Pulmonary Embolism And Infarction

The most common pulmonary complication in hospitalized patients, pulmonary embolism is an obstruction of the pulmonary arterial bed by a dislodged thrombus or foreign substance. It strikes an estimated 6 million adults each year in the United States, resulting in 100,000 deaths.

Although pulmonary infarction may be so mild as to be asymptomatic, massive embolism (more than 50% obstruction of pulmonary arterial circulation) and infarction can be rapidly fatal.

Causes

More than 90 percent of the blood clots that cause pulmonary embolism usually form in the deep veins of the legs, a condition called deep vein thrombosis. Although it is uncommon, an embolism can also form from fat that escapes from the bone marrow when a bone is fractured, or from amniotic fluid during childbirth.

Signs and symptoms

Total occlusion of the main pulmonary artery is rapidly fatal; smaller or fragmented emboli produce symptoms that vary with the size, number, and location of the emboli. Usually, the first symptom of pulmonary embolism is dyspnea, which may be accompanied by anginal or pleuritic chest pain.

Other clinical features include tachycardia, productive cough (sputum may be blood-tinged), low-grade fever, and pleural effusion. Less common signs include massive hemoptysis, splinting of the chest, leg edema and, with a large embolus, cyanosis, syncope, and distended neck veins.

In addition, pulmonary embolism may cause pleural friction rub and signs of circulatory collapse (weak, rapid pulse; hypotension) and hypoxia (rest-lessness).

Diagnosis

The patient history reveals any predisposing conditions for pulmonary embolism. The following diagnostic tests are also helpful:

• Chest X-ray helps to rule out other pulmonary diseases; it also shows areas of atelectasis, elevated diaphragm and pleural effusion, prominent pulmonary artery and, occasionally, the characteristic wedge-shaped infiltrate suggestive of pulmonary infarction.
• Lung scan shows perfusion defects in areas beyond occluded vessels; however, it doesn't rule out microemboli.
• Pulmonary angiography is the most definitive test but requires a skilled angiographer and radiologic equipment; it also poses some risk to the patient. Its use depends on the uncertainty of the diagnosis and the need to avoid unnecessary anticoagulant therapy in highrisk patients.
• Electrocardiography (EGG) is inconclusive but helps distinguish pulmonary embolism from myocardial infarction. In extensive embolism, the ECG may show right axis deviation; right bundlebranch block; tall, peaked P waves; depression of ST segments and T-wave inversions (indicating right heart strain); and supraventricular tachyarrhythmias.

If pleural effusion is present, thoracentesis may rule out empyema, which indicates pneumonia.

Treatment

In pulmonary embolism, treatment is designed to maintain adequate cardiovascular and pulmonary function during resolution of the obstruction and to prevent recurrence of embolic episodes.

Oxygen and anticoagulants

Because most emboli resolve within 10 to 14 days, treatment consists of oxygen therapy, as needed, and anticoagulation with heparin to inhibit new thrombus formation. Heparin therapy is monitored by daily coagulation studies (partial thromboplastin time [PTT]).

Drug therapy

Patients with massive pulmonary embolism and shock may need fibrinolytic therapy with urokinase, streptokinase, or alteplase to enhance fibrinolysis of the pulmonary emboli and remaining thrombi. Emboli that cause hypotension may require the use of vasopressors. Treatment of septic emboli requires antibiotics, not anticoagulants, and evaluation for the infection's source, particularly endocarditis.

Surgery

Interruption of the inferior vena cava is used for patients who can't take anticoagulants, who have recurrent emboli during anticoagulant therapy, or who have been treated with thrombolytic agents or pulmonary thromboendarterectomy.

Surgery (which shouldn't be done without angiographic evidence of pulmonary embolism) consists of vena cavalligation, plication, or insertion of a device (umbrella filter) to filter blood returning to the heart and lungs. To prevent postoperative venous thromboembolism, a combination of heparin and dihydroergotamine may be given.

Prevention

If you have any of the risk factors for pulmonary embolism, you can reduce the risk of developing this condition by taking drugs such as heparin, especially immediately before and after surgery. Leg exercises, elastic support stockings, and leg compression stockings can also help keep the blood moving in the legs, which will lower the risk of pulmonary embolism. See your doctor immediately if you have any signs of deep vein thrombosis or pulmonary embolism.