Discrete event simulation of emergency department activity: A platform for system-level operations research

Objectives: This article explores the potential of discrete event simulation (DES) methods to advance system-level investigation of emergency department (ED) operations. To this end, the authors describe the development and operation of Emergency Department SIMulation (EDSIM), a new platform for computer simulation of ED activity at a Level 1 trauma center. The authors also demonstrate one potential application of EDSIM by using simulated ED activity to compare two patient triage methods. Methods: The Extend DES modeling package was used to develop a model of ED activity for a five-day period in July 2003. Model input includes staffing levels, facility characteristics, and patient data drawn from electronic patient tracking databases, billing records, and a detailed review of 674 ED charts. The accuracy of model output was tested by comparing predicted and known patient service times. The EDSIM model,vas then used to compare the fast-track triage approach with an alternative acuity ratio triage (ART) approach whereby patients were assigned to staff on an acuity ratio basis. Results: The EDSIM model predicts average patient service times within 10% of actual values. The accuracy of individual patient paths, however, was variable. In the authors' model, 28% of individual patient treatment times had an absolute error of less than one hour, and 59% less than three hours. A preliminary comparison of two triage methods showed that the ART approach reduced imaging bottlenecks and average treatment times for high-acuity patients, but resulted in an overall increase in average service time for low-acuity patients. Conclusions: The EDSIM model provides a flexible platform for studying ED operations as they relate to average treatment times for ED patients, but the model will require further refinement to predict individual patient times. A comparative study of triage methods suggests that ART provides a mix of benefits and drawbacks, but further investigation will be required to substantiate these preliminary findings.