Model of Event Evolution

The findings just discussed, as well as the larger system issues raised by Reason and Perrow, can be summarized in a model of event evolution ( Fig. 83-3 ).^{[64] [65] [66] [67] [68] [69] [70] [71] [72] [73] [74] [75] [76] [200]}

Similar models incorporating some of the same features have also been described.^{[201] [202] [203]} Underlying aspects of the system can generate latent failures. Either by random chance or because of interactions between the latent failures, an event may be triggered in one of four components of the operational system in the OR: the anesthetist, the surgeon, the patient, or the equipment. Anesthetists have traditionally been most interested in events they triggered themselves (such as esophageal intubation), but, in fact, most events are initiated by a combination of underlying patient disease and another of the triggering factors. Most

Figure 83-3 Chain of accident evolution in anesthesia. As in Reason's model (see Fig. 83-13 ), underlying latent failures (and the organizational culture) predispose to the triggering of an accident sequence by equipment, the patient, the surgeon, the anesthesiologist, and other personnel. This sequence can be prevented by prophylactic measures such as preoperative evaluation and treatment of patient diseases or pre-use checkout of life support equipment. Once a problem occurs, it may remain self-limited or it may evolve further down the accident chain. Using dynamic decision-making, the anesthetist must detect and correct the problems that do occur at the earliest possible point in the chain of evolution. The interruption of the accident chain is made more difficult when there is tight coupling within the system, when there are multiple interacting problems, or when problems disrupt recovery processes. Efficient use of incident analysis may make it easier in the future to prevent or interrupt problem evolution. (Redrawn with modification from Gaba DM, Fish KJ, Howard SK: Crisis Management in Anesthesiology. New York, Churchill Livingstone, 1994.)

1. A single problem worsens and by itself evolves into an adverse outcome.
2. The problem begins to evolve but remains self-limited without any intervention.
3. Multiple small problems combine to trigger a problem that can evolve into an adverse outcome; the original problems by themselves would not have evolved further.
4. A single problem triggers another problem that evolves into an adverse outcome.
5. An evolving problem should be able to be stopped, but the recovery pathway is faulty.
6. Two problems are triggered. Attention focused on one (minor) problem distracts attention from the (serious) evolution of another.

The system has a variety of interruption points at which the occurrence of problems can be prevented (preoperative evaluation of patients and pre-use checkout of equipment). Moreover, although anesthesiology is far more dynamic than many medical domains, it is relatively slow compared to many human activities, such as sports, driving, and combat flying. Thus, events often evolve slowly enough that the process of accident evolution can be thwarted

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In the prospective studies of intraoperative events cited earlier, there was a surprisingly high incidence of undesirable situations, whereas the rate of actual patient harm was quite low. The patient's safety was frequently protected only by the skilled intervention of a trained anesthetist. Note that this is a markedly different picture from that in commercial aviation, although the accident rate in aviation is very low. There are about 30,000 airline flights per day in the United States, and there are very few serious incidents or accidents, although the exact number is unknown. The total accident rate from all causes (not counting terrorist acts) for major airline flights between 1982 and 2001 was 0.38 per 100,000 departures. Air carrier accidents with one or more fatalities occurred at a rate of 0.045 per 100,000 departures. In 2002 there were no fatalities in United States airline or commuter aviation (National Transportation Safety Board (NTSB) web site: www.ntsb.gov/aviation/ Stats.htm).

The actual number of events in aviation matching the "impact event" criteria given earlier is not known, but it is probably at least 100 times greater than the number of accidents. Even so, this still makes aviation incidents far less frequent than the 3% to 5% rate of "significant" impact events in anesthesia. Thus, based on these data, it is clear that the intraoperative management of abnormal, dynamically changing events remains the critical locus of anesthesia skill.