A unified model of patient safety (or “Who froze my cheese?”)

Students of patient safety rely on a few foundational models to explain the iatrogenic causes of patient harm. Reason’s classic Swiss cheese model1 encapsulates the idea that although an organisation such as a hospital has many defences against error (the cheese), once in a while holes in the defences line up to allow an error through. Heinrich’s iceberg model reminds us that while some harm events are reported (the tip), most remain unrecorded because they are relatively minor or do not lead to harm (perhaps because, to mix metaphors, a bit of cheese luckily got in the way).2

We propose a generalised model of patient safety that unifies these two foundational models to create a more expansive theory for patient safety. This unified theory, we contend, can better explain the nature of patient harm and our responses to it.