Can alveolar-arterial oxygen gradient predict severity of pulmonary embolism?

Background The perceived risk for pulmonary embolism (PE) can be assessed by oxygenation and calculation of the alveolar-arterial (A-a) oxygen (O-2) gradient. We attempt to evaluate the efficacy of A-a O-2 gradient for the diagnosis of PE and if it can predict the degree of severity of PE. Patient and methods This study is a prospective study conducted on 70 patients presented by signs or symptoms of suspected acute PE. Arterial-blood gases including arterial partial pressure of oxygen (PaO2), partial pressure of carbon dioxide (PaCO2), and arterial oxygen saturation (SaO(2)) and computed tomography pulmonary angiography were done on admission. Results Fifty patients proved to have PE by computed tomography pulmonary angiography. The patients were divided into (a) nonhigh-risk and (b) high-risk groups. There was a significant difference between the two groups regarding pulmonary artery obstructive index. Although A-a gradients were high in all studied patients with positive PE in comparison to negative PE patients, there was no significant difference between high-risk and nonhigh-risk groups regarding PaO2 (mmHg), arterial oxygen saturation, %, A-a O-2, PaCO2. In addition, no significant relationship was detected between arterial-blood gas parameters regarding PaO2 and SaO(2) with pulmonary artery obstructive index; also PaCO2 and A-a O-2 gradients were nonsignificant. Conclusion The A-a O-2 gradient values are clinically important in the diagnosis of patients with PE because it is easy to perform and is a bedside test. However, it may be incapable of detection of severity of PE.