmonary embolism.

    • Inflammatory bowel disease (such as Crohn’s disease or ulcerative colitis)
    • Prenancy and Childbirth
    • Cancer
    • Stroke
    • Heart disease
    • Heart surgery
    • Trauma to the legs
    • Inflammation of a vein
    • Asthma
    • Pneumonia
    • History of pulmonary embolism
    • Sickle cell disease
    • Lung disease
    • Drug use

    Pulmonary embolism can be difficult to diagnose. First, your doctor must suspect pulmonary embolism on the basis of your symptoms. Because pulmonary embolism is associated with many symptoms, it is easily confused with several other conditions, such as heart attack, pneumonia, congestive heart failure, or even panic attacks.

    Even if your doctor suspects pulmonary embolism, it is often difficult to detect. Several diagnostic tests are available. They include:

    • Assay for D-dimer. This blood test measures a substance that accumulates during blood clot formation. However, this test is not always conclusive, as high levels of D-dimer are typical in many hospitalized patients—especially if they have cancer or pneumonia or have had surgery. This test is most useful in an otherwise healthy person. A very low D-dimer test result indicates that a person does not have a blood clot.
    • V/Q (ventilation/perfusion) scan. This study compares the flow of air with the flow of blood through the lungs. Because an embolus affects bloodflow but not airflow, a scan of an embolus should reveal normal breathing but abnormal bloodflow. However, uncertain results are common, especially if the patient also has pneumonia or other lung diseases.
    • Computed tomography (CT) scan. CT scans provide a rapid and usually accurate diagnosis. However, this test may miss small emboli in smaller arteries. For this test, the doctor injects iodine dye—which is visible on x-rays—into a vein in your arm, and then you will lie very still inside a circular scanner for about an hour while the test takes place.
    • Pulmonary angiography. This test enables your doctor to see the flow of blood through the pulmonary arteries, and is the most definitive way to detect an embolism. However, it involves some risk to you, is expensive, and can only be done at larger medical centers. To perform pulmonary angiography, the doctor inserts a tube (catheter) into a large vein in the groin, and then threads it up through the vein into the right side of the heart, and then into the pulmonary arteries. He or she then injects an iodine dye, which is visible on x-rays, into the catheter. The dye is only visible in arteries through which blood is flowing, making a blockage easily detectable.

    Other tests may be given to rule out other possible causes of your symptoms. Other conditions, such as such as pneumonia, heart attack, asthma, or pulmonary hypertension, may produce symptoms similar to those of pulmonary embolism. Some of the tests used to detect or rule out these conditions include:

    • Arterial blood gas measurement. This procedure tests the amount of oxygen and carbon dioxide in your blood. You may have abnormal amounts of these gases if you have a pulmonary embolism; however, abnormal levels also occur with many other conditions.
    • Electrocardiogram (ECG). An ECG is a test of heart activity, and it may be abnormal if you have pulmonary embolism. An ECG can also help determine if you are having a heart attack.
    • Chest x-ray. An x-ray of the chest can indicate pulmonary embolism as well as other disorders, such as a collapsed lung or pneumonia.

    Doctors may concentrate on trying to diagnose deep venous thrombosis, as this condition is the most likely cause of pulmonary embolism. Tests for deep venous thrombosis include:

    • Doppler ultrasonography. This test has replaced venography in most hospitals because it is safer, less expensive, and noninvasive. Sound waves, rather than x-rays, are used to examine the veins to determine whether or not you have a blood clot. This test can provide a two- or three-dimensional computerized image and assess whether or not blood is flowing normally.
    • Magnetic resonance imaging. This study, also known as MRI, is noninvasive and especially useful in examining veins of the thigh and pelvis. For this study, you will lie in a tunnel inside a machine that uses a large, powerful magnet to create images of the inside of your body.
    • Venography. This test is performed by injecting dye into a vein on top of the foot. X-rays are then taken of the leg and pelvis, and a clot shows up as a dye-free area. Venography is painful. It can also occasionally cause phlebitis, a painful inflammation of the veins that sometimes leads to thrombosis. It is not generally performed unless other studies are inconclusive.

    Click to enlarge: Chest x-ray

    Figure 02. Chest x-ray

    If you are confined to bed, wear compression stockings to decrease the incidence of deep venous thrombosis. Compression stockings are available to promote circulation. They work by intermittently filling with air and squeezing the legs.

    Avoid long periods of immobilization. People traveling long distances should keep their legs uncrossed, stretch their legs often, and get up and walk around at least every hour.

  • Prevention and Screening

    If you are confined to bed, wear compression stockings to decrease the incidence of deep venous thrombosis. Compression stockings are available to promote circulation. They work by intermittently filling with air and squeezing the legs.

    Avoid long periods of immobilization. People traveling long distances should keep their legs uncrossed, stretch their legs often, and get up and walk around at least every hour.

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