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One appealing approach to mitigating human errors is the one proposed by James Reason [Ref. 1]. Generally referred to as the "Swiss cheese" model of human error trapping, he describes four levels of human failure, with each level influencing the next (seen in Figure 1). These failures are likened to holes in a Swiss cheese. Working backwards in time from the adverse event, the first level depicts those "unsafe acts" that ultimately led to the mishap.
This level generates the most investigation and, consequently, is the level where most causal factors are uncovered. After all, it is typically the actions or lack thereof that are directly linked to the adverse event. For instance, failing to properly administer a medication may yield grave consequences, as in the recent death in a California hospital where a nurse gave a cancer patient an enteral solution intravenously instead of through a feeding tube [Ref. 2]. Represented as "holes" in the Swiss cheese model, these active failures are typically the last unsafe acts committed by caregivers.
What makes the "Swiss cheese" model particularly useful in investigating adverse events is that it forces investigators to address latent failures within the causal sequence of events. The latent failures are also "holes," but in different slices of cheese. As their name suggests, latent failures, unlike their active counterparts, may lie dormant or undetected for hours, days, weeks or even longer, until one day, they adversely affect the unsuspecting caregiver. Consequently, they may be overlooked by investigators — even those with the best intentions.
Within this concept of latent failures, Reason described three more levels of human failure. The first involves the condition of the caregiver as it affects performance. Referred to as preconditions for unsafe acts, this level involves conditions such as mental fatigue, poor communication and coordination practices, and frequent interruptions. Not surprising, if fatigued caregivers fail to communicate and coordinate their activities, poor decisions are made and errors often result.
Figure 1 — The "Swiss Cheese" Model of Human Error Causation [Ref. 3].
But why do communication and coordination break down in the first place? In many instances, the breakdown in good practices can be traced back to instances of unsafe supervision, the next level of human failure. If, for example, inexperienced caregivers are unfamiliar with certain tasks, such as medication delivery and dosing, or lack experience with utilizing medical equipment — from ventilators to laboratory machines — errors from lack of sufficient supervision are prone to happen. To make matters worse, the lack of quality assurance audits, support system, training and availability of qualified personnel can increase the potential for more errors. In a sense, these caregivers were "set up" for failure.
Reason's model doesn't stop at the supervisory level; the organization itself can impact performance at all levels. For instance, in times of fiscal austerity, funding is often cut and as a result, training is curtailed and work load becomes excessive. Not surprisingly, failures will begin to appear, all of which will affect performance and errors. Therefore, it makes sense that if the adverse events are to be prevented, they must be analyzed in entirety and foreseen beyond the caregiver. Ultimately, causal factors at all levels within the organization must be addressed if any prevention system is going to succeed. One needs to know what these system failures or "holes" are, so that they can be identified during investigations or, better yet, detected and corrected before an adverse event occurs.
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