Abstract:
Disclosed herein are improved, efficient electrosurgical probes suitable for tissue vaporization and cutting of tissue structures, more particularly for performing electrosurgical cutting, ablation (volumetric tissue vaporization), coagulating and/or modification within a body tissue, cavity or vessel or on the surface of a patient. The system and method of the present invention optionally include means for irrigation and/or aspiration of the surgical site and therefore may be used in relatively dry environments for, for instance, oral, otolaryngological, laparoscopic, and dermatologic procedures.

Description:
PRIORITY  
       [0001]     This application claims the benefit of U.S. Provisional Application Ser. No. 60/648,105 filed Jan. 28, 2005. In addition, this application is a continuation-in-part of co-pending U.S. patent application Ser. No. 10/911,309 filed Aug. 4, 2004 which, in turn, claims the benefit of U.S. Provisional Application Ser. No. 60/493,729 filed Aug. 11, 2003. The contents of these three applications are hereby incorporated by reference herein in their entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to the field of electrosurgery, and, more particularly, to high efficiency surgical devices and methods which use of high frequency (RF) electrical power for cutting, bulk removal by vaporization (ablation), coagulation and treatment of tissue in a conductive liquid environment, as well as other forms of tissue treatment such as shrinking, lesion formation, sculpting and thermal treatment with or without externally supplied liquids.  
       BACKGROUND OF THE INVENTION  
       [0003]     The present invention provides a system and method for performing electrosurgical cutting, ablation (volumetric tissue vaporization), coagulating or modification within a body tissue, cavity or vessel on the surface of a patient. The system and method of the invention herein disclosed may be used in relatively dry environments for, for instance, oral, otolaryngological, laparoscopic, and dermatologic procedures.  
         [0004]     Electrosurgical procedures require a proper electrosurgical generator, which supplies the Radio Frequency (RF) electrical power, and a proper surgical electrode (also known as an electrosurgical probe). Under appropriate conditions the desired surgical effects are accomplished.  
         [0005]     Note: in common terminology and as used herein the term “electrode” may refer to one or more components of an electrosurgical device (such as an active electrode or a return electrode) or to the entire device, as in an “ablator electrode”. Electrosurgical devices may also be referred to as “probes”.  
         [0006]     Electrosurgical procedures rely on the application of RF electrical power using an electrode (or probe) for cutting, ablation or coagulation of tissue structures in a joint space which is filled by liquid. Many types of electrosurgical devices can be used; however, they can be divided to two general categories: monopolar devices and bipolar devices. When monopolar electrosurgical devices are used, the RF current generally flows from an exposed active electrode, through the patient&#39;s body, to a passive, return current electrode that is externally attached to a suitable location on the patient body. In this way the patient&#39;s body is part of the return current circuit. When bipolar electrosurgical devices are used, both the active and the return current electrodes are exposed, and are typically positioned in close proximity to each other and the active site. The RF current flows from the active electrode to the return electrode, through the nearby tissue and conductive fluids. Monopolar and bipolar devices in many fields of electrosurgery operate according to the same principles.  
         [0007]     During the last several years, specialized arthroscopic electrosurgical probes called ablators have been developed. Examples of such instruments include ArthroWands manufactured by Arthrocare (Sunnyvale, Calif.), VAPR electrodes manufactured by Mitek Products Division of Johnson &amp; Johnson (Westwood, Mass.) and electrodes by Stryker Corporation (Kalamazoo, Mich.) and Smith and Nephew Endoscopy (Andover, Mass.). These ablators differ from conventional electrosurgical probes in that they are designed for the bulk removal of tissue by vaporization in a conductive liquid environment, rather than for the cutting of tissue or for coagulation of bleeding vessels.  
         [0008]     Recently the use of electrosurgery with conductive fluids for urology, gynecology and other procedures is also becoming popular. Previously, mostly non-conductive fluids were used for these applications.  
         [0009]     While standard electrodes are capable of ablation (bulk vaporization), their geometries are not efficient for accomplishing this task. During ablation, water within the target tissue is vaporized. Because volumes of tissue are vaporized rather than discretely cut out and removed from the surgical site, the power requirements of ablator electrodes are generally higher than those of other arthroscopic electrosurgical electrodes. The geometry and design of the electrode and the characteristics of the RF power supplied to the electrode greatly affect the power required for ablation (vaporization) of tissue. Electrodes with inefficient designs require higher power levels than those with efficient designs.  
         [0010]     During electrosurgery procedures in conductive fluids, most of the RF energy delivered to an electrode is dissipated in the fluid and in the adjacent tissue as heat, thereby raising the temperature of the fluid within the cavity and of the adjacent tissue. A substantial fraction of the RF power is used for the creation of sparks (arcs) in the vicinity of the electrodes. These sparks accomplish the tissue vaporization and cutting. In summary, the sparks are essential for tissue vaporization (ablation), while heating of the liquid and tissue away from the active electrode tip always occurs but has no desirable clinical effect.  
         [0011]     The heating of the irrigation fluid and especially the adjacent tissue is not beneficial to the patient. On the contrary, this may substantially increase the likelihood of patient burns. For this and other reasons, improved, efficient electrosurgical electrodes are desirable for tissue vaporization and cutting of tissue structures.  
         [0012]     An electrosurgical probe, in general, is composed of a metallic conductor surrounded by a dielectric insulator (e.g., formed of plastic, ceramic or glass) along the length, with the exception of the exposed metallic electrode. The probe electrode is often immersed in a conducting fluid, either filling a natural or created cavity or applied as irrigant to a “dry” site, and is brought in contact with the tissue structure during the electrosurgical procedure. The probe is energized, typically at a voltage of few hundred to a few thousand volts, using an RF generator operating at a frequency between 100 kHz to over 4 MHz. This voltage induces a current in the conductive liquid and nearby tissue. This current heats the liquid and tissue, the most intense heating occurring in the region very close to the electrode where the current density is highest. At points where the current density is sufficiently high, the liquid boils locally and many steam bubbles are created, the steam bubbles eventually insulating part or all of the electrode. Electrical breakdown in the form of an arc (spark) occurs in the bubbles which insulate the electrode. The sparks in these bubbles are channels of high temperature ionized gas, or plasma (temperature of about a few thousand degrees Kelvin). These high current density sparks, heat, evaporate (ablate) or cut the tissue (depending on the specific surgical procedure and the probe geometry) that is in contact with the spark.  
