Demand and capacity imbalance in the emergency department, and patient outcomes

Abstract

Background: An emergency department (ED) is always open and continuously needs to balance the inflow and demand for emergency service with available capacity. When demand exceeds the available capacity of an ED, it is referred to as crowding. Crowding is a critical concern for EDs worldwide, and there is evidence that it is associated with increased mortality, morbidity, and an unsustainable working environment. One of the most critical factors impacting crowding is the access to hospital beds at the right level of care to allow for a timely admission of patients. The long-term trend across the OECD countries is that the number of hospital beds per capita is declining. This development is mainly positive and driven by improvements in diagnostics and clinical care, resulting in more efficient use of resources. However, reducing hospital beds without a concurrent innovation that leads to a reduction in the demand for inpatient care will likely lead to an increased bed occupancy that could result in crowding and poor outcomes for patients.

Aims: This doctoral thesis aims to improve the knowledge of demand and capacity imbalance in the ED and how this impacts patient outcomes. More specifically 1. Is hospital bed occupancy associated with increased mortality? 2. Is hospital bed occupancy associated with crowding? 3. Is crowding associated with increased mortality?

Methods: The thesis includes four studies, three large retrospective cohort studies, analyzing around 2 million adult ED visits in each study using survival analysis. Hazard ratios are estimated using a cox proportional hazards model. The model is adjusted for potential confounding factors such as case-mix and arrival time. The model allows for differences between hospitals in the underlying risk, and seasonal trends are considered using calendar time as the underlying time scale. The remaining study is a descriptive study of the developments of crowding and key input, throughput, and output factors during the first wave of COVID-19 at a university hospital.

Results: Aim 1) Study I found no statistically significant association between hospital bed occupancy and 30-day mortality. Aim 2) In Study I, there was an association between bed occupancy and crowding. For each 10% increase in bed occupancy, the length of stay in the ED increased by 16 minutes for all patients and 28 minutes for admitted patients. In Study III, there was an association between emergency ward occupancy and crowding with an estimated correlation (95% CI) between mean ED LOS and mean emergency ward bed occupancy of 0.94 (0.55 – 0.99). Aim 3) Study II identified a statistically significant association between crowding and 30-day mortality with an estimated HR (95% CI) of 1.08 (1.03-1.14) in the high category of crowding, which included the top 5% of ED visits most exposed to crowding. The study included visits from Stockholm County during 2012-2016. Study IV used the same methodology but included visits to 14 EDs in four counties during 2015-2019. The results were mixed, and only Stockholm county had robust associations between crowding and mortality. Estimated HRs for 30-day mortality in Stockholm county in the subgroup analysis for admitted patients was 1.06 (1.01-1.12) in the moderate category and 1.11 (1.01-1.22) in the high. During the study period, the average hospital bed occupancy in Stockholm was 101% compared to 92% in Skåne and 81% in Östergötland.

Conclusions: A relative increase in hospital bed occupancy is not necessarily associated with increased mortality among patients seeking care at the ED. It is, however, associated with additional workload and increased crowding in the ED. The association between crowding and mortality varies by hospital, and there are statistically significant associations in some, but not all. Since the association is not universal, it may potentially be avoidable. An additional finding is that there are signs that a high hospital bed occupancy may modify and reinforce the association between crowding and mortality. If this would be the case, patients exposed to a combination of boarding and crowding may be at risk of poor outcomes. Investigating outcomes and mechanisms for this patient group should be a priority in future research.