Abstract:
A method for suppressing arc formation during an electrosurgical tissue treatment procedure includes the steps of supplying pulsed current from an energy source to tissue and measuring the pulsed current supplied from the energy source. The method also includes the steps of comparing an instantaneous measured pulse to a predetermined threshold and controlling the pulsed current supplied from the energy source based on the comparison between the instantaneous measured pulse and the predetermined threshold.

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to an electrosurgical system and method and, more particularly, to arc detection and suppression for electrosurgical tissue treatment procedures such as vessel sealing and tissue ablation. 
     2. Background of Related Art 
     Energy-based tissue treatment is well known in the art. Various types of energy (e.g., electrical, ohmic, resistive, ultrasonic, microwave, cryogenic, laser, etc.) are applied to tissue to achieve a desired result. Electrosurgery involves application of high radio frequency electrical current to a surgical site to cut, ablate, coagulate or seal 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 bipolar electrosurgery, 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 electrode such that an electrical circuit is formed between the two electrodes (e.g., electrosurgical forceps). In this manner, the applied electrical current is limited to the body tissue positioned between the electrodes. 
     Electrical arc formation is a discharge of current that is formed when a strong current flows through normally nonconductive media such as air (e.g., a gap in a circuit or between two electrodes). Electrical arc formation is problematic when occurring at the site of tissue being treated during an electrosurgical procedure. The arcing results in increased current being drawn from the electrosurgical generator to the electrical arc, thereby increasing the potential of damage to tissue due to the presence of increased levels of current and to the electrosurgical generator due to overcurrent conditions. 
     SUMMARY 
     According to an embodiment of the present disclosure, a method for suppressing arc formation during an electrosurgical tissue treatment procedure includes the steps of supplying pulsed current from an energy source to tissue and measuring the pulsed current supplied from the energy source. The method also includes the steps of comparing an instantaneous measured pulse to a predetermined threshold and controlling the pulsed current supplied from the energy source based on the comparison between the instantaneous measured pulse and the predetermined threshold. 
     According to another embodiment of the present disclosure, a method for suppressing arc formation during an electrosurgical tissue treatment procedure includes the steps of supplying pulsed current from a current source to tissue and measuring each pulse of the supplied pulsed current. The method also includes the steps of comparing each measured pulse to a predetermined threshold and terminating each measured pulse if the measured pulse exceeds the predetermined threshold. 
     According to another embodiment of the present disclosure, an electrosurgical system includes an electrosurgical generator adapted to supply pulsed current to an electrosurgical instrument for application to tissue and a current limiting circuit operably coupled to the electrosurgical generator and configured to measure each pulse of the pulsed current for comparison with a predetermined threshold. Each pulse is controlled based on the comparison. 
    
    
     
       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  illustrates a relationship between current source voltage vs. time for tissue undergoing treatment in accordance with two contrasting scenarios; and 
         FIG. 4  is a circuit diagram of a current limiting circuit 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. 
     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). 
     Fig. lA is a schematic illustration of a monopolar electrosurgical system  1  according to one embodiment of the present disclosure. The system  1  includes an electrosurgical instrument  2  (e.g., monopolar) having one or more electrodes for treating tissue of a patient P (e.g., electrosurgical cutting, ablation, etc.). More particularly, 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  (see  FIG. 2 ) of the generator  20 , allowing the instrument  2  to coagulate, seal, 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  of the generator  20  (see  FIG. 2 ). 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. 
       FIG. 1B  is a schematic illustration of a bipolar electrosurgical system  3  according to the present disclosure. The system  3  includes a bipolar electrosurgical forceps  10  having one or more electrodes for treating tissue of a patient P. The electrosurgical forceps  10  includes opposing jaw members  11  and  13  having an active electrode  14  and a return electrode  16 , respectively, disposed therein. The active electrode  14  and the return electrode  16  are connected to the generator  20  through cable  18 , which includes the supply and return lines  4 ,  8  coupled to the active terminal  30  and return terminal  32 , respectively (see  FIG. 2 ). The electrosurgical forceps  10  is coupled to the generator  20  at a connector  21  having connections to the active terminal  30  and return terminal  32  (e.g., pins) via a plug disposed at the end of the cable  18 , wherein the plug includes contacts from the supply and return lines  4 ,  8 . 
     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  may include one or more display screens for providing the user with variety of output information (e.g., intensity settings, treatment complete indicators, etc.). The controls allow the user to adjust power of the RF energy, waveform parameters (e.g., crest factor, duty cycle, etc.), and other parameters to achieve the desired waveform suitable for a particular task (e.g., coagulating, tissue sealing, intensity setting, etc.). 
