Pulmonary Embolism

Pulmonary embolism is an obstruction of the pulmonary arterial bed that occurs when a mass - such as a dislodged thrombus -lodges in a pulmonary artery branch, partially or completely obstructing it. This causes a ventilation-perfusion mismatch, resulting in hypoxemia, as well as intrapulmonary shunting.

The prognosis varies. Although the pulmonary infarction that results from embolism may be so mild that it's asymptomatic, massive embolism (more than 50% obstruction of pulmonary arterial circulation) and infarction can cause rapid death.

Causes

In most patients, pulmonary embolism results from a dislodged thrombus (blood clot) that originates in the leg veins. More than half of such thrombi arise in the deep veins of the legs; usually multiple thrombi arise. Other, less common sources of thrombi include the pelvic, renal, and hepatic veins, the right side of the heart, and the upper extremities.

Rarely, pulmonary embolism results from other types of emboli, including bone, air, fat, amniotic fluid, tumor cells, or a foreign object, such as a needle, a catheter part, or talc (from drugs intended for oral administration that are injected I.V. by addicts).

The risk increases with long-term immobility, chronic pulmonary disease, heart failure or atrial fibrillation, thrombophlebitis, polycythemia vera, thrombocytosis, cardiac arrest, defibrillation, cardioversion, autoimmune hemolytic anemia, sickle cell disease, varicose veins, recent surgery, age over 40, osteomyelitis, pregnancy, lower-extremity fractures or surgery, burns, obesity, vascular injury, cancer, and oral contraceptive use.

Signs and Symptoms

• The following signs and symptoms may occur (in the order they are typically seen):

  • Chest pain: Pain is very sharp and stabbing in nature, has a sudden onset, and is worse when taking a deep breath (referred to as pleuritic chest pain).
  • Shortness of breath
  • Anxiety or apprehension
  • Cough: Usually, this cough is dry, but it may be associated with blood.
  • Sweating
  • Passing out

Diagnostic tests

Lung perfusion scan (lung scintiscan) can show a pulmonary embolus and ventilation scan (usually performed with a lung perfusion scan) confirms the diagnosis.

Pulmonary angiography may show a pulmonary vessel filling defect or an abrupt vessel ending, both of which indicate pulmonary embolism. Although this is the most definitive test, it's only used if the diagnosis can't be confirmed any other way and anticoagulant therapy would put the patient at significant risk.

Electrocardiography (ECG) helps to distinguish pulmonary embolism from myocardial infarction. If the patient has an extensive embolism the ECG shows right axis deviation, right bundle-branch block, tall peaked P waves, depressed ST segments. T-wave inversions (a sign of right ventricular heart strain), and supraventricular tachyarrhythmias.

Chest X-ray helps to rule out other pulmonary diseases, although it's inconclusive in the 1 to 2 hours after embolism. It may also show areas of atelectasis, an elevated diaphragm, pleural effusion, a prominent pulmonary artery and, occasionally, the characteristic wedge-shaped infiltrate that suggests pulmonary, infarction.

Arterial blood gas (ABG) analysis sometimes reveals decreased levels of the partial pressures of arterial oxygen and carbon dioxide from tachypnea.

Thoracentesis may rule out empyema, a sign of pneumonia, if the patient has pleural effusion.

Magnetic resonance imaging can identify blood flow changes that point to an embolus or identify the embolus itself.

Treatment

The goal of treatment is to maintain adequate cardiovascular and pulmonary function until the ob struction resolves and to prevent any recurrence. (Most emboli resolve within 10 to 14 days.)

Treatment for an embolism caused by a thrombus generally consists of oxygen therapy as needed and anticoagulation with heparin to inhibit new thrombus formation. The patient on heparin therapy needs daily or frequent coagulation studies (partial thromboplastin time). The patient may also receive warfarin for 3 to 6 months depending on his risk factors. This patient's prothrombin time should be monitored daily and then biweekly.

If the patient has a massive pulmonary embolism and shock, he may need fibrinolytic therapy with urokinase, streptokinase, or alteplase. Initially, these thrombolytic agents dissolve clots within 12 to 24 hours. Seven days later, these drugs lyse clots to the same degree as heparin therapy alone.

If the embolus causes hypotension, the patient may need a vasopressor. A septic embolus requires antibiotic therapy, not anticoagulants, and evaluation for the infection's source, most likely endocarditis.

If the patient can't take anticoagulants or develops recurrent emboli during anticoagulant therapy, surgery is needed. Surgery consists of vena caval ligation, plication, or insertion of a device (umbrella filter) to filter blood returning to the heart and lungs. Angiographic demonstration of pulmonary embolism should take place before surgery.

To prevent postoperative venous thromboembolism, the patient may require a vascular compression device applied to his legs. Or he can receive a combination of heparin and dihydroergotamine, which is more effective than heparin alone.

If the patient has a fat embolus, oxygen therapy is needed. He may also need mechanical ventilation, corticosteroids and, if pulmonary edema arises, diuretics.

Prevention

• stopping smoking
• maintaining a healthy weight for your height
• taking daily exercise.