Patent Publication Number: US-8968295-B2

Title: Electrosurgical apparatus with high speed energy recovery

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 12/205,298, now U.S. Pat. No. 8,287,529, filed on Sep. 5, 2008, entitled “ELECTROSURGICAL APPARATUS WITH HIGH SPEED ENERGY RECOVERY,” the contents of which are incorporated by reference herein in their entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to an electrosurgical system and method and, more particularly, to an electrosurgical generator configured to dynamically control energy output. 
     2. Background of Related Art 
     Electrosurgery involves application of high radio frequency electrical current to a surgical site to cut, seal, ablate, or coagulate tissue. In monopolar electrosurgery, a source or active electrode delivers radio frequency energy from the electrosurgical generator to the tissue and a return electrode carries the current back to the generator. In monopolar electrosurgery, the source electrode is typically part of a surgical instrument held by the surgeon and applied to the tissue to be treated. A patient return electrode is placed remotely from the active electrode to carry the current back to the generator. 
     In bipolar electrosurgery, a hand-held instrument typically carries two electrodes, e.g., electrosurgical forceps. One of the electrodes of the hand-held instrument functions as the active electrode and the other as the return electrode. The return electrode is placed in close proximity to the active (i.e., current supplying) electrode such that an electrical circuit is formed between the two electrodes. In this manner, the applied electrical current is limited to the body tissue positioned between the two electrodes. 
     Conventional electrosurgical generators include a high voltage direct current power supply connected to a radio frequency (RF) output stage that converts DC energy generated by the power supply into RF energy. The power supply includes an output filter which substantially eliminates undesirable frequencies (e.g., noise) from the DC energy and stores large amounts of energy. Rapid tissue desiccation during the application of RF energy creates a potential for patient burn hazards due to excess energy dosage at the tissue site when the power source fails to rapidly alter the supplied energy dosage in response with dynamic changes in tissue impedance. Rising tissue impedance levels caused by desiccation unload the energy source and sustain the energy delivered to the tissue due to the large amount of stored energy in the output filter. 
     SUMMARY 
     According to one embodiment of the present disclosure, a circuit for controlling the discharging of stored energy in an electrosurgical generator includes a pulse modulator which controls an output of a power supply. At least one comparator is configured to provide an error signal to the pulse modulator based on a comparison between an output generated by the power supply and a feedback signal generated in response to the application of energy to tissue. A discharge circuit is configured to control the discharge of the output of the power supply to an inductive load disposed in parallel with the output of the power supply based on the comparison between the power supply output and the feedback signal. 
     According to another embodiment of the present disclosure, a circuit for controlling the discharging of stored energy in an electrosurgical generator includes a pulse modulator which controls an output of a power supply. At least one comparator is configured to provide an error signal to the pulse modulator based on a comparison between an output generated by the power supply and a feedback signal generated in response to the application of energy to tissue. A discharge circuit has a first switching component configured to discharge the output of the power supply to an inductive load disposed in parallel with the output of the power supply if the feedback signal is less than the power supply output and a second switching component configured to control switching of the first switching component based on the discharge rate of the output to the inductive load. 
     The present disclosure also provides a method for controlling the discharging of stored energy in an electrosurgical generator. The method includes applying energy stored in an output of a power supply to tissue. The method also includes generating at least one control signal based on at least one of a sensed tissue property and a sensed energy delivery property, (i.e. power, voltage, current, time etc.). The method also includes generating an error signal based on a comparison between the at least one control signal and the energy stored in the output. The method also includes discharging the stored energy to an inductive load in parallel with the output of the power supply based upon the comparison between the energy stored in the output and the control signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments of the present disclosure are described herein with reference to the drawings wherein: 
         FIG. 1A  is a schematic block diagram of a monopolar electrosurgical system in accordance with an embodiment of the present disclosure; 
         FIG. 1B  is a schematic block diagram of a bipolar electrosurgical system in accordance with an embodiment of the present disclosure; 
         FIG. 2  is a schematic block diagram of a generator in accordance with an embodiment of the present disclosure; 
         FIG. 3  is a circuit diagram of a power supply in accordance with an embodiment of the present disclosure; and 
         FIG. 4  is a flow chart diagram of a method for controlling the discharge of energy stored in an output of an electrosurgical generator according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Particular embodiments of the present disclosure are described hereinbelow with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail to avoid obscuring the present disclosure in unnecessary detail. 
