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Definition: pulmonary embolism from The Hutchinson Unabridged Encyclopedia with Atlas and Weather Guide

In medicine, condition in which a blood clot becomes lodged in the lungs. The clot usually migrates in the circulatory system from a vein in the lower abdomen or legs. The condition is characterized by a sudden pain in the chest. It can be fatal if the clot is large. Smaller clots can be removed surgically or dissolved by the use of fibrinolytic drugs.


Summary Article: Pulmonary Embolism
from Encyclopedia of Global Health

Pulmonary embolism (PE) is a common and potentially life-threatening disease that affects 0.5 to 1 per 1,000 people yearly. PE usually results from a blood clot that originates in the deep veins of the legs or pelvis and travels to the pulmonary vessels, where it becomes lodged and prevents proper blood flow to the lung tissue. This serious disease is among the more difficult to detect because of its vague and nonspecific symptoms.

Individuals with PE most commonly present with difficulty breathing (dyspnea) and/or chest pain, symptoms that can be caused by many different medical problems. Risk factor assessment may help physicians determine the likelihood of PE, but even patients without identifiable risk factors have been found with pulmonary emboli. Fortunately, anticoagulation treatment is highly effective at preventing death and disease recurrence when PE is detected early.

Pulmonary emboli result from venous thrombi (blood clots) that travel through the blood stream as emboli and lodge in the pulmonary vessels of the lungs. Thrombi that cause PE usually form in the deep veins of the legs or pelvis, and approximately half of people with documented deep vein thrombosis (DVT) are found to have a PE. Very large emboli may lodge at the bifurcation of the pulmonary arteries, forming what is known as a saddle embolus and leading to rapid circulatory failure or sudden death. Most emboli, however, lodge in smaller vessels and may lead to acute changes in respiratory and cardiovascular function.

Obstruction of the pulmonary arteries compromises respiratory function by elevating vascular resistance in the lungs and impairing gas exchange. Cardiac ischemia reduces right ventricular function which can then lead to decreased cardiac output.

Although DVT and, subsequently, PE can occur in anyone, there are factors that increase the likelihood of an event. Those that are most strongly associated with PE include major surgery, trauma, advanced age, history of prior PE or DVT, immobility, smoking, obesity, medical illness, cancer, and pregnancy.

PE is among the most difficult medical conditions to accurately diagnose because its symptoms are often vague and nonspecific. Sudden dyspnea at rest is the most frequent symptom, along with tachypnea (rapid breathing). Other symptoms include increased heart rate, sharp chest pain, low-grade fever, acute onset of cough, unexplained loss of consciousness, and hemoptysis (coughing up blood). Physicians must, therefore, have a high index of suspicion in patients that present with any of these vague symptoms.

A number of studies are available to aide in the diagnosis of a PE. In individuals who have a low probability of PE based on their risk factors, measurement of the plasma D-dimer concentration can be performed through a simple blood test. If the concentration is normal in these low-risk individuals, PE may be ruled out. If the concentration is elevated, or if the individual has risk factors that make having a PE more likely, further testing must be performed. Although chest X-rays and electrocardiograms are frequently taken, these tests rarely provide evidence to support the diagnosis of PE. Instead, they are helpful in identifying and ruling out other causes of chest pain.

The so-called gold standard test for detection of PE is contrast pulmonary angiography, a procedure in which a catheter is inserted into a central vein and passed through the heart to inject dye into the pulmonary arteries. The test is highly sensitive, but it is also expensive and carries significant risks. Because of these limitations, pulmonary angiography is not typically a first-line diagnostic tool. Ventilation-perfusion (V/Q) lung scanning using nuclear isotopes is less invasive and expensive than pulmonary angiography. V/Q scans detect areas of the lungs that are ventilated but not receiving blood and can be read as normal, low probability, indeterminate, and high probability. For low probability and indeterminate scans, the patient must undergo pulmonary angiography or high-resolution computed tomographic angiography (CTA) for a more definitive answer. CTA is also highly accurate, but patients receive significant doses of radiation during the scan.

Treatment for PE is immediate anticoagulation with subcutaneous low molecular weight heparins or intravenous unfractionated heparin. For individuals with signs of a serious PE, such as those with hypotension or cyanosis, thrombolytic therapy is often used. However, there are serious risks associated with the use of thrombolytics, including the risks of bleeding and intracranial hemorrhage.

Before leaving the hospital patients are then transitioned to warfarin, an oral blood thinner. It is suggested that patients with identifiable risk factors be anticoagulated for a minimum of three months, and that those without know risk factors be on anticoagulants for at least six months.

    SEE ALSO:
  • Angina; Fainting; Fever; Pulmonology.

BIBLIOGRAPHY
  • David Garcia; Walter Ageno; Edward Libby, “Update on the Diagnosis and Management of Pulmonary Embolism,” British Journal of Haematology (v.131/3, 2005).
  • J. Willis Hurst; Douglas C. Morris, Chest Pain (Futura, 2001).
  • Celina Martinez, M.D.
    Johns Hopkins University
    Copyright © 2008 by SAGE Publications, Inc.

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