The impact of electrosurgical heat on optical force feedback sensors

Electrosurgery enables cutting and coagulation (desiccation) of tissue for Minimally Invasive Surgery. Measurements performed by TNO with an infrared camera showed that the forceps of an endoscopic instrument can be over 300°C in temperature. During electro-surgery the surgeon relies on the power control and endoscopic images to perform the procedure successfully. Manipulation of tissue with the present forceps does not give accurate tissue information due to the presence of friction in the transmission mechanism and in turn force, control of the operating surgeon is poor. The latest developed instruments incorporates sensors and actuators that enable better control of force application on the tissue and give a better feeling of the tissue to the surgeon. TNO works for EFI BV on the development of a surgical instrument that senses and controls the gripping force even during electrosurgery. Electric sensors and actuators experience Electro Magnetic Interference during the use of electro-surgery, making it impossible to control the force. The high temperature that arises at the forceps influences and possibly destroys the sensors when positioned nearby the heat source. Based on the experience with optical fiber sensors TNO has developed an instrument that is immune to EMI and withstands temperatures up to 200°C. This optical sensor is based on a Fiber Bragg Grating (FBG). The FBG read out system, named the interrogator, transfers the optical fiber signal from the mechanical local strain. By this way the force exerted on the tissue and its resistance can be measured. However this sensor system is also sensitive to temperature changes. To control accurately he gripping force, the measurement must be independent of temperature. Therefore the thermal load at the forceps were measured and analyzed. The results are used for the instrument design and location of sensors