L'elettrobisturi: modellizzazione circuitale per valutazioni EMC

Biomedical equipment malfunction means risks for users’ health and safety; in fact very often they either support/substitute the patients’ vital activities ( as in the case of the pacemaker and the implantable -PM or ICD), or they guarantee the working place safety inside sanitary structures ( alarm systems in operating rooms).
In medical fields it‘s necessary, for personal protection, to consider first the electromagnetic compatibility of the equipments that could be contemporaneously employed, since the generation of varying electromagnetic fields, in time, can be cause of interference inducing momentary or definitive malfunctions.
The electrosurgical unit is used in a lot of surgical procedures since it exploits the thermal effect due to the passage, in the body, of high frequency electric current (temperature increase due to the joule effect), thus provoking the cut of the tissue and/or the coagulation of possible present haemorrhages.
The current on the patient and the current in the devices’ circuits can both determine electromagnetic fields, which possibly interact with other biomedical devices; therefore they are of primary importance in the evaluations of electromagnetic compatibility (EMC) of the electrosurgical unit.
These considerations have motivated the modelling of an electric circuit able to simulate the operation of the electrosurgical unit and to allow to determine the current waveform and its values
The electrosurgical unit can be used in three different operation modes, according to its effects: pure cut, pure coagulation or both of them.
These effects on the tissue are obtained through dissimilar current waveforms, therefore characterized by different intensity and duration, causing peculiar electromagnetic emissions.
It has been necessary a circuit modelling to regulate the output signal parameters (duty cycle and amplitude) which can discriminate the possible mode of operation, so to make an electromagnetic compatibility comparison possible.
Different surgical procedures in the employment of electrosurgical unit require heterogeneous power output values to get a same effect, that is operating in the same operation mode.
It has been necessary to make output power adjustable, being this an influence parameter of influence on the electromagnetic field sources.
Simulations were carried on to compare measurable currents, in reference to an operation mode carried out hypothetical applications based on the need of different powers.
Besides, operation modes have been compared hypothesizing a same power supplied to the patient.
Possible future developments aim to the realization of a more adherent model to the device components, in order to make the electrosurgical unit internal current simulation more realistic.