Alveolar-arterial oxygen gradients in elderly patients with suspected pulmonary embolism

To determine the usefulness of the alveolar-arterial oxygen gradient for detecting pulmonary embolism in elderly patients presenting to the emergency department.

Retrospective cohort analysis.

Two university-affiliated community hospitals.

Consecutive patients more than 64 years old who underwent pulmonary angiography for the presumed diagnosis of acute pulmonary embolism.

Arterial blood gas samples were chosen for comparative analysis only if obtained when the pulmonary embolism first was suspected clinically (before lung scans or angiograms) and the patient was breathing room air. Predicted PaO2 and alveolar-arterial gradients were calculated for each patient.

A total of 123 patients met all study criteria; mean +/- SD patient age was 74 +/- 6 years. Fifty-four patients (44%) had angiographically documented emboli. In this cohort, the mean PaO2 was 61.4 mm Hg (range, 34.3 to 83.8 mm Hg), and the mean alveolar-arterial gradient was 46.6 mm Hg (range, 19 to 75 mm Hg). In three patients, the alveolar-arterial gradient was normal for their age. However, in comparison with the 69 patients with normal pulmonary angiograms, there was no significant difference in PaO2 (mean, 59.9 mm Hg) or the alveolar-arterial gradient (mean, 46.0 mm Hg).

An elevated alveolar-arterial oxygen gradient is entirely nonspecific in the elderly population and is of minimal use in the diagnosis of acute pulmonary embolism. A normal alveolar-arterial gradient should not preclude further diagnostic procedures if there is a high index of suspicion.