An in vivo analysis of safe laparoscopic grasping thresholds for colorectal surgery

Abstract

Background: Analysis of safe laparoscopic grasping thresholds for the colon has not been performed. This study aimed to analyse tissue damage thresholds when the colon is grasped laparoscopically, correlating histological changes to mechanical compressive forces.

Methods: An instrumented laparoscopic grasper was used to measure the forces applied to porcine colon, with data captured and plotted as a force-time (f-t) curve. Haematoxylin and eosin histochemistry of tissue subjected to 10, 20, 40, 50 and 70 N for 5, 30 and 60 s was performed, and the area of colonic circular and longitudinal muscle was compared in grasped and un-grasped regions. The area under the f-t curve was calculated as a measure of the accumulated force applied, known as the force-time product (FTP).

Results: FTP ranged from 55.7 to 3793 N.s. Significant differences were observed between the muscle area of the grasped and un-grasped regions in both longitudinal and circular muscle at 50 N and above for all grasping times. For the longitudinal muscle, significant differences were observed between grasped and un-grasped areas at 20 N force for 30 s (mean difference = 59 mm², 95% CI 41-77 mm², P = 0.04), 20 N force for 60 s (mean difference = 31 mm², 95% CI 21.5-40.5 mm², P = 0.006) and 40 N force for 30 s (mean difference 37 mm², 95% CI 27-47 mm², P = 0.006). Changes in histology correlated with mechanical forces applied to the longitudinal muscle at a FTP over 300 N s.

Conclusions: This study characterizes the grasping forces that result in histological changes to the colon and correlates these with a mechanical measurement of the applied force. The findings will contribute to the development of smart laparoscopic graspers with active constraints to prevent excessive grasping and tissue injury.

Keywords: Colon; Grasping; Laparoscopy.

Fig. 1

Diagram of instrumented grasper with instrumented module containing load cell and potentiometer

Fig. 2

Measurement area as performed per protocol

Fig. 3

Schematic diagram showing method of calculating the area under the curve and therefore the force–time product (FTP)

Fig. 4

Graph showing grasped versus un-grasped measures for the longitudinal muscle with P values shown above each parameter

Fig. 5

Graph showing grasped versus un-grasped measures for the circular muscle with P values shown above each parameter

Fig. 6

FTP plotted for all parameters. A dashed line separates region A and region B. Region B denotes the parameters where a statistically significant difference was found between both the circular and the longitudinal muscle measures and their corresponding un-grasped regions