A patient finishes the examination and treatment that required a treatment bay. The bay can now be used for someone else.
But there is a problem: the patient is not ready to leave the emergency department.
Perhaps a further step in the care process is still pending. Perhaps the patient needs to wait for a decision, a transfer or the arrangements that will allow their departure. Whatever the reason, the patient must remain somewhere.
Where should they go?
It is a simple question, but it exposes a gap in how we think about emergency department capacity. We tend to count treatment bays, observation beds and other designated spaces. Yet patients do not always move neatly from one area to the next, and not every patient who leaves a treatment bay is ready to leave the department.
Leaving the treatment bay does not necessarily mean that the patient’s journey through the emergency department is over.
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When the treatment bay is no longer the right place
A treatment bay serves a particular purpose. It provides a space for clinical assessment, examination and treatment.
But the patient’s needs can change as care progresses. At some point, the patient may no longer need to occupy that bay, even though the next stage of the process has not yet been completed.
Keeping the patient in the bay may prevent another patient from using it. Moving the patient, however, requires somewhere appropriate for them to go.
Observation may be necessary for some patients, while others may need a different kind of temporary location while they await the next step. Patients waiting for hospital admission introduce another situation: they may remain in the emergency department because an inpatient bed is not yet available.
These circumstances are not identical. In particular, the concept explored here should not be confused with hospital boarding, which commonly refers to patients who require admission but remain in the emergency department while waiting for an inpatient bed.
The broader issue is what happens whenever a patient has left the treatment bay but must continue to remain within the department’s care process.
In the DFU model developed as part of my research, I examined this situation through the concept of the patient in transit: a patient who has left the treatment bay but has not yet completed their journey through the emergency department.
The question then becomes architectural as much as operational. If the patient no longer needs a treatment bay, but still needs a place within the service, has the department been designed to accommodate that stage?
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What happens when there is nowhere to go?
To explore this problem, I used the eighth experiment in the DFU simulation model.
The experiment maintained 16 treatment bays, demand of 10 patients per hour, an average bay occupancy time of 90 minutes, 12 observation places, 20 inpatient beds and 15 corridor places.
Over the 24-hour simulation horizon, 44 patients left a treatment bay but continued within the care process. Of these, 23 passed through the corridor.
In the longer simulation horizons, the number of patients who left the treatment bay but remained within the process reached 47, with 23 passing through the corridor.
These are results from a simulated model, not observations from a real hospital. They illustrate how patients can continue to require space after leaving a treatment bay, and how the corridor can become part of that journey when the system’s designated spaces do not accommodate the flow as intended.
The figures also raise an important question: what does it mean when a corridor becomes part of the patient pathway?
A corridor is designed primarily to allow movement between spaces. When patients begin to use it as a place to wait, the space is serving a function different from its intended purpose. That can affect circulation and interfere with the movement of other patients and staff.
The issue is therefore not simply where to put a patient who has left a bay. It is whether the department has a suitable place for that stage of the care process.
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Designing for the stage between treatment and departure
This question led to one of the proposals developed in my Master’s Final Project: a clinical transit room.
The idea is to provide a designated space for patients who no longer need to occupy a treatment bay but must remain temporarily within the emergency department while their care process continues.
This would not be another treatment bay under a different name, nor would it automatically replace an observation area. Its purpose would be to address a different functional need: accommodating patients during the transition between the treatment-bay phase and the next step in their journey.
The distinction matters because the different spaces in an emergency department should respond to different patient needs. Observation, treatment and transit are not interchangeable functions. Their precise roles, staffing requirements and suitability for particular patients would need to be defined through clinical and operational planning.
The simulation experiment does not establish that a clinical transit room will, by itself, reduce overcrowding or improve clinical outcomes. That would require further assessment, including the definition of the room’s intended use and evaluation of how it would operate within a real department.
What the experiment does provide is a reason to examine a stage of the patient journey that can otherwise be overlooked when capacity is assessed primarily through the number of treatment bays and observation places.
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A space is only useful if it fits the process
For hospital architects and engineers, this changes the design question.
It is not enough to ask how many treatment bays an emergency department needs, or how many observation beds it should contain. We must also understand what happens when patients no longer need one space but cannot yet move to the next.
That requires connecting three things that are often considered separately: the actual care process, the movement of patients through the department and the architectural spaces intended to support that movement.
When these elements do not fit together, staff may have to improvise. Patients may end up in areas not designed for waiting, and spaces intended to support circulation may become occupied by patients who have nowhere else to go.
A well-designed emergency department should anticipate these transitions rather than leave them to be resolved after the building is in use.
The patient journey does not end when the treatment bay becomes available. Hospital design must also provide for the stages that connect treatment with departure.
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.