Abstract:
Electrosurgery method and apparatus. In the method, tissue is cut or coagulated, with an electrically low conductive liquid providing cooling. In another method, skin is cut by electrosurgery in a dry field using a low duty cycle signal energizing the cutting electrode, minimizing tissue charring. A combination coagulation and cutting electrode performs both functions. The cutting is performed by a blade edge generating a local plasma adapted for cutting. Superimposed on the blade edge is an electrode of greater surface area electrically insulated from the cutting electrode, for coagulation. In another version, a single component cutting/coagulation blade (electrode) has a cutting and a flat partially insulated portion defining through holes in the insulation for coagulation. Also provided is an electrical circuit whereby each electrode is isolated by a filter from cross talk and feedback of the RF signal from the other electrode, minimizing arcing.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Application No. 60/856,549 filed Nov. 2, 2006, title “Probe for Cutting Coagulation and Fulguration,” inventors: Daniel V. Palanker, Paul O. Davison and Alexander B. Vankov, incorporated by reference here in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates generally to surgical methods and apparatus and particularly to electrosurgery. 
       BACKGROUND 
       [0003]    Plasma-mediated thermo-electric cutting for surgery is well known, see for instance, Palanker U.S. Pat. Nos. 6,135,988 and 6,780,178. See also Eggers et al. U.S. Pat. Nos. 6,047,700 and 5,697,882. These disclose plasma-mediated cutting of soft biological tissue where the tissue is immersed or profused with saline solution which, of course, is an electrically conductive medium. See also Palanker et al. U.S. Pat. No. 7,238,185 and McClurken et al. U.S. Pat. No. 7,115,139. For instance, Palanker et al. U.S. Pat. No. 7,238,185 discloses apparatus and method for cutting biological tissue where the tissue being cut is submerged in a conductive liquid medium. The cutting apparatus has a cutting electrode and a return electrode. Both electrodes are immersed in the conductive medium and a voltage (signal) applied between them in order to heat the medium, thus producing a vapor cavity around the cutting portion of the blade and ionizing a gas inside the vapor cavity to produce a plasma. 
         [0004]    However, in actual surgical procedures such as carried out on people or animals, often the tissues are not immersed in a naturally occurring conductive medium such as blood or internal bodily fluids. Then typically a conductive medium such as saline solution is introduced as part of the surgical procedure (“wet field” electrosurgery). Typically the saline or other conductive medium is introduced onto or into the surgical field as part of the surgical procedure. The present inventors have recognized that this requirement to provide the conductive fluid is a drawback since in some cases fluid obscures the surgical field; it somewhat complicates the surgical procedure, and unless the conductive fluid is kept replenished it may cause a breakdown in the plasma regime, thus interfering with the cutting. Also, electric current flowing through the conductive fluid away from the tissue results in unnecessary power dissipation and associated increase in collateral tissue damage. 
         [0005]    An additional technical problem is that electrosurgical equipment typically is used for three main classes of procedures. First, there is cutting of tissue. Next, there is coagulation (sealing) of blood vessels. Next, there is fulguration or ablation which is a species of coagulation typically involving somewhat different levels of heat application, but also for sealing or closing tissue. Some existing electrosurgical equipment provides all of these. However, the amount and type of electrical energy applied for each of these is different and all-purpose devices are generally somewhat unsatisfactory. Moreover, combining such functions in one device is problematic since the types of RF energy applied to achieve the plasma typically differ substantially for each of the three. 
       SUMMARY 
       [0006]    Disclosed here is a method suitable for plasma-mediated electro-thermal cutting of tissue where the tissue to be cut is not bathed or submerged in an electrically conductive medium. In one embodiment, the electrosurgery takes place with the tissue being cut or coagulated while being in contact with a low conductive liquid supplied during the surgical procedure (not natural bodily fluids), meaning a liquid which is a relatively poor conductor of electricity. (This does not refer to its thermo-conductive properties which differ from the electro-conductive properties.) As well known, generally bodily fluids such as blood, bile and other internal bodily fluids such as in joints are high in dissolved salts or other ions and hence relatively electrically conductive. For purposes of this disclosure such fluids are considered conductive since they will typically sustain an electric current at relatively low voltages. A low conductive liquid in this sense includes, for instance, water, glycine, oils, mixtures of water and non-ionic compounds and various other liquids or semi-liquids well known in the field. While these are inherently thermally conductive (as are all fluids), their electro-conductive properties are poor and in an electrical sense they are more insulators than conductors. The provision here of such a liquid or semi-liquid which is of low conductivity has the advantage that it provides local convective and conductive cooling. Cooling is useful here since the applied RF signal and resulting plasma typically cause a considerable elevation in temperature of the adjacent tissue being operated on. This may result in local burning or charring of the tissue which is undesirable. 
