Knowledge Translation of the PERC Rule for Suspected Pulmonary Embolism

A Blueprint for Reducing the Number of CT Pulmonary Angiograms

Michael J. Drescher, MD; Jeremy Fried, MD; Ryan Brass, MD; Amanda Medoro, MD; Timothy Murphy, MD; João Delgado, MD


Western J Emerg Med. 2017;18(6):1091-1097. 

In This Article

Abstract and Introduction


Introduction Computerized decision support decreases the number of computed tomography pulmonary angiograms (CTPA) for pulmonary embolism (PE) ordered in emergency departments, but it is not always well accepted by emergency physicians. We studied a department-endorsed, evidence-based clinical protocol that included the PE rule-out criteria (PERC) rule, multi-modal education using principles of knowledge translation (KT), and clinical decision support embedded in our order entry system, to decrease the number of unnecessary CTPA ordered.

Methods We performed a historically controlled observational before-after study for one year pre- and post-implementation of a departmentally-endorsed protocol. We included patients > 18 in whom providers suspected PE and who did not have a contraindication to CTPA. Providers entered clinical information into a diagnostic pathway via computerized order entry. Prior to protocol implementation, we provided education to ordering providers. The primary outcome measure was the number of CTPA ordered per 1,000 visits one year before vs. after implementation.

Results CTPA declined from 1,033 scans for 98,028 annual visits (10.53 per 1,000 patient visits (95% CI [9.9–11.2]) to 892 scans for 101,172 annual visits (8.81 per 1,000 patient visits (95% CI [8.3–9.4]) p<0.001. The absolute reduction in PACT ordered was 1.72 per 1,000 visits (a 16% reduction). Patient characteristics were similar for both periods.

Conclusion Knowledge translation clinical decision support using the PERC rule significantly reduced the number of CTPA ordered.


In recent years the pursuit of the diagnosis of pulmonary embolism (PE) has been the focus of much discussion in the medical literature. PE is common, difficult to diagnose, and potentially lethal if missed.[1] Computed tomography pulmonary angiogram (CTPA) is currently the preferred test to diagnose PE. However, excessive testing in the pursuit of the diagnosis of PE has long been an area of concern.[2]

To enable clinicians to confidently rule out PE while reducing the number of unnecessary CTPAs, several clinical rules have been developed and validated. These include the Wells criteria and the Pulmonary Embolism Rule-Out Criteria (PERC).[3,4] A low-probability Wells score, along with a negative D-dimer[5] or a negative PERC score, can rule out a PE with a high enough degree of certainty that the number of patients who would benefit from further testing to increase that certainty would be less than the number harmed by the side effects of the testing itself and the harmful consequences of false-positive results, including needless anticoagulation.[6] Despite clear evidence that the use of validated clinical rules can effectively be used to rule out the diagnosis of PE, anecdotally they are not universally or even commonly applied.

Previous studies have described the use of computerized clinical decision support (CDS) rules whereby clinicians are reminded of relevant clinical rules during the ordering process. However, the effectiveness of this approach has been inconsistent. Raja et al. reported success in reducing the number of CTPA ordered and increase in yield, whereas Drescher et al. reported that CDS was unsuccessful in reducing the number of CTPA ordered and was not accepted by the clinicians ordering the tests.[7,8] In the former study, some limited physician education was done prior to implementing the CDS, whereas in the latter none is described. In addition, these studies used CDS based on Wells criteria for risk assessment of PE along with the use of D-dimer testing. PERC is an established clinical rule by which low-risk patients can be safely ruled out for the diagnosis of PE without the use of any ancillary testing. Our CDS was designed to incorporate this validated clinical rule along with Wells criteria and D-dimer testing as needed. To our knowledge, this is the first reported incorporation of PERC into a computerized CDS system.

Knowledge translation (KT) is a field of endeavor defined by the Canadian Institutes of Health as "a dynamic and iterative process that includes the synthesis, dissemination, exchange and ethically sound application of knowledge to improve health, provide more effective health services and products, and strengthen the health care system."[9] This definition recognizes the fact that knowledge creation and dissemination is not sufficient to affect clinical care and decision-making. We designed an explicit KT-based educational process to accompany the introduction of our CDS tool. We hypothesized that the combination of a CDS tool, a targeted education effort, and regular feedback to providers on their utilization rates would reduce the number of unnecessary CTPA ordered.


Excessive use of CTPA in the emergency department (ED) is associated with risks and costs to patients and systems of care. Although the increased risk of cancer to an individual patient from a single CTPA is low, the stochastic effects of ionizing radiation from CTs increase the population incidence of neoplastic disease.[10] In addition, the use of CTPA involves contrast medium, which can be nephrotoxic and lead to allergic reactions. Severe, life-threatening reactions including anaphylaxis occur in 0.1% of people receiving contrast media.[11] Recently, an increase in major adverse advents associated with CT contrast-induced nephropathy has been reported.[12] Testing for PE also carries implications for cost, throughput, patient satisfaction and resource allocation, as well as the risks of long-term anticoagulation in patients with false-positive or clinically insignificant positive findings.

Goals of This Investigation

We hypothesized that a coordinated KT effort involving the adoption of a department-endorsed, evidence-based clinical protocol, a multi-modal educational program, and CDS embedded in our computerized order entry system, would lead to a decrease in the number of CTPA ordered.