Bathtubs and eggboxes – how to avoid common errors in fixing hospital flow
Managing patient flow in hospitals is one of the biggest challenges in healthcare. When hospitals reach capacity, it’s tempting to believe that adding more beds or expanding facilities will solve the problem. But this approach only delays the inevitable. To truly improve flow, hospitals need to address the underlying imbalance between the rate of patient admissions and discharges.
The eggbox and the bathtub
To understand hospital flow, two simple metaphors help to capture the problem: An overcrowded hospital is like an eggbox, moving eggs between slots doesn’t make the box less full. My emergency medicine colleague Rob Perry uses the metaphor of the bathtub: if a bathtub is filling up faster than it’s draining, a bigger bathtub only postpones the overflow. The key isn’t increasing the size of the tub—it’s increasing the rate at which water (or in this case, patients) flows out.
The variables of flow
Hospital flow boils down to three essential metrics: the number of people referred to the hospital (outside of the scope of this blog), the proportion of those who are admitted, and the time it takes from admission to discharge. If more patients are coming in than going out, the system will eventually overflow, regardless of how many beds the hospital has.
Why fragmented systems slow things down
Hospital flow is influenced by the complexity of the processes involved. Queuing theory—the mathematical study of waiting lines—reveals that the more steps are involved in a process, the slower it becomes. Having three people involved in a patient’s care instead of one increases delay exponentially. Similarly, "carve-outs"—special treatment paths for certain patient groups—create bottlenecks that slow down the entire system. Defining more groups of patients with specific needs, let’s say decreeing that patients with COPD require a chest ward, reduces flexibility and slows overall flow.
Another major issue is patient transfers between clinical areas. Transfers between clinical areas add between one and two days to the length of a hospital stay. The reasons for this are not entirely clear—it may be due to inefficiencies in communication, the need for each new clinical team to get familiar with a transferred patient, or simply logistical delays. Whatever the cause, it creates a measurable slowdown in patient flow.
What works: Effective strategies for better flow
There are two main ways to improve hospital flow: reducing the number of admissions and increasing the speed of progress in hospital.
Reducing admissions can be achieved through Same Day Emergency Care (SDEC), hot clinics, telephone appointments and consultant triage—where senior doctors assess patients at the front door—can all reduce the number of patients requiring admission.
Most patients in UK hospitals are elderly. Immobilisation is the greatest threat to their recovery. Prioritizing mobilisation speeds up recovery, reduces complications and shortens hospital stays.
Having consistent teams of clinicians working with the same patients over several days builds trust and improves decision-making speed. Research by Michael West shows that teams with clear goals and strong communication are more productive. We developed a model of care around this concept and the model for improvement. Defining explicit and specific goals for both the acute condition (i.e. can be discharged if heart rate < 120 bpm) and functional recovery (can go home if able to walk 15 meters to toilet) can help teams to prioritise what matters most to patients.
What doesn’t work: The "fudge" solutions
Many hospitals rely on quick fixes—known as "fudges"—to handle temporary surges in patient numbers. These include treating patients in corridors, moving them to discharge lounges, and reverse boarding. A consultant in a well-organised emergency department might see 25 patients per session; in a crowded department, that number can drop to 8–10, leading to fewer discharges and increased backlogs. Discharge lounges don’t solve the problem. Unless the cost of operating a discharge lounge is much lower than the cost of keeping a patient on a ward, there is no overall benefit. Reverse boarding and moving patients to different areas disrupts established workflows and reduces efficiency.
While these strategies may create the illusion of increased capacity, they don’t solve the core problem of flow. Importantly they add no value to a patient’s journey and dramatically increase expensive waste and inefficiencies. Moving eggs between slots in an egg-box does not make the egg box less full.
The true cost of poor flow
The biggest hidden cost of poor flow is the impact on staff morale and productivity. NHS staff care deeply about patient safety and professional autonomy, and working in an overcrowded, chaotic environment undermines both. Disillusioned staff are less productive, which further reduces discharge rates and compounds the problem.
Building a sustainable flow strategy
The key to solving hospital flow issues lies in systematic, evidence-based management of patient intake and progress. Simulation through mathematical models or games can help to understand the problem and test solutions.
Improving hospital flow requires a focus on strategies that increase progress of individual patients and patient groups and reduce unnecessary admissions.
Investing in SDEC, early mobilisation, and standardised pathways delivers real results. Strong team communication, clear progress criteria, and trust between staff and patients are the critical facilitators.
