In an attempt to independently verify the performance characteristics of one brand of commercially available simulators, we undertook a multi-site comparison of the performance of six fully operational METI (Medical Education Technologies Inc., Sarasota, FL, USA) simulators. The METI Human Patient Simulator (HPS) is a plastic manikin with respiratory and cardiovascular functionality. This includes mechanical lungs, palpable pulses, heart and lung sounds; with life-like cardiorespiratory data that are displayed using standard clinical monitors. The HPS is operated by a computer program with sophisticated physiological and pharmacological models that rely on feedback from a range of peripheral devices. Clinical problems or scenarios are created by manipulating these integrated physiological and pharmacological models using METI-HPS scenario files.
To generate physiological data for comparison, we distributed an identical scenario file to the participating centres. Five of the simulators were METI-C simulators running software version 5.5, and simulator 1 was a METI-B running software version 5.2. The simulators were all breathing room air and half were intubated with a tracheal tube. The scenario began with a 2 min physiologically normal baseline, followed by automatic transitions that included progressive haemorrhage and increases in both shunt fraction and oxygen consumption. The final transition to total neuromuscular blockade resulted in death from hypoxaemic cardiac arrest. Three iterations of the scenario were run on each simulator. At 1 min intervals the simulated physiological data were automatically recorded to log files. Data were analysed using repeated measures of analysis of variance using SYSTAT version 10.
The data from simulator 6 were strikingly different from the others, caused by an unrecognized defective gas analyser that was impairing the physiological model. These data were excluded from the statistical analysis. The physiological trends recorded from the five remaining simulators were similar, but there were statistically significant differences (P<0.0001) between simulators for heart rate, systolic and diastolic blood pressure, cardiac output, tidal volume, ventilatory frequency, alveolar partial pressure of oxygen and carbon dioxide, and arterial partial pressure of carbon dioxide. The differences were greatest for tidal volume and are shown in Figure 1. There were no statistically significant differences within any one simulator during the repeated iterations of the scenario.
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The important finding was an unrecognized malfunction in a fully operational simulator. This is important when considering the educational and evaluative roles that simulators are likely to play in the future. We must be confident that simulators are both reliable and valid, not only because of the need to avoid negative transfer and potentially harmful training, but also in the interests of fairness to examination candidates when simulators are used in certification and re-certification. Our initial question regarding the variability in simulated physiological performance in properly functioning simulators remains inadequately answered.
1 Boston, MA, USA 2 Wellington, New Zealand 3 Richmond, VA, USA 4 Mainz, Germany 5 Heidelberg, Germany
Acknowledgments
We would like to thank Tom Boeker MD, Heidelberg and the Bristol Medical Simulation Centre for their assistance.
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