Differentiating properties of occupancy rate and workload to estimate crowding: A Swedish national cross-sectional study

Background Emergency department (ED) crowding causes increased patient morbidity and mortality. ED occupancy rate (OR; patients by treatment beds) is a common measure of crowding, but the comparability of ORs between EDs is unknown. The objective of this investigation was to investigate differences in ORs between EDs using staff-perceived workload as reference. Methods This was a national cross-sectional study in Sweden. EDs provided data on census, treatment beds, staffing, and workload (1-6) at 5 time points. A baseline patient turnover was calculated as the average daily census by treatment beds, denoted turnover per treatment bed (TTB), for each ED. A census ratio (CR), current by daily census, was calculated to adjust for differences in the number of treatment beds. Results Data were returned from 37 (51%) EDs. TTB varied considerably (mean = 4, standard deviation = 1.6; range, 2.1-9.2), and the OR was higher in EDs with TTB >4 compared with <= 4, 0.86 versus 0.43 (0.43; 95% confidence interval [CI], 0.27-0.59), but not workload, 2.75 versus 2.52 (0.23; 95% CI, -0.19 to 0.64). After adjusting for confounders, both TTB (k = -0.3; 95% CI, -0.49 to -0.14) and OR (k = 3.4; 95% CI, 1.76-5.03) affected workload. Correlation with workload was better for CR than for OR (r = 0.75 vs 0.60, respectively). Conclusion OR is affected by patient-to-treatment bed ratios that differ significantly between EDs and should be accounted for when measuring crowding. CR is not affected by baseline treatment beds and is a better comparable measure of crowding compared with OR in this national comparator study.