Electrosurgical generator with adaptive power control

Abstract

An electrosurgical generator has an output power control system that causes the impedance of tissue to rise and fall in a cyclic pattern until the tissue is desiccated. The advantage of the power control system is that thermal spread and charring are reduced. In addition, the power control system offers improved performance for electrosurgical vessel sealing and tissue welding. The output power is applied cyclically by a control system with tissue impedance feedback. The impedance of the tissue follows the cyclic pattern of the output power several times, depending on the state of the tissue, until the tissue becomes fully desiccated. High power is applied to cause the tissue to reach a high impedance, and then the power is reduced to allow the impedance to fall. Thermal energy is allowed to dissipate during the low power cycle. The control system is adaptive to tissue in the sense that output power is modulated in response to the impedance of the tissue.

Description

[0001]This application is a Continuation of U.S. application Ser. No. 08 / 838,548, filed on Apr. 9, 1997, now U.S. Pat. No. 6,033,399, the contents of which are incorporated herein by reference.BACKGROUND[0002]1. Field of the Invention[0003]The present invention relates to an electrosurgical generator with an adaptive power control, and more particularly to an eleosurgical generator that controls the output power in a manner that causes impedance of tissue to rise and fall cyclically until the tissue is completely desiccated.[0004]2. Background of the Disclosure[0005]Electrosurgical generators are used by surgeons to cut and coagulate tissue of a patient. High frequency electrical power is produced by the electrosurgical generator and applied to the surgical site by an electrosurgical tool. Monopolar and bipolar configurations are common in electrosurgical procedures.[0006]Electrosurgical generators are typically comprised of power supply circuits, front panel interface circuits, and...

AI Technical Summary

Benefits of technology

[0019]An advantage of the present invention is that it can coagulate tissue with a reduced level of tissue charring. Another benefit of the present invention is that it has improved tissue sealing characteristics. Yet another benefit of the present invention is that it reduces thermal spread and thereby reduces damage to adjacent tissue. Yet another advantage of the present invention is that it reduces the tendency for eschar buildup on the electrosurgical tool. Yet another advantage of the present invention is that large vessels and ducts can be electrosurgically sealed.

[0020]It is thought that impedance of tissue can rise and fall depending on several factors, including output power, output voltage, output current, temperature, and pressure on the tissue exerted by surgical graspers. The present invention addresses changes in impedance of tissue that can be attributed to electrosurgical power application, wherein the power can be adjusted by changing the output voltage or the output current. The present invention causes the tissue impedance to rise and fall repeatedly until the tissue is completely desiccated. The present invention adjusts the output power in a manner that is based on feedback from a tissue impedance measurement.

[0021]According to the present invention, the impedance of the tissue rises and falls in response to relatively low frequency cycling of the electrosurgical power. The electrosurgical power is raised and lowered (also referenced herein as “cycled”) at a relatively low frequency, and the impedance of the tissue is thereby caused to rise and fall at approximately the same frequency until the tissue becomes desiccated. The manner in which the electrosurgical power is raised and lowered may be accomplished in several ways which incorporate well known principles of control system design.

[0022]The frequency of power cycling in the present invention is different from the RF modulation frequency of the electrosurgical waveforms, which are typically in the range of one hundred kilohertz to one megahertz. The frequency of power cycling of the present invention is also different from the duty cycle of generators that causes a coagulation effect on tissue, which is typically in the frequency range above one thousand hertz. The frequency range of power cycling in the present invention is typically between one and twenty hertz. Both the RF modulation and the duty cycling of present electrosurgical generators may occur simultaneously with the power cycling of the present invention.

[0023]The frequency at which the electrosurgical power is raised and lowered (i.e. cycled or modulated) should not be too high, otherwise the impedance of the tissue will not be able to rise and fall in response with an amplitude that will produce additional benefits. Similarly, the frequency should not be too low, otherwise the beneficial aspects of the invention will not become apparent because the tissue will desiccate without any appreciable modulation. The range of effective frequencies of the present invention has been called “thermal bandwidth.”

[0024]The behavior of the tissue impedance is possibly related to the thermal time constant of the tissue. There are additional factors that affect the tissue impedance, including the water content in the tissue and steam. After the tissue is desiccated, which is indicated by a high measured impedance, further application of electrosurgical power will cause undesirable charring. Thus, it is preferred to have impedance monitoring to determine the appropriate time for terminating the electrosurgical power. Impedance monitoring is also preferred so that the modulation frequency of the electrosurgical power can be automatically adjusted and kept within the thermal bandwidth.

Problems solved by technology

The application of electrosurgical power is known to cause the impedance of tissue to fall to a local minimum and then rise monotonically thereafter.

If the electrosurgical power is applied for too long, the tissue may char and stick to the electrode.

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