Systems and methods for selective electrosurgical treatment of body structures

[0002] The present invention is a continuation-in-part of U.S. patent application Ser. No. 08/990,374 entitled “Systems and Methods for Electrosurgical Endoscopic Sinus Surgery, filed on Dec. 15, 1997 now U.S. Pat. No. 6,109,268, which is a continuation-in-part of U.S. patent application Ser. No. 08/485,219, filed on Jun. 7, 1995 now U.S. Pat. No. 5,697,281, the complete disclosures of which are incorporated herein by reference for all purposes. The invention is also a continuation-in-part of U.S. patent application entitled “Systems and Methods for Electrosurgical Spine Surgery,” filed on Feb. 20, 1998, the complete disclosure of which is incorporated herein by reference for all purposes.

[0003] This application is also related to commonly assigned U.S. patent application Ser. No. 08/942,580 entitled “Systems and Methods for Electrosurgical Tissue Contraction”, filed on Oct. 2, 1997, Provisional Patent Application Nos. 60/062,996 and 60/062,997, non-provisional U.S. patent application Ser. No. 08/970,239 entitled “Electrosurgical Systems and Methods for Treating the Spine”, filed Nov. 14, 1997, and Ser. No. 08/977,845 entitled “Systems and Methods for Electrosurgical Dermatological Treatment”, filed on Nov. 25, 1997, U.S. application Ser. No. 08/753,227, filed on Nov. 22, 1996, and PCT International Application, U.S. National Phase Serial No. PCT/US94/05168, filed on May 10, 1994, now U.S. Pat. No. 5,697,909, which was a continuation-in-part of application Ser. No. 08/059,681, filed on May 10, 1993, which was a continuation-in-part of application Ser. No. 07/958,977, filed on Oct. 9, 1992 which was a continuation-in-part of application Ser. No. 07/817,575, filed on Jan. 7, 1992, the complete disclosures of which are incorporated herein by reference for all purposes. The present invention is also related to commonly assigned U.S. Pat. No. 5,683,366, filed Nov. 22, 1995, and U.S. Pat. No. 5,697,536, filed on Nov. 18, 1996, the complete disclosures of which are incorporated herein by reference for all purposes.

[0004] The present invention relates generally to the field of electrosurgery, and more particularly to surgical devices and methods which employ high frequency electrical energy to treat tissue in regions of the body adjacent to nerves or other sensitive body structures, such as the head and neck, the spine, the brain and the like.

[0005] Many surgical procedures involve the treatment and/or removal of soft tissue closely adjacent to other non-target body structures, such as nerves, bone or cartilage (e.g., articular cartilage). One of the major difficulties with these procedures is discriminating between the target soft tissue and the non-target body structure, and then being capable of removing or otherwise modifying the soft tissue without damaging the non-target structure. Particularly troublesome are those surgical procedures which require the surgeon to remove tissue adjacent to nerves (the cordlike structures which convey impulses between a part of the central nervous system and a region of the body).

[0006] Many surgical procedures require the manipulation of surgical instruments in and around important nerves in the body. For example, surgical procedures within the nasal cavity (e.g., FESS procedures) often require the surgeon to remove polyps, turbinates or other sinus tissue adjacent to the optic or olfactory nerves, which are the central processes for sight and smell. Surgical procedures within the mouth often involves ablation or contraction of tissue (e.g., in the tongue or uvula) near the hypoglossal nerve, which controls movements of the tongue. Similarly, in spinal procedures (e.g., treatment of herniated discs or spinal fusion), the surgeon must often remove or modify tissue closely adjacent to the spinal nerves near their roots at the spinal cord. One of the significant problems with these procedures is that conventional surgical instruments generally do not differentiate between the target tissue and the surrounding nerves, which may result in nerve injury of impairment of nerve function. Nerve injury can lead to muscle paralysis, pain, exaggerated reflexes, loss of bladder control, impaired cough reflexes, spasticity and other conditions. Moreover, the neurons within some nerves typically do not regenerate after injury.

[0007] In the past several years, powered instrumentation, such as microdebrider devices and lasers, has been used to treat tissue in various procedures, such as removing polyps or other swollen tissue in functional endoscopic sinus surgery. Microdebriders are disposable motorized cutters having a rotating shaft with a serrated distal tip for cutting and resecting tissue. The handle of the microdebrider is typically hollow, and it accommodates a small vacuum, which serves to aspirate debris. In this procedure, the distal tip of the shaft is delivered to the target site, and an external motor rotates the shaft and the serrated tip, allowing the tip to cut tissue at the target site, such as sinus tissue, spinal tissue, or the like. While microdebriders have been promising, they are not very precise, and it is often difficult, during the procedure, to differentiate between the target tissue, and other neighboring body structures, such as cartilage, bone or nerves. Thus, the surgeon must be extremely careful to minimize damage to the cartilage and bone at the target site, and to avoid damaging the nerves that extend through the target site.

[0008] Lasers were initially considered ideal for many surgical procedures because lasers ablate or vaporize tissue with heat, which also acts to cauterize and seal the small blood vessels in the tissue. Unfortunately, lasers are both expensive and somewhat tedious to use in these procedures. Another disadvantage with lasers is the difficulty in judging the depth of tissue ablation. Since the surgeon generally points and shoots the laser without contacting the tissue, he or she does not receive any tactile feedback to judge how deeply the laser is cutting. Because healthy tissue, cartilage, bone and/or nerves often lie within close proximity of the target tissue, it is essential to maintain a minimum depth of tissue damage, which cannot always be ensured with a laser.

[0009] Recently, RF energy has been used to remove or otherwise treat tissue in open and endoscopic procedures. This procedure typically involves the use of a monopolar electrode that directs RF current into the target tissue to desiccate or destroy tissue in the tongue. Of course, such monopolar devices suffer from the disadvantage that the electric current will flow through undefined paths in the patient's body, thereby increasing the risk of unwanted electrical stimulation to portions of the patient's body. In addition, since the defined path through the patient's body has a relatively high impedance (because of the large distance or resistivity of the patient's body), large voltage differences must typically be applied between the return and active electrodes in order to generate a current suitable for ablation or cutting of the target tissue. This current, however, may inadvertently flow along body paths having less impedance than the defined electrical path, which will substantially increase the current flowing through these paths, possibly causing damage to or destroying surrounding tissue or neighboring peripheral nerves.

[0010] The present invention provides systems, apparatus and methods for selectively applying electrical energy to structures in regions of the patient's body adjacent to non-target body structures, such as nerves, cartilage and bone. The systems and methods of the present invention are particularly useful for ablation, resection, contraction and hemostatis of soft tissue that is closely adjacent to nerves, such as tissue within the head and neck, the spine, the brain and the like.

[0011] Methods of the present invention comprise positioning an electrosurgical instrument, such as a probe or catheter, in close proximity to a first body structure adjacent to a second body structure so that one or more electrode terminal(s) are brought into at least partial contact or close proximity with the first and second body structures. High frequency voltage is then applied between the electrode terminal(s) and one or more return electrode(s) to cut, remove, ablate, contract, coagulate, vaporize, desiccate or otherwise modify the first body structure without damaging the second body structure. The first body structure is typically soft tissue, such as sinus, mucosal, spinal, or brain tissue, and the second body structure typically comprises a structure either having different electrical or molecular properties than soft tissue, such as bone, cartilage, adipose tissue, nerves and the like. The present invention provides a method for automatically discriminating between the two body structures such that the soft tissue is removed or otherwise modified, while the second structure is left relatively unaffected by the procedure.