         [0013]     The spark generation and tissue heating, modification or destruction very close to the electrode tip are a beneficial and desirable effect. At the same time, the induced current heats liquid and tissue farther away from the immediate vicinity of the electrode tip. This heating is undesirable and potentially dangerous because it may uncontrollably damage tissue structures in surrounding areas and also deep under the surface. The design of higher efficiency probes is desirable as it would lead to less heating of fluid and tissue not in close proximity, and give the surgeon a larger margin of safety during the procedure.  
         [0014]     Ablation (vaporizing) electrodes currently in use, whether monopolar or bipolar, have an active electrode surrounded by an insulator significantly larger in size than the ablating surface of the electrode. For ablators with a circular geometry, the diameter of the portion of the probe which generates ablative arcs (the “working” diameter) is generally not greater than 70 to 80 percent of the diameter of the insulator (the “physical” diameter) and therefore only about 50% of the physical probe area can be considered effective. This increases the size of the distal end of the electrode necessary to achieve a given ablative surface size, and, for some procedures performed in internal body cavities, necessitates the use of large bore cannulae, an undesirable condition.  
         [0015]     Many surgical procedures are not performed inside a natural or formed body cavity and as such are not performed on structures submerged under a conductive liquid. In laparoscopic procedures, for instance, the abdominal cavity is pressurized with carbon dioxide to provide working space for the instruments and to improve the surgeon&#39;s visibility of the surgical site. Other procedures, such as oral surgery, the ablation and necrosis of diseased tissue, or the ablation of epidermal tissue, are also typically performed in an environment in which the target tissue is not submerged. In such cases, it is necessary to provide a conductive irrigant to the region surrounding the active electrode(s), and frequently also to aspirate debris and liquid from the site. Such irrigant may be applied by a means external to the instrument; however, having an irrigation means internal or attached to the instrument generally provides better control and placement. This is also true for aspiration of fluid and debris. External means may be used for aspiration from the site; however, aspiration through the instrument distal end provides improved fluid control and may, in some cases, draw tissue toward the active electrode thereby enhancing performance.  
         [0016]     Electrosurgical devices having means for irrigating a site, and/or means for aspirating fluid, bubbles and debris from a site are well known. Smith, in U.S. Pat. No. 5,195,959, disclose an electrosurgical device with suction and irrigation. Bales, et al., in U.S. Pat. No. 4,682,596 disclose a catheter for electrosurgical removal of plaque buildup in blood vessels, the catheter having lumens for supplying irrigant to the region of the instrument distal tip and for aspirating debris from the region. Hagen, in U.S. Pat. No. 5,277,696, discloses a high frequency coagulation instrument with means for irrigation and aspiration from the region of the instrument tip. Pao, in U.S. Pat. No. 6,674,499, discloses a coaxial bipolar probe with suction and/or irrigation. Eggers, in U.S. Pat. No. 6,066,134, discloses a method for electrosurgical cutting and coagulation which uses a bipolar probe having means for irrigating and aspirating from the region of the probe distal tip. The Eggers device uses the irrigant flow to provide a return path to a return electrode recessed axially a distance away from the active electrode(s).  
         [0017]     The placement and volume of aspiration flow through an electrosurgical instrument in the region of an active electrode, or even through the active electrode, may adversely affect the performance of the instrument. Electrosurgery, particularly procedures in which tissue is vaporized, is a thermal process. Aspiration which draws fluid through or around the active electrode surfaces draws away process heat, thereby decreasing heating of the conductive irrigant in the region so as to decrease bubble production and ablative arcing. This makes the device less efficient thereby requiring increased power to achieve acceptable performance.  
       SUMMARY OF THE INVENTION  
       [0018]     It is accordingly an object of this invention to produce an electrosurgical probe which has high efficiency.  
         [0019]     It is also an object of this invention to produce an electrosurgical probe which has a distal end of compact size.  
         [0020]     It is further an object of this invention to produce an electrosurgical probe which may be used in applications in which the target tissue is not submerged in a conductive liquid.  
         [0021]     It is additionally an object of this invention to produce an electrosurgical probe which has an irrigation means.  
         [0022]     It is finally an object of this invention to produce an electrosurgical probe which has an aspiration means.  
         [0023]     These and other objects are accomplished in the invention herein disclosed which is an advanced, high efficiency, electrosurgical probe equipped with one or more additional metallic electrodes which are not connected directly to any part of power supply circuit. This electrode may contact the surrounding conducting liquid and/or tissue. The potential of this electrode is “floating” and is determined by the size and position of the electrode, the tissue type and properties, and the presence or absence of bodily fluids or externally supplied fluid. This “floating” electrode is mounted in such a way that one portion of the electrode is in close proximity to the probe tip, in the region of high potential. Another portion of the floating electrode is placed farther away, in a region of otherwise low potential. This low region may be in the conductive fluid, in contact with tissue, or both.  
         [0024]     The floating electrode generates and concentrates high power density in the vicinity of the active region, and results in more efficient liquid heating, steam bubble formation and bubble trapping in this region. This increases the probe efficiency, which allows the surgeon to substantially decrease the applied RF power and thereby reduce the likelihood of patient burns and injury. The probe may be operated so that the portion of the floating electrode in close proximity to the active electrode has sufficient current density to produce vaporization of the liquid and arcing so as to vaporize tissue. Alternatively, the probe may be operated so that the floating electrode contacts tissue and portions of the floating electrode in contact with the tissue have sufficient current density to thermally coagulate blood vessels. This is particularly useful for achieving hemostasis in vascular tissue, such as, for instance, that present when performing tonsillectomies.  
