A-a Gradient Is of Little Use in Evaluating for PE

Physicians are trained early to calculate the alveolar-arterial oxygen gradient when evaluating patients with potential pulmonary embolism. These American authors considered the measure's utility in a retrospective analysis of 152 ED patients who had pulmonary angiography for suspected PE during a four-year period. Of these patients, 56% had prior cardiopulmonary disease.

Fifty-nine patients (39%) had emboli confirmed. There was no significant difference between PE-positive and PE-negative patients in mean A-a oxygen gradient or PaO₂ regardless of cardiopulmonary history. Various combinations of A-a gradient, PaO₂, and PaCO₂ failed to exclude PE in at least 25% of patients with prior cardiopulmonary disease and in more than 35% with no such …