Imagine an emergency department struggling to cope with demand. Patients are waiting for treatment, and the department appears to need more space.
The solution seems obvious: add more treatment bays.
With more bays available, patients should be treated sooner and the department should work more efficiently. And, to some extent, that is exactly what happens.
But there is another question worth asking: what happens to patients when they no longer need a treatment bay but still cannot leave the emergency department?
That is where the picture becomes more complicated.
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When adding capacity improves one part of the system
To explore this question, I used the DFU simulation model developed as part of my research.
In the second experiment, I kept patient demand constant at 10 patients per hour and average treatment-bay occupancy at 90 minutes. I then ran 17 simulations, varying the number of treatment bays from 8 to 24 while keeping the other parameters and the random seed constant.
The results revealed an important distinction.
As the number of treatment bays increased, average length of stay decreased and bay occupancy fell. In other words, adding bays did improve the department’s performance on these measures.
So far, this is exactly what we might expect.
But the experiment also revealed something less obvious: more treatment bays did not eliminate congestion throughout the department.
As more patients moved through the treatment bays, more of them reached the next stage of their journey without sufficient space to continue. The corridor reached its maximum capacity in every configuration from 12 to 24 bays.
The additional capacity helped patients move through one part of the system, but it did not ensure that the rest of the system could accommodate them.
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Where do patients go when they leave the bay?
The third experiment explored this question from a different angle.
This time, I kept demand at 10 patients per hour, treatment-bay occupancy at 90 minutes and the number of treatment bays fixed at 16. I varied only the capacity of the observation area, from 12 to 20 beds.
Increasing observation capacity reduced average length of stay and the number of patients left outside designated areas because of overcrowding. However, bay occupancy increased slightly, and the corridor continued to reach its maximum capacity.
Once again, improving one part of the system produced benefits without resolving every capacity problem.
The two experiments are complementary, but they should not be confused with a single comparison. The first examined the effect of changing the number of treatment bays; the second examined the effect of changing observation capacity. Each isolated a different part of the system.
Together, they illustrate why the effects of an intervention depend on how the different stages of emergency care interact.
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The problem is not simply how many bays we have
None of this means that expanding treatment bays or observation areas is a mistake. Both interventions can improve performance, as the simulations demonstrate.
The question is whether the proposed expansion addresses the constraint that is limiting the system as a whole.
If treatment bays are the main bottleneck, adding bays may be an appropriate response. If patients cannot move into observation, transit or hospital admission, adding treatment bays alone may leave that constraint unresolved.
And if congestion persists in the corridor even after observation capacity increases, the analysis needs to go further. We need to understand what is preventing patients from progressing through the remaining stages.
For hospital architects and engineers, this changes the starting point for design.
Instead of asking only how many treatment bays an emergency department needs, we should also ask what happens before patients enter them, what happens while they occupy them, and where they go when they no longer need them.
The design must accommodate not just individual spaces, but the relationships between them.
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Designing for the entire patient journey
An emergency department is not a collection of independent rooms. It is a connected process through which patients must move.
Adding capacity at one point can improve performance. But if the following stages cannot accommodate the resulting flow, congestion may persist elsewhere.
The challenge is therefore not simply to provide more space. It is to understand where capacity is needed, how patients move between stages and what prevents that movement from continuing.
The right question is not just how many treatment bays an emergency department needs. It is whether the whole department has the capacity to keep patients moving.
Sources:
- → Asplin BR, Magid DJ, Rhodes KV, Solberg LI, Lurie N, Camargo CA Jr. A conceptual model of emergency department crowding. Annals of Emergency Medicine. 2003;42(2):173–180.
- → Morley C, Unwin M, Peterson GM, Stankovich J, Kinsman L. Emergency department crowding: A systematic review of causes, consequences and solutions. PLOS ONE. 2018;13(8).
About this research
This article draws on a four-month research project conducted as part of my Master’s Final Project in Hospital Engineering and Architecture at the University of Cádiz, Spain, which received a grade of 9.5/10.
The research examines demographic trends, hospital designs and functional plans, emergency care processes, and the perspectives of emergency department professionals gathered through surveys. It culminates in the development of a digital twin simulation model designed to explore multiple scenarios and analyse how different factors affect emergency department operational capacity.