         [0025]     These innovative electrosurgical devices with floating electrodes may be very effective in other medical procedures other than evaporation (ablation), such as, for instance, for thermal treatments, lesion formation, tissue sculpting, and tissue “drilling”, with or without externally supplied liquids.  
         [0026]     The electrosurgical device herein disclosed is a probe which has a proximal portion forming a handle, and an elongated distal portion having at its distal end at least one active electrode and at least one floating electrode. The active electrode is connected via cabling and means within the handle portion to an electrosurgical generator. In a preferred embodiment, at least a portion of the distal-most portion of at least one floating electrode is in close proximity to at least one active electrode. In a further preferred embodiment, the elongated distal portion is tubular, having a first lumen connected via a means within the handle portion to an external irrigant source, and a second, dielectric tube having a second lumen disposed within the first lumen and connected via a means within the handle portion to an external vacuum source. Irrigant is supplied via the first lumen and means at the distal tip to the region between at least one active electrode and the portion of at least one floating electrode in close proximity to the active electrode. Liquid and ablation products are aspirated from the region of the probe tip by the second lumen and means at the distal tip.  
         [0027]     In other embodiments, the probe has irrigation supplied to the probe tip via both lumens and no aspiration through the probe is used. In other embodiments, the irrigation is through the first or second lumen only. In further embodiments, the probe is equipped with aspiration but not irrigation, the irrigant being applied to the site by an external device.  
         [0028]     Additional preferred embodiments include added features which enhance the probe efficiency, for example by increasing the rate of bubble generation when voltage is first applied to the probe.  
         [0029]     In still other embodiments, the active electrode and floating electrode form an array of protuberances in which the active and floating electrodes are interspersed.  
         [0030]     In yet other embodiments, the probe is configured for producing holes in tissue.  
         [0031]     These and other objects and features of the invention will become more fully apparent when the following detailed description is read in conjunction with the accompanying figures and examples. However, it is to be understood that both the foregoing summary of the invention and the following detailed description are of a preferred embodiment, and not restrictive of the invention or other alternate embodiments of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0032]      FIG. 1  shows an electrosurgical system formed in accordance with the principles of this invention.  
         [0033]      FIG. 2  shows an electrosurgical probe formed in accordance with the principles of this invention.  
         [0034]      FIG. 3  is an expanded perspective view of the distal end of the object of  FIG. 2 .  
         [0035]      FIG. 4  is a plan view of the objects of  FIG. 3 .  
         [0036]      FIG. 5  is a side elevational sectional view of the objects of  FIG. 3  at location A-A of  FIG. 4 .  
         [0037]      FIG. 6  is a side elevational view of the objects of  FIG. 3 .  
         [0038]      FIG. 7  is a distal end view of the objects of  FIG. 3 .  
         [0039]      FIG. 8  is an axial sectional view of the objects of  FIG. 3  at location A-A of  FIG. 7 .  
         [0040]      FIG. 9  is an axial sectional view of the objects of  FIG. 3  at location B-B of  FIG. 7 .  
         [0041]      FIG. 10  is an expanded sectional view of the distal portion of the object of  FIG. 2  during use.  
         [0042]      FIG. 11  is an expanded perspective view of the distal portion of an alternate embodiment.  
         [0043]      FIG. 12  is an expanded plan view of the distal portion of another embodiment.  
         [0044]      FIG. 13  is a side elevational sectional view of the objects of  FIG. 12  at location A-A of  FIG. 12 .  
         [0045]      FIG. 14  is a perspective view of the objects of  FIG. 12 .  
         [0046]      FIG. 15  is a side sectional view of the objects of  FIG. 12  in use.  
         [0047]      FIG. 16  is an expanded perspective view of the distal portion of an alternate embodiment.  
         [0048]      FIG. 17  is a perspective view of the distal portion of another alternate embodiment.  
         [0049]      FIG. 18  is a perspective view of the objects of  FIG. 17  positioned for use to show the irrigant flow path.  
         [0050]      FIG. 19   a  is an expanded side elevational view of the distal portion of another alternate embodiment.  
         [0051]      FIG. 19   b  is an auxiliary sectional view at location C-C of  FIG. 19   a.    
         [0052]      FIGS. 20   a  through  20   e  are an expanded view of an efficiency enhancing portion of the objects of  FIG. 19   b  during use showing the function of the portion.  
         [0053]      FIG. 21  is an auxiliary sectional view at location C-C of  FIG. 19   a  of an alternate embodiment which is a modification of the embodiment of  FIGS. 19   a  and  19   b.    
         [0054]      FIG. 22  is an expanded plan view of the distal portion of another alternate embodiment.  
         [0055]      FIG. 23  is a side sectional view of the objects of  FIG. 22  at location A-A of  FIG. 22 .  
         [0056]      FIG. 24  is a perspective view of the objects of  FIG. 22 .  
         [0057]      FIG. 25  is a sectional view of the object of  FIG. 22  during use.  
         [0058]      FIG. 26  is a perspective view of another embodiment for forming holes in tissue.  
         [0059]      FIG. 27  is an expanded plan view of the distal end of the objects of  FIG. 26 .  
         [0060]      FIG. 28  is a side elevational sectional view of the objects of  FIG. 27  as shown in  FIG. 27 .  
         [0061]      FIG. 29  is a sectional view of the objects of  FIG. 27  during use. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0062]     The words “a”, “an”, and “the” as used herein mean “at least one” unless otherwise specifically indicated.  
         [0063]     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification, including definitions, will control.  
