Swiss Cheese Model
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The Swiss Cheese Model of accident causation is a way of thinking about how negative outcomes occur.

The model was developed in the business and aviation industries to help reduce negatives outcomes and produce better systems.

The Swiss Cheese Model basic principle

Imagine that each step in a process is like a slice of Swiss Cheese. It has holes in it. The holes mean that errors can be missed, and unintended consequences can result.

Errors and bad outcomes occur when the holes in the slices line up and allow an error to pass through at every step.

The more slices that you add (the more steps in your process, or the more safety nets that there are), the the less likely the error is to occur – because there are more slices to pass through. And, by improving your processes at each step, you can reduce the ‘size of the holes’ in the cheese.

Swiss Cheese Model in Medicine
Swiss Cheese Model

An error or negative outcome can almost always be traced to a whole multitude of factors, not just an individual mistake. In this way, we try to build systems within healthcare to minimise errors and negative outcomes. People (even doctors!) will always make mistakes. This doesn’t make them bad people, or bad doctors and doesn’t mean that we should blame them. Nobody goes to work to do a bad job. But we can build systems to try to ensure that when these mistakes happen, they are less likely to result in a negative outcome.

The negative outcome could have been prevented at any stage of the process if different processes had existed.


A medical example

Lets look at an example.

An 84 year old male nursing home resident falls over during the night and breaks his hip.

Negative outcome – broken hip. 

This is a very common scenario, and in no way am I trying to imply that these can always be prevented. Its just an example. This example could quite easily also take place on a geriatric ward.

He has a history of getting up in the night to go to the toilet. Usually he uses a 4 wheeled walker to mobilise, but this time he tried to go to the toilet unaided. He usually presses the buzzer when he wants to get up in the night to get help, but the buzzer was broken.

Last year he had a fall and broke his humerus which required an ORIF (open reduction and internal fixation) in theatre. Three years ago he broke his wrist in a fall when he was living at home. His GP was aware of these fractures, but hasn’t got around to organising investigations or treatment for osteoporosis.

For the past 2 days he has been getting increasingly confused and the staff at the nursing home thought his urine was a bit smelly, but the nurse on duty forgot to mention it to the doctor when he came to visit.

Over the last 24 hours his blood pressure has been dropping. His usual BP is about 160/95. It has shown a steady decline to 123/76 over the last 24 hours. His heart rate has also been increasing. His baseline is about 60, but when the nurse last checked it before bed, it was 89.

The Slices of Swiss Cheese

Lets look a the steps in the system where this could have been prevented.

  • GP could have started him on treatment for osteoporosis. (Caveat – treatment is probably not very effective)
  • Bedside buzzer was broken so help wasn’t sought for mobilising, and 4WW wasn’t used
  • Patient was confused – likely secondary to a UTI – but doctor was not informed, so he wasn’t assessed nor any treatment given
  • Observations show a trend towards sepsis / infection, but have not fallen outside ‘normal’ limits yet. So even with a good EWS (Early Warning Score) system in place, a review may not have been triggered. (Another caveat – Nursing homes might not have a formal monitoring or early warning score system in place)

Improving Systems

If we look at a deeper analysis we can look at the systems in place for each of the factors above and work out how to improve each of those systems:

  • Guidelines for the treatment of osteoporosis
  • Nursing home policies for broken equipment and when and how it should be fixed
  • Nursing home policy around when to call a doctor to review a patient
  • Nurse training around spotting patterns in observations

Each one of these processes is a ‘slice’ of the Swiss cheese. And when each step in the process failed, we passed through a ‘hole’ in the Swiss cheese – all the way to the end – to the broken hip.

The Swiss Cheese model can be applied not just to medical scenarios, but also as a way of interpreting negative outcomes and errors in almost any field.

For another medical example of the Swiss cheese model, read this case analysis on abdominal pain.

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Dr Tom Leach

Dr Tom Leach MBChB DCH EMCert(ACEM) FRACGP currently works as a GP and an Emergency Department CMO in Australia. He is also a Clinical Associate Lecturer at the Australian National University, and is studying for a Masters of Sports Medicine at the University of Queensland. After graduating from his medical degree at the University of Manchester in 2011, Tom completed his Foundation Training at Bolton Royal Hospital, before moving to Australia in 2013. He started almostadoctor whilst a third year medical student in 2009. Read full bio

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