Background/aim Simulation modelling has proven a useful approach for capturing the dynamic nature of emergency departments (EDs) and informing improvements to clinical and operational processes alike. However, few models have simulated the impact of the UK Department of Health's 4 h operational standard, which arguably has placed pressure to improve standards and performance, promoting the use of wait-reduction strategies to cope with the target in practice. The aim of this study was to determine the impact a re-prioritisation strategy has on the 4 h target by simulating the operation of an ED using a model that represents the flow of patients through the department.

Methods This study was based on a district general hospital in West London. To ascertain patients' length of stay, the hospital's historical records and staff rotas were used to obtain data on activities, timeframes and resources on three separate representative weeks and included all patients' arrival time, mode of arrival, whether the patient was referred to minors, majors, paediatrics or the resuscitation unit, and whether the patient was admitted or discharged, and at what time.

Results The close correlation (r=0.98) in distributions between actual length of stay and simulated length of stay demonstrates that the model of the ED accurately replicates the 4 h peak caused by the use of re-prioritisation.

Conclusion The model accurately reproduced the use of a dominant wait-reduction strategy to identify patients approaching the breach and re-prioritise them to expedite treatment and remove them from the department by the 4 h target.