         [0064]     An electrosurgical probe is a metallic electrode coated with dielectric except for an exposed portion at the electrode tip. This tip is an active element of the probe. When placed into conductive liquid-tissue media and energized, the probe induces electrical current in the conducting liquid and nearby tissue. This current deposits energy into the liquid and tissue raising their temperatures and creating the desired clinical effect. The highest energy deposition is in close proximity to the tip where current density is largest.  
         [0065]     Power density in close proximity of the tip depends primarily on the applied voltage, the shape and size of the exposed portion of the electrode, and surrounding liquid/tissue electrical conductivity. Also it is affected by the return current electrode size, shape, and position. In general, positioning the return electrode in closer proximity to the active electrode increases the power density in the region near the electrode tip.  
         [0066]     In the case of a monopolar probe, the return current is collected by a large return electrode (sometimes called dispersive electrode or return pad) placed on the patient&#39;s body far away from the probe tip. The power concentration capability of a monopolar probe is determined by the shape of the exposed electrode: the smaller and sharper the tip is, the better its power concentration capability.  
         [0067]     In the case of bipolar probes the return current electrode is placed in moderate proximity to the active electrode (generally from 1 to 10 mm). Some additional power concentration takes place in comparison with the monopolar probe with the same shape of active electrode. The power concentration capability can be controlled additionally by the shape and position of the return electrode. Decreasing the distance between the return electrode and the active electrode increases the power concentration. A problem arises when the probe is generating sparks. (Recall that this is the goal of probe operation in ablation-tissue evaporation or cutting, for example). If the return electrode is placed sufficiently close to the tip to achieve a substantial increase of power concentration, the breakdown (arcing within bubbles) takes place between the tip and return electrode. The spark conductive channel connects the active electrode to the return current electrode and the power supply is loaded directly by the spark. Usually this leads to extra high-energy deposition in the spark between metallic electrodes resulting in localized melting and vaporization of the electrodes themselves. This results in shorting of the power supply and destruction of both the active and return electrodes with little clinical benefit to the patient.  
         [0068]     A good bipolar probe design must avoid arcing between the active and return electrodes. Usually this is achieved by placing the return electrode a sufficiently large distance away from the active electrode to prevent direct breakdown between electrodes. Nevertheless, periodic arcing may take place so that both electrodes are eroded and eventually destroyed, especially in an aggressive mode of operation. Therefore, the additional degree of power concentration achievable by bipolar probes is severely limited.  
         [0069]     The electrosurgical device of the present invention has one or more additional metallic electrodes which are not connected directly to any part of the power supply circuit, and therefore are called “floating”. These floating electrodes are in contact with the tissue and/or liquid in proximity to the active electrode. The electrical potential of these additional electrodes is not fixed, but rather is “floating” and is determined by size and position of the electrode and the electrical conductivity of the tissue and/or liquid surrounding the distal end of the device. This electrode is positioned in such a way that one end of the electrode is in close proximity to the active electrode. Another portion of the floating electrode is positioned in a region of low potential in the liquid and/or tissue. The addition of this floating potential electrode thereby substantially modifies the electrical field distribution, and energy deposition, in the vicinity of the active electrode without the possibility of electrode destruction since the floating electrode is not directly connected to the electrical power supply.  
         [0070]     In the absence of sparking (arcing within bubbles) this electrode increases power density in the vicinity of the probe tip. This is because the floating electrode extends from a high potential region (near the active electrode), to a region with low potential (farther from the active electrode), and “shorts” these points together. The probe floating potential will be in between the potentials of these points. The presence of the electrode decreases the potential near the active electrode, therefore increasing the electric field, current and power density in the region near the active electrode. A floating electrode works about the same way as any extended conductive object in the electrostatic field. The higher power density results in more efficient liquid heating and steam bubble formation, which allows one to decrease the power applied to probe for a given effect. In the presence of the “floating” electrode more sparks are generated in the active region, since this region is larger. Bubble trapping (the retention of bubbles in selected areas to insulate these areas for improved ablator efficiency) is greatly enhanced with proper design of the floating electrode, insulator and the active electrode.  
         [0071]     Sparks are an active element of an electrosurgical process. A spark is generated in a steam bubble if the bubble field (voltage difference across a bubble) is sufficient for breakdown. Usually sparks are generated in bubbles that are close to the active electrode of the probe because current density and field intensity are largest in this region.  
         [0072]     The breakdown or spark inside a bubble is an electrically conductive channel of partly ionized pressurized gas. This medium is called highly collisional plasma. The basic property of this plasma is that the conductivity is proportional to the plasma density. Higher plasma temperatures are associated with higher ionization rates, plasma densities and conductivity.  
         [0073]     Usually energy is deposited into highly collisional plasmas by electric current driven by voltage applied to electrodes at the ends of a plasma channel. In the case of a plasma channel formed inside of a bubble, the inner parts of the bubble surface with the largest voltage difference act as the electrodes to which the channel is connected. Most frequently, but not always, one of these electrodes is a metallic surface of the active electrode and the other is the opposite surface of the bubble or the surface of the tissue.  
         [0074]     Electrically, the plasma channel is characterized by its impedance. The efficiency of energy deposition strongly depends on the ratio between the plasma channel and the power supply impedance. Efficiency (the portion of applied energy deposited to the plasma) as high as 50% can be achieved for matched conditions in which the power supply impedance equals the spark (plasma channel) impedance. If the channel impedance is too large or too small, the power deposition in the plasma is decreased. The power source for the plasma channel formation is the step voltage created by current flow in the conductive liquid surrounding the bubble. The effective impedance of the power supply is of the same order as the impedance of liquid with dimensions of a bubble. That means that the maximum power deposited into the arc channel is on the order of the power deposited into a volume of the bubble size filled with liquid. Deviation of the channel impedance from its optimum value results in decreased power deposition into the channel. These principles are valid if at least one of the channel electrodes is the inner liquid surface of bubble.  