         [0007]    Thus the present method for cutting or otherwise operating on (e.g., coagulating) tissue generally includes the steps of contacting the tissue with a plasma generating electrode wherein the electrode is at least partially surrounded by a low conductive fluid supplied from a source external to the body, and applying an electric signal, having in some cases a low duty-cycle, to the electrode that is in contact with the low conductive fluid. The signal causes the formation of a plasma along the electrode between the electrode and the tissue and this plasma performs the tissue cutting or other operation. 
         [0008]    As used here, the term low conductive fluid includes liquids and semi-liquids and semi-solids such as gels and suspensions. A typical such fluid is pure water and others such as glycine, either in its pure form or mixed with water. Other suitable liquids are ocular visoelastic fluid, perfluorocarbons and other oils. Other mixtures of water and non-ionic compounds also result in a low conductive fluid. Generally low conductivity here refers to a resistivity above 1,000 ohm-cm. As well known, electrical resistance is equal to resistivity×length÷area. Resistivity is typically expressed in units of Ohm·meter or Ohm·cm. Hence low conductive fluid here includes not only distilled or deionized water, but also water or other liquids that may contain very small amounts of ions or otherwise are very slightly conductive so their conductivity is at least an order of magnitude less than that of natural bodily liquids. 
         [0009]    The electrode here used with the cooling fluid may be any one of the well known electro-surgery types or other types. A particular type is disclosed here but this is not limiting. Other types are disclosed in the above referenced patents, and also see U.S. Patent Application Publication No. 2004/0199157, inventor Daniel V. Palanker, incorporated herein by reference in its entirety, disclosing yet another electrode. The electrode typically defines an edge. The edge, however, is not like that of an ordinary knife which does the cutting solely via mechanical application to the tissue being cut. Instead here the edge of the electrode focuses for the electric field induced by the applied electrical signal. This field concentrated at the edge generates a local plasma discharge. Hence the edge may be tapered or flat or sharp, but need not be of any particular dimensions or level of sharpness. In some cases the edge itself may be relatively dull. The tissue cutting may be assisted by mechanical force supplied by the edge of the electrode, as in conventional cutting. Moreover, the electrode conventionally may be configured as a monopolar or bipolar cutting tool in terms of the electrode arrangement. A return electrode (in close proximity to the primary electrode) or a grounding pad (for the monopolar arrangement) is provided spaced apart from the primary electrode to serve as a current return path. The return electrode is typically placed as a pad on tissue having contact with the tissue being cut, or in conductive liquid having such contact. 
         [0010]    In general here, the plasma is formed along the edge of the electrode by application of an electrical signal to the electrode. To further decrease the heat accumulation and associated collateral tissue damage, low duty cycle waveforms are used. As well known, duty-cycle refers to the proportion of time that the energy is actually being applied. Low duty-cycle here typically refers to duty-cycles of less than 10% which may be, for instance, 1% or less, or 0.1% or less. In some cases the low duty-cycle refers to the pulse voltage regime that is applied to the electrode. For instance, a pulsed low duty-cycle signal may include a plurality of pulse bursts that are separated by more than one millisecond (e.g., has a frequency of less than 1 KHz) where each burst is shorter than one millisecond. The burst of pulses may include pulses that are biphasic (e.g., of alternating polarity) and the pulses may have different peak voltages. Again, none of this is limiting. The low duty-cycle is intended to minimize tissue charring or burning. 
         [0011]    Note that the presence of the low conductive fluid here has little or no effect on the plasma generation or the cutting or other capabilities of the apparatus. Thus tissue may be cut or otherwise affected by the plasma when the electrode is initially dry, that is, surrounded by for instance ambient air only, and continue to be cut as the blade (electrode edge) becomes immersed in the low conductive fluid and also natural conductive fluid such as blood. Hence for the present method to be operative there is no need for the electrode edge to be fully immersed in the low conductive fluid during the entire time of cutting or coagulation or ablation. Since the purpose of the fluid here is cooling, as long as enough fluid is provided for sufficient time to remove heat as desired, that is adequate. For instance, when skin is cut to begin a surgical procedure, there may be no need to initially supply the low conductive fluid which may be introduced into the wound only after the skin has been penetrated. 
