Airway simulators and mannequins: a case of high infidelity?

M Y grandfather, a lieutenant colonel in the United States Air Force (USAF), was responsible for the training of all civilian mechanics in the USAF from 1948 to 1952. In this position, he received reports of injuries to his mechanics from around the world and knew well how tools were misused. I was reminded of his aphorism as I read the article by Schebesta et al. in this month’s ANESTHESIOLOGY. The authors used computed tomography scans to compare the upper airway anatomy of four high-fidelity patient simulators and two airway trainers with normal humans. They found that none of the mannequins had anatomic dimensions that consistently replicated the sample of human subjects assessed. The authors state that because the calculated pharyngeal space is particularly important for the fit of supraglottic devices, the comparison of this volume in humans with the volume in mannequins was their primary outcome. They found that the calculated volume of the pharyngeal space in the mannequins varied from 2.2 to 5.1 times that of the human subjects. The boundaries of the airway space in mannequins may be similar to those that we create when we manage an airway with a laryngoscope or a supraglottic airway, which may explain why people using these mannequins tend to report a satisfactory simulation experience. This study, however, did not consider the compressibility of “tissues” in mannequins or the frictional interaction between airway appliances and mannequins. These properties, although harder to assess, contribute to the sense of realism when using mannequins and simulators. What are we to make of these findings? Although mannequins and simulators are commercially successful and have become firmly integrated in medical education, most of us would agree that they are not 100% realistic. To assess the utility and limitations of these devices we should review some terms associated with fidelity. We usually think of fidelity as “adherence to fact or detail” or “accuracy, exactness,” but in the simulation literature, fidelity can be defined as the extent to which the appearance and behavior of a simulator match the appearance and behavior of the system simulated. We must distinguish engineering or physical fidelity (the degree to which the training environment replicates the physical characteristics of the real task) from functional fidelity (the degree to which the skills in the real task are captured in the simulation) and psychologic fidelity (how the simulation makes the user feel). The goal of a virtual training system is to enhance performance in a real-world task. Transfer of training is the process by which knowledge, skills, and abilities acquired through training are applied in an actual situation. We can envision a spectrum of applications for simulators, from highly useful to less useful and possibly harmful. On the useful end of the spectrum, we have our medical students and junior residents practice basic airway skills on a mannequin before a first attempt on a patient. This application is an example of basic skill acquisition or transfer of training. In addition to novice training, an anatomic model may be useful for intermediate or advanced training, such as learning the mechanics of manipulating a flexible bronchoscope or the intricacies bronchial anatomy. Simulators are helpful for