Patient Prioritization in Emergency Department Triage Systems: An Empirical Study of the Canadian Triage and Acuity Scale (CTAS)

Emergency departments (EDs) typically use a triage system to classify patients into priority levels. However, most triage systems do not specify how exactly to route patients across and within the assigned triage levels. Therefore, decision makers in EDs often have to use their own discretion to route patients. Also, how patient waiting is perceived and accounted for in ED operations is not clearly understood. In this paper, using patient-level ED visit data, we structurally estimate the waiting cost structure of ED patients as perceived by the decision makers who make ED patient routing decisions. We derive policy implications and make suggestions for improving triage systems. We analyze the patient routing behaviors of ED decision makers in four EDs in the metro Vancouver, British Columbia, area. They all use the Canadian Triage and Acuity Scale, which has a wait time-related target service level objective. We propose a general discrete choice framework, consistent with queueing literature, as a tool to analyze prioritization behaviors in multiclass queues under mild assumptions. We find that the decision makers in all four EDs (1) apply a delay-dependent prioritization across different triage levels; (2) have a perceived marginal ED patient waiting cost that is best fit by a piece-wise linear concave function in wait time; (3) generally follow, in the same triage level, the first-come first-served principle, but their adherence to the principle decreases for patients who wait past a certain threshold; and (4) do not use patient complexity as a major criterion in prioritization decisions.