         [0012]    Another advantage of immersion in a non-conductive fluid is that electric current is concentrated in the area of contact of the electrode with tissue. If the electrode is held in a conductive fluid, current will flow not only through the tissue but also through the fluid around it, and thus more heat will be deposited at the site. In addition, if the electrode is held in air above the tissue, dielectric breakdown (plasma arc) can occur between the electrode and tissue in multiple location along the electrode surface, connecting the electrode with the tissue and resulting in energy dissipation at the locations of contact of the arcs with tissue. Since the threshold of dielectric breakdown in liquids in much higher than in the air, the addition of a non-conductive fluid will prevent arcing in the areas other than at locations of the direct contact of electrode with tissue. This will result in much better localization of the energy deposition into the tissue, leading to reduced collateral damage. 
         [0013]    Also provided here is a method of electrosurgical dry field tissue cutting, whereby human or animal skin tissue is cut (resected) without application thereto of any conductive or non-conductive fluid. Note that skin is essentially devoid of conductive natural bodily fluids such as blood, etc. and so is by its nature a dry field. This method is accomplished by application of a relatively low power electrical signal to the cutting electrode which cuts the skin (both epidermis and dermis) cleanly, without charring or burning. 
         [0014]    Also disclosed here is an electrosurgery apparatus, also referred to in the field as a cutting head, which includes a first portion intended for the coagulation (or fulguration or ablation) function and a second portion intended for the tissue cutting function. These portions are combined so that the two portions are each associated with an electrode at the terminus of the cutting head. The two electrodes are spaced quite close together but isolated electrically. The operator (surgeon) selects at any one time whether he wishes to cut or coagulate. The associated electrode is then energized with a suitable electrical signal (typically of different frequency duty-cycle, etc.) for each function. The two electrodes are each optimized for their intended function in terms of their configuration. The two electrodes, while located closely adjacent one another, are separated by insulating (dielectric) material. 
         [0015]    Moreover, in one embodiment each electrode is provided with a suitable band pass filter to prevent cross talk or feedback of the RF signal applied to each electrode from propagating in the other of the electrodes. In one embodiment the coagulation electrode is a C-shaped structure, that is, having a curved shape, and is superimposed on a rounded edge which defines part of the cutting edge for the cutting electrode function. The two electrodes are electrically insulated from one another by a dielectric material and fastened together by, for instance, epoxy material. The separation between them is enough to prevent arcing there between. In one embodiment two such coagulation electrodes are provided, driven by the same RF signal and with one being located on each side of the cutting electrode to provide even coagulation on each side of the cut. 
         [0016]    In another embodiment, a single component electrode blade performs cutting and coagulation. The exposed blade edge is used for cutting. The blade flat part is used for coagulation. The flat part is mostly electrically insulated, but the insulation defines a plurality of through holes, partly exposing the underlying flat part of the blade. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0017]      FIGS. 1A ,  1 B show a method for electrosurgery using a low conductive fluid. 
           [0018]      FIG. 2  shows an overview of a hand piece of an electrosurgery apparatus for a dual function head as described herein. 
           [0019]      FIG. 3  shows detail of the structure of the  FIG. 2  device. 
           [0020]      FIGS. 4A and 4B , respectively, show detail of the present cutting electrode and coagulation electrodes. 
           [0021]      FIGS. 4C and 4D  show another version of a dual function electrode structure. 
           [0022]      FIG. 5  shows a schematic diagram of a circuit for filtering of the electrical signals applied to the  FIG. 2  device. 
       
    
    
     DETAILED DESCRIPTION 
     Electrosurgery with Cooling Fluid 
       [0023]      FIG. 1A , which bears some similarity to FIG. 1 of U.S. Pat. No. 7,238,185, shows an apparatus  10  for cutting material  12  submerged in a low conductivity liquid medium  14 .  FIG. 1B  shows detail of  FIG. 1A , enlarged. Note that in U.S. Pat. No. 7,238,185 this medium  14  is expressly described as being a conducting liquid medium and the electrode generates the plasma in the conducting liquid medium. That is a difference between present  FIG. 1B  and FIG. 1 of U.S. Pat. No. 7,238,185 since in present  FIG. 1  the plasma is generated in the tissue being operated on, and the electrode is in effect in contact with the tissue in order to generate the plasma. Material  12  is biological tissues including, for instance, muscle tissue  12 A, nerve tissue  12 B, bone  12 C and connective tissue  12 D. 