     In general, the present disclosure provides for an electrosurgical generator including a power supply configured to rapidly re-direct stored output energy through inductive energy transfer utilizing a controlled switching circuit to regulate, in real-time, the level of power sourced to the RF energy delivered to tissue during treatment. 
     More specifically, when the generator senses increased impedance in tissue due to rapid tissue desiccation, the generator of the present disclosure can control, in real time, the amount of treatment energy applied to tissue through use of a so-called “discharge” circuit. The discharge circuit provides a rapid response and time rate control of the electrosurgical energy delivered to tissue by discharging energy stored in an output filter of the power supply into an inductive load based on a feedback signal generated by the controller. The feedback signal may be based on a sensed tissue property (e.g., impedance) and/or an energy property (e.g., voltage, output energy level, etc.). This control provides for more accurate application of target treatment energy levels to treat tissue. 
     The generator according to the present disclosure can perform monopolar and bipolar electrosurgical procedures, including vessel sealing procedures. The generator may include a plurality of outputs for interfacing with various electrosurgical instruments (e.g., a monopolar active electrode, return electrode, bipolar electrosurgical forceps, footswitch, etc.). Further, the generator includes electronic circuitry configured for generating radio frequency power specifically suited for various electrosurgical modes (e.g., cutting, blending, division, etc.) and procedures (e.g., monopolar, bipolar, vessel sealing, ablation). 
       FIG. 1A  is a schematic illustration of a monopolar electrosurgical system according to one embodiment of the present disclosure. The system includes a monopolar electrosurgical instrument  2  including one or more active electrodes  3 , which can be electrosurgical cutting probes, ablation electrode(s), etc. Electrosurgical RF energy is supplied to the instrument  2  by a generator  20  via a supply line  4 , which is connected to an active terminal  30  ( FIG. 2 ) of the generator  20 , allowing the instrument  2  to coagulate, ablate and/or otherwise treat tissue. The energy is returned to the generator  20  through a return electrode  6  via a return line  8  at a return terminal  32  ( FIG. 2 ) of the generator  20 . The active terminal  30  and the return terminal  32  are connectors configured to interface with plugs (not explicitly shown) of the instrument  2  and the return electrode  6 , which are disposed at the ends of the supply line  4  and the return line  8 , respectively. 
     The present disclosure may be adapted for use with either monopolar or bipolar electrosurgical systems.  FIG. 1B  shows a bipolar electrosurgical system according to the present disclosure that includes an electrosurgical forceps  10  having opposing jaw members  50  and  55 . The forceps  10  includes a shaft member  64  having an end effector assembly  40  disposed at the distal end thereof. The end effector assembly  40  includes two jaw members  50  and  55  movable from a first position wherein the jaw members  50  and  55  are spaced relative to another to a closed position wherein the jaw members  50  and  55  cooperate to grasp tissue therebetween. Each of the jaw members  50  and  55  includes an electrically conductive sealing plate  112  and  122 , respectively, connected to the generator  20  that communicates electrosurgical energy through the tissue held therebetween. 
     Electrically conductive sealing plates  112  and  122 , which act as active and return electrodes, are connected to the generator  20  through cable  23 , which includes the supply and return lines coupled to the active and return terminals  30 ,  32  ( FIG. 2 ). The electrosurgical forceps  10  is coupled to the generator  20  at the active and return terminals  30  and  32  (e.g., pins) via a plug  92  disposed at the end of the cable  23 , wherein the plug includes contacts from the supply and return lines. Electrosurgical RF energy is supplied to the forceps  10  by generator  20  via a supply line connected to the active electrode and returned through a return line connected to the return electrode. 
     Forceps  10  generally includes a housing  60  and a handle assembly  74  that includes moveable handle  62  and handle  72  which is integral with the housing  60 . Handle  62  is moveable relative to handle  72  to actuate the end effector assembly  40  to grasp and treat tissue. The forceps  10  also includes shaft  64  that has a distal end  68  that mechanically engages the end effector assembly  40  and a proximal end  69  that mechanically engages the housing  60  proximate a rotating assembly  80  disposed at a distal end of the housing  60 . 
     With reference to  FIG. 1B , the generator  20  includes suitable input controls (e.g., buttons, activators, switches, touch screen, etc.) for controlling the generator  20 . In addition, the generator  20  includes one or more display screens for providing the surgeon with variety of output information (e.g., intensity settings, treatment complete indicators, etc.). The controls allow the surgeon to adjust power of the RF energy, waveform, and other parameters to achieve the desired waveform suitable for a particular task (e.g., coagulating, tissue sealing, division with hemostasis, etc.). Further, the forceps  10  may include a plurality of input controls which may be redundant with certain input controls of the generator  20 . Placing the input controls at the forceps  10  allows for easier and faster modification of RF energy parameters during the surgical procedure without requiring interaction with the generator  20 . 
