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Investigators from the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) recently reported that 12 percent of patients with pulmonary embolism (PE) had a normal alveolar-arterial (A-a) oxygen gradient (see Journal Watch accession number 950131003). Now the authors have reanalyzed these data to determine whether the combination of a normal A-a gradient (20 mm Hg or less), normal PaO2 (80 mm Hg or more), and normal pCO2 (35 mm Hg or more) exclude PE more reliably than a normal A-a gradient alone.
The study population included 768 patients with suspected PE who underwent pulmonary angiography; PE was documented in 277. Twenty patients (7 percent) with PE had normal results on all three blood gas values. Overall, 70 patients (th…