         [0024]    Apparatus  10  includes handpiece  19  terminating in cutting electrode  16 . Suitable material for the electrode  16  for instance would be tungsten, titanium, molybdenum, stainless steel or alloys thereof. Again, this is not limiting. The cutting electrode  16  is surrounded by insulating layer  20 . A return electrical path is provided by conventional patient grounding pad  22 . Insulating layer  20  can be any suitable dielectric material. Fluid  14  is supplied via handpiece  19  at  18 ,  20  which define an outlet near electrode  16 . Fluid  14  may alternatively by supplied via a separate tubing or conduit, not part of handpiece  19 , in any case from an external reservoir. 
         [0025]    Also provided is a voltage control unit  24  also known as a radio frequency (RF) generator which provides the electrical (radio frequency in this case) signals which energize the apparatus via lead or leads  62 . In this case unit  24  has a pulse control for pulsing the voltage in accordance with a predetermined modulation format, see U.S. Pat. No. 7,238,185 incorporated herein by reference. 
         [0026]    In this case a thin layer of a plasma  28  is formed around the cutting blade  16 . Thus electrode  16  is immersed in the low conductive fluid  14  and put in contact with tissue  12  and a suitable RF signal applied to electrode  16 , such that tissue  12  is heated to produce a vapor cavity region  30  around the blade  16  adjacent to the tissue. Vapor cavity region  30  is thereby filled with water vapor and other gasses  32  emanating from the tissue  12  during the vaporization. The layer of gas  32  is ionized in the strong electric field around the cutting electrode  16  to make a thin layer of plasma  28 . 
         [0027]    The actual nature of the applied electrical signals which are suitable to create the desired plasma effect is well known in the field. For instance, in one case the applied signal is an RF (radio frequency) signal having a frequency in the range of 100 KHz to 10 MHz. Typically this energy is applied in the form of bursts of pulses. Each burst typically has a duration in the range of 10 microseconds to 1 millisecond. The individual pulses in each burst typically each have a duration of 0.1 to 10 microseconds with an interval therebetween of 0.1 to 10 microseconds. The actual pulses are typically square waves and bi-phasic, that is alternating positive and negative amplitudes. Generally the interval between pulses must be shorter than a lifetime of the plasma vapor cavity in order to maintain the cavity and the plasma regime during each pulse burst. In one embodiment the bursts each are separated by a duration of at least one millisecond. Typically the time between the pulse bursts is sufficient so that the duty-cycle is relatively low as explained above. This minimizes the undesirable heating effects. However, as indicated here the provision of the cooling fluid reduces heating problems also. Typically the plasma has a temperature greater than 100° C. 
       Combination Cutting and Coagulation Apparatus 
       [0028]    The following discloses a new electrode configuration intended for a combination cutting and coagulation and fulguration and ablation, shown also in  FIG. 1A  but not required for the method of  FIG. 1A . An overview of the hand piece  80  (corresponding to handpiece  19  in  FIG. 1A ) is shown in  FIG. 2  for the present such combination device. This figure omits the pulse generator  24  and associated electrical lead or leads  62  shown in  FIG. 1A , which are provided for the  FIG. 2  apparatus but not shown here for simplicity. The  FIG. 2  device  80  is mostly conventional in configuration except as disclosed further herein. It includes a hand grip portion  82  with hand grip ridges as shown on the lower part thereof. This portion is intended to be held in the surgeon&#39;s hand. Two control buttons  84 ,  86  activate electric switches (not shown) which are provided for purposes of respectively selecting the cutting or coagulation regimes. Note that the ablation function can also be carried out, in the cutting regime, by a sweeping of the cutting electrode over the region to be ablated. The rear portion  88  is for balance and for holding the electrical leads extending there from which terminate in a conventional electrical connector (not shown) which connects to lead (or leads)  62  to the generator  24  (also not shown in  FIG. 2 ). The dimensions of the device of  FIG. 2  are such that it is comfortably held in a hand, yet small enough for surgery for the intended application. The working end of the device of  FIG. 2  includes at its distal end the electrode tip assembly  92 , described below with reference to  FIG. 3 . Assembly  92  is attached to the body portion  82  by an intermediate portion (shaft)  96 . The intermediate portion  96  carries the electrical leads to the tip assembly  92  as described with reference to  FIG. 3 . In a typical situation, the entire assembly  80  is disposable and is disposed of after each surgery. Of course, this disposable aspect is not limiting. The materials for the device of  FIG. 2  are conventional and the portions shown are typically molded from plastic with the exception of the electrical leads and electrode tip assembly  92 , whose configuration is described further below. 
