Abstract
<jats:p>Background and importance Emergency Department (ED) crowding is an increasing public health concern, with evidence of harms to patients, the public and healthcare systems. When the number of patients requiring emergency care exceeds the capacity of EDs, operational decisions must be made regarding the best place of care for patients. It is not known if there is an association between place of escalation area care (for example 'ramping' in an ambulance, or in an ED corridor) and patient outcomes. Objective(s) This study aimed to assess the association between the relative proportion of all escalation area care that a site provided in an ambulance (the Ambulance:Escalation Index) and all-cause 28-day mortality. Design A secondary analysis of a prospective cohort study. Adult patients of 16 years or older, attending EDs in England, Wales and Northern Ireland in March 2025. Intervention or exposure (if any) The Ambulance:Escalation Index, a site-level indicator of the proportion of all time in escalation area care provided in an ambulance. Outcome measures and analysis The profile of site-level ambulance use was presented descriptively. Multivariable survival analysis was used to assess the primary outcome, all-cause 28-day mortality. Main results Of 131 EDs using escalation area, 82 (62.6%) used ambulances as a place of escalation area care. There was a significant association between a site's increasing use of ambulances as escalation areas and mortality; for each 5% increase in the proportion of a site's total escalation area care delivered in ambulances, there was a 2.1% increase in the hazard of death by 28 days (HR 1.021, 95% CI 1.002-1.041, p=0.032). Conclusion Emergency Department crowding is associated with poor outcomes irrespective of where departments are forced to deliver care; however this study suggests that there is excess mortality where escalation area care is more often delivered in ambulances.</jats:p>