         [0075]     The energy which is deposited to a plasma channel (spark) is determined by the energy density in the surrounding conductive liquid. As taught previously herein, the additional metallic “floating” electrode described in this patent application significantly increases the energy density in the region surrounding the active electrode. This makes it possible to substantially increase the power deposited into the spark. Since the floating electrode can be placed very close to the probe tip, the largest probability is for breakdown and plasma channel formation in the region between the two metallic electrodes—the active electrode and the floating potential electrode. The plasma channel current can now be supported not by a bubble size fraction of the induced current, but by a much larger volume of current flow that is determined by the size of floating electrode. This floating electrode additionally concentrates current delivered to the spark. The optimum spark current can be controlled by adjusting the size and position of the floating electrode. Arcing, then, can occur through bubbles between the active and floating electrodes, or from either electrode through bubbles in contact with that electrode.  
         [0076]     In summary, the subject of this invention is an advanced, electrosurgical probe equipped with an additional “floating potential electrode”. The floating electrode concentrates the power (i.e. increases the power density) in the active region, which leads to more efficient liquid heating, steam bubble formation, and spark generation in this region. Arcing occurs from the floating electrode as well as the active electrode resulting in a probe in which the distal tip has a “working” diameter equal to the “physical” diameter in the case of probes having a radial symmetry. This is in contrast to an electrically active area normally being only about 50% of the physical area of the device.  
         [0077]     More particularly, the device herein disclosed is an electrosurgical probe having a proximal portion forming a handle and a distal portion having at least one active electrode and at least one floating electrode at its distal end. The active electrode is connected via a cable passing through the proximal handle portion to a suitable RF energy source. The elongated distal portion has at least one lumen for supplying conductive irrigant to the probe distal tip, and a means for aspirating vapor and liquid from the region of the probe distal tip.  
         [0078]     The floating electrode favorably affects bubble formation and trapping, and therefore enhances the probe&#39;s performance. This results in high efficiency operation, allowing the surgeon to substantially decrease the applied RF power and thereby reduce the likelihood of patient burns and injury, while at the same time maintaining high performance operation.  
         [0079]     The method of the present invention includes the step of positioning the electrosurgical probe adjacent to target tissue at a surgical site so that at least one of the active electrodes and at least a portion of at least one of the floating electrodes are in close proximity to the target tissue. Conductive irrigant is supplied to the probe distal tip in the region between the active electrode(s) and the target tissue, and between the portion of the floating electrode in close proximity to the tissue, and the tissue. Other portions of the floating electrode(s) may be in contact with target tissue, adjacent tissue, or conductive irrigant. Vacuum is supplied via means within the elongated distal portion to the probe distal tip so as to remove excess irrigant and ablation products. The probe is energized producing high current density and arcing in portions of the active electrode and floating electrode in close proximity to the target tissue. Lower density current flow from regions of the floating electrode(s) in contact with adjacent target tissue results in desiccation of the adjacent tissue so as to achieve hemostasis. While energized, the probe is moved across the target tissue with a brushing or sweeping motion, or intermittently energized for a brief period of time and repositioned so as to affect the target tissue.  
         [0080]     In a preferred embodiment, the floating electrode is an annular ring surrounding a single active electrode having ribs formed in its surface, the floating and active electrodes being separated by a ceramic insulator. Irrigant is supplied to the region between the floating and active electrodes, and aspiration is via a single aspirating port in the distal surface of the active electrode. In another embodiment, features formed in the active electrode distal surface minimize aspiration flow between the ribs so as to improve ablator efficiency. In another embodiment, radial slots are formed in the distal surface of the floating electrode to allow improved irrigation of the region surrounding the probe distal tip, and to increase the current density at the floating electrode distal surface. In yet another embodiment intended for applications in which the probe is oriented more or less vertically with the distal end downward additional irrigant is supplied to the probe distal end via a flow path along the outer surface of the elongated distal portion from the handle portion. The flow path is established by selective application of hydrophilic and/or hydrophobic coatings. In still another embodiment, the active and floating electrodes have protrusions which are interspersed in an array, the floating electrode protrusions being affixed to a portion of the floating electrode which is in the low-potential region of the electric field. Another embodiment is configured so as to function as a “tissue drill”.  
         [0081]     The current invention is useful also for medical procedures in which tissue is thermally treated rather than removed by vaporization, such as, for instance, cardiology, oncology and treatment of tumors, sometimes referred to as lesion formation. In these applications the device is brought into close proximity, or contact, with tissue with or without the presence of externally applied conductive fluid at the site for thermal treatment. The voltage applied to the active electrode is reduced to a level which produces current densities insufficient for forming sparks and the associated bubbles. Tissue is heated to a desired temperature for a predetermined time sufficient for lesion formation. The floating electrode intensifies the electric field in the region surrounding the active electrode so as to produce a larger, more controlled and more uniform lesion.  
         [0082]     Hereinafter, the present invention is described in more detail by reference to the exemplary embodiments. However, the following examples only illustrate aspects of the invention and in no way are intended to limit the scope of the present invention. As such, embodiments similar or equivalent to those described herein can be used in the practice or testing of the present invention.  
         [0083]     Referring to the figures,  FIG. 1  shows an electrosurgical system  100  formed in accordance with the principles of this invention. System  100  has an electrosurgical generator  102  connected via cable  24  to electrosurgical probe  10 , an irrigant source  104  which supplies conductive liquid to probe  10  via tubing  26 , and a vacuum source  106  connected via tubing  28  to probe  10 .  