         [0029]      FIG. 3  shows in a perspective view detail of the electrode tip assembly  92  and the nearest part of the intermediate portion  96 .  FIG. 3  is a semi-exploded view as described hereinafter. In  FIG. 3 , the cutting blade subassembly (electrode)  102  includes the actual cutting electrode. Associated therewith and fixed thereto is the left side coagulation electrode subassembly  104  and the right side coagulation electrode subassembly  106  (mostly not visible). Electrical insulation, which is plastic heat shrink tubing  108  and  110 , is provided for electrodes  104  and  106 . Also provided are lengths of heat shrink plastic tubing  112  and  114 . As indicated by the arrow associated with insulation  114 , this piece of tubing is meant to be slid forward during assembly of this device. (It is shown in the retracted view merely for purposes of illustration.) 
         [0030]    The RF energizing signals are provided to the three electrodes  102 ,  104 ,  106  by respectively a length of wire  116  and a second length of wire  118 . In one embodiment, these are 30 gauge insulated wire. The three electrodes are adhered together by an epoxy adhesive layer indicated at  124 . (A similar epoxy layer, not visible, adheres electrode  106  to electrode  102 .) A length of large diameter plastic heat shrink tubing  120  is provided and slides forward as indicated by the arrow during the assembly of the device at the factory. This is intended to be slid all the way forward to cover the other pieces of insulating tubing at location d. Dimensions a and b are respectively 0.030 inches (0.75 mm) and 0.02 inches (0.5 mm). Of course these dimensions are merely illustrative. These dimensions define the distance between the edge of the cutting electrode  102  and the coagulation electrodes  104 ,  106 . Note that the right hand side (lower) coagulation electrode subassembly  106  is mostly not visible in  FIG. 3  because it is on the bottom side of the apparatus  92 . Hence in this particular embodiment, there are two coagulation electrodes, one on the top which is mostly visible at  104 , and a second only partly visible at  106 . This allows even coagulation on both sides of the cut. These same two coagulation electrodes each perform fulguration, at a different power setting than used for coagulation. 
         [0031]    Not shown in  FIG. 3  is the coaxial tubing  97  for fluid delivery of  FIG. 2 , which fits around coaxially the left most (rear) part of tubing  120 . The terminus of tubing  97  defines the opening portion  18 , 20  of  FIG. 1B  which delivers the cooling fluid  14  to the area being operated on. In another embodiment, tubing  97  is omitted since the  FIG. 3  apparatus does not require the cooling fluid, or cooling fluid may be delivered by other means. Also, tubing  97  may be used to deliver conductive fluid, such as saline solution, depending on the intended use by the surgeon. 
         [0032]      FIGS. 4A and 4B  respectively show perspective views of part of the cutting blade subassembly  102  and the left side (upper) coagulation electrode subassembly  104 . The right side (lower) coagulation electrode subassembly  106  is essentially a mirror image of the  FIG. 4B  component. The cutting blade subassembly  102  of  FIG. 3  is relatively simple. In this embodiment it includes a support piece of annealed sheet titanium 0.1 mm thick as shown in  FIG. 4A , to which is spot welded a slightly wider cutting blade of approximately similar shape and made of stainless steel (or titanium) sheet which is 0.01 inch (0.25 mm) thick. The actual edge  126  thereof is honed to a sharp edge tapered at e.g. 10 0  on one side only. A number of each of these components is typically conventionally machined, stamped, or etched out of a large sheet of metal. In one embodiment, the entire structure  102  is approximately 0.61 inches (15 mm) long and its width is 0.217 inches (5.5 mm). The rounded edge  126  here is, e.g., a section of a circle (not limiting). 
