Recently, Britt et al. measured the difference in mental workload when transitioning from the FLS system to fresh cadavers.1 They trained their participants to proficiency2 for intracorporeal suturing on the rubber FLS Penrose drains and observed substantial increases in suturing times and subjective workload when the participants attempted to suture bowel tissue. There are many reasons why mental workload would be higher for the cadaver over the FLS simulator. Our goal was to address one possibility: perceived differences in the properties of the rubber drain and cadaver bowel tissue. We hypothesized that differences in the stiffness and elasticity of human bowel tissue and the rubber drains contribute to the increased mental workload. To explore this idea, we used the psychophysical scaling method of magnitude estimation.3-4 Participants assigned comparative numerical values to the properties of the bowel tissue to identify potential perceived differences between the two media.
Eight surgical assistants (SA) participated in this IRB approved study. They were trained to proficiency in intracorporeal suturing on the FLS system. They practiced suturing on the FLS Penrose drains for 30 minutes and then performed three sutures in the bowel of a fresh cadaver using Stryker high definition endoscopic towers and Stryker 10 mm 30 degree scopes. The fresh cadavers were soft embalmed using the Modified Thiel method with nitrate salts to maintain tissue flexibility and allow insufflation.
The participants used the magnitude estimation procedure and provided estimates for stiffness and elasticity. They were told to consider the Penrose drain as the standard with a value of 100 and to provide numerical estimates of the perceived differences in sensation of the bowel tissue (e.g., if the bowel tissue felt half as stiff as the drain they should give it the number 50).
Data from five of SA students were available for analysis. The magnitude estimates were analyzed with one sample t tests as deviations from the standard. The perceived elasticity increased from 100 to 174 (SD = 25), t(4) = 6.59, p < .003, Cohen’s D = .86. Regarding stiffness, the reported values decreased from 100 to 81 (SD = 40.1) which was not significant, p > .05. However, all but one participant reported a decrease in stiffness. With that participant removed, the decrease in stiffness dropped from 100 to 71 (SD = 21.3), t(3) = 4.53, p < .02, Cohen’s D = .81.
The results show that participants did indeed perceive differences between the human bowel tissue and the rubber Penrose drains. Specifically, they rated the elasticity of the human bowel nearly two times greater than that of the rubber drain. The bowel tissue was rated slightly less stiff than the rubber drain. Although the estimates were obtained with a small sample the Cohen’s D values for both properties were quite large indicating a large effect. These results suggest that differences in properties of the cadaver tissue and the rubber drain are clearly perceivable and may contribute to the increased workload observed by Britt et al.1 when trainees transition from FLS to a more realistic surgical environment.
1. Britt RC, Scerbo, MW, Montano, M, Kennedy R, Prytz, E, Stefanidis, D. Intracorporeal suturing: Transfer from FLS to cadavers results in substantial increase in mental workload. Paper presented at the 2014 Consortium of Accredited Education Institutes for the American College of Surgeons. Chicago, IL.
2. Ritter M, Scott DJ. Design of a proficiency-based skills training curriculum for the Fundamentals of Laparoscopic Surgery. Surg Innov; 2007;14:107-12.
3. Stevens, SS. The measurement of loudness. J Acoust Soc Am 1955; 27:815-820.
4. Gescheider GA. Psychophysics: Method, theory, and applications, 2nd ed. 1985. Hillsdale, NJ: Erlbaum.
Dmitrios Stefanidis receives honoraria for teaching fromCR Bard and WL Gore. Mark Scerbo receives grant support from Medical Cyberworlds.
© 2014 Society for Simulation in Healthcare