[0012] In one aspect of the invention, a method is provided for removing or ablating soft tissue that is adjacent to a nerve structure, such as swollen nasal tissue within the sinuses, disc tissue within the spine, tumor tissue within the brain and the like. In this method, one or more electrode terminal(s) are positioned adjacent to the target tissue, either endoscopically, transluminally, or directly in an open procedure. An electrically conductive fluid, such as isotonic saline, is delivered to the target site to substantially surround the electrode terminal(s) with the fluid. Alternatively, a more viscous fluid, such as an electrically conductive gel, may be applied to the target site such that the electrode terminal(s) are submerged within the gel during the procedure. In both embodiments, high frequency voltage is applied between the electrode terminal(s) and one or more return electrode(s) to remove at least a portion of the tissue. According to the present invention, the electrical energy is selectively applied to soft tissue to ablate this tissue, while minimizing energy delivery to the adjacent nerves. In particular, applicant has found that the present invention is capable of completely removing soft tissue closely adjacent to nerves without causing nerve function impairment or any significant changes to the tissue in nerve fibers or the surrounding epineurium.

[0013] In one embodiment, the soft tissue is removed by molecular dissociation or disintegration processes. In this embodiment, the high frequency voltage applied to the electrode terminal(s) is sufficient to vaporize an electrically conductive fluid (e.g., gel or saline) between the electrode terminal(s) and the soft tissue. Within the vaporized fluid, a ionized plasma is formed and charged particles (e.g., electrons) are accelerated towards the tissue to cause the molecular breakdown or disintegration of several cell layers of the tissue. This molecular dissociation is accompanied by the volumetric removal of the tissue. The short range of the accelerated charged particles within the plasma layer confines the molecular dissociation process to the surface layer to minimize damage and necrosis to the underlying tissue. This process can be precisely controlled to effect the volumetric removal of tissue as thin as 10 to 150 microns with minimal heating of, or damage to, surrounding or underlying tissue structures. The small depths of collateral tissue damage provided by the present invention allows the surgeon to remove tissue close to a nerve without causing collateral damage to the nerve fibers. A more complete description of this phenomena is described in commonly assigned U.S. Pat. No. 5,683,366, the complete disclosure of which is incorporated herein by reference

[0014] In another embodiment, systems and methods are provided for distinguishing between the fatty tissue (e.g., adipose tissue) immediately surrounding nerve fibers and the normal tissue that is to be removed during the procedure. Nerves usually comprise a connective tissue sheath, or epineurium, enclosing the bundles of nerve fibers to protect these nerve fibers. This protective tissue sheath comprises a fatty tissue (e.g., adipose tissue) having substantially different electrical properties than the normal target tissue. The system of the present invention measures the electrical properties of the tissue at the tip of the probe with one or more electrode terminal(s). These electrical properties may include electrical conductivity at one, several or a range of frequencies (e.g., in the range from 1 kHz to 100 MHz), dielectric constant, capacitance or combinations of these. In this embodiment, an audible signal may be produced when the sensing electrode(s) at the tip of the probe detects the fatty tissue surrounding a nerve, or direct feedback control can be provided to only supply power to the electrode terminal(s) either individually or to the complete array of electrodes, if and when the tissue encountered at the tip or working end of the probe is normal tissue based on the measured electrical properties.

[0015] In yet another embodiment, applicant has discovered that the mechanisms of the present invention can be manipulated to ablate or remove certain tissue structures, while having little effect on other body structures. As discussed above, the present invention employs a technique of vaporizing electrically conductive fluid to form a plasma layer or pocket around the electrode terminal(s), and then inducing the discharge of energy from this plasma or vapor layer to break the molecular bonds of the tissue structure. Energy evolved by the energetic electrons (e.g., 4 to 5 eV) can subsequently bombard a molecule and break its bonds, dissociating a molecule into free radicals, which then combine into final gaseous or liquid species. The energy evolved by the energetic electrons may be varied by adjusting a variety of factors, such as: the number of electrode terminals; electrode size and spacing; electrode surface area; asperities and sharp edges on the electrode surfaces; electrode materials; applied voltage and power; current limiting means, such as inductors; electrical conductivity of the fluid in contact with the electrodes; density of the fluid; and other factors. Accordingly, these factors can be manipulated to control the energy level of the excited electrons. Since different tissue structures have different molecular bonds, the present invention can be configured to break the molecular bonds of certain tissue, while having too low an energy to break the molecular bonds of other tissue. For example, fatty tissue, (e.g., adipose) tissue has double bonds that require a substantially higher energy level than 4 to 5 eV to break. In an exemplary embodiment, the present invention does not ablate or remove such fatty tissue.

[0016] In another aspect of the invention, a method includes positioning one or more electrode terminal(s) in close proximity to a target site adjacent to a nerve structure. High frequency voltage is applied to the electrode terminal(s) to elevate the temperature of collagen fibers within the tissue at the target site from body temperature (about 37° C.) to a tissue temperature in the range of about 45° C. to 90° C., usually about 60° C. to 70° C., to substantially irreversibly contract these collagen fibers without damaging the nerve. In a preferred embodiment, an electrically conducting fluid is provided between the electrode terminal(s) and one or more return electrode(s) positioned proximal to the electrode terminal(s) to provide a current flow path from the electrode terminal(s) away from the tissue to the return electrode(s).

[0017] The current flow path may be generated by directing an electrically conducting fluid along a fluid path past the return electrode and to the target site, or by locating a viscous electrically conducting fluid, such as a gel, at the target site, and submersing the electrode terminal(s) and the return electrode(s) within the conductive gel. The collagen fibers may be heated either by passing the electric current through the tissue to a selected depth before the current returns to the return electrode(s) and/or by heating the electrically conducting fluid and generating a jet or plume of heated fluid, which is directed towards the target tissue. In the latter embodiment, the electric current may not pass into the tissue at all. In both embodiments, the heated fluid and/or the electric current elevates the temperature of the collagen sufficiently to cause hydrothermal shrinkage of the collagen fibers.

[0018] The contraction of collagen tissue is particularly useful in procedures for treating obstructive sleep disorders, such as snoring or sleep apnea, and for treating herniated discs by shrinking the nucleus pulposis of the herniated disc. In the former procedure, one or more electrode terminal(s) are introduced into the patient's mouth, and positioned adjacent the target tissue, selected portions of the tongue, tonsils, soft palate tissues (e.g., the uvula), hard tissue and mucosal tissue. An endoscope or other type of viewing device, may also be introduced, or partially introduced, into the mouth to allow the surgeon to view the procedure (the viewing device may be integral with, or separate from, the electrosurgical probe). Electrically conductive fluid is applied as described above, and high frequency voltage is applied to the electrode terminal(s) and one or more return electrode(s) to, for example, ablate or shrink sections of the uvula without causing unwanted nerve damage to nerves extending under and around the selected sections of tissue.

[0019] FIG. 1A illustrates a bundle of nerve fibers enclosed within an outer protective sheath or epineurium;

[0020] FIG. 1B illustrates a single nerve fiber;

[0021] FIG. 2 is a perspective view of an electrosurgical system incorporating a power supply and an electrosurgical probe for tissue ablation, resection, incision, contraction and for vessel hemostasis according to the present invention;

[0022] FIG. 3 is a side view of an electrosurgical probe according to the present invention;

[0023] FIG. 4A is a cross sectional view of the electrosurgical probe of FIG. 1;

[0024] FIG. 4B is an end view of the probe of FIG. 2

[0025] FIG. 5 is an exploded view of a proximal portion of the electrosurgical probe;

[0026] FIGS. 6-11(A-C) are end views of alternative embodiments of the probe of FIG. 2, incorporating aspiration electrode(s);

[0027] FIG. 12 illustrates an endoscopic sinus surgery procedure, wherein an endoscope is delivered through a nasal passage to view a surgical site within the nasal cavity of the patient;

[0028] FIG. 13 illustrates an endoscopic sinus surgery procedure with one of the probes described above according to the present invention;

[0029] FIGS. 14A and 14B illustrate a detailed view of the sinus surgery procedure, illustrating ablation of tissue according to the present invention;

[0030] FIG. 15 illustrates a procedure for treating obstructive sleep disorders, such as sleep apnea, according to the present invention;

[0031] FIGS. 16-19 illustrate a method of performing a microendoscopic discectomy according to the principles of the present invention; and

[0032] FIG. 20 is a schematic of another electrosurgical system for discriminating between body structures having different electrical properties, illustrating a plurality of inductors functioning as current limiting elements to a plurality of electrodes on the distal end of an electrosurgical probe.

