INTRODUCTION. The purpose of this study is to determine the typical forces that instruments must be able to exert on tissue when performing surgery in the abdomen while accessing the tissue through natural orifices. The feasibility of NOTES is currently limited by a number of factors including the lack of suitable instruments. Current instruments are unstable and it is not possible to exert forces in directions other than the main axis of the instrument. Although the development of devices for NOTES are well underway there is currently very little published regarding how much force is required to manipulate tissue during NOTES procedures.
METHODS. Sensorized instruments were used during experiments to measure typical tissue handling forces during NOTES procedures in our porcine appendectomy test bed. A two-channel gastroscope (Olympus, Model GIF-2T160) was used during the experiments. Two instruments were selected for performing the measurements: the grasping forceps and the endoscopic scissors. These instruments were modified such that two strain gauges were placed close to the tip of the instruments to measure the forces applied by the gripper when manipulating tissue and by the scissors when placing the tool for proper cutting. Strain gauge calibration was performed prior to the data collection. By comparing the calibrated signals to force sensor measurements, sensing accuracy was determined to be 0.18 N.
After obtaining ethics approval, force data and video were recorded in two female pigs while performing transgastric and transperineal appendectomy. The data were divided into groups: pull tissue, push tissue in, push tissue sideways, or cut. Maximum forces and average forces were calculated in each case. Furthermore, the total average forces in each of the approaches were compared using the Mann-Whitney non-parametric test for two-sided data assuming non-equal variances.
RESULTS. The results showed that for the transgastric approach the average forces required were significantly less than in the transperineal (retroflexed) approach (43% less, p < 0.0001), and that the maximum forces required were about 8 N and 16 N in the transgastric and transperineal approaches respectively. The forces were higher than 5 N in 1.6% of the measurements in the transgastric approach and 2.9% in the transperineal approach. The results also showed that the forces were highest when the grasper was pulling on the tissue (as opposed to pushing inwards or sideways). The results of these experiments indicate that instruments proposed in the literature for NOTES, with a design limit of 5 N, might not be able to handle tissues properly.
CONCLUSIONS. This study presents an experimental measurement of tissue manipulation forces in an in vivo NOTES procedure. This information is valuable for research groups looking to develop NOTES devices. It is recommended that NOTES instruments be designed to easily handle forces as high as 16 N.
Session: Podium Presentation
Program Number: S012