Pulmonary Embolism

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 [Page 1455]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.

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