RESUMO
Abstract Introduction: The real-time measurement of active power delivered to patients during the electrosurgical act is still an engineering challenge. Besides, there is no electrosurgical unit on the market capable of doing it according to the normative requirement. Methods This work presents the design of an electronic structure capable to probe the electrosurgical equipment output electrical signals, using low-costs very common resistors, and High Frequency distortions compensation circuits, and process them to provide an analogue signal proportional to the active power, allowing the knowledge and control of the energy delivered to the biological tissue. The reading circuits and the active power calculation method are presented. The power calculation is performed in two stages. The first one consists of a multiplier circuit that uses the readings voltage and current quantities to determine the instantaneous output power, and the second stage is formed by an integrating circuit which determines the average power value, resulting in a rippled continuous voltage, proportional to the active power delivered to the patient or biological tissue. Results Practical tests of the compensation technical are statistically evaluated by means of linear regressions. Results of 23 tests are summarized in a way to demonstrate de effectiveness of the proposed system. Conclusion Analysis of the results demonstrate the efficiency of the proposed system, whose average error is lower than 5%, and correlating them with the standard IEC 60601-2-2, that regulates the operation of electrosurgery units.
RESUMO
Abstract Introduction: Despite of more than a hundred years of electrosurgery, only a few electrosurgical equipment manufacturers have developed methods to regulate the active power delivered to the patient, usually around an arbitrary setpoint. In fact, no manufacturer has a method to measure the active power actually delivered to the load. Measuring the delivered power and computing it fast enough so as to avoid injury to the organic tissue is challenging. If voltage and current signals can be sampled in time and discretized in the frequency domain, a simple and very fast multiplication process can be used to determine the active power. Methods This paper presents an approach for measuring active power at the output power stage of electrosurgical units with mathematical shortcuts based on a simple multiplication procedure of discretized variables – frequency domain vectors – obtained through Discrete Fourier Transform (DFT) applied on time-sampled voltage and current vectors. Results Comparative results between simulations and a practical experiment are presented – all being in accordance with the requirements of the applicable industry standards. Conclusion An analysis is presented comparing the active power analytically obtained through well-known voltage and current signals against a computational methodology based on vector manipulation using DFT only for time-to-frequency domain transformation. The greatest advantage of this method is to determine the active power of noisy and phased out signals with neither complex DFT or ordinary transform methodologies nor sophisticated computing techniques such as convolution. All results presented errors substantially lower than the thresholds defined by the applicable standards.