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

Abstract

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. [Ann Emerg Med. 2003;42:266-275.]

Introduction

Emergency physicians are frequently faced with the challenge of excluding or diagnosing pulmonary embolism. Studies at academic emergency departments (EDs) in Charlotte, NC, Detroit and Royal Oak, MI, Phoenix, AZ, Toledo, OH, and St. Louis, MO,1, 2, 3 have shown that emergency physicians order a pulmonary vascular imaging study (either a scintillation ventilation-perfusion lung scan or a contrast-enhanced computed tomographic [CT] angiogram of the chest) on approximately 0.6% to 2.0% of all patients visiting the ED at these hospitals. If these data are generalized to the US population, between 500,000 and 2 million ED patients undergo a pulmonary vascular imaging study annually. The cost (in US dollars) to the hospital to perform a ventilation-perfusion or CT scan is $100 to $200 in Canada and $200 to $500 in the United States, and the charge to the patient is more than $1,000 for either test in the United States.4, 5, 6 Both tests expose the patient to ionizing radiation. A further limitation is that these tests might be available only at certain times and can require several hours to complete.

Accordingly, multiple investigators interested in pulmonary embolism have focused on the utility of sensitive, inexpensive, less invasive, and more rapid methods to rule out pulmonary embolism. This report examines the published data evaluating D -dimer measurement in conjunction with other criteria to exclude the diagnosis of pulmonary embolism. We suggest the adoption of 3 guiding principles for the pulmonary embolism rule-out strategy: safety, efficiency, and feasibility.