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Pulmonary Embolism

Pulmonary embolism is usually caused by an embolism from a thrombosis in the larger veins above the knee. A deep venous thrombosis can be found in at least 80% of cases of pulmonary emboli.

Risk Factors For Pulmonary Embolism

Venous Stasis. Prolonged immobilization, stroke, myocardial infarction, heart failure, obesity, varicose veins, anesthesia,

Endothelial Injury. Surgery, trauma, central venous access catheters, pacemaker wires, previous

Hypercoagulable State. Malignant disease, high estrogen level (oral contraceptives).

Hematologic Disorders. Polycythemia, leukocytosis, thrombocytosis, antithrombin III deficiency, protein C deficiency, protein S deficiency, antiphospholipid syndrome, inflammatory bowel disease.

Diagnosis of Pulmonary Embolism

Signs and Symptoms of Pulmonary Embolism. Pleuritic chest pain, shortness of breath, tachycardia, hypoxemia, hypotension, hemoptysis, cough, syncope.

Classic triad of dyspnea, chest pain, and hemoptysis is seen in 20% of patients; the majority of patients have only a few subtle or ambiguous symptoms. Most pulmonary emboli are

A deep venous thrombosis may be indicated by an edematous limb with an erythrocyanotic appearance, dilated superficial veins, and elevated skin temperature.

The best diagnostic approach to pulmonary embolism is to search for an alternative diagnosis that can be more readily proved. If this is accomplished, the workup for pulmonary embolism can be ended. However, if no other satisfactory explanation can be found in a patient with findings suggestive of, the workup must be pursued to completion.

Diagnostic Evaluation

Chest Films are nonspecific and insensitive for pulmonary embolism. The chest film may be normal, or it may show an ele vated hemidiaphragm, focal infiltrates, large or small pleural effu sions, or atelectasis.

Electrocardiogram abnormalities are nonspecific. The tracing is often normal; the most commonly seen abnormality is sinus tachycardia. Occasionally, acute right ventricular strain causes tall and peaked P waves in lead II, right axis deviation, right bundle branch block, a classic S1-Q3-T pattern, or atrial fibrillation.

Blood Gas Studies

There is no level of arterial oxygen that can rule out pulmonary embolism. Most patients with pulmonary embolism have a normal arterial oxygen. Impaired gas exchange is best assessed by using the room air, alveolar-to-arterial (A-a)oxygen gradient:

A-a oxygen gradient = 147 - [ 1.2 (PCO2) + measured pAO2]

A normal gradient should be no higher than 10 plus one tenth of the patient's age.

A normal A-a oxygen gradient is seen in 5-15% of patients with pulmonary emboli but is inconsistent with massive pulmonary embolism and hypotension. An elevated gradient is nonspe cific and may be produced by almost any pulmonary disease.

Ventilation-perfusion Scan: Virtually all patients suspected of having pulmonary emboli need a V/Q scan. Unfortunately, the V/Q scan is most often nondiagnostic; patterns other than "normal" and "high-probability" are nondiagnostic. Pulmonary angiography is necessary when the V/Q scan is nondiagnostic.

Venous Imaging

If the V/Q scan is nondiagnostic, a workup for deep venous thrombosis (DVT) should be pursued using duplex ultrasound and impedance plethysmography. The identification of DVT in a patient with signs and symptoms suggesting pulmonary embolism proves the diagnosis of pulmonary embolism.

Inability to demonstrate a source of DVT does not significantly lower the likelihood of pulmonary embolism because clinically asymptomatic DVT may not be detectable.

Patients with a nondiagnostic V/Q scan and no demonstrable site of DVT should proceed to pulmonary angiography.


Contrast pulmonary arteriography is the "gold standard" for the diagnosis of pulmonary embolism, with unmatched sensitivity and specificity.

False-negative results occur in