An embodiment of the present invention relates generally to a method of providing a boost mode in an electrosurgical generator apparatus, and more particularly, to a method of providing a boost mode wherein the boost output power level is based on a measured impedance of tissue.
Devices used for controlling monopolar and bipolar electrode tools are well known in the art. U.S. Pat. No. 5,318,563, the contents of which are incorporated by reference herein, relates to electrosurgical radio frequency (RF) generators. The electrodes in the prior art systems are used for cutting and coagulation of tissue. An RF current is generated between the electrodes and is applied to the tissue. Regarding bipolar tools in particular, cutting occurs by application of the concentrated RF current to destroy cells placed between the electrodes.
It is found, however, that when the electrodes are placed in contact with the body prior to activation, the output voltage of the RF amplifier is decreased. As a result, the cutting ability of the electrosurgical tool is hindered. One solution has been to provide a short, initial boost to the power output level of the generator upon activation of the electrosurgical tool. The brief power output surge is enough to overcome the impedance caused by the tissue to allow cutting to begin. After the surge, the power output level returns to normal and cutting proceeds in the typical fashion.
The general practice has been to set the boost voltage to a certain level and use the same level regardless of the conditions. This can lead to an increase in collateral damage in the tissue caused solely by the power surge. For example, the impedance of tissue between individuals may vary greatly, and even within the same individual, different tissues exhibit various impedance levels. The impedance is correspondingly proportional to an amount of cell destruction caused by the generator apparatus. Therefore, a constant boost voltage of, for example, 1100 V may cause more unintended damage in a patient or tissue with a lower impedance level than in a patient or tissue having a higher impedance level.
It is desirable to provide a method of generating a boost voltage in an electrosurgical generator apparatus while minimizing the collateral damage to surrounding tissue when the boost voltage is applied. It is further desirable to provide an electrosurgical apparatus that provides a variable boost voltage for minimizing collateral damage to surrounding tissue.
Briefly stated, an embodiment of the present invention comprises a method of controlling output power of an electrosurgical generator apparatus that controls a variable output signal to a pair of electrodes. The method includes setting the output power of the generator apparatus to a selected power output level. An impedance is measured across the electrodes using an impedance monitoring circuit when the electrodes are applied to an area of tissue. The output power of the generator apparatus is changed to a boost power output level greater than the selected power output level. The boost power output level corresponds to a calculation based at least in part on the measured impedance. The method further includes applying the output signal to the electrodes at the boost power output level for a first time duration. The power of the output signal applied to the electrodes is changed to the selected power output level after the first time duration.
Another embodiment of the present invention comprises an electrosurgical generator apparatus that controls a variable output signal to a pair of electrodes. The generator apparatus includes a controller for controlling the generator apparatus. An impedance monitoring circuit detects an impedance as measured across the electrodes when the electrodes are applied to an area of tissue. A memory stores predetermined values for calculating a boost power output level based at least in part on the measured impedance. The controller is configured to change a selected power output level to the boost power output level based at least in part on the measured impedance for a first time duration and change the boost power output level to the selected power output level after the first time duration.
The foregoing summary, as well as the following detailed description of preferred embodiments of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustration, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.
Certain terminology is used in the following description for convenience only and is not limiting. The words “right”, “left”, “lower”, and “upper” designate directions in the drawings to which reference is made. The words “inwardly” and “outwardly” refer to directions toward and away from, respectively, the geometric center of the apparatus and designated parts thereof. The terminology includes the above-listed words, derivatives thereof, and words of similar import. Additionally, the words “a” and “an”, as used in the claims and in the corresponding portions of the specification, mean “at least one.”
Referring to the drawings in detail, wherein like reference numerals indicate like elements throughout, there is shown in
The RF generator 50 includes a housing 52, a display screen 54, such as a cathode ray tube (CRT), liquid crystal display (LCD), or the like, on the front panel 52a and a connector panel 56 on the rear panel 52b. The display screen 54 is preferably a touch panel. Control knobs 57a, 57b on the front panel 52a may be used for selecting output power. A power cord (not shown) of the conventional type as is known in the art is connected to a power source to provide power to the RF generator 50 via a source power plug adapter 49. Preferably, the RF generator 50 is supplied with between about 110-125 volts of alternating current (VAC) at 60 Hertz (Hz) or about 220-240 VAC at 50 Hz, and may be selected using the voltage supply switch 48. But, other supply voltages and frequencies of AC voltage or other direct current (DC) voltages may be supplied without departing from the present invention. The RF generator 50 also includes an on/off power switch 53. The RF generator 50 may also include one or more speakers or audio outputs (not shown) for generating indicator beeps and/or vocal instructions in one or more selectable languages.
The RF generator 50 may be connected to either a monopolar electrosurgical tool (e.g., as shown in
A monopolar electrosurgical tool 40mp is shown in
Referring to
The impedance monitor circuit 76 is connected in parallel with an RF output and filter of the RF amplifier 68. Impedance is thereby detected using the electrodes 44a, 44b of the surgical pen 40, and the actual impedance of the tissue to be cut or coagulated may be calculated. The impedance value is used by the main controller U1 to determine a boost voltage to apply at the initial cutting stage, as described in further detail below. The main controller U1 further includes a partial short circuit detection monitor 75, shown in
It will be appreciated by those skilled in the art that the RF generator 50 need not utilize a touchscreen 54a for displaying and selection of information. For example, selections may be made by an operator using conventional knobs, switches, or the like. Further, information may be conveyed to the operator using alphanumeric light emitting diode (LED), LCD, or other displays known in the art.
At block 202, when the electrodes 44a, 44b of the surgical pen are applied to an area of tissue, the impedance monitor circuit 76 measures an impedance. At block 204, the value of the measured impedance is used by the main controller U1 to determine a boost power output level that is greater than (or equal to) the desired power output level. In preferred embodiments, the controller U1 additionally accounts for the desired power output level and determines the boost power output level as a multiple of the desired power output level. For example,
Returning to
In preferred embodiments, other characteristics of the output signal supplied to the surgical pen 40 may additionally be altered. For example, the waveform supplied by the RF amplifier 68 during the boost time duration tb may differ from the waveform supplied thereafter. A Malis waveform, described in U.S. Pat. No. 4,590,934, the contents of which are incorporated by reference herein, may be applied during the boost time duration tb. Periodic damping, a distinctive feature of the Malis waveform, provides further protection from collateral damage to the tissue. Once the boost time duration tb has expired, RF amplifier 68 may return to a sine waveform. The peak amplitude of both the first and second waveforms may differ. Other waveforms (such as, for example, an impulse waveform) or combinations thereof may be used in keeping with preferred embodiments of the present invention. Other preferred embodiments of the present invention may include combinations of the signal variations described above or other variations such as to wavelength, frequency, or the like.
The boost power output level is applied only for a short duration tb, long enough to overcome the tissue impedance and begin the cutting procedure. Preferably the boost power output voltage is applied for tb=200 ms. The main controller U1 at block 208 therefore determines whether the boost time duration tb has expired. If not, the electrodes 44a, 44b continue to receive the boost power output from the RF generator 50. Once the boost time duration tb has expired, at block 210 the power output level is reduced to the initial desired power output level and cutting thereafter proceeds in the normal fashion.
It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that the invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.
This application claims the benefit of U.S. Provisional Patent Application No. 61/037,794, filed on Mar. 19, 2008, entitled “Electrosurgical Generator Having Boost Mode Control Based on Impedance,” the entire contents of which are incorporated by reference herein.
Number | Date | Country | |
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61037794 | Mar 2008 | US |