A numerical study of the relevance of the electrode-tissue contact area in the application of soft coagulation

Abstract

Monopolar electrocoagulation is a well-established surgical technique to achieve hemostasis by selectively destroying biological tissue through the application of high-frequency alternating current. However, this technique is associated with unwanted tissue damage. In this context, computational simulation is a valuable tool that can improve our understanding of such complex processes and highlight important application parameters in the direction of an improved control function to achieve safer and more reliable results. Despite its critical role in surgical applications, the influence of the electrode-tissue contact area has received little to no attention in previous simulation studies. To address this gap, the present study investigates the sensitivity of temperature distribution and necrotic volume formation to variations in electrode-tissue contact area. For this purpose, a multiphysics finite element model was developed to simulate HF current induced soft coagulation using a ball electrode under varying contact areas. Our findings demonstrate that variations in the contact area significantly impact temperature development and, consequently, necrosis formation. These results highlight the crucial role of the contact area in the electrocoagulation process and its associated necrosis formation. Furthermore, it was observed that when the boiling point of water is reached inside the tissue, complete necrosis has not yet formed at the contact site, which could lead to further undesired effects. Consequently, it is essential to consider the contact area in computational simulations and the development of novel control features for safer and more reliable electrocoagulation.

Keywords: Electrode-tissue contact surface; Finite element modeling; HF soft coagulation.

Fig. 1

Schematic representation of the time-dependent simulation study of a monopolar soft-coagulation model. The figure shows the 3-second long coagulation process at three different points in time: First, at the initial state of the simulation (at ). Second, after a simulation time of 1 second (at ) and third, after a simulation time of 3 seconds (at ). Additionally, variables like the diameter of the electrode d, the height b and width a of the tissue block, the height of the sphere segment h, the circular arc s of the contact area, the applied voltage boundary conditions and , as well as a schematic representation of the necrotic zone and its boundary at are shown.

Fig. 2

Simulated relationship between the electrode displacement and the resulting arc length as well as the corresponding contact area . The seven data points for were extracted from the mechanical contact simulation and used to calculate the associated contact areas . The fitted curves and are shown for illustrative purposes only and were not used for further analytical approximations.

Fig. 3

Simulated (a) maximum tissue temperature and (b) necrotic tissue volume as a function of application time t and electrode to tissue contact area . Due to the voltage activation at the simulation time , both graphs show the development of and from this time until the end of the application time ().

Fig. 4

Simulated maximum tissue temperature and tissue necrosis volume as a function of the application time t at four different contact areas .

Fig. 5

Shown is the simulated time at which the tissue temperature has reached 100  as a function of the contact areas . Furthermore, the extent of necrosis at the time points is indicated by the bars at the corresponding contact areas .

Fig. 6

Simulated spatial temperature distribution at the contact location at the end of the application time () for the seven different contact areas. The temperature field is shown in the color scale from dark blue for to light yellow for . The necrosis boundary is illustrated in the temperature field and given by a damage parameter of .

Fig. 7

Simulated spatial tissue damage distribution at the contact location at the end of the application time () for the seven different contact areas. The state of tissue damage is shown in the color scale from dark purple as healthy tissue to yellow for necrotic tissue. The necrosis boundary is illustrated in the damage field by a red line and is given by .