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

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.

Real-Time Measurement of the Tool-Tissue Interaction in Minimally Invasive Abdominal Surgery: The First Step to Developing the Next Generation of Smart Laparoscopic Instruments.

Introduction Analysis of force application in laparoscopic surgery is critical to understanding the nature of the tool-tissue interaction. The aim of this study is to provide real-time data about manipulations to abdominal organs. Methods An instrumented short fenestrated grasper was used in an in vivo porcine model, measuring force at the grasper handle. Grasping force and duration over 5 small bowel manipulation tasks were analyzed. Forces required to retract gallbladder, bladder, small bowel, large bowel, and rectum were measured over 30 seconds. Four parameters were calculated-T(hold), the grasp time; T(close), time taken for the jaws to close; F(max), maximum force reached; and F(rms), root mean square force (representing the average force across the grasp time). Results Mean F(max) to manipulate the small bowel was 20.5 N (±7.2) and F(rms) was 13.7 N (±5.4). Mean T(close) was 0.52 seconds (±0.26) and T(hold) was 3.87 seconds (±1.5). In individual organs, mean F(max) was 49 N (±15) to manipulate the rectum and 59 N (±13.4) for the colon. The mean F(max) for bladder and gallbladder retraction was 28.8 N (±7.4) and 50.7 N (±3.8), respectively. All organs exhibited force relaxation, the F(rms) reduced to below 25 N for all organs except the small bowel, with a mean F(rms) of less than 10 N. Conclusion This study has commenced the process of quantifying tool-tissue interaction. The static measurements discussed here should evolve to include dynamic measurements such as shear, torque, and retraction forces, and be correlated with evidence of histological damage to tissue.

Index admission laparoscopic cholecystectomy for patients with acute biliary symptoms: results from a specialist centre.

BACKGROUND: Index admission laparoscopic cholecystectomy (ALC) is the treatment of choice for patients admitted with biliary symptoms but is performed in less than 15% of these admissions. We analysed our results for ALC within a tertiary hepatobiliary centre. METHODS: Data from all cholecystectomies carried out under the care of the two senior authors from 1998 to 2008 were prospectively collected and interrogated. RESULTS: 1710 patients underwent cholecystectomy of which 439 (26%) were ALC. Patients operated on acutely did not have a significantly different complication rate (P= 0.279; 4% vs.3%). Factors predicting complications were abnormal alkaline phosphatase (ALP) (P= 0.037), dilated common bile duct (CBD) (P= 0.026), cholangitis (P= 0.040) and absence of on table cholangiography (OTC) (P= 0.011). There were no bile duct injuries. Patients undergoing ALC had a higher rate of conversion to an open procedure (P < 0.001:10% vs.3%). The proportion of complicated disease was higher in the ALC group (P < 0.001; 70% vs.31%). Only complicated disease (P= 0.006), absence of OTC (P < 0.001) and age greater than 65 years (P < 0.001) were predictive of conversion on multivariate analysis. CONCLUSIONS: Laparoscopic cholecystectomy can be performed safely in patients with acute biliary symptoms and should be considered the gold standard for management of these patients thus avoiding avoidable readmissions and life-threatening complications. A higher conversion rate to an open procedure must be accepted when treating more complicated disease. It is the severity of disease rather than timing of surgery which most probably predicts complications and conversions.

Feasibility of a phased acoustic array for monitoring acoustic signatures from meshing gear teeth.

This paper investigates the feasibility of sensing damage emanating from rotating drivetrain elements such as bearings, gear teeth, and drive shafts via airborne paths. A planar phased acoustic array is evaluated as a potential fault detection scheme for detecting spatially filtered acoustic signatures radiating from gearbox components. Specifically, the use of beam focusing and steering to monitor individual tooth mesh dynamics is analyzed taking into consideration the constraints of the array/gearbox geometry and the spectral content of typical gear noise. Experimental results for a linear array are presented to illustrate the concepts of adaptive beam steering and spatial acoustic filtering. This feasibility study indicates that the planar array can be used to track the acoustic signatures at higher harmonics of the gear mesh frequency.