       FIG. 2  shows a schematic block diagram of the generator  20  having a controller  24 , a power supply  27 , an RF output stage  28 , and a sensor module  22 . The power supply  27  may provide DC power to the RF output stage  28  which then converts the DC power into RF energy and delivers the RF energy to the forceps  10 . The controller  24  includes a microprocessor  25  having a memory  26  which may be volatile type memory (e.g., RAM) and/or non-volatile type memory (e.g., flash media, disk media, etc.). The microprocessor  25  includes an output port connected to the power supply  27  and/or RF output stage  28  which allows the microprocessor  25  to control the output of the generator  20  according to either open and/or closed control loop schemes. 
     A closed loop control scheme generally includes a feedback control loop wherein the sensor module  22  provides feedback to the controller  24  (i.e., information obtained from one or more sensing mechanisms that sense various tissue parameters such as tissue impedance, tissue temperature, output current and/or voltage, etc.). The controller  24  then signals the power supply  27 , which then adjusts the DC power supplied to the RF output stage, accordingly. The controller  24  also receives input signals from the input controls of the generator  20  and/or forceps  10 . The controller  24  utilizes the input signals to adjust the power output of the generator  20  and/or instructs the generator  20  to perform other control functions. 
     The microprocessor  25  is capable of executing software instructions for processing data received by the sensor module  22 , and for outputting control signals to the generator  20 , accordingly. The software instructions, which are executable by the controller  24 , are stored in the memory  26  of the controller  24 . 
     The controller  24  may include analog and/or logic circuitry for processing the sensed values and determining the control signals that are sent to the generator  20 , rather than, or in combination with, the microprocessor  25 . 
     The sensor module  22  may include a plurality of sensors (not explicitly shown) strategically located for sensing various properties or conditions, e.g., tissue impedance, voltage at the tissue site, current at the tissue site, etc. The sensors are provided with leads (or wireless) for transmitting information to the controller  24 . The sensor module  22  may include control circuitry which receives information from multiple sensors, and provides the information and the source of the information (e.g., the particular sensor providing the information) to the controller  24 . 
     More particularly, the sensor module  22  may include a real-time voltage sensing system (not explicitly shown) and a real-time current sensing system (not explicitly shown) for sensing real-time values related to applied voltage and current at the surgical site. Additionally, an RMS voltage sensing system (not explicitly shown) and an RMS current sensing system (not explicitly shown) may be included for sensing and deriving RMS values for applied voltage and current at the surgical site. 
     The measured or sensed values are further processed, either by circuitry and/or a processor (not explicitly shown) in the sensor module  22  and/or by the controller  24 , to determine changes in sensed values and tissue impedance. Tissue impedance and changes thereto may be determined by measuring the voltage and/or current across the tissue and then calculating changes thereof over time. The measured and calculated values may be then compared with known or desired voltage and current values associated with various tissue types, procedures, instruments, etc. This may be used to drive electrosurgical output to achieve desired impedance and/or change in impedance values. As the surgical procedure proceeds, tissue impedance fluctuates in response to adjustments in generator output as well as removal and restoration of liquids (e.g., steam bubbles) from the tissue at the surgical site. The controller  24  monitors the tissue impedance and changes in tissue impedance and regulates the output of the generator  20  in response thereto to achieve the desired and optimal electrosurgical effect. 
     Referring to  FIG. 3 , there is shown a block diagram of the power supply  27  including a control circuit  100  in series with a switching circuit  145 . The control circuit  100  includes a first comparator  110  (e.g., an operational amplifier) having positive and negative input pins +A 1  and −A 1 , respectively. Positive input pin +A 1  is configured to receive an applied control signal (e.g., a variable DC voltage) from the controller  24  based on any one or more tissue parameters provided by the sensor module  22 . Negative input pin −A 1  is configured to receive a proportionally scaled feedback voltage of the power source output (e.g., connected to the RF output stage  28 ) to match the applied control signal on input pin +A 1 , as will be discussed in further detail below. 