         [0033]    The coagulation electrode subassembly  104  of  FIG. 4B  is more complicated since it exhibits three dimensionally as shown in the  FIG. 4B  perspective view. The active (exposed) portion of the electrode is the C-shaped section  128 , which as shown is slightly raised. In one embodiment, the C-shaped section has an overall thickness of 0.008 inches (0.2 mm) and the raised portion is 0.004 inches (0.1 mm) thick. The open part of the C-shaped section subtends approximately a 60° arc. The total length of the  FIG. 4B  structure in one embodiment is 0.681 inches (17.3 mm). Again this component is typically one of many etched or stamped or machined out of a large sheet of, e.g., titanium, which has been annealed for hardness. The overall diameter of the C-shaped section in one embodiment is approximately 0.138 inches (3.5 mm). The other coagulation electrode  106  is essentially similar but a mirror image, since it lies on the other side of the cutting electrode. 
         [0034]    With reference to  FIG. 3 , not shown is an overall glass or other electric insulating layer covering most of the structure but leaving the C-shaped section of electrode  104  (and electrode  106 ) exposed and also leaving exposed the actual edge  126  of the cutting blade portion  102 . Moreover there is similar insulation (dielectric) provided between each of cutting blade subassembly  102  and the two coagulation electrodes  104 ,  106 . This typically again is a coating of glass or ceramic approximately 0.005 to 0.5 mm thick, preferably 0.01 to 0.2 mm thick. The insulation extends to the proximal portion of each electrode. The glass type insulation is typically applied by a conventional process of dipping each relevant component prior to assembly in liquid (molten) glass and then annealing the glass. In  FIG. 3 , wire  116  provides the RF signal for the coagulation function and is spot welded or otherwise attached to the proximal terminal (and uninsulated) portions of both coagulation electrodes  104  and  106 . The other wire  118  similarly attaches to the terminal proximal portion of cutting blade subassembly  102 . 
         [0035]    Further with regard to  FIG. 3 , in general the exposed C-shaped surface area of each of the coagulation electrodes  104 ,  106  is much larger than that of the exposed cutting edge  126  of electrode  102 , since most of the cutting blade assembly  102  (except its edge) is covered by the insulation material so that typically only the actual edge  126  is exposed and this lies more or less flush with the surrounding insulating material. The width of the exposed edge  126  is in the range of 0.01 to 0.1 mm. The larger exposed surface area of the coagulation electrodes  104 ,  106  makes coagulation of large tissue surfaces or blood vessels easier due to the extended area of contact and increased application of electrical power. To prevent electrical arc between the cutting and coagulation electrodes potentially leading to electrode damage, sufficient spacing between the electrodes is provided. In general, the less the distance between electrodes, the more arcing, therefore it is desirable to maintain a certain minimum spacing between cutting and coagulation electrodes as provided by the  FIG. 3  configuration. 
         [0036]    Further, the particular electrode configuration as shown in  FIG. 3  is not limiting. For instance in one embodiment, the cutting electrode instead of being a relatively large plate, mostly covered by insulation, is instead a length of wire partially embedded in an insulating body with a portion of the wire exposed. An exposed edge of a plate is equivalent in terms of plasma generation to a wire. Again this wire is separated from the coagulation electrode by a suitable minimum distance along its length to prevent arcing. 
         [0037]    In these figures the return electrode is not shown since it is typically a separate grounding pad structure or equivalent of conventional type as in  FIG. 1A , not necessarily part of the cutting/coagulation hand piece  80 . However, that is not limiting. 
         [0038]    Note moreover that the apparatus of  FIG. 3  does not show how it would be used in conjunction with the introduction of the low conductivity liquid into the operating field. In one embodiment, the liquid is introduced into the surgical field by a separate length of tubing, not part of the  FIG. 2  or  FIG. 3  structures. In other embodiments a tubing or conduit is incorporated or defined in the hand piece  80  of  FIG. 2  with its distal end connected to a reservoir of suitable liquid and terminating near the working end of the  FIG. 3  structure, such as in the vicinity of the electrode assembly  92 . The surgeon conventionally controls the rate of liquid delivery (e.g., 10 to 200 ml/min) through the tubing or conduit. 