         [0084]     As seen in  FIG. 2 , the electrosurgical instrument  10  formed in accordance with the principles of this invention has a proximal portion  12  forming a handle having a proximal end  14  and a distal end  16 , and an elongated distal portion  18  having a proximal end  20  and a distal end  22 . Proximal end  20  of distal portion  18  is rigidly affixed to distal end  16  of handle  20 . Proximal end  14  of handle  12  has passing therefrom cable  24  which connects to electrosurgical unit  102  ( FIG. 1 ), first tube  26  connects to irrigant source  104 , and second tube  28  connects to vacuum source  106 . Near distal end  16  of portion  12 , first activation button  30  and second activation button  32  are connected via cable  24  to electrosurgical unit  102 . Distal end  22  of elongated distal portion  18  comprises an active electrode  34 .  
         [0085]     Referring now to  FIGS. 3 through 9  showing expanded view of distal end  22  of distal portion  18 , active electrode  34  has an angled distal surface  36  forming a plurality of ribs  38  separated by grooves  40 . Aspiration port  42  is connected by tube  44  and means within proximal portion  12 , to second tube  28  ( FIG. 2 ). As best seen in  FIG. 8 , when viewed axially electrode  34  has a cross-section having cylindrical portions  46  and planar portions  48 . Proximal end  50  of electrode  34  is assembled to distal end  52  of outer tube  54 , cylindrical portions  46  of electrode  34  locating in counterbore  56  of tube  54 . Tubular insulator  60 , formed of a suitable dielectric material, surrounds distal portion  62  of electrode  34 . Floating electrode  64 , made of a suitable metallic material, surrounds distal portion  58  of insulator  60 , and is mounted thereto. Distal angled surface  66  of floating electrode  64  is more or less coplanar with surface  36  of electrode  34 . Dielectric coating  70  surrounds the outer surface of outer tube  54  and proximal portion  72  of insulator  60 . Passages  74  formed by cylindrical inner surface  76  of insulator  60  and planar surfaces  48  of active electrode  34  connect with lumen  78  of outer tube  54  via milled passage portions  80  of active electrode  34 . Flow paths  82  formed by passages  74 , milled passage portions  80  of active electrode  34 , and lumen  78  of outer tube  54  connect via a means in proximal handle portion  12  to second tube  26  which is connected to irrigant source  104  ( FIG. 1 ).  
         [0086]     Referring now to  FIG. 10  showing instrument  10  in use, irrigant  84  supplied via flow paths  82  to passages  74  floods the region surrounding active electrode  34  and floating electrode  64 . RF power supplied to active electrode  34 , and conducted to floating electrode  64  by irrigant  84  causes boiling of the saline in contact with active electrode  34  and floating electrode  64 , particularly at edges of the electrodes. Arcing through bubbles contacting either active electrode  34  or floating electrode  64  and tissue vaporizes the tissue in contact with the bubbles. Bubbles and debris from the ablation process (collectively  86 ) is aspirated from the region via aspiration port  42  by suction supplied by vacuum source  106  ( FIG. 1 ) via second tube  28  ( FIG. 2 ), means within proximal portion  12 , and tube  44 .  
         [0087]     An alternate embodiment, shown in  FIG. 11 , is identical to that shown in  FIGS. 3 through 9  except that cylindrical portion  88  of active electrode  34  extends aspiration port  42  so that it is coplanar with surface  36  of electrode  34 . Extending the aspiration port in this manner minimizes aspirating flow between ribs  38  in grooves  40  so as to minimize cooling of the ribs by the flow. This, in turn, increases the efficiency of the ablator since less process heat is removed by the aspiration flow.  
         [0088]     In another embodiment shown in  FIGS. 12 through 14 , active electrode  34 , insulator  60  and floating electrode  64  are truncated so as to produce distal planar surface  90  on electrode  34 , distal planar surface  92  on insulator  60 , and distal planar surface  94  on floating electrode  64 . Surfaces  90 ,  92  and  94  are normal to axis  91  of active electrode  34 . Surface  90  and  94  are more or less coplanar. Surface  92  is recessed axially distance  96  from surfaces  90  and  94 .  
         [0089]     Referring now to  FIG. 15 , showing the embodiment of  FIGS. 12 through 14  in use, for example, removing a tonsil from the tonsilar bed, the tonsil is pulled away from the tonsilar bed by a force applied to the tonsil by a grasping instrument. Instrument  10  is used to separate the tonsil from the tonsil bed by resecting tissue between the tonsil and the bed. As with the embodiment of  FIG. 10 , irrigant  84  supplied via flow paths  82  to passages  74  floods the region surrounding active electrode  34  and floating electrode  64 . RF power supplied to active electrode  34 , and conducted to floating electrode  64  by irrigant  84  causes boiling of the saline in contact with active electrode  34  and floating electrode  64 , particularly at edges of the electrodes. Arcing through bubbles contacting either active electrode  34  or floating electrode  64  and tissue vaporizes the tissue in contact with the bubbles. Bubbles and debris from the ablation process (collectively  86 ) is aspirated from the region via aspiration port  42  by suction supplied by vacuum source  106  ( FIG. 1 ) via second tube  28  ( FIG. 2 ), means within proximal portion  12 , and tube  40 . Current  200  flows from the active electrode through the conductive liquid to the tissue through which it is conducted to the remotely affixed return electrode. A portion of the current  202  in the region in close proximity to floating electrode  64  and active electrode  34  flows from active electrode  34  through the conductive liquid to the portion of floating electrode  64  in the high-potential part of the electric field. This current  202  then flows through floating electrode  64  to a lower potential part of floating electrode  64 , and from there through conductive liquid and tissue in contact with electrode  64  to the return electrode. Current density in the high-potential region of the electric field adjacent to floating electrode  64  is high, generally sufficient to cause boiling of the conductive liquid at the surface of floating electrode  64  and arcs  204  within the bubbles formed. Some of current flow  202  between active electrode  34  and floating electrode  64  follows a path through bubbles formed at active electrode  34  to adjacent tissue thereby vaporizing the tissue, and from the tissue to floating electrode  64  by arcing within bubbles formed at floating electrode  64  thereby vaporizing additional tissue. Current density in the portion of floating electrode  64  in the lower-potential portion of the electric field is less than that in the high-potential region. The current density is insufficient to cause boiling of the saline and ablative arcing. It is, however, sufficient to cause desiccation of tissue in contact with floating electrode  64  so as to coagulate bleeders, particularly oozing surfaces such as those found in the region of the tonsils.  
