James Reason's Swiss Cheese Theory

James Reason's Swiss Cheese Theory

James Reason proposed the image of "Swiss cheese" to explain the occurrence of system failures, such as medical mishaps [1-2]. According to this metaphor, in a complex system, hazards are prevented from causing human losses by a series of barriers. Each barrier has unintended weaknesses, or holes - hence the similarity with Swiss cheese. These weaknesses are inconstant - i.e., the holes open and close at random. When by chance all holes are aligned, the hazard reaches the patient and causes harm. This model draws attention to the health care system, as opposed to the individual, and to randomness, as opposed to deliberate action, in the occurrence of medical errors. The Swiss cheese model is frequently referred to and widely accepted by patient safety professionals. This was summarised by safety expert Ronald Westrum in a testimony before a United States Advisory Committee on Blood Safety and Availability on April 25, 2000 [1]:

"Reason's model has become the common language through which complex accidents can be understood. I remember being at one conference where six speakers in a row got up and showed Swiss cheese diagrams as a kind of academic overkill. The popularity of this model obviously comes from its wide application. It's generally felt, as I said, this provides a common ground for discussing system safety."[3]

There is no clear evidence, however, that the Swiss cheese metaphor is understood in the same way by all concerned. In this study, I explored the understanding of the Swiss cheese model by professionals who work in healthcare quality improvement.

There was substantial variability among respondents as to what the various features of the model represent. The murkiest notion appeared to be the representation of the medical error itself. Few of the respondents recognised that an active error is a type of weakness in defences against patient harm within the health care system, represented by a hole in the Swiss cheese model (a "hole" is either an active or a latent error). The model is almost too successful in placing emphasis on systemic causes of patient harm, as opposed to an individual's failure.

The variability in interpretations revealed in this survey is more understandable if one considers the evolution of Reason's model between 1990 and 2000. In the first rendition of the model, what was predicted was an accident, latent errors were placed as antecedents of the accident trajectory at ...