A local operational definition of pediatric emergency department overcrowding: an 8-year retrospective observational cohort study from the OACS+ project.

BACKGROUND: Emergency department (ED) overcrowding is increasingly observed worldwide and is associated with impaired care quality and patient outcomes. However, no universally accepted definition or measurement method exists. This challenge is particularly relevant in pediatric EDs (PEDs), where crowding is shaped by patient volume, staffing, local care structures, spatial capacity, and temporally fluctuating demand, including infectious surges. OBJECTIVE: This study aimed to derive a locally applicable operational definition of PED overcrowding reflecting the care structures and demand patterns of the University Hospital Augsburg (UKA) PED and supporting future validation, prediction, and intervention studies. METHODS: We conducted an 8-year retrospective cohort study (2017-2024) including 141,008 PED visits by children aged 0-18 years at UKA. Candidate parameters included patients leaving without being seen (LWBS), length of stay (LOS), time to triage, and patient-to-staff ratio (ps-ratio). Descriptive analyses covered 2017-2024, whereas ps-ratio analyses were restricted to 2020-2024, when nursing staffing data were available. Correlation analyses assessed bivariate relationships. ROC analyses derived local ps-ratio thresholds using daily LWBS events, operationalized as ≥1 and ≥2 events/day, as binary internal reference anchors. Time-series models examined temporal trends and lockdown-related shifts. RESULTS: The ps-ratio showed the strongest correlations with LOS (r = 0.612) and LWBS (r = 0.428). ROC analyses identified local ps-ratio thresholds between 2.03 and 2.20 patients per nurse, depending on the LWBS anchor and model specification. A rounded threshold of approximately 2.2 patients per nurse showed moderate and broadly stable discrimination (raw ≥ 1 LWBS/day: AUC = 0.73). Time-series modeling for 2020-2024 showed a nonlinear ps-ratio trend and a marked level shift during the COVID-19 lockdown period. PED demand was characterized by high self-referral rates, predominantly lower-acuity presentations, weekend and holiday clustering, and temporal fluctuations in visit volume. CONCLUSIONS: Locally derived operational definitions may improve interpretation of PED overcrowding by linking patient demand to staffing capacity and local care structures. In the OACS + cohort, the ps-ratio emerged as a staffing-sensitive, clinically interpretable operational marker. The proposed threshold should be considered a locally derived exploratory benchmark requiring external validation before application elsewhere.