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 (PaO 2 ), partial pressure of carbon dioxide (PaCO 2 ), 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 PaO 2 (mmHg), arterial oxygen saturation, %, A-a O 2 , PaCO 2 . In addition, no significant relationship was detected between arterial-blood gas parameters regarding PaO 2 and SaO 2 with pulmonary artery obstructive index; also PaCO 2 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.