         [0090]     Referring yet to  FIG. 15 , a separation force  206  is applied to the tonsil. Distal end  22  of instrument  10  is brought into close proximity to the tonsil adjacent to the tonsil bed. Irrigation and aspiration are supplied to the distal region. The probe is briefly energized so that tissue is ablated in the region of active electrode  34  and floating electrode  64 . The probe is repositioned to a new location and again briefly energized so as to vaporize additional tissue. Instrument  10  is advanced axially into the tissue while being repositioned laterally so as to vaporize a portion of the tonsil. Simultaneously, current flow from floating electrode  64  desiccates tissue in contact with electrode  64  so as to achieve and maintain hemostasis. When the tonsil is freed from the tonsil bed, additional tissue can be removed from the tonsil bed by reorienting instrument  10  so that surface  36  of active electrode  34  and surface  66  of floating electrode  64  are adjacent the tonsil bed. Tissue is then ablated (vaporized) from the site in the manner previously herein described ( FIG. 10 ).  
         [0091]     In another embodiment shown in  FIG. 16 , floating electrode  64  has a plurality of slots  210  formed in angled surface  66  so as to allow enhanced irrigation of the region, irrigant flowing outwardly through the slots. By adjusting the number and width of slots  210  the portion of floating electrode  64  in the high-potential portion of the electric field can be reduced so as to achieve higher current densities at floating electrode  64 . This causes enhanced bubble formation and ablative arcing at floating electrode  64 .  
         [0092]     In yet another embodiment intended for use in applications such as that shown in  FIG. 15  in which the probe is held more or less vertically irrigant flows down the outside of the elongated distal section. In the embodiment shown in  FIG. 17 , irrigant is supplied to distal end  22  of elongated distal portion  18  by a flow path  220  on the outer surface of dielectric coating  70 . In one embodiment, the flow path is formed by a hydrophilic coating applied to path  220 . In another embodiment path  220  is formed by a hydrophobic coating applied to portion  222  of the outer surface of dielectric coating  70  not part of path  220 . In yet another embodiment path  220  is formed by a hydrophilic coating applied to path  220  and a hydrophobic coating applied to portion  222 . Irrigation port  226  in distal end  16  of handle  12  supplies irrigant to proximal end  228  of path  220 , the irrigant being supplied from an external source  104  via tube  26  ( FIG. 1 ) and means within handle portion  12 . In use (see  FIG. 18 ), irrigant  230  flows from port  226  down path  220  to distal end  22  of elongated distal portion  18  where it provides conductive liquid for the ablation process. In some embodiments irrigant  230  supplements irrigant provided by the means previously herein described in previous embodiments. In other embodiments all irrigant is supplied via path  220 .  
         [0093]     Numerous changes may be made to the device and method without departing from the principles of the invention herein disclosed. For instance, in previous embodiments both suction and irrigation were supplied to distal end  22  of elongated portion  18 . Other embodiments are anticipated in which irrigation is supplied to the surgical site via instrument  10  while aspiration of fluid and debris from the site is done by an external device. In these embodiments, irrigant is supplied in the manner previously herein described along path  82  ( FIG. 10 ) and/or along path  220  ( FIGS. 16 and 17 ) and may also be supplied along the path formed by port  42  and tube  44  used in previous embodiments for aspiration. Any combination of irrigation paths may be used.  
         [0094]     Similarly, embodiments are anticipated in which irrigant is supplied by an external means to the site rather than by instrument  10  and aspiration is through instrument  10 . Aspiration may be via the passage formed by port  42  and tube  44  ( FIGS. 5 and 10 ) as in the previous embodiments or may be via path  82  ( FIG. 10 ) used in previous embodiments for irrigation.  
         [0095]     In the embodiment shown in  FIGS. 3 through 9 , distal angled surface  66  of floating electrode  64  is more or less coplanar with surface  36  of electrode  34 . Under some circumstances, it may be advantageous to have surface  66  of floating electrode  64  displaced distally a predetermined distance from surface  36  of electrode  34 . Accordingly embodiments having this distal offset between the surfaces is anticipated. In other embodiments portions of the distal-most surface of the floating electrode are displaced distally from the distal surface of the active electrode while other portions of the floating electrode surface are displaced proximally from the active electrode surface.  
         [0096]     In another embodiment, features are formed in the distal-most surface of insulator  60 , or in ribs  38  of active electrode  34  which enhance bubble formation and electrode efficiency. In one such embodiment, the distal portion  22  of which is shown in  FIG. 19   a , and a section view of which is show in  FIG. 19   b , grooves  240  are formed adjacent to ribs  38 , grooves  240  having first walls  242  formed by angled surfaces of insulator  60 , and second walls  244  formed by the lateral surfaces of ribs  38 . Wall pairs  242  and  244  form an included angle  246  preferably in the range from 5 to 70 degrees, and more preferably in the range from 10 to 45 degrees.  FIGS. 20   a  through  20   e  show an expanded view of ribs  38  and adjacent grooves  240  when voltage is first supplied to active electrode  34  while the assembly is submerged in conductive liquid. When voltage is first supplied (see  FIG. 20   a ) current  246  flows from all uninsulated surfaces heating the adjacent liquid. Convection currents and fluid flow in the region surrounding active electrode  34  decreases the fluid temperatures in the region. Fluid within grooves  240  is not cooled by these mechanisms due to the narrow width of the grooves. Fluid cannot flow readily into and out of grooves  240 . Fluid within grooves  240  heats at a higher rate than other fluid in other regions surrounding active electrode  34 . As seen in  FIG. 20   b , showing the ribs  38  and grooves  240  a short time after  FIG. 20   a , heating of the liquid in grooves  240  causes boiling of the fluid in the grooves forming bubbles  250 . After additional time has elapsed, as shown in  FIG. 20   c , grooves  240  are filled with bubbles  250  insulating surfaces  244  within grooves  240  so as to increase the impedance of the probe tip. When additional time has elapsed (see  FIG. 20   d ), bubbles fill the region between ribs  38  insulating further surfaces  244 . As seen in  FIG. 20   e , eventually bubbles  250  begin to cover the ablating surfaces of ribs  38  and arcing occurs within the bubbles. To summarize, liquid within grooves  240  heats at a higher rate than other fluid surrounding active electrode  34  thereby quickly creating bubbles  150  within grooves  240 . The bubbles  150  generated insulate the lateral surfaces of the ribs  38  of electrode  34 , and reach the distal-most surfaces of electrode  34  where acing occurs within the bubbles. In this manner grooves  240  increase the efficiency of ablator electrode  10 .  