         [0039]    The fluid delivery aspect is thereby illustrated in  FIG. 2 , where tubing  97  is coaxial with intermediate portion  96 . The arrows illustrate the fluid flow from tubing  97 . At the distal end of the rear portion  88  is connected tubing  99  for the fluid, connecting to valve  101  and hence to a fluid reservoir such as a bag of pure water (not shown). Tubing  99  connects to tubing  97  via a conduit extending through hand piece  80 . Typically coaxial tubing  97  terminates 10 to 20 mm from the end of intermediate portion  96 . 
         [0040]      FIG. 4C  shows another type of combination cutting and coagulation electrode  170 , but having a single blade used for both functions. Hence this is an alternative to and corresponds in terms of function to the dual electrode structure of  FIGS. 3 and 4A  and  4 B, but is simpler in construction.  FIG. 4C  only illustrates the blade, not the electrical leads or hand piece which would be similar to that of  FIG. 2 . Note that only one electrical lead would be needed with the  FIG. 4C  electrode.  FIG. 4C  shows this electrode in a plan view. It includes a base or rear portion  172  for attachment of the electrical lead. The working portion  174  has about the same overall length, width and thickness and edge configuration as structure  102  in  FIG. 4A , and is of a similar material, and is similarly electrically insulated, except for edge  178 , by an overlayer of e.g. glass electrical insulation  180 . 
         [0041]    Electrical insulation layer  180  defines a number (e.g., 10 to 100) of openings  186  which each expose the underlying metal of the blade portion  174 . The openings  186  are more or less evenly spaced apart and are each in the range of 1 to 100 μm in diameter, preferably 10 to 50 μm. The glass insulation layer  180  is e.g. 0.05 to 0.25 mm thick. As shown in side cross sectional view in  FIG. 4D  (not to scale), electrode  170  has the insulating layer  180  on both its flat sides  192 ,  194  both sides also defining openings  186 . Note that in  FIG. 4D  the blade edge is shown as being tapered; the tapering is somewhat exaggerated for purposes of illustration in this figure. 
         [0042]    In use, the electrode edge  178  is used for cutting, and the flat sides  192 ,  194  with the penetrated insulation layer  180 , for coagulation, similar to use of the  FIG. 3  electrodes. The surgeon chooses coagulation or cutting at any one time, by activating the appropriate controls such as buttons  84 , 86  in  FIG. 2  so as to supply suitable pulsed energy to the electrode  170 . 
         [0043]      FIG. 5  shows an electrical circuit  140  in schematic form, which typically is provided in the handle portion  82  of the hand piece  80  of  FIG. 2  on a suitable circuit board for use with the  FIG. 3  dual electrode. This circuit has two arms. The upper arm is coupled to wire (lead)  116 , which in turn connects to the two coagulation electrodes  104  and  106  (not shown). The lower arm is coupled to the second wire (lead)  118 , which connects to the cutting blade subassembly (electrode)  102 . The upper arm of  FIG. 5  includes a band pass filter  142 , including an inductance  146  and a capacitance  148 . However this is merely representative of any sort of band pass (or band stop) filter. The bottom portion includes a different value band pass filter  152 , including in this case inductor  154  and capacitor  156 , again not meant to be limiting but merely to illustrate a band pass (or band stop) filter. 
         [0044]    In this embodiment, two different electrical signals are provided as is conventional, one for coagulation and the second for cutting as controlled by hand piece  80  buttons  84 ,  86  or a foot switch (not shown). Typically coagulation uses a lower frequency RF signal than does cutting. In this case as illustrated, the coagulation RF signal applied to lead  158  is at a frequency of 0.46 MHz. (The other characteristics of this signal are not indicated here since this is merely an indication of the nature of this signal.) As indicated by the arrow, this signal is intended propagate to the coagulation electrodes  104 ,  106 . An RF signal of different 4 MHz frequency is applied to lead  160  which is not necessarily connected to lead  158  and this 4 MHz signal is intended to connect to the cutting blade electrode  102 . The source of both these RF signals is the RF generator unit  24  shown in  FIG. 1 . 
         [0045]    The present inventors have recognized the technical problem that the cutting electrode  102  here lies in close proximity to an arc source (electrodes  104 ,  106 ) useful for large scale coagulation which may lead to breakdown of the gap between the electrodes  102  and  104  or  106 , especially when a wet cutting head is partially exposed to air. Breakdown of this gap, e.g., shorting, may cause damage to the delicate cutting electrode and may also result in damage to the power supply unit  24 . Even if the cutting electrode  102  is connected to ground to protect the RF generator  24 , an arc between the coagulation electrodes  104 ,  106  and cutting electrode  102  may destroy either electrode when a high voltage bipolar waveform is used as the energizing signal. Even when electrically floating, electrodes can still conduct enough current through cable (lead) capacitance in order to damage the cutting edge of the cutting electrode  102 , which is quite thin. 