       FIG. 2  shows a schematic block diagram of the generator  20  having a controller  24 , a DC power supply  27 , and an RF output stage  28 . The power supply  27  is connected to a conventional AC source (e.g., electrical wall outlet) and is adapted to provide high voltage DC power to an RF output stage  28  that converts high voltage DC power into RF energy. RF output stage  28  delivers the RF energy to an active terminal  30 . The energy is returned thereto via the return terminal  32 . 
     The generator  20  may include a plurality of connectors to accommodate various types of electrosurgical instruments (e.g., instrument  2 , electrosurgical forceps  10 , etc.). Further, the generator  20  may be configured to operate in a variety of modes such as ablation, monopolar and bipolar cutting coagulation, etc. The generator  20  may also include a switching mechanism (e.g., relays) to switch the supply of RF energy between the connectors, such that, for example, when the instrument  2  is connected to the generator  20 , only the monopolar plug receives RF energy. 
     The controller  24  includes a microprocessor  25  operably connected to 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 that is operably connected to the power supply  27  and/or RF output stage  28  allowing the microprocessor  25  to control the output of the generator  20  according to either open and/or closed control loop schemes. Those skilled in the art will appreciate that the microprocessor  25  may be substituted by any logic processor (e.g., control circuit) adapted to perform the calculations discussed herein. 
     A closed loop control scheme or feedback control loop is provided that includes sensor circuitry  22  having one or more sensors for measuring a variety of tissue and energy properties (e.g., tissue impedance, tissue temperature, output current and/or voltage, etc.). The sensor circuitry  22  provides feedback to the controller  24 . Such sensors are within the purview of those skilled in the art. The controller  24  then signals the HVPS  27  and/or RF output phase  28  which then adjust DC and/or RF power supply, respectively. The controller  24  also receives input signals from the input controls of the generator  20  or the instrument  10 . The controller  24  utilizes the input signals to adjust power outputted by the generator  20  and/or performs other control functions thereon. 
     In particular, sensor circuitry  22  is adapted to measure tissue impedance. This is accomplished by measuring voltage and current signals and calculating corresponding impedance values as a function thereof at the sensor circuitry  22  and/or at the microprocessor  25 . Power and other energy properties may also be calculated based on collected voltage and current signals. The sensed impedance measurements are used as feedback by the generator  20 . In embodiments, sensor circuitry  22  may be operably coupled between RF output stage  28  and active terminal  30 . 
     A current limiting circuit  40  is operably coupled between the power supply  27  and the RF output stage  28  and is configured to instantaneously control the pulsed current output of power supply  27  on a pulse-by-pulse basis. More specifically, the current limiting circuit  40  is configured to monitor the pulsed current output of power supply  27  and, for each output pulse, the current limiting circuit  40  measures the instantaneous current of the pulse and compares the measured instantaneous current to a predetermined threshold current. In some embodiments, the predetermined threshold current may be the maximum allowable current output of the power supply  27 . If the measured instantaneous current exceeds the predetermined threshold current, the current limiting circuit  40  controls the pulsed current output of power supply  27  and/or terminates the measured pulse, as will be discussed in further detail below with reference to  FIGS. 3 and 4 . 
     In one embodiment, current limiting circuit  40  includes suitable components preconfigured to measure instantaneous current on a pulse-by-pulse basis and control (e.g., adjust, terminate, suspend, etc.) output of generator  20  based on a comparison between the measured current and the predetermined threshold current, as will be discussed in detail below. For example, in some embodiments, the predetermined threshold current may be between about 4.5 A and about 6 A. In another embodiment, the predetermined threshold current may be, for example, data stored in memory  26  and configured to be compared to each current pulse measured by current limiting circuit  40  for processing by microprocessor  25 . Based on this comparison, the microcontroller  25  generates a signal to controller  24  to control the pulsed output current of generator  20 . 
       FIG. 3  illustrates the relationship between a current source voltage v cs  (e.g., the voltage across power supply  27 ) vs. time “t” waveform  50 , wherein current limiting circuit  40  is not utilized, and a corresponding current voltage source v cs  vs. time “t” waveform  60  taken over the same time range as waveform  50 , wherein current limiting circuit  40  is utilized in accordance with embodiments described by the present disclosure. Waveforms  50  and  60  illustrate, by way of example, the pulsed output current of generator  20  resulting from the contrasting scenarios discussed above. Waveform  50  is illustrated for purposes of contrast with waveform  60  (described below) to show the benefit of using current limiting circuit  40  to detect and suppress electrical arc formation at the tissue site. Electrical arc formation at the site of the tissue being treated results in increased current being drawn from the generator  20  to the electrical arc, thereby increasing the potential of damage to tissue caused by the presence of increased current and to the generator  20  due to overcurrent conditions. 
     Waveform  50  illustrates the pulsed output current of RF output stage  28  including an abnormal pulse  55  that represents a significantly increased voltage v cs  between time intervals t a  and t b . As described above, the abnormal pulse  55  may be caused by the occurrence of electrical arcing at the tissue site that results in increased current drawn from power supply  27  to the electrical arc and, thus, an increase in voltage v cs , for the duration of pulse  55  (e.g., time interval t a ≦time “t”≦time interval t b ). 