     When the power source output fails to match the applied control signal, the resulting voltage difference at positive and negative input pins +A 1  and −A 1  causes the first comparator  110  to output an analog error signal (e.g., analog voltage) to drive a pulse modulator (“PM”)  115 . PM may be, for example, a pulse width modulator, a phase shift modulator or any such device known in the art for converting the analog error signal to a digital pulse control signal. The PM  115  converts the analog error signal to a digital pulse control signal (e.g., digital voltage) to implement control of a full-bridge power stage  120  by phase shifting the switching of one half-bridge with respect to the other. It allows constant frequency pulse-width modulation to provide high efficiency at high frequencies and can be used either as a voltage mode or current mode controller. More specifically, an AC/DC converter  125  converts an available ac signal (e.g., from an ac line voltage) to a de signal to drive the full-bridge power stage  120 , the output of which is, in turn, controlled by the digital pulse control signal to reflect the applied control signal from the controller  24 . The resulting controlled output of the full-bridge power stage  120  drives an output filter  130  (e.g., a low-pass filter), having an inductor  132  and an output capacitor  134 , to generate a DC output voltage V, across the output capacitor  134 . The resulting output voltage V, is converted to RF energy by the RF output stage  28  and output to the electrosurgical instrument. A feedback compensator  140  continuously monitors the output voltage V, (e.g., input to the RF output stage  28 ) and, in turn, provides a proportionally scaled feedback of the power source output to input pin −A 1  of the first comparator  110  to match the applied control signal from the controller  24 . 
     With continued reference to  FIG. 3 , discharging of energy is achieved in real-time using an active discharge circuit (ADC)  145 —a component of the power supply  27 —that switches inductor  150  using a first switching component  160  in parallel with the output capacitor  134  to discharge the energy therefrom, as will be discussed in further detail below. The ADC  145  includes a second comparator  180  (e.g., an operational amplifier) having negative and positive input pins −A 2  and +A 2  operably coupled to the positive and negative input pins +A 1  and −A 2  of the first comparator  110 , respectively. In this manner, the input pins −A 2  and +A 2  of the second comparator  180  continuously monitor the difference between the applied control signal from the controller  24  on positive input pin +A 1  and the proportionally scaled feedback of the power source output on negative input pin −A 1 . 
     An inductive load  150  (e.g., an inductor) is connected in parallel with the output filter  130  and in series with the first switching component  160 . The first switching component  160  is normally off and may be a transistor, such as a field-effect transistor (FET), metal-oxide semiconductor field-effect transistor (MOSFET), insulated gate bipolar transistor (IGBT), relay, or the like. A first resistive element  162  is in series with the first switching component  160  and with ground  168 , which is known as a source follower circuit. The source follower limits the amount of current that flows through the first resistive element  162 , the switching component  160 , and the inductor  150 . 
     In the case of the power source output being greater than the applied control signal (i.e., −A 1 &gt;+A 1 ), the switching circuit  145  utilizes inductive energy transfer to rapidly re-direct the stored output energy of the power source  27  away from the RF output stage  28  until the power source output matches the applied control signal (i.e., −A 1 =+A 1 ). More specifically, the second comparator  180  provides a drive voltage sufficient to close the first switching component  160  to discharge the stored energy from the output capacitor  134  to the inductive load  150 . The activation of the first switching component  160  causes a conduction current I Q1  to discharge from the capacitor  134  to ground  168  through the inductive load  150  and the first resistive element  162  to generate corresponding voltages V Lr  and V R1 , respectively. That is, while the first switching component  160  is switched on, the inductive load  150  absorbs the energy discharged by the output capacitor  134  to rapidly decrease the output voltage V c  until the power source output again matches the applied control signal (i.e., −A 1  =+A 1 ). Under this match condition, the second comparator  180  no longer provides the sufficient drive voltage, resulting in the first switching component  160  to return to the normally off position to interrupt the flow of the conduction current I Q1  through the inductive load  150 . The interruption of current flow through the inductive load  150  causes the magnetic flux field on the inductive load  150  to collapse due to a back electromagnetic force of voltage thereacross (e.g., a so-called “back EMF effect”). The back EMF voltage turns on diode  155 , connected in shunt with the inductive load  150 , to become forward-biased, providing a path for the inductor  150  magnetic flux and conductive current to be reset to zero. In addition this process prevents the back EMF voltage from increasing to a level sufficient to cause damage and/or stress to other components of the ADC  145  (e.g., the first switching component  160 , the first resistive element  162 , etc.). 
