Retraction Force Measurement During Transgastric and Transvaginal NOTES

Abstract

Background: Organ retraction is often ineffective during NOTES. Force measurement at NOTES is difficult and has not been previously attempted. There is extreme variability of the force exerted by the endoscope in different positions and angles. Aims: 1) Develop methods to measure forces exerted by endoscopes and instruments during NOTES 2) Measure force required for adequate gallbladder retraction/exposure. 3) Compare transgastric and transvaginal forces at the bench and in an intact animal. Methods: Bench measurements were performed using forward viewing endoscopes and an electronic force gauge. In the case of the intact pig the endoscope was passed into the peritoneum through a CRE 18-20 mm balloon dilated gastric incision. The force exerted by the endoscope was transmitted by the endoscope to an external force gauge through a rod that was passed through the anterior abdominal wall using a purpose built trochar attached to a force gauge. Pushing forces were measured with the transgastric endoscope in straight and retroflexed positions. Forces were measured in Newtons (1N) (1N = 0.098 kg). Results: Bench Measurements: The mean force (0.64 N) exerted by the transgastric retroflexed endoscope was significantly less (p < .05) than that exerted by a straight transvaginal endoscope (4.59N). The mean force exerted by a transvaginal laparoscope (9.27N) was significantly greater (p < .05) than that exerted by a transvaginal endoscope (4.59 N). Forces transmitted via a biopsy forceps inserted through the channel of a transgastric retroflexed endoscope (.936 N) and a straight transvaginal endoscope (4.64N) were also measured. These did not differ significantly from the forces transmitted by the retroflexed transgastric and straight transvaginal endoscopes alone (.64N and 4.59N respectively). Intact pig: the mean retroflexed transgastric force (.5N) exerted by the endoscope was significantly less than that exerted by straight transgastric (3.53 N) endoscope (p < .05). The mean force required to adequately retract the gallbladder and liver was 6.63 N. Conclusions: New methods for measuring forces exerted during NOTES procedures were developed. Forces exerted by laparoscopes were orders of magnitude greater than those exerted via flexible endoscopes. Force exerted by a retroflexed endoscope was significantly less than with a straight endoscope. More force can be exerted for retraction using the scope transvaginally than transgastrically (p < .05). The mean force, required to retract the gallbladder is significantly greater than the force exerted by a flexible endoscope.