     Similar to waveform  50 , waveform  60  illustrates the pulsed output current of power supply  27  including an abnormal pulse  65  that represents a significantly increased voltage v cs  starting at time interval t a  similar to abnormal pulse  55  discussed above. However, in this instance, the abnormal pulse  65  is instantaneously detected by current limiting circuit  40 , and terminated at time interval t b-1 . More specifically, the abnormal pulse  65  is measured and compared to the predetermined threshold current, and terminated at time interval t b-1  since the measured pulse exceeds the predetermined threshold current. This is in contrast to the duration of abnormal pulse  55 , which without the benefit of detection and termination via current limiting circuit  40  endures from time interval t a  to time interval t b . Since the above described comparison is repeated for each pulse, the current limiting circuit  40  of the present disclosure operates to regulate the duty cycle and, thus, the RMS current of the pulsed current output of the generator  20  to prevent or suppress arc formation, thereby minimizing potential damage to tissue from increased drawing of current to the electrical arc. 
     Current limiting circuit  40  may include any suitable components to enable operation as described hereinabove such as, for example, current sense resistors, shunt resistors, transistors, diodes, switching components, transformers, and the like. Although shown in the illustrated embodiments as being operably coupled between power supply  27  and RF output stage  28 , current limiting circuit  40  may be integrated within power supply  27  or RF output stage  28  or may be operably coupled between RF output stage  28  and active terminal  30 . 
       FIG. 4  shows, by way of example, a circuit schematic of current limiting circuit  40  according to some embodiments of the present disclosure. In this example, current limiting circuit  40  includes a current sense resistor  42  that operates in conjunction with an op-amp  44 , a comparator  46 , a plurality of resistors  43   a - f , and a microprocessor  48 , to control the pulsed current output of power supply  27  that is supplied to instrument  2  or forceps  10  on a pulse-by-pulse basis, as discussed hereinabove. 
     As power supply  27  supplies pulsed current to RF output stage  28 , a potential difference V cs  is generated across current sense resistor  42  and received, as input, at the non-inverting or positive input of op-amp  44 . V cs  is proportional to the pulsed current output of power supply  27 . Op-amp  44  generates an output voltage signal that is fed back to the inverting or negative input of op-amp  44  (e.g., negative feedback), causing op-amp  44  to drive its output voltage signal toward a level that minimizes the differential voltage between its positive and negative inputs. The output voltage signal of op-amp  44  is received, as input, at the positive input of comparator  46 . A reference voltage V REF  (e.g., 3.3 volts) that is proportional to the predetermined threshold current is applied to the negative input of comparator  46  for comparison to the input voltage signal received from op-amp  44 . In this way, the pulsed current output of power supply  27  is compared to the predetermined threshold current on a pulse-by-pulse basis by way of comparison, at comparator  46 , between V REF  and the input voltage signal from op-amp  44 . This comparison dictates the output of comparator  46 , which will change either from “high” to “low” or from “low” to “high” as the input voltage signal from op-amp  44  exceeds V REF . The “high” or “low” output of comparator  46  signals microprocessor  48  to control the output of RF output stage  28  accordingly. As the input voltage signal from op-amp  44  exceeds V REF  comparator  46  signals the microprocessor  48  to cause RF output stage  28  to interrupt or terminate the instantaneous current pulse (e.g., pulse  65 ) being supplied to instrument  2  or forceps  10 . For example, in some embodiments, RF output stage  28  includes one or more suitable switching components (not shown) such as a transistor that opens or closes in response to an output signal (e.g., turn-on voltage) received from microprocessor  48 . In this scenario, when the switching component is closed, the pulsed current output of power supply  27  is delivered un-interrupted to instrument  2  or forceps  10  via RF output stage  28  and, when the switching component is open, the pulsed current output of power supply  27  is shunted to ground through resistors  43   a  and  43   b  rather than being supplied to instrument  2  or forceps  10 . The termination or interruption of an instantaneous current pulse being supplied to instrument  2  or forceps  10  operates to suppress or terminate electrical arcing that may be formed at the tissue site. By terminating the instantaneous current pulse, the voltage V Cs  across the current sense resistor  42  decreases below V REF  such that the output voltage signal from op-amp  44  is less than V REF  by comparison. The resulting output of comparator  46  operates to signal the RF output stage  28  to continue or re-establish (e.g., via closing of the switching component) delivery of pulsed current output from power supply  27  to instrument  2  or forceps  10  for application to tissue. In this way, current limiting circuit  40  controls on a pulse-by-pulse basis whether or not pulsed current is supplied to instrument  2  or forceps  10 . 
     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.