         [0046]    Therefore to reduce cross talk between the cutting and coagulation energizing signals, two different frequencies are used here for cutting and coagulation as in  FIG. 5 . The band pass filters  142 ,  152  provided as shown in  FIG. 5  isolate the two signals. As illustrated this prevents the cross talk of the 4 MHz frequency signal from propagating back up into the upper arm of  FIG. 5 . Similarly filter  152  prevents the coagulation signal of 0.46 MHz frequency, even though picked up in wire  118 , from propagating to the lower arm. Band stop filters can be used instead of band pass filters if the energizing frequencies are shifted far enough from one another for complete isolation. 
         [0047]    In this way both the coagulation and cutting electrodes may be supplied with their signals from the same RF generator  24  and in some cases may even be supplied by the same output line from the generator  24 . In this case a common node  164  is provided as shown in  FIG. 5  to which both the cutting and coagulation RF signals at respectively 4 MHz and 0.46 MHz are applied. The filters  142 ,  152  prevent the undesired signal from propagating down to the respective wires  116  and  118  in each arm of the circuit of  FIG. 5 . In other embodiments the common node  164  is not present, and separate signals are provided to lines  158  and  160  from the RF generator unit  24 . 
       Dry Field Skin Tissue Cutting 
       [0048]    Also disclosed here is a method of cutting (resecting) skin tissue including the epidermis (outer layer) and dermis (under layer) using an electrosurgery electrode in a dry field environment. “Dry field” here refers to the absence of naturally occurring conductive bodily fluids and the absence of a conductive fluid applied to skin (such as saline solution). Note that the epidermis by definition is free of blood vessels. The underlying dermis does have some blood vessels, but the blood supply is limited since the blood vessels are small. In the surgical field, it is conventional that to cut skin electrosurgically a conductive fluid is needed to prevent tissue charring. Generally therefore skin is cut using a conventional scalpel. This is because the use of the added conductive fluid is difficult since the fluid tends to not remain alongside the electrode and thereby maintenance of the plasma regime along the electrode is problematic. 
         [0049]    In accordance with the present invention, dry skin or skin with only a non-conductive fluid in it or on it is cut using an electrosurgical electrode of conventional configuration or as described above. The pulsed electrical energy applied to the electrode is controlled to be of relatively low power (much lower than is conventional in electrosurgery), so no skin charring occurs. Typically the amount of peak electrical power is at least 100 Watts, and the duty cycle of the electrical signal is 15% or less. 
         [0050]    With regard to the nature of the relatively low power also see e.g. copending and commonly owned and published U.S. application Ser. No. 10/779,529, filed Feb. 13, 2004, inventor Daniel Palanker, incorporated herein by reference in its entirety, and also the above disclosure of suitable energization of the electrode. For instance, the signal applied to the electrode is in one case an RF signal having a frequency in the range of 100 KHz to 10 MHz. Typically this energy is applied in the form of bursts of pulses. Each burst typically has a duration in the range of 10 microseconds to 1 millisecond. The individual pulses in each burst typically have a duration of 0.1 to 10 microseconds, with an interval therebetween of 0.1 to 10 microseconds, as above. Typically the pulse bursts each are separated by a duration of at least 1 millisecond, thereby providing the low duty cycle. This minimizes the heating effects. 
         [0051]    This relatively low power signal maintains the desired plasma regime, and allows for tissue cooling between bursts. Thus it allows for cutting the human epidermis and dermis with minimal charring. Generally any resulting tissue damage is no more than that resulting from cutting skin with a conventional (non-electrosurgery) scalpel. The resulting wound therefore would heal as quickly as a wound created by a conventional scalpel. This approach has the advantage of allowing the surgeon to use the same electrosurgical apparatus for skin cutting as for surgery within the body. It also allows for cutting and coagulation using the same instrument. 
         [0052]    This disclosure is illustrative but not limiting; further modifications will be apparent to those skilled in the art in light of this disclosure and are intended to fall within the scope of the appended claims.