[0033] The present invention provides systems and methods for selectively applying electrical energy to a target location within or on a patient's body, particularly including tissue in the head and neck, such as the ear, mouth, pharynx, larynx, esophagus, nasal cavity and sinuses. The head and neck procedures may be performed through the mouth or nose using speculae or gags, or using endoscopic techniques, such as functional endoscopic sinus surgery (FESS). These procedures may include the removal of swollen tissue, chronically-diseased inflamed and hypertrophic mucus linings, polyps, turbinates and/or neoplasms from the various anatomical sinuses of the skull, the turbinates and nasal passages, in the tonsil, adenoid, epi-glottic and supra-glottic regions, and salivary glands, submucus resection of the nasal septum, excision of diseased tissue and the like. In other procedures, the present invention may be useful for collagen shrinkage, ablation and/or hemostasis in procedures for treating swollen tissue (e.g., turbinates) or snoring and obstructive sleep apnea (e.g., soft palate, such as the uvula, or tongue/pharynx stiffening, and midline glossectomies), for gross tissue removal, such as tonsillectomies, adenoidectomies, tracheal stenosis and vocal cord polyps and lesions, or for the resection or ablation of facial tumors or tumors within the mouth and pharynx, such as glossectomies, laryngectomies, acoustic neuroma procedures and nasal ablation procedures. In addition, the present invention is useful for procedures within the ear, such as stapedotomies, tympanostomies or the like.

[0034] The present invention may also be useful for treating tissue or other body structures in the brain or spine. These procedures include tumor removal, laminectomy/disketomy procedures for treating herniated disks, decompressive laminectomy for stenosis in the lumbosacral and cervical spine, medial facetectomy, posterior lumbosacral and cervical spine fusions, treatment of scoliosis associated with vertebral disease, foraminotomies to remove the roof of the intervertebral foramina to relieve nerve root compression and anterior cervical and lumbar diskectomies. These procedures may be performed through open procedures, or using minimally invasive techniques, such as thoracoscopy, arthroscopy, laparascopy or the like.

[0035] In the present invention, high frequency (RF) electrical energy is applied to one or more electrode terminals in the presence of electrically conductive fluid to remove and/or modify the structure of tissue structures. Depending on the specific procedure, the present invention may be used to: (1) volumetrically remove tissue, bone, ligament or cartilage (i.e., ablate or effect molecular dissociation of the body structure); (2) cut or resect tissue or other body structures; (3) shrink or contract collagen connective tissue; and/or (4) coagulate severed blood vessels.

[0036] In some procedures, e.g., soft palate or tongue/pharynx stiffening or shrinkage of the nucleus pulposis in herniated discs, it is desired to shrink or contract collagen connective tissue at the target site. In these procedures, the RF energy heats the tissue directly by virtue of the electrical current flow therethrough, and/or indirectly through the exposure of the tissue to fluid heated by RF energy, to elevate the tissue temperature from normal body temperatures (e.g., 37° C.) to temperatures in the range of 45° C. to 90° C., preferably in the range from about 60° C. to 70° C. Thermal shrinkage of collagen fibers occurs within a small temperature range which, for mammalian collagen is in the range from 60° C. to 70° C. (Deak, G., et al., “The Thermal Shrinkage Process of Collagen Fibres as Revealed by Polarization Optical Analysis of Topooptical Staining Reactions,” Acta Morphologica Acad. Sci. of Hungary, Vol. 15(2), pp 195-208, 1967). Collagen fibers typically undergo thermal shrinkage in the range of 60° C. to about 70° C. Previously reported research has attributed thermal shrinkage of collagen to the cleaving of the internal stabilizing cross-linkages within the collagen matrix (Deak, ibid). It has also been reported that when the collagen temperature is increased above 70° C., the collagen matrix begins to relax again and the shrinkage effect is reversed resulting in no net shrinkage (Allain, J. C., et al., “Isometric Tensions Developed During the Hydrothermal Swelling of Rat Skin,” Connective Tissue Research, Vol. 7, pp 127-133, 1980). Consequently, the controlled heating of tissue to a precise depth is critical to the achievement of therapeutic collagen shrinkage. A more detailed description of collagen shrinkage can be found in U.S. patent application No. Unassigned, filed on Oct. 2, 1997, entitled “Systems And Methods For Electrosurgical Tissue Contraction” (Attorney Docket No. 16238-001300).

[0037] The preferred depth of heating to effect the shrinkage of collagen in the heated region (i.e., the depth to which the tissue is elevated to temperatures between 60° C. to 70° C.) generally depends on (1) the thickness of the tissue, (2) the location of nearby structures (e.g., nerves) that should not be exposed to damaging temperatures, (3) the location of the collagen tissue layer within which therapeutic shrinkage is to be effected and/or (4) the volume of contraction desired to relieve pressure on the spinal nerve. The depth of heating is usually in the range from 0 to 3.5 mm. In the case of collagen within the soft palate, spinal discs or the uvula, the depth of heating is preferably in the range from about 0.2 to about 2 mm.

[0038] In another method of the present invention, the tissue structures are volumetrically removed or ablated. In this procedure, a high frequency voltage difference is applied between one or more electrode terminal(s) and one or more return electrode(s) to develop high electric field intensities in the vicinity of the target tissue site. The high electric field intensities lead to electric field induced molecular breakdown of target tissue through molecular dissociation (rather than thermal evaporation or carbonization). Applicant believes that the tissue structure is volumetrically removed through molecular disintegration of larger organic molecules into smaller molecules and/or atoms, such as hydrogen, oxides of carbon, hydrocarbons and nitrogen compounds. This molecular disintegration completely removes the tissue structure, as opposed to dehydrating the tissue material by the removal of liquid within the cells of the tissue, as is typically the case with electrosurgical desiccation and vaporization.

[0039] The high electric field intensities may be generated by applying a high frequency voltage that is sufficient to vaporize an electrically conducting fluid over at least a portion of the electrode terminal(s) in the region between the distal tip of the electrode terminal(s) and the target tissue. The electrically conductive fluid may be a gas or liquid, such as isotonic saline, delivered to the target site, or a viscous fluid, such as a gel, that is located at the target site. In the latter embodiment, the electrode terminal(s) are submersed in the electrically conductive gel during the surgical procedure. Since the vapor layer or vaporized region has a relatively high electrical impedance, it increases the voltage differential between the electrode terminal tip and the tissue and causes ionization within the vapor layer due to the presence of an ionizable species (e.g., sodium when isotonic saline is the electrically conducting fluid). This ionization, under optimal conditions, induces the discharge of energetic electrons and photons from the vapor layer and to the surface of the target tissue. This energy may be in the form of energetic photons (e.g., ultraviolet radiation), energetic particles (e.g., electrons) or a combination thereof. A more detailed description of this cold ablation phenomena, termed Coblation™, can be found in commonly assigned U.S. Pat. No. 5,683,366 the complete disclosure of which is incorporated herein by reference.

