pulmonary embolism (PE), the blockage of a pulmonary artery by fat, air, tumor tissue, or a thrombus that usually arises from a peripheral vein (most frequently one of the deep veins of the legs). Predisposing factors include an alteration of blood constituents with increased coagulation, damage to blood vessel walls, and stagnation or immobilization, especially when associated with pregnancy and childbirth, congestive heart failure, polycythemia, or surgery. Pulmonary embolism is difficult to distinguish from myocardial infarction and pneumonia. It is characterized by dyspnea, anxiety, sudden chest pain, shock, and cyanosis. Pulmonary infarction, which often occurs within 24 hours after the formation of a pulmonary embolus, is further characterized by pleural effusion, hemoptysis, leukocytosis, fever, tachycardia, atrial arrhythmias, and striking distension of the neck veins. Analysis of blood gases reveals arterial hypoxia and hypocapnia. Pulmonary embolism is detected by chest radiographic films, pulmonary angiography, and radioscanning of the lung fields. Two thirds of patients with a massive pulmonary embolus die within 2 hours. Initial resuscitative measures include external cardiac massage, oxygen, vasopressor drugs, embolectomy, and correction of acidosis. The formation of further emboli is prevented by the use of anticoagulants, sometimes the use of streptokinase or urokinase, and also surgical intervention. Ambulation, exercise, and use of sequential compression devices on the lower extremities also are recommended for prevention. A vena cava filter may be inserted if pulmonary emboli recur.