         [0097]     Another embodiment, having grooves  240  for the purpose of increasing electrode efficiency, is shown in section view in  FIG. 21 . Ribs  38  have a distal-most portion with a triangular cross-section, the proximal portion of the triangular portion being below distal surface  61  of insulator  60  so as to form grooves  240 . Grooves  240  have an included angle  246  formed by surfaces  244  of ribs  38  and surfaces  242  of insulator  64 . The embodiment of  FIG. 21  functions in the same manner as that of  FIGS. 19 and 20 .  
         [0098]     In yet another embodiment shown in  FIGS. 22 through 24 , active electrode  34  and floating electrode  64  form an array of protrusions. Active electrode  34  forms protrusions  300 . Floating electrode  64  forms protrusions  302 . Insulator  60  forms an assembly having a first portion  306  and a second portion  308 , protrusions  302  and  304  protruding from surface  310  of first portion  306 . Second portion  308  electrically isolates electrodes  34  and  64 . Elongated conductive member  312  has at its distal end active electrode  34  and at its proximal end handle portion  12 . Dielectric coating  70  covers member  312 . Elongated tubular member  314 , positioned adjacent to elongated member  312  and affixed thereto has a proximal end connected via means within handle portion  12  to a conductive irrigant source, and a distal end  316  having therein orifices  318  in communication with lumen  319 . Floating electrode  64  has a proximal portion  320  forming protrusions  302 , the portion  322  to which they are attached, and surface  324 . Floating electrode  64  also has a distal portion  326 .  
         [0099]     Referring now to  FIG. 25 , during use distal end  22  of ablator  10  is positioned such that at least one each of protrusions  300  of active electrode  34  and protrusions  302  of floating electrode  64  are in close proximity to the target tissue. Conductive irrigant  340  supplied by tubular member  314  via orifices  318  floods the region of the target tissue in close proximity to protrusions  300  and  302 . Surface  324  of proximal portion  322  and/or distal portion  326  of floating electrode  64  are in contact with irrigant  340  and/or tissue in proximity to the target tissue. When voltage is supplied to active electrode  34 , an electric field is established. Current  342  flows from protrusions  300  to the target tissue and from there to the remotely placed return electrode. Current also flows from protrusions  300  to protrusions  302  of floating electrode  64  in high potential regions of the electric field, through the floating electrode to lower potential regions of the electric field, and therefrom to the return electrode via tissue and conductive irrigant in contact with the portion of floating electrode  64  in low-potential regions of the electric field. Current flow through conductive irrigant  340  causes boiling of the irrigant resulting in bubbles  250 , and arcs  252  within bubbles resulting in vaporization of tissue. This arcing occurs at protrusions  300  of active electrode  34  and also at some protrusions  302  of floating electrode  64  which are in high potential portions of the electric field. Current flow from the portions of floating electrode  64  in the lower-potential region of the electric field, particularly from surface  324 , does not have sufficient density to form bubbles resulting in arcing; however, the current density is sufficient to cause heating of adjacent fluid and tissue so as to achieve and maintain hemostasis.  
         [0100]     The electrosurgical device of the present invention may also be advantageously used for producing holes in tissue. In certain circumstances, such as when making holes with large depth to diameter ratios, it may be desirable to supply conductive fluid to the probe distal end. An embodiment incorporating such a fluid supply means is shown in  FIGS. 26 through 28 . Electrosurgical probe  840  has a proximal handle portion  842  with buttons  844  and  846  for controlling an electrosurgical power supply to which it is connected by cable  848 . Distal portion  850  has a distal tip assembly  852 . Tube  880  is connected to a source of conductive liquid which is supplied via a means in handle  842  and a lumen in distal portion  850  to distal tip assembly  852 . Referring now to  FIGS. 27 and 28 , distal tip assembly  852  has an active electrode  854  separated by insulator  856  from floating electrode  858 . Dielectric coating  870  covers a proximal portion of insulator  856 , a proximal portion of active electrode  854 , and the rest of distal portion  850 . Lumen  872  supplies conductive liquid  884  to distal end  874  of active electrode  854  and the region surrounding electrode  854 , insulator  856  and the distal end of floating electrode  858 .  
         [0101]     Referring now to  FIG. 29 , during use probe  840  is advanced distally into the tissue, distal surface  888  of active electrode  854  and distal surface  892  of floating electrode  858  having current density sufficient to cause vaporization of tissue. Conductive liquid  890  supplied by lumen  872  fills the region surrounding the probe tip and helps flush bubbles  864  and products of tissue vaporization proximally through gap  866  formed between distal assembly  852  and the tissue. Lower current density heating from the more proximal region  867  of floating electrode  858  desiccates tissue with which it is in contact so as to stop bleeding.  
         [0102]     All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety.  
         [0103]     While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention.