DIAGNOSTIC VALUE OF GAS EXCHANGE TESTS IN PATIENTS WITH CLINICAL SUSPICION OF PULMONARY EMBOLISM.

Prediletto R, et al. Crit Care (Lond) 1999;3(4):111-116.

OBJECTIVE: To assess the value of parameters derived from arterial blood gas tests 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 dioxide (PaCO2) in 773 consecutive patients with suspected pulmonary embolism who were enrolled 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 embolism, 12, 14 and 35% had normal P(A-a)O2, PaO2 and PaCO2, respectively. Of 191 patients with abnormal scans and negative angiograms, 11, 13 and 55% had normal P(A-a)O2, PaO2 and PaCO2, respectively. The proportions of patients with normal/near-normal scans who had normal P(A-a)O2, PaO2 and PaCO2 were 20, 25 and 37%, respectively. No differences were observed in the mean values of arterial blood gas data between patients with pulmonary embolism and those who had abnormal scans and negative angiograms. Among the 773 patients with suspected pulmonary embolism, 364 (47%) had prior cardiopulmonary disease. Pulmonary embolism was diagnosed in 151 (41%) of 364 patients with prior cardiopulmonary disease, and in 161 (39%) of 409 patients without prior cardiopulmonary disease. Among patients with pulmonary embolism, there was no difference in arterial blood gas data between patients with and those without prior CPD.

CONCLUSION: These data indicate that arterial blood gas tests are of limited value in the diagnostic work-up of pulmonary embolism if they are not interpreted in conjunction with clinical and other laboratory tests.

ARTERIAL BLOOD GAS ANALYSIS IN THE ASSESSMENT OF SUSPECTED ACUTE PULMONARY EMBOLISM.

Stein PD, et al. Chest 1996 Jan;109(1):78-81.

PURPOSE: The utility of arterial blood gas levels in excluding the diagnosis of acute pulmonary embolism (PE) was evaluated.

METHODS: Data are from the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED). PE was diagnosed or excluded by pulmonary angiography. Among 330 patients with no prior cardiopulmonary disease, 130 patients had PE and 200 did not. Among 438 patients with prior cardiopulmonary disease, 147 had PE and 291 did not. Definitions were low PaO2 (< 80 mm Hg), low PaCO2 (< 35 mm Hg), and high alveolar-arterial oxygen gradient (P(A-a)O2 [> 20 mm Hg]).

RESULTS: Among patients with no prior cardiopulmonary disease who had values of the PaO2 and PaCO2 that were not low and a P(A-a)O2 that was normal, 16 of 42 or 38% (95% confidence interval [CI] = 24 to 54%) had PE. Among patients with prior cardiopulmonary disease who had PaO2 and PaCO2 values that were not low and a P(A-a)O2 that was normal, 4 of 28 or 14% (95% CI = 4 to 33%) had PE. Other combinations of blood gas levels and the P(A-a)O2 gradient, failed to exclude PE in larger percentages of patients.

CONCLUSION: With various combinations of the PaO2 of 80 mm Hg or more, the PaCO2 of 35 mm Hg or higher, and the P(A-a)O2 gradient of 20 mm Hg or less, PE could not be excluded in more than 30% of patients with no prior cardiopulmonary disease and PE could not be excluded in more than 14% of patients with prior cardiopulmonary disease. Blood gas levels, therefore, are of insufficient discriminant value to permit exclusion of the diagnosis of PE.