The swiss cheese model: how small errors line up to big ones
human error human factors swiss cheese Oct 08, 2026
We have all had that moment in theatre where something small feels slightly off. A label that is a touch unclear, a drug drawn up a minute earlier than usual, a monitor alarm silenced just a fraction too quickly. On their own these things rarely cause harm. But patient safety experts have long understood that it is not the single slip that hurts patients, it is what happens when several small gaps line up at once.
This is the idea behind the Swiss cheese model of system safety. Every layer of defence in our workplace, whether it is a checklist, a double check, equipment design or simple human vigilance, has tiny holes. Most of the time those holes do not matter because another layer catches the problem. Trouble only occurs when the holes momentarily align, letting a hazard pass straight through every safeguard to reach the patient.
🧀 Holes exist in every system, even well run ones
🧀 Active failures are the slips and lapses happening in the moment
🧀 Latent conditions are the quieter background pressures, like fatigue, workload or unclear processes
🧀 Harm happens when gaps across different layers line up together
🧀 Reporting near misses helps the whole team find where the holes are forming
As an anaesthetic nurse, you are one of those protective layers. Your vigilance during drug checks, patient identification and intraoperative monitoring is often the very thing that stops small gaps elsewhere from aligning. Acting as a genuine second set of eyes for the anaesthetist, especially during induction and critical moments, is not extra diligence. It is the system working as intended.
Understanding this model helps us move away from blame and toward curiosity. When something nearly goes wrong, the useful question is never who slipped up, but which holes opened and how we can close them next time.
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References:
Reason, J. (2000). Human error: models and management. BMJ, 320(7237), 768-770.
Moloney, J. (2014). Error modelling in anaesthesia: slices of Swiss cheese or shavings of Parmesan. British Journal of Anaesthesia, 113(6), 905-906.
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