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

Objective: To assess the value of parameters derived from arterial blood gastests in the diagnosis of pulmonary embolism.Method: We measured alveolar-arterial partial pressure of oxygen [P(A-a)O2]gradient, PaO2 and arterial partial pressure of carbon diaxide (PaCO2) in 773consecutive patients with suspected pulmonary embolism who were enrolled inthe Prospective Investigative Study of Acute Pulmonary Embolism.Diagnosis: The study design required pulmonary angiography in all patientswith abnormal perfusion scans.Results: Of 773 scans, 270 were classified as normal/near-normal and 503 asabnormal. Pulmonary embolism was diagnosed by pulmonary angiography in 312of 503 patients with abnormal scans. Of 312 patients with pulmonary embolism,12, 14 and 35% had normal P(A-a)O2, PaO2 and PaCO2, respectively. Of 191patients with abnormal scans and negative angiograms, 11, 13 and 55% hadnormal P(A-a)O2, PaO2 and PaCO2, respectively. The proportions of patientswith normal/near-normal scans who had normal P(A-a)O2, PaO2 and PaCO2were 20, 25 and 37%, respectively. No differences were observed in the meanvalues of arterial blood gas data between patients with pulmonary embolism andthose who had abnormal scans and negative angiograms. Among the 773patients with suspected pulmonary embolism, 364 (47%) had priorcardiopulmonary disease. Pulmonary embolism was diagnosed in 151 (41%) of364 patients with prior cardiopulmonary disease, and in 161 (39%) of 409patients without prior cardiopulmonary disease. Among patients with pulmonaryembolism, there was no difference in arterial blood gas data between patientswith and those without prior CPD.Conclusion: These data indicate that arterial blood gas tests are of limited valuein the diagnostic work-up of pulmonary embolism if th