     The ADC  145  includes a second normally off switching component  170  that provides so-called “turn-on limiting” of the first switching component  160  to control the flow of the conduction current I Q1  through the inductive load  150 . More specifically, the second switching component  170  operates to monitor the voltage drop V R1  across the first resistive element  162  caused by the conduction current I Q1 . Resistors  164  and  166  establish the threshold for component  170  turn on limiting. As the conduction current I Q1  through the first switching component  160  increases, the voltage drop V R1  across the first resistive element  162  increases to drive the second switching component  170  on, when the threshold for turn on limiting of component  170  is reached. The turn on of the second switching component  170  effectively reduces the drive voltage applied to the first switching component  160  to a steady state value from the second comparator  180 , thereby regulating the current flow through the first switching component  160 . The resulting reduced drive voltage of the first switching component  160  stabilizes the flow of conduction current I Q1  through the first switching component  160  and, thus, through the first resistive element  162  thereby regulating the voltage drop V R1  thereacross. In this manner, the output voltage V c  across the output capacitor  134  discharges at an incremental time rate of change, represented by equation (1) below:
 
 Vc= 1 /C*∫   0   t   I   Q1   dt   (1)
 
     Where: 
     Vc is the output voltage across the capacitor  134 ; 
     C is the capacitance of the capacitor  134 ; and 
     I Q1  is the conductive current through the inductive load  150 . 
     In the illustrated embodiment, one or more resistive elements  164  and  166  are utilized to set the desired proportion of the voltage drop V R1  across the first resistive element  162  sufficient to turn on the second switching element  170 . That is, each of resistive elements  164  and  166  may be interchanged with resistive elements of various resistance values to vary the proportion of the voltage drop V R1  across the first resistive element  162  at which the second switching component  170  turns on. For example, the resistance ratio provided by the combination of the resistive elements  164  and  166 , adjusts the proportion of the voltage drop V R1  necessary to turn on the second switching component  170 . The resistive elements  164  and  166  of  FIG. 3  are illustrative only in that a single resistive element (not explicitly shown) or, alternatively, a plurality of resistive elements (not explicitly shown) in parallel and/or in series may replace the resistive elements  164  and  166  between the first switching component  160  and the second switching component  170  to achieve substantially the same purpose. 
     A buffer  172  (e.g., one or more resistors) between the first switching component  160  and the output of the second comparator  180  provides an isolation buffer therebetween when the second switching component  170  is turned on. As seen in  FIG. 3 , absent the buffer  172 , the output of the second comparator  180  is shorted to ground  168  due to the closure of the second switching component  170 . In this way, the buffer  172  operates to prevent a so called “over current” condition on the second comparator  180  during the closure of the second switching component  170 . 
       FIG. 4  illustrates a method  200  for controlling the discharge of energy stored in an output of an electrosurgical generator. In step  210 , energy is supplied to tissue. More specifically, the power supply  27  provides DC power to the RF output stage  28 . The RF output stage  28  converts the DC power into RF energy and delivers the RF energy to tissue (e.g., via forceps  10 ). In step  220 , the sensor module  22  generates a feedback signal to the controller  24  based on any one or more sensed tissue and/or energy properties. In step  230 , a comparison is made between a control voltage generated by the controller  24  in response to the sensor feedback signal and the output voltage V c  sampled by feedback compensator  140 . In step  240 , based on the comparison of step  230 , an error signal is generated by the first comparator  110  and provided to the PM  115 . PM  115  drives the full bridge power stage  120  to develop the output voltage Vc on capacitor  134 , based on any one or more sensed tissue and/or energy properties. In step  250 , the switching circuit  145  controls the discharging of the output capacitor  134  by redirecting the power supply  27  stored energy using the inductive load  150  in response to a reduction of required RF energy delivered to the tissue, based on any one or more sensed tissue and/or energy properties. Sensor module  22  provides feedback to controller  24  regarding the reduced RF energy need, whereby controller  24  then communicates a reduced control voltage to the power supply  27 . Comparator  180  automatically monitors the reduced control voltage, where −A 2  is now less than +A 2 , to drive switch  160  on. The turn on of switch  160  redirects the stored energy of output capacitor  134 . As a result, the redirected stored energy in the power supply  27  lowers the output voltage Vc and rapidly reduces the delivered RF energy of the RF output stage  28 . 
     While several embodiments of the disclosure have been shown in the drawings and/or discussed herein, it is not intended that the disclosure be limited thereto, as it is intended that the disclosure be as broad in scope as the art will allow and that the specification be read likewise. Therefore, the above description should not be construed as limiting, but merely as exemplifications of particular embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.