[0040] The present invention applies high frequency (RF) electrical energy in an electrically conducting fluid environment to remove (i.e., resect, cut or ablate) or contract a tissue structure, and to seal transected vessels within the region of the target tissue. The present invention is particularly useful for sealing larger arterial vessels, e.g., on the order of 1 mm or greater. In some embodiments, a high frequency power supply is provided having an ablation mode, wherein a first voltage is applied to an electrode terminal sufficient to effect molecular dissociation or disintegration of the tissue, and a coagulation mode, wherein a second, lower voltage is applied to an electrode terminal (either the same or a different electrode) sufficient to achieve hemostasis of severed vessels within the tissue. In other embodiments, an electrosurgical probe is provided having one or more coagulation electrode(s) configured for sealing a severed vessel, such as an arterial vessel, and one or more electrode terminals configured for either contracting the collagen fibers within the tissue or removing (ablating) the tissue, e.g., by applying sufficient energy to the tissue to effect molecular dissociation. In the latter embodiments, the coagulation electrode(s) may be configured such that a single voltage can be applied to coagulate with the coagulation electrode(s), and to ablate or contract with the electrode terminal(s). In other embodiments, the power supply is combined with the coagulation probe such that the coagulation electrode is used when the power supply is in the coagulation mode (low voltage), and the electrode terminal(s) are used when the power supply is in the ablation mode (higher voltage).

[0041] In the method of the present invention, one or more electrode terminals are brought into close proximity to tissue at a target site, and the power supply is activated in the ablation mode such that sufficient voltage is applied between the electrode terminals and the return electrode to volumetrically remove the tissue through molecular dissociation, as described below. During this process, vessels within the tissue will be severed. Smaller vessels will be automatically sealed with the system and method of the present invention. Larger vessels, and those with a higher flow rate, such as arterial vessels, may not be automatically sealed in the ablation mode. In these cases, the severed vessels may be sealed by activating a control (e.g., a foot pedal) to reduce the voltage of the power supply into the coagulation mode. In this mode, the electrode terminals may be pressed against the severed vessel to provide sealing and/or coagulation of the vessel. Alternatively, a coagulation electrode located on the same or a different probe may be pressed against the severed vessel. Once the vessel is adequately sealed, the surgeon activates a control (e.g., another foot pedal) to increase the voltage of the power supply back into the ablation mode.

[0042] The present invention is particularly useful for removing or ablating tissue around nerves, such as spinal or cranial nerves, e.g., the olfactory nerve on either side of the nasal cavity, the optic nerve within the optic and cranial canals, the palatine nerve within the nasal cavity, soft palate, uvula and tonsil the spinal cord and the surrounding dura mater, etc. One of the significant drawbacks with the prior art microdebriders and lasers is that these devices do not differentiate between the target tissue and the surrounding nerves or bone. Therefore, the surgeon must be extremely careful during these procedures to avoid damage to the bone or nerves within and around the nasal cavity. In the present invention, the Coblation™ process for removing tissue results in extremely small depths of collateral tissue damage as discussed above. This allows the surgeon to remove tissue close to a nerve without causing collateral damage to the nerve fibers.

[0043] In addition to the generally precise nature of the novel mechanisms of the present invention, applicant has discovered an additional method of ensuring that adjacent nerves are not damaged during tissue removal. According to the present invention, systems and methods are provided for distinguishing between the fatty tissue immediately surrounding nerve fibers and the normal tissue that is to be removed during the procedure. As shown in FIGS. 1A and 1B, nerves 2 usually comprise a connective tissue sheath, or epineurium 4, enclosing the bundles of nerve fibers 6, each bundle being surrounded by its own sheath of connective tissue (the perineurium) to protect these nerve fibers. The outer protective tissue sheath or epineurium 4 typically comprises a fatty tissue (e.g., adipose tissue) having substantially different electrical properties than the normal target tissue, such as the turbinates, polyps, mucus tissue or the like, that are, for example, removed from the nose during sinus procedures. The system of the present invention measures the electrical properties of the tissue at the tip of the probe with one or more electrode terminal(s). These electrical properties may include electrical conductivity at one, several or a range of frequencies (e.g., in the range from 1 kHz to 100 MHz), dielectric constant, capacitance or combinations of these. In this embodiment, an audible signal may be produced when the sensing electrode(s) at the tip of the probe detects the fatty tissue 4 surrounding a nerve 6, or direct feedback control can be provided to only supply power to the electrode terminal(s) either individually or to the complete array of electrodes, if and when the tissue encountered at the tip or working end of the probe is normal tissue based on the measured electrical properties.

[0044] In one embodiment, the current limiting elements (discussed in detail above) are configured such that the electrode terminals will shut down or turn off when the electrical impedance reaches a threshold level. When this threshold level is set to the impedance of the fatty tissue 4 surrounding nerves 6, the electrode terminals will shut off whenever they come in contact with, or in close proximity to, nerves. Meanwhile, the other electrode terminals, which are in contact with or in close proximity to nasal tissue, will continue to conduct electric current to the return electrode. This selective ablation or removal of lower impedance tissue in combination with the Coblation™ mechanism of the present invention allows the surgeon to precisely remove tissue around nerves or bone. Applicant has found that the present invention is capable of volumetrically removing tissue closely adjacent to nerves without impairment the function of the nerves, and without significantly damaging the tissue of the epineurium.

[0045] In addition to the above, applicant has discovered that the Coblation™ mechanism of the present invention can be manipulated to ablate or remove certain tissue structures, while having little effect on other tissue structures. As discussed above, the present invention uses a technique of vaporizing electrically conductive fluid to form a plasma layer or pocket around the electrode terminal(s), and then inducing the discharge of energy from this plasma or vapor layer to break the molecular bonds of the tissue structure. Based on initial experiments, applicants believe that the free electrons within the ionized vapor layer are accelerated in the high electric fields near the electrode tip(s). When the density of the vapor layer (or within a bubble formed in the electrically conducting liquid) becomes sufficiently low (i.e., less than approximately 10²⁰atoms/cm³for aqueous solutions), the electron mean free path increases to enable subsequently injected electrons to cause impact ionization within these regions of low density (i.e., vapor layers or bubbles). Energy evolved by the energetic electrons (e.g., 4 to 5 eV) can subsequently bombard a molecule and break its bonds, dissociating a molecule into free radicals, which then combine into final gaseous or liquid species.

[0046] The energy evolved by the energetic electrons may be varied by adjusting a variety of factors, such as: the number of electrode terminals; electrode size and spacing; electrode surface area; asperities and sharp edges on the electrode surfaces; electrode materials; applied voltage and power; current limiting means, such as inductors; electrical conductivity of the fluid in contact with the electrodes; density of the fluid; and other factors. Accordingly, these factors can be manipulated to control the energy level of the excited electrons. Since different tissue structures have different molecular bonds, the present invention can be configured to break the molecular bonds of certain tissue, while having too low an energy to break the molecular bonds of other tissue. For example, fatty tissue, (e.g., adipose) tissue has double bonds that require a substantially higher energy level than 4 to 5 eV to break. Accordingly, the present invention in its current configuration generally does not ablate or remove such fatty tissue. Of course, factors may be changed such that these double bonds can also be broken in a similar fashion as the single bonds (e.g., increasing voltage or changing the electrode configuration to increase the current density at the electrode tips).

[0047] The electrosurgical probe or catheter will comprise a shaft or a handpiece having a proximal end and a distal end which supports one or more electrode terminal(s). The shaft or handpiece may assume a wide variety of configurations, with the primary purpose being to mechanically support the active electrode and permit the treating physician to manipulate the electrode from a proximal end of the shaft. The shaft may be rigid or flexible, with flexible shafts optionally being combined with a generally rigid external tube for mechanical support. Flexible shafts may be combined with pull wires, shape memory actuators, and other known mechanisms for effecting selective deflection of the distal end of the shaft to facilitate positioning of the electrode array. The shaft will usually include a plurality of wires or other conductive elements running axially therethrough to permit connection of the electrode array to a connector at the proximal end of the shaft.

