The diagnosis of pulmonary embolism.

Objective documentation of pulmonary embolism is an essential prerequisite for appropriate treatment (Figure 7). A chest film, as well as measurement of arterial blood gases, should be obtained immediately, and if the lung fields are essentially normal, a lung scan should then be performed. If the scan shows a definite perfusion defect characteristic of embolism, this provides sufficient evidence to establish a diagnosis of pulmonary embolism. The presence of hypoxemia with a low arterial pO2, further confirms the suspicion of a ventilation-perfusion abnormality, and anticoagulant therapy with heparin should be initiated immediately. Should the chest film show abnormalities in the same anatomic areas in which perfusion defects are present on the scan, further investigation by pulmonary arteriography is required to substantiate the diagnosis. The use of pulmonary angiography for documentation of pulmonary embolism is also indicated at the outset when certain specific disorders that confuse scan interpretation are also present-chronic obstructive lung disease, emphysema, asthma, congestive cardiac failure. Assessment of the arterial blood oxygenation simultaneously with the estimated occlusion and the hemodynamic data can be used as a prognostic index as therapy progresses.