Diagnostic value of gas exchange tests in patients with clinical suspicionof pulmonary embolism

Objective: To assess the value of parameters derived from arterial blood ga s tests in the diagnosis of pulmonary embolism. Method: We measured alveolar-arterial partial pressure of oxygen [P(A-a) O- 2] gradient, PaO2 and arterial partial pressure of carbon diaxide (PaCO2) i n 773 consecutive patients with suspected pulmonary embolism who were enrol led in the Prospective Investigative Study of Acute Pulmonary Embolism. Diagnosis: The study design required pulmonary angiography in all patients with abnormal perfusion scans. Results: Of 773 scans, 270 were classified as normal/near-normal and 503 as abnormal. Pulmonary embolism was diagnosed by pulmonary angiography in 312 of 503 patients with abnormal scans. Of 312 patients with pulmonary emboli sm, 12, 14 and 35% had normal P(A-a)O-2, PaO2 and PaCO2, respectively. Of 1 91 patients with abnormal scans and negative angiograms, 11, 13 and 55% had normal P(A-a)O-2, PaO2 and PaCO2, respectively. The proportions of patient s with normal/near-normal scans who had normal P(A-a)O-2, PaO2 and PaCO2 we re 20, 25 and 37%, respectively. No differences were observed in the mean v alues of arterial blood gas data between patients with pulmonary embolism a nd those who had abnormal scans and negative angiograms. Among the 773 pati ents with suspected pulmonary embolism, 364 (47%) had prior cardiopulmonary disease. Pulmonary embolism was diagnosed in 151 (41%) of 364 patients wit h prior cardiopulmonary disease, and in 161 (39%) of 409 patients without p rior cardiopulmonary disease. Among patients with pulmonary embolism, there was no difference in arterial blood gas data between patients with and tho se without prior CPD. Conclusion: These data indicate that arterial blood gas tests are of limite d value in the diagnostic work-up of pulmonary embolism if they are not int erpreted in conjunction with clinical and other laboratory tests.