Finite Element Analysis On The Effect Of Operating Parameters Of Electrosurgical Unit On Tissue Lesion And Tissue Adhesion

Given the development of medical technology and the increasing requirement of operation security and postoperative recovery, electrosurgical units have gradually replaced traditional medical apparatus such as scalpels and hemostatic forceps recently, and then are becoming indispensable medical apparatus for large and medium-sized hospitals. During the operation process of electrosurgical units, high-frequency (usually 200 kHz to 3 MHz) and high-voltage current is conducted from the electrode tip of electrosurgical unit to tissues, and thus lots of heat flux is produced to heat the tissues. As a result, cutting and hemostasis are done simultaneously. The working principle of electrosurgical units would inevitably lead up to tissue lesion and tissue adhesion during the process of operation. Understanding the critical temperature of tissue adhesion upon electrodes and the effect of the operating parameters on tissue lesion would be helpful for the optimum design and clinical operation of electrosurgical units.In this thesis, tissue lesion and tissue adhesion under different cutting conditions were investigated using ex vivo testing and finite element analysis, aiming to reveal the effect of operating parameters of electrosurgical unit. Main results and conclusions were as follows:(1) In cut mode, as the power was increased to 12 W, tissue adhesion upon electrodes changed from coagulated denaturation tissue to yellow eschar, and the critical temperature of yellow eschar was 148.4℃; As the power was increased to 60 W, tissue adhesion upon electrodes changed from yellow eschar to black eschar, and the critical temperature of yellow eschar was 373.9℃. Adhesive energy of black eschar on the electrode was much higher than that of yellow eschar.(2) With the power of electrosurgical unit increasing, the area and extent of tissue lesion changed nonlinearly. As the power was gradually increased from 20 W to 60 W, only local variation instead of significant increase occurred to lesion area. As the power was increased from 60 W to 70 W, the lesion area increased significantly, and the extent of tissue lesion aggravated remarkably. In addition, with the gap between the tissue and electrode decreasing, the extent of tissue lesion was aggravated. The temperature in tissues increased sharply about±1.8 mm away from the center of electrode along the cutting direction, while the temperature increased sharply about±1.2 mm away from the center of electrode perpendicular to the cutting direction.(3) In coagulate mode, the zone of tissue lesion was enlarged with the increase of either the output voltage or the operating time. At a given output voltage and operation time, the width of tissue lesion was larger than its depth, but the degree of tissue lesion was much severer in depth. It was also found that the distribution curve of the current density within the tissue was basically consistent with that of tissue temperature, which suggested that the tissue temperature was directly affected by the current density. That is, the larger the current density within the tissue was, the higher the tissue temperature was.