Experimental Visualisation of Potential Distribution in Electrosurgery C. Knopf * , S. Kl¨ ockner † , O. Kanoun ‡ , J. Himmel * * Ruhr West University of Applied Sciences, Mellinghoferstraße 55, 45473 M¨ ulheim an der Ruhr, Germany Email: christoph.knopf@hs-ruhrwest.de and joerg.himmel@hs-ruhrwest.de † Olympus Winter & Ibe GmbH, Kuehnstraße 61, 22045 Hamburg, Germany ‡ Chemnitz University of Technology, Reichenhainer Straße 70, 09126 Chemnitz, Germany Abstract—The transurethral resection (TUR) is a standard technique in urological treatment procedures. Both, monopolar and bipolar electrosurgical systems, are used for TUR. Whereas electrical and physical processes in surgery surroundings are well understood for monopolar systems, there is no sufficient data base for the assessment of the processes with the use of bipolar systems. In this context a multi-electrode measuring system was developed to visualize the spatial potential distribution around bipolar electrosurgical devices as a first step to risk analysis. To simulate the anatomic surroundings of a transurethral surgery a cylinder filled with isotonic saline solution was used as a complexity reduced experimental environment. Index Terms—Transurethral resection (TUR), bipolar, poten- tial distribution, spatial resolution, electrosurgery, visualisation. I. I NTRODUCTION In the years 2008 to 2010 in Germany 353,100 surgical pro- cedures on prostate and 739,343 on bladder were performed. 59.8% of the prostate and 40% of the bladder operations performed in Germany, were carried out as a transurethal resection (TUR) [1]–[3]. Thereby, bipolar electrosurgical sys- tems are a serious alternative to monopolar electrosurgical systems due to its offer of several safety advantages [4]–[8]. An increased application of bipolar electrosurgical systems is also shown by higher sales volume in comparison to monopolar systems [9]. The current knowledge about the electrical and physical pro- cesses in the surgery surroundings during TUR is based on fundamental investigations of Fastenmeier and Flachenecker. Conventional monopolar systems and only prototypes of pre- liminary considerations to bipolar systems are investigated relating to the 2D potential and current distribution in the cutting plane of the electrosurgical device. In combination with long-time experienced data monopolar systems are well understood and described. [10]–[13] Investigation results for monopolar systems do not allow conclusions concerning the processes during bipolar TUR and pure theoretical considerations only supply a simplified description of the reality. Because there are little experienced data for bipolar systems and many different types of resecto- scopes, depending on the manufacturer, are available on the market, it is difficult to set the TUR-parameter. Thus, a risk analysis is difficult. Aim of this research is to provide an equipment to measure the spatial potential distribution around bipolar electrosurgical devices. The resulting 3D data are the metrological basis for further calculations on the way to risk analysis. In this publication first the metrological method and the theoretical background are explained, second experimental investigations concerning time stability and qualitative assessment of the set- up are considered and finally results for the spatial potential distribution are presented. II. THEORY AND METHOD The resection electrode of the bipolar electrosurgical device (or resectoscope) is not rotationally symmetric. Hence an asymmetric potential distribution is expected and a spatial potential distribution measurement is needed. Considering size of resectoscopes used in adult urology, about 480 measuring points are proposed for a sufficient spatial resolution of potential. Two approaches to measure the spatial potential distribution are possible. Either an one-electrode measuring system, which is moveable in all three directions in space, or a multi-electrode measuring system, which is moveable in one direction in space, is needed. The expenditure of time and number of plasma ignitions by an one electrode system is 4 h and 480 ignitions if one measuring cycle is about 30 sec. A multi-electrode system with e.g. 24 electrodes reduces the measuring time to 15 min and the number of ignitions to 20. The experience gained from former tests shows that no resection electrode change is necessary for a measurement consisting of 20 ignitions. Due to these facts we pursue the multi-electrode measuring system to measure the spatial potential distribution. For both approaches a complete data set consists of several individual measurements which are performed successively. Hence a quasi-static electric flow field is required. For electrosurgical applications a working frequency between 300 kHz and 5 MHz is used [4]. After activating the bipo- lar resection system plasma is ignited around the resection electrode of the resectoscope. During polarity reversal of the alternating field, shortly not enough power is provided to keep the plasma ignited, so it dies. But a high impedance in the surroundings of the resection electrode enables the plasma to reignite with increasing voltage. Due to the time behaviour of the alternating current the uneven-numbered harmonics of the oscillator, used for the construction of an electrosurgical unit, SSD'13 1569696323 1 2013 10th International Multi-Conference on Systems, Signals & Devices (SSD) Hammamet, Tunisia, March 18-21, 2013 978-1-4673-6457-7/13/$31.00 ©2013 IEEE