Design of a factorial experiment with randomization restrictions to assess medical device performance on vascular tissue

Background: Energy-based surgical scalpels are designed to efficiently transect and seal blood vessels using thermal energy to promote protein denaturation and coagulation. Assessment and design improvement of ultrasonic scalpel performance relies on both in vivo and ex vivo testing. The objective of this work was to design and implement a robust, experimental test matrix with randomization restrictions and predictive statistical power, which allowed for identification of those experimental variables that may affect the quality of the seal obtained ex vivo. Methods: The design of the experiment included three factors: temperature (two levels); the type of solution used to perfuse the artery during transection (three types); and artery type (two types) resulting in a total of twelve possible treatment combinations. Burst pressures of porcine carotid and renal arteries sealed ex vivo were assigned as the response variable. Results: The experimental test matrix was designed and carried out as a split-plot experiment in order to assess the contributions of several variables and their interactions while accounting for randomization restrictions present in the experimental setup. The statistical software package SAS was utilized and PROC MIXED was used to account for the randomization restrictions in the split-plot design. The combination of temperature, solution, and vessel type had a statistically significant impact on seal quality. Conclusions: The design and implementation of a split-plot experimental test-matrix provided a mechanism for addressing the existing technical randomization restrictions of ex vivo ultrasonic scalpel performance testing, while preserving the ability to examine the potential effects of independent factors or variables. This method for generating the experimental design and the statistical analyses of the resulting data are adaptable to a wide variety of experimental problems involving large-scale tissue-based studies of medical or experimental device efficacy and performance

Thermal spread of vessel-sealing devices evaluated in a clinically relevant in vitro model

Introduction: Bipolar vessel-sealing devices (VSDs) have advantages in urological surgeries (less hemorrhage, shorter operating time). However, these instruments can cause thermal injuries, which can result in neural damage and necrosis. The objectives of this study were to establish a reproducible in vitro model for standardized assessment of electrosurgical devices and to evaluate whether optimized placement of surgical instruments can reduce the thermal spread. Methods: We evaluated thermal spread of two VSDs in vitro using thin bovine muscle strips. Thermal injury was measured using an infrared camera, temperature probes and histology. The recordings were made with the VSD alone and with a rectangular clamp next to the VSD. Results: Both instruments showed a significant temperature spread of 2.5 mm lateral to the VSD. The placement of a metal clamp next to the VSD significantly reduced the temperature spread. Histological examinations were able to underline these findings. Conclusions: In this study we describe a straightforward clinically relevant in vitro model for the evaluation of future electrosurgical instruments. We demonstrated that the thermal spread of VSD could be further reduced by optimized placement of an additional surgical instrument. Our results could help surgeons protect sensitive structures like nerves in the vicinity of the VSD

The use of the LigaSure device and the Stapler in closure of the small bowel: a comparative ex vivo study

Purpose To evaluate the feasibility and effectiveness of the LigaSure device in closing divisions of the small bowel in an ex vivo porcine model. Methods Two types of closure were performed: stumps created by ‘‘muco-mucosa’’ fusion and stumps created by ‘‘sero-serosa’’ fusion. For each type of closure, different power levels of the LigaSure system were tested in com-bination with different numbers of applications and then compared with the Stapler group. Results With both types of intestinal closure, the highest value of burst pressure was obtained with the application of a power level of three bars and one frequency application. The high burst pressure of the muco-mucosa stump group was significantly lower than that of the Stapler group (41.8 ±5.9 vs. 75.8±5.9, respectively, p\0.01). No differences were found between the high burst pressure of the sero-serosa stump group and the Stapler group (74.1 ±5.5 vs. 75.8±5.9, respectively,p=0.2). Conclusions Our preliminary results showed that the LigaSure is an efficient tool for closing the intestines when sero-serosa stumps are created. The second step of our work will be to evaluate the feasibility of this tool in cre-ating intestinal anastomos