Is Inpatient Volume Or Emergency Department Crowding A Greater Driver Of Ambulance Diversion?

Inpatient volume has long been believed to be a contributing factor to ambulance diversion, which can lead to delayed treatment and poorer outcomes. We examined the extent to which both daily inpatient and emergency department (ED) volumes at specified hospitals, and diversion levels (that is, the number of hours ambulances were diverted on a given day) at their nearest neighboring hospitals, were associated with diversion levels in the period 2005-12. We found that a 10 percent increase in patient volume was associated with a sevenfold greater increase in diversion hours when the volume increase occurred among inpatients (5 percent) versus ED visitors (0.7 percent). When the next-closest ED experienced mild, moderate, or severe diversion, the study hospital's diversion hours increased by 8 percent, 23 percent, and 44 percent, respectively. These findings suggest that efforts focused on managing inpatient volume and flow might reduce diversion more effectively than interventions focused only on ED dynamics.