Managing emergency department overcrowding: analysis through a dynamic simulation model of the impact of organizational variables on emergency department processes.

Emergency department (ED) overcrowding is a major global healthcare challenge associated with increased mortality, prolonged waiting times, and inefficient use of hospital resources. Although ED crowding is commonly described through the input-throughput-output framework, the relative effectiveness of organizational interventions targeting each component remains uncertain. A hybrid dynamic simulation model integrating discrete-event simulation and agent-based modeling was developed to create a digital twin of the Emergency Department of a large university hospital in Northern Italy. The model was calibrated using real-world operational data and validated against observed process indicators. Alternative organizational scenarios targeting input, throughput, and output factors were simulated. Primary outcomes were time to first medical contact and overall ED length of stay. Diverting 12% of low-priority patients who did not require hospitalization produced modest improvements, reducing time to first medical contact by 14% and ED length of stay by 11.6%. Increasing diagnostic capacity through the addition of a second X-ray room showed negligible effects on ED performance. In contrast, eliminating the clinical workload associated with the management of "boarding" patients awaiting hospital admission resulted in substantially greater improvements, reducing time to first medical contact by approximately 70% and ED length of stay by about 50%. Interventions targeting the output phase of the ED process, particularly those addressing the organizational burden associated with boarding patients, have a substantially greater impact on reducing overcrowding than strategies focused on decreasing patient inflow or increasing diagnostic resources. Hospital-wide bed management strategies appear essential to effectively mitigate ED overcrowding.