Usefulness of noninvasive diagnostic tools for diagnosis of acute pulmonary embolism in patients with a normal chest radiograph.

The value of bedside examination and noninvasive tests in the diagnosis of acute pulmonary embolism (PE) among patients with a normal chest radiograph was investigated. Normal chest radiographs were present in 20 of 260 patients (8%) with acute PE and in 113 of 642 (18%) with suspected acute PE, in whom the diagnosis was excluded. A partial pressure of oxygen in arterial blood less than or equal to 70 mm Hg in a dyspneic patient with a normal chest radiograph was more often seen among patients with PE (9 of 17, 53%) than among patients in whom PE was excluded (18 of 93, 19%; p less than 0.01). However, no combinations of blood gases, signs and symptoms were strictly diagnostic. High probability ventilation/perfusion scans among patients with a normal chest radiograph were indicative of PE in only 6 of 9 patients (67%). Among patients with low-probability ventilation/perfusion scans, 8 of 47 (17%) had PE. This study showed that the combination of dyspnea and hypoxia in a patient with a normal chest radiograph is a useful clue to the diagnosis of PE. Although intuition suggested that ventilation/perfusion scans would yield better results in patients with a normal chest radiograph, the ability to diagnose PE by ventilation/perfusion scans in this subset of patients was not enhanced, except by a reduction of the percentage of patients with intermediate probability scans.