[0048] For procedures within the nose, the shaft will have a suitable diameter and length to allow the surgeon to reach the target site (e.g., a blockage in the nasal cavity or one of the sinuses) by delivering the probe shaft through one of the nasal passages or another opening (e.g., an opening in the eye or through an opening surgically creating during the procedure). Thus, the shaft will usually have a length in the range of about 5-25 cm, and a diameter in the range of about 0.5 to 5 mm. For procedures requiring the formation of a small hole or channel in tissue, such as treating swollen turbinates, the shaft diameter will usually be less than 3 mm, preferably less than about 1 mm. Likewise, for procedures in the ear, the shaft should have a length in the range of about 3 to 20 cm, and a diameter of about 0.3 to 5 mm. For procedures in the mouth or upper throat, the shaft will have any suitable length and diameter that would facilitate handling by the surgeon. For procedures in the lower throat, such as laryngectomies, the shaft will be suitably designed to access the larynx. For example, the shaft may be flexible, or have a distal bend to accommodate the bend in the patient's throat. In this regard, the shaft may be a rigid shaft having a specifically designed bend to correspond with the geometry of the mouth and throat, or it may have a flexible distal end, or it may be part of a catheter. A more complete description of such systems and methods for treating tissue in the head and neck can be found in U.S. patent application entitled “Systems and Methods for Electrosurgical Endoscopic Sinus Surgery, filed on Dec. 15, 1997, previously incorporated herein by reference.

[0049] For endoscopic procedures within the spine, the shaft will have a suitable diameter and length to allow the surgeon to reach the target site (e.g., a disc) by delivering the shaft through the thoracic cavity, the abdomen or the like. Thus, the shaft will usually have a length in the range of about 5.0 to about 30.0 cm, and a diameter in the range of about 0.2 to about 20 mm. Alternatively, the shaft may be delivered directly through the patient's back in a posterior approach, which would considerably reduce the required length of the shaft. In any of these embodiments, the shaft may also be introduced through rigid or flexible endoscopes. Specific shaft designs will be described in detail in connection with the figures hereinafter. A more complete description of systems and methods for spine surgery can be found in U.S. patent application entitled “Systems and Methods for Electrosurgical Spine Surgery, filed on Feb. 20, 1998, previously incorporated herein by reference.

[0050] In an alternative embodiment, the probe may comprise a long, thin needle (e.g., on the order of about 1 mm in diameter or less) that can be percutaneously introduced through the patient's back directly into the spine. The needle will include one or more active electrode(s) for applying electrical energy to tissues within the spine. The needle may include one or more return electrode(s), or the return electrode may be positioned on the patient's back, as a dispersive pad. In either embodiment, sufficient electrical energy is applied through the needle to the active electrode(s) to either shrink the collagen fibers within the spinal disk, or to ablate tissue within the disk.

[0051] The current flow path between the electrode terminal(s) and the return electrode(s) may be generated by submerging the tissue site in an electrical conducting fluid (e.g., within a viscous fluid, such as an electrically conductive gel) or by directing an electrically conducting fluid along a fluid path to the target site (i.e., a liquid, such as isotonic saline, or a gas, such as argon). This latter method is particularly effective in a dry environment (i.e., the tissue is not submerged in fluid) because the electrically conducting fluid provides a suitable current flow path from the electrode terminal to the return electrode. A more complete description of an exemplary method of directing electrically conducting fluid between the active and return electrodes is described in parent application Ser. No. 08/485,219, filed Jun. 7, 1995 (docket no. 16238-000600), previously incorporated herein by reference.

[0052] In some procedures, it may also be necessary to retrieve or aspirate the electrically conductive fluid after it has been directed to the target site. In addition, it may be desirable to aspirate small pieces of tissue that are not completely disintegrated by the high frequency energy, or other fluids at the target site, such as blood, mucus, the gaseous products of ablation, etc. Accordingly, the system of the present invention will usually include a suction lumen in the probe, or on another instrument, for aspirating fluids from the target site. In addition, the invention may include one or more aspiration electrode(s) coupled to the distal end of the suction lumen for ablating, or at least reducing the volume of, non-ablated tissue fragments that are aspirated into the lumen. The aspiration electrode(s) function mainly to inhibit clogging of the lumen that may otherwise occur as larger tissue fragments are drawn therein. The aspiration electrode(s) may be different from the ablation electrode terminal(s), or the same electrode(s) may serve both functions. A more complete description of probes incorporating aspiration electrode(s) can be found in conmmonly assigned, co-pending patent application entitled “Systems And Methods For Tissue Resection, Ablation And Aspiration”, filed Jan. 21, 1998, the complete disclosure of which is incorporated herein by reference.

[0053] The present invention may use a single active electrode terminal or an electrode array distributed over a contact surface of a probe. In the latter embodiment, the electrode array usually includes a plurality of independently current-limited and/or power-controlled electrode terminals to apply electrical energy selectively to the target tissue while limiting the unwanted application of electrical energy to the surrounding tissue and environment resulting from power dissipation into surrounding electrically conductive liquids, such as blood, normal saline, electrically conductive gel and the like. The electrode terminals may be independently current-limited by isolating the terminals from each other and connecting each terminal to a separate power source that is isolated from the other electrode terminals. Alternatively, the electrode terminals may be connected to each other at either the proximal or distal ends of the probe to form a single wire that couples to a power source.

[0054] The active electrode(s) are typically mounted in an electrically insulating electrode support that extends from the electrosurgical probe. In some embodiments, the electrode support comprises a plurality of wafer layers bonded together, e.g., by a glass adhesive or the like, or a single wafer. The wafer layer(s) have conductive strips printed thereon to form the electrode terminal(s) and the return electrode(s). In one embodiment, the proximal end of the wafer layer(s) will have a number of holes extending from the conductor strips to an exposed surface of the wafer layers for connection to electrical conductor lead traces in the electrosurgical probe or handpiece. The wafer layers preferably comprise a ceramic material , such as alumina, and the electrode will preferably comprise a metallic material, such as gold, copper, platinum, palladium, tungsten, silver or the like. Suitable multilayer ceramic electrodes are commercially available from e.g., VisPro Corporation of Beaverton, Oreg.

[0055] In one configuration, each individual electrode terminal in the electrode array is electrically insulated from all other electrode terminals in the array within said probe and is connected to a power source which is isolated from each of the other electrode terminals in the array or to circuitry which limits or interrupts current flow to the electrode terminal when low resistivity material (e.g., blood, electrically conductive saline irrigant or electrically conductive gel) causes a lower impedance path between the return electrode and the individual electrode terminal. The isolated power sources for each individual electrode terminal may be separate power supply circuits having internal impedance characteristics which limit power to the associated electrode terminal when a low impedance return path is encountered. By way of example, the isolated power source may be a user selectable constant current source. In this embodiment, lower impedance paths will automatically result in lower resistive heating levels since the heating is proportional to the square of the operating current times the impedance. Alternatively, a single power source may be connected to each of the electrode terminals through independently actuatable switches, or by independent current limiting elements, such as inductors, capacitors, resistors and/or combinations thereof. The current limiting elements may be provided in the probe, connectors, cable, controller or along the conductive path from the controller to the distal tip of the probe. Alternatively, the resistance and/or capacitance may occur on the surface of the active electrode terminal(s) due to oxide layers which form selected electrode terminals (e.g., titanium or a resistive coating on the surface of metal, such as platinum).

