Process modeling of emergency department patient flow: effect of patient length of stay on ED diversion.

A discreet event simulation methodology has been used to establish a quantitative relationship between Emergency Department (ED) performance characteristics, such as percent of time on ambulance diversion and the number of patients in queue in the waiting room, and the upper limits of patient length of stay (LOS). A simulation process model of ED patient flow has been developed that took into account a significant difference between LOS distributions of patients discharged home and patients admitted into the hospital. Using simulation model it has been identified that ED diversion could be negligible (less than approximately 0.5%) if patients discharged home stay in ED not more than 5 h, and patients admitted into the hospital stay in ED not more than 6 h Using full factorial design of experiments with two factors and the model's predicted percent diversion as a response function, other combinations of LOS upper limits have been determined that would result in low ED percent diversion as well. It has also been determined that if the number of patients exceeds 11 in queue in ED waiting room then the diversion percent is rapidly increasing.