Methodology for a rapid protocol to rule out pulmonary embolism in the emergency department

We propose an emergency department (ED) pulmonary embolism rule-out protocol based on pretest probability assessment coupled with either a negative D-dimer assay result or a negative D-dimer assay result plus a normal alveolar dead-space measurement. We examine the safety, efficiency, and feasibility of such a protocol, paying special attention to implicit and explicit strategies of pretest probability assessment among patients with suspected pulmonary embolism. Finally, we assess the potential effect of the proposed pulmonary embolism rule-out protocol on use of imaging resources and ED throughput.