[0056] The tip region of the probe may comprise many independent electrode terminals designed to deliver electrical energy in the vicinity of the tip. The selective application of electrical energy to the conductive fluid is achieved by connecting each individual electrode terminal and the return electrode to a power source having independently controlled or current limited channels. The return electrode(s) may comprise a single tubular member of conductive material proximal to the electrode array at the tip which also serves as a conduit for the supply of the electrically conducting fluid between the active and return electrodes. Alternatively, the probe may comprise an array of return electrodes at the distal tip of the probe (together with the active electrodes) to maintain the electric current at the tip. The application of high frequency voltage between the return electrode(s) and the electrode array results in the generation of high electric field intensities at the distal tips of the electrode terminals with conduction of high frequency current from each individual electrode terminal to the return electrode. The current flow from each individual electrode terminal to the return electrode(s) is controlled by either active or passive means, or a combination thereof, to deliver electrical energy to the surrounding conductive fluid while minimizing energy delivery to surrounding (non-target) tissue.

[0057] The application of a high frequency voltage between the return electrode(s) and the electrode terminal(s) for appropriate time intervals effects cutting, removing, ablating, shaping, contracting or otherwise modifying the target tissue. The tissue volume over which energy is dissipated (i.e., a high current density exists) may be precisely controlled, for example, by the use of a multiplicity of small electrode terminals whose effective diameters or principal dimensions range from about 5 mm to 0.01 mm, preferably from about 2 mm to 0.05 mm, and more preferably from about 1 mm to 0.1 mm. Electrode areas for both circular and non-circular terminals will have a contact area (per electrode terminal) below 25 mm², preferably being in the range from 0.0001 mm²to 1 mm², and more preferably from 0.005 mm²to 0.5 mm². The circumscribed area of the electrode array is in the range from 0.25 mm²to 75 mm², preferably from 0.5 mm²to 40 mm², and will usually include at least two isolated electrode terminals, preferably at least five electrode terminals, often greater than 10 electrode terminals and even 50 or more electrode terminals, disposed over the distal contact surfaces on the shaft. The use of small diameter electrode terminals increases the electric field intensity and reduces the extent or depth of tissue heating as a consequence of the divergence of current flux lines which emanate from the exposed surface of each electrode terminal.

[0058] The area of the tissue treatment surface can vary widely, and the tissue treatment surface can assume a variety of geometries, with particular areas and geometries being selected for specific applications. Active electrode surfaces can have areas in the range from 0.25 mm²to 75 mm², usually being from about 0.5 mm²to 40 mm². The geometries can be planar, concave, convex, hemispherical, conical, linear “in-line” array or virtually any other regular or irregular shape. Most commonly, the active electrode(s) or electrode terminal(s) will be formed at the distal tip of the electrosurgical probe shaft, frequently being planar, disk-shaped, or hemispherical surfaces for use in reshaping procedures or being linear arrays for use in cutting. Alternatively or additionally, the active electrode(s) may be formed on lateral surfaces of the electrosurgical probe shaft (e.g., in the manner of a spatula), facilitating access to certain body structures in endoscopic procedures.

[0059] In the representative embodiments, the electrode terminals comprise substantially rigid wires protruding outward from the tissue treatment surface of the electrode support member. Usually, the wires will extend about 0.1 to 4.0 mm, preferably about 0.2 to 1 mm, from the distal surface of the support member. In the exemplary embodiments, the electrosurgical probe includes between about two to fifty electrically isolated electrode terminals, and preferably between about three to twenty electrode terminals.

[0060] The electrically conducting fluid should have a threshold conductivity to provide a suitable conductive path between the return electrode(s) and the electrode terminal(s). The electrical conductivity of the fluid (in units of milliSiemans per centimeter or mS/cm) will usually be greater than 0.2 mS/cm, preferably will be greater than 2 mS/cm and more preferably greater than 10 mS/cm. In an exemplary embodiment, the electrically conductive fluid is isotonic saline, which has a conductivity of about 17 mS/cm.

[0061] In some embodiments, the electrode support and the fluid outlet may be recessed from an outer surface of the probe or handpiece to confine the electrically conductive fluid to the region immediately surrounding the electrode support. In addition, the shaft may be shaped so as to form a cavity around the electrode support and the fluid outlet. This helps to assure that the electrically conductive fluid will remain in contact with the electrode terminal(s) and the return electrode(s) to maintain the conductive path therebetween. In addition, this will help to maintain a vapor or plasma layer between the electrode terminal(s) and the tissue at the treatment site throughout the procedure, which reduces the thermal damage that might otherwise occur if the vapor layer were extinguished due to a lack of conductive fluid. Provision of the electrically conductive fluid around the target site also helps to maintain the tissue temperature at desired levels.

[0062] The voltage applied between the return electrode(s) and the electrode array will be at high or radio frequency, typically between about 5 kHz and 20 MHz, usually being between about 30 kHz and 2.5 MHz, preferably being between about 50 kHz and 500 kHz, more preferably less than 350 kHz, and most preferably between about 100 kHz and 200 kHz. The RMS (root mean square) voltage applied will usually be in the range from about 5 volts to 1000 volts, preferably being in the range from about 10 volts to 500 volts depending on the electrode terminal size, the operating frequency and the operation mode of the particular procedure or desired effect on the tissue (i.e., contraction, coagulation or ablation). Typically, the peak-to-peak voltage will be in the range of 10 to 2000 volts, preferably in the range of 20 to 1200 volts and more preferably in the range of about 40 to 800 volts (again, depending on the electrode size, the operating frequency and the operation mode).

[0063] As discussed above, the voltage is usually delivered in a series of voltage pulses or alternating current of time varying voltage amplitude with a sufficiently high frequency (e.g., on the order of 5 kHz to 20 MHz) such that the voltage is effectively applied continuously (as compared with e.g., lasers claiming small depths of necrosis, which are generally pulsed about 10 to 20 Hz). In addition, the duty cycle (i.e., cumulative time in any one-second interval that energy is applied) is on the order of about 50% for the present invention, as compared with pulsed lasers which typically have a duty cycle of about 0.0001%.

[0064] The preferred power source of the present invention delivers a high frequency current selectable to generate average power levels ranging from several milliwatts to tens of watts per electrode, depending on the volume of target tissue being heated, and/or the maximum allowed temperature selected for the probe tip. The power source allows the user to select the voltage level according to the specific requirements of a particular FESS procedure, arthroscopic surgery, dermatological procedure, ophthalmic procedures, open surgery or other endoscopic surgery procedure. A description of a suitable power source can be found in U.S. Provisional Application No. 60/062,997, filed on Oct. 23, 1997 entitled “Systems And Methods For Electrosurgical Tissue And Fluid Coagulation” (Attorney Docket No. 16238-007400), the complete disclosure of which has been incorporated herein by reference.

[0065] The power source may be current limited or otherwise controlled so that undesired heating of the target tissue or surrounding (non-target) tissue does not occur. In a presently preferred embodiment of the present invention, current limiting inductors are placed in series with each independent electrode terminal, where the inductance of the inductor is in the range of 10 uH to 50,000 uH, depending on the electrical properties of the target tissue, the desired tissue heating rate and the operating frequency. Alternatively, capacitor-inductor (LC) circuit structures may be employed, as described previously in co-pending PCT application No. PCT/US94/05168, the complete disclosure of which is incorporated herein by reference. Additionally, current limiting resistors may be selected. Preferably, these resistors will have a large positive temperature coefficient of resistance so that, as the current level begins to rise for any individual electrode terminal in contact with a low resistance medium (e.g., saline irrigant or conductive gel), the resistance of the current limiting resistor increases significantly, thereby minimizing the power delivery from said electrode terminal into the low resistance medium (e.g., saline irrigant or conductive gel).

