The Characterization, Simulation, and Effect of Abdominal Wall Resistance on Resident Laparoscopic Trainer Performance

Scott W Schimpke, MD, John C Kubasiak, MD, Benjamin R Veenstra, MD, Jonathan A Myers, MD, Keith W Millikan, MD, Daniel J Deziel, MD, Jennifer Poirier, PhD, Minh B Luu. Rush University Medical Center

Introduction: Abdominal wall thickness is associated with increased resistance experienced by surgeons during laparoscopic surgery.  The effect of this increased resistance on surgical performance, both in simulation and in the operating room, is unknown.   The goal of this study was to analyze the relationship between a patient’s BMI, abdominal wall thickness, and the resultant force needed to overcome trocar resistance.  Furthermore, we hypothesized that adding resistance to a standard FLS trainer, to simulate an obese abdominal wall, would negatively affect resident performance.

Methods: The BMI, abdominal wall thickness, and force measurements on the 5 mm mid-clavicular right subcostal trocar were prospectively collected on 21 patients undergoing laparoscopic cholecystectomy from 2014-2015.  For the simulated portion of the study, an FLS trainer box was used.  A resistance model was developed by the addition of a synthetic rubber mold.  The performance of general surgery residents (n= 30) during the standard FLS peg transfer task was tested in both the standard box and the resistance model.  Task completion time and number of peg drops were recorded.  PGY1 through PGY5 residents were randomized to start either with or without resistance.

Results: A total of 21 patients were included in the study, with an average BMI of 33.9 (range 13.7-45.8).  Abdominal wall thickness and force needed to overcome trocar resistance ranged from 1 to 7 cm (mean 4.6 cm, SD 1.6) and 0.5 to 21.5 N (mean 10.5 N, SD 6.2).  There were positive associations between BMI, abdominal wall thickness, and the average maximum force needed to overcome abdominal wall resistance on the trocar. Pearson correlation coefficients ranged from 0.61 to 0.78, and all were statistically significant (p ≤ .002).  Resident performance in the trainer box was negatively affected in the resistance model, which simulated the forces analogous to a BMI of 29.7 based on linear regression analysis of the aforementioned data.  The mean peg transfer times were 92.8 and 199 seconds without and with resistance, respectively (p = 0.03).   Task times in both the standard and resistance models decreased with increased level of resident training.

Conclusions: We demonstrate a positive association between patient BMI and trocar resistance.  When applied in a simulation model, increased resistance negatively affected resident performance at all levels of training.  Further studies are needed to investigate the role of simulated abdominal wall resistance in laparoscopic trainers.

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