A parsimonious discrete event simulation to evaluate interventions targeted at ED overcrowding and inpatient access block: a protocol

Health services around the world are struggling to manage increased demand for constrained emergency department (ED) and inpatient capacity. Many interventions that target ED overcrowding and access block have been implemented. The evaluation of these services is complicated by high risk of bias, but also that the main intervention effects are spillover effects, e.g., the main benefit of reducing ED presentations is for patients who continue to present at an ED. This protocol describes a simple discrete event simulation that is calibrated to represent the observed arrival and discharge of patients at and from an ED. The model inputs are then adjusted to reflect the counterfactual scenario in which the evaluated intervention was not implemented, reflecting expected increases in ED presentations and inpatient admissions or reduced availability of inpatient beds. Patient outcomes and costs are modelled as a function of time to discharge from the ED. The model provides a basis for generating meaningful and comparable outcomes for the wide range of potential interventions that could be implemented to target ED overcrowding and access block.