[0066] It should be clearly understood that the invention is not limited to electrically isolated electrode terminals, or even to a plurality of electrode terminals. For example, the array of active electrode terminals may be connected to a single lead that extends through the probe shaft to a power source of high frequency current. Alternatively, the probe may incorporate a single electrode that extends directly through the probe shaft or is connected to a single lead that extends to the power source. The active electrode may have a ball shape (e.g., for tissue vaporization and desiccation), a twizzle shape (for vaporization and needle-like cutting), a spring shape (for rapid tissue debulking and desiccation), a twisted metal shape, an annular or solid tube shape or the like. Alternatively, the electrode may comprise a plurality of filaments, a rigid or flexible brush electrode (for debulking a tumor, such as a fibroid, bladder tumor or a prostate adenoma), a side-effect brush electrode on a lateral surface of the shaft, a coiled electrode or the like. In one embodiment, the probe comprises a single active electrode terminal that extends from an insulating member, e.g., ceramic, at the distal end of the probe. The insulating member is preferably a tubular structure that separates the active electrode terminal from a tubular or annular return electrode positioned proximal to the insulating member and the active electrode.

[0067] Referring to FIG. 2, an exemplary electrosurgical system 11 for treatment of tissue or other body structures will now be described in detail. Electrosurgical system 11 generally comprises an electrosurgical handpiece or probe 10 connected to a power supply 28 for providing high frequency voltage to a target site and a fluid source 21 for supplying electrically conducting fluid 50 to probe 10. In addition, electrosurgical system 11 may include an endoscope (not shown) with a fiber optic head light for viewing the surgical site, particularly in spinal or sinus procedures or procedures in the ear or the back of the mouth. The endoscope may be integral with probe 10, or it may be part of a separate instrument. The system 11 may also include a vacuum source (not shown) for coupling to a suction lumen or tube 205 (see FIG. 3) in the probe 10 for aspirating the target site.

[0068] As shown, probe generally includes a proximal handle 19 and an elongate shaft 18 having an array 12 of electrode terminals 58 at its distal end. A connecting cable 34 has a connector 26 for electrically coupling the electrode terminals 58 to power supply 28. The electrode terminals 58 are electrically isolated from each other and each of the terminals 58 is connected to an active or passive control network within power supply 28 by means of a plurality of individually insulated conductors (not shown). A fluid supply tube 15 is connected to a fluid tube 14 of probe 10 for supplying electrically conducting fluid 50 to the target site.

[0069] Power supply 28 has an operator controllable voltage level adjustment 30 to change the applied voltage level, which is observable at a voltage level display 32. Power supply 28 also includes first, second and third foot pedals 37, 38, 39 and a cable 36 which is removably coupled to power supply 28. The foot pedals 37, 38, 39 allow the surgeon to remotely adjust the energy level applied to electrode terminals 58. In an exemplary embodiment, first foot pedal 37 is used to place the power supply into the “ablation” mode and second foot pedal 38 places power supply 28 into the “coagulation” mode. The third foot pedal 39 allows the user to adjust the voltage level within the “ablation” mode. In the ablation mode, a sufficient voltage is applied to the electrode terminals to establish the requisite conditions for molecular dissociation of the tissue (i.e., vaporizing a portion of the electrically conductive fluid, ionizing charged particles within the vapor layer and accelerating these charged particles against the tissue). As discussed above, the requisite voltage level for ablation will vary depending on the number, size, shape and spacing of the electrodes, the distance in which the electrodes extend from the support member, etc. Once the surgeon places the power supply in the “ablation” mode, voltage level adjustment 30 or third foot pedal 39 may be used to adjust the voltage level to adjust the degree or aggressiveness of the ablation. A more complete description of an exemplary power supply for use with the present invention can be found in co-pending Provisional Patent Application entitled “Systems And Methods For Electrosurgical Tissue And Fluid Coagulation”, filed Feb. 18, 1998, the complete disclosure of which is incorporated herein by reference for all purposes.

[0070] Of course, it will be recognized that the voltage and modality of the power supply may be controlled by other input devices. However, applicant has found that foot pedals are convenient methods of controlling the power supply while manipulating the probe during a surgical procedure.

[0071] In the coagulation mode, the power supply 28 applies a low enough voltage to the electrode terminals (or the coagulation electrode) to avoid vaporization of the electrically conductive fluid and subsequent molecular dissociation of the tissue. The surgeon may automatically toggle the power supply between the ablation and coagulation modes by alternatively stepping on foot pedals 37, 38, respectively. This allows the surgeon to quickly move between coagulation and ablation in situ, without having to remove his/her concentration from the surgical field or without having to request an assistant to switch the power supply. By way of example, as the surgeon is sculpting soft tissue in the ablation mode, the probe typically will simultaneously seal and/or coagulation small severed vessels within the tissue. However, larger vessels, or vessels with high fluid pressures (e.g., arterial vessels) may not be sealed in the ablation mode. Accordingly, the surgeon can simply step on foot pedal 38, automatically lowering the voltage level below the threshold level for ablation, and apply sufficient pressure onto the severed vessel for a sufficient period of time to seal and/or coagulate the vessel. After this is completed, the surgeon may quickly move back into the ablation mode by stepping on foot pedal 37. A specific design of a suitable power supply for use with the present invention can be found in U.S. Provisional Patent Application No. 60/062,997, filed Oct. 23, 1997, entitled “Systems And Methods For Electrosurgical Tissue And Fluid Coagulation” (Attorney Docket No. 16238-007400), previously incorporated herein by reference.

[0072] FIGS. 3-5 illustrate an exemplary electrosurgical probe 20 constructed according to the principles of the present invention. As shown in FIG. 2, probe 20 generally includes an elongated shaft 100 which may be flexible or rigid, a handle 204 coupled to the proximal end of shaft 100 and an electrode support member 102 coupled to the distal end of shaft 100. Shaft 100 preferably comprises a plastic material that is easily molded into the shape shown in FIG. 3. In an alternative embodiment (not shown), shaft 100 comprises an electrically conducting material, usually metal, which is selected from the group comprising tungsten, stainless steel alloys, platinum or its alloys, titanium or its alloys, molybdenum or its alloys, and nickel or its alloys. In this embodiment, shaft 100 includes an electrically insulating jacket 108, which is typically formed as one or more electrically insulating sheaths or coatings, such as polytetrafluoroethylene, polyimide, and the like. The provision of the electrically insulating jacket over the shaft prevents direct electrical contact between these metal elements and any adjacent body structure or the surgeon. Such direct electrical contact between a body structure (e.g., tendon) and an exposed electrode could result in unwanted heating and necrosis of the structure at the point of contact causing necrosis.

[0073] Handle 204 typically comprises a plastic material that is easily molded into a suitable shape for handling by the surgeon. Handle 204 defines an inner cavity (not shown) that houses the electrical connections 250 (FIG. 5), and provides a suitable interface for connection to an electrical connecting cable 22 (see FIG. 2). Electrode support member 102 extends from the distal end of shaft 100 (usually about 1 to 20 mm), and provides support for a plurality of electrically isolated electrode terminals 104 (see FIG. 4B). As shown in FIG. 3, a fluid tube 233 extends through an opening in handle 204, and includes a connector 235 for connection to a fluid supply source, for supplying electrically conductive fluid to the target site. Fluid tube 233 is coupled to a distal fluid tube 239 that extends along the outer surface of shaft 100 to an opening 237 at the distal end of the probe 20, as discussed in detail below. Of course, the invention is not limited to this configuration. For example, fluid tube 233 may extend through a single lumen (not shown) in shaft 100, or it may be coupled to a plurality of lumens (also not shown) that extend through shaft 100 to a plurality of openings at its distal end. Probe 20 may also include a valve 17 (FIG. 2) or equivalent structure for controlling the flow rate of the electrically conducting fluid to the target site.

[0074] As shown in FIGS. 4A and 4B, electrode support member 102 has a substantially planar tissue treatment surface 212 and comprises a suitable insulating material (e.g., ceramic or glass material, such as alumina, zirconia and the like) which could be formed at the time of manufacture in a flat, hemispherical or other shape according to the requirements of a particular procedure. The preferred support member material is alumina, available from Kyocera Industrial Ceramics Corporation, Elkgrove, Ill., because of its high thermal conductivity, good electrically insulative properties, high flexural modulus, resistance to carbon tracking, biocompatibility, and high melting point. The support member 102 is adhesively joined to a tubular support member (not shown) that extends most or all of the distance between support member 102 and the proximal end of probe 20. The tubular member preferably comprises an electrically insulating material, such as an epoxy or silicone-based material.

[0075] In a preferred construction technique, electrode terminals 104 extend through pre-formed openings in the support member 102 so that they protrude above tissue treatment surface 212 by the desired distance. The electrodes are then bonded to the tissue treatment surface 212 of support member 102, typically by an inorganic sealing material. The sealing material is selected to provide effective electrical insulation, and good adhesion to both the alumina member 102 and the platinum or titanium electrode terminals 104. The sealing material additionally should have a compatible thermal expansion coefficient and a melting point well below that of platinum or titanium and alumina or zirconia, typically being a glass or glass ceramic

[0076] In the embodiment shown in FIGS. 3-5, probe 20 includes a return electrode 112 for completing the current path between electrode terminals 104 and a high frequency power supply 28 (see FIG. 2). As shown, return electrode 112 preferably comprises an annular conductive band coupled to the distal end of shaft 100 slightly proximal to tissue treatment surface 212 of electrode support member 102, typically about 0.5 to 10 mm and more preferably about 1 to 10 mm. Return electrode 112 is coupled to a connector 258 that extends to the proximal end of probe 10, where it is suitably connected to power supply 10 (FIG. 2).

[0077] As shown in FIG. 3, return electrode 112 is not directly connected to electrode terminals 104. To complete this current path so that electrode terminals 104 are electrically connected to return electrode 112, electrically conducting fluid (e.g., isotonic saline) is caused to flow therebetween. In the representative embodiment, the electrically conducting fluid is delivered through an external fluid tube 239 to opening 237, as described above. Alternatively, the fluid may be delivered by a fluid delivery element (not shown) that is separate from probe 20. In some microendoscopic discectomy procedures, for example, the trocar cannula may be flooded with isotonic saline and the probe 20 will be introduced into this flooded cavity. Electrically conducting fluid will be continually resupplied with a separate instrument to maintain the conduction path between return electrode 112 and electrode terminals 104.

[0078] In alternative embodiments, the fluid path may be formed in probe 20 by, for example, an inner lumen or an annular gap between the return electrode and a tubular support member within shaft 100 (not shown). This annular gap may be formed near the perimeter of the shaft 100 such that the electrically conducting fluid tends to flow radially inward towards the target site, or it may be formed towards the center of shaft 100 so that the fluid flows radially outward. In both of these embodiments, a fluid source (e.g., a bag of fluid elevated above the surgical site or having a pumping device), is coupled to probe 90 via a fluid supply tube (not shown) that may or may not have a controllable valve. A more complete description of an electrosurgical probe incorporating one or more fluid lumen(s) can be found in parent application U.S. Pat. No. 5,697,281, filed on Jun. 7, 1995 (Attorney Docket 16238-0006000), the complete disclosure of which has previously been incorporated herein by reference.

[0079] Referring to FIG. 4B, the electrically isolated electrode terminals 104 are spaced apart over tissue treatment surface 212 of electrode support member 102. The tissue treatment surface and individual electrode terminals 104 will usually have dimensions within the ranges set forth above. In the representative embodiment, the tissue treatment surface 212 has a circular cross-sectional shape with a diameter in the range of about 1 mm to 30 mm, usually about 2 to 20 mm. The individual electrode terminals 104 preferably extend outward from tissue treatment surface 212 by a distance of about 0.1 to 8 mm, usually about 0.2 to 4 mm. Applicant has found that this configuration increases the high electric field intensities and associated current densities around electrode terminals 104 to facilitate the ablation of tissue as described in detail above.

[0080] In the embodiment of FIGS. 3-5, the probe includes a single, larger opening 209 in the center of tissue treatment surface 212, and a plurality of electrode terminals (e.g., about 3-15) around the perimeter of surface 212 (see FIG. 4A). Alternatively, the probe may include a single, annular, or partially annular, electrode terminal at the perimeter of the tissue treatment surface. The central opening 209 is coupled to a suction or aspiration lumen 213 (see FIG. 3) within shaft 100 and a suction tube 211 (FIG. 3) for aspirating tissue, fluids and/or gases from the target site. In this embodiment, the electrically conductive fluid generally flows from opening 237 of fluid tube 239 radially inward past electrode terminals 104 and then back through the central opening 209 of support member 102. Aspirating the electrically conductive fluid during surgery allows the surgeon to see the target site, and it prevents the fluid from flowing into the patient's body, e.g., into the spine, the abdomen or the thoracic cavity. This aspiration should be controlled, however, so that the conductive fluid maintains a conductive path between the active electrode terminal(s) and the return electrode.

[0081] Of course, it will be recognized that the distal tip of probe may have a variety of different configurations. For example, the probe may include a plurality of openings 209 around the outer perimeter of tissue treatment surface 212 (this embodiment not shown in the drawings). In this embodiment, the electrode terminals 104 extend from the center of tissue treatment surface 212 radially inward from openings 209. The openings are suitably coupled to fluid tube 233 for delivering electrically conductive fluid to the target site, and aspiration lumen 213 for aspirating the fluid after it has completed the conductive path between the return electrode 112 and the electrode terminals 104.

[0082] In some embodiments, the probe 20 will also include one or more aspiration electrode(s) coupled to the aspiration lumen for inhibiting clogging during aspiration of tissue fragments from the surgical site. As shown in FIG. 6, one or more of the active electrode terminals 104 may comprise loop electrodes 140 that extend across distal opening 209 of the suction lumen within shaft 100. In the representative embodiment, two of the electrode terminals 104 comprise loop electrodes 140 that cross over the distal opening 209. Of course, it will be recognized that a variety of different configurations are possible, such as a single loop electrode, or multiple loop electrodes having different configurations than shown. In addition, the electrodes may have shapes other than loops, such as the coiled configurations shown in FIGS. 6 and 7. Alternatively, the electrodes may be formed within suction lumen proximal to the distal opening 209, as shown in FIG. 8. The main function of loop electrodes 140 is to ablate portions of tissue that are drawn into the suction lumen to prevent clogging of the lumen.

[0083] Loop electrodes 140 are electrically isolated from the other electrode terminals 104, which can be referred to hereinafter as the ablation electrodes 104. Loop electrodes 140 may or may not be electrically isolated from each other. Loop electrodes 140 will usually extend only about 0.05 to 4 mm, preferably about 0.1 to 1 mm from the tissue treatment surface of electrode support member 104.

[0084] Referring now to FIGS. 7 and 8, alternative embodiments for aspiration electrodes will now be described. As shown in FIG. 7, the aspiration electrodes may comprise a pair of coiled electrodes 150 that extend across distal opening 209 of the suction lumen. The larger surface area of the coiled electrodes 150 usually increases the effectiveness of the electrodes 150 on tissue fragments passing through opening 209. In FIG. 8, the aspiration electrode comprises a single coiled electrode 152 passing across the distal opening 209 of suction lumen. This single electrode 152 may be sufficient to inhibit clogging of the suction lumen. Alternatively, the aspiration electrodes may be positioned within the suction lumen proximal to the distal opening 209. Preferably, these electrodes are close to opening 209 so that tissue does not clog the opening 209 before it reaches electrodes 154. In this embodiment, a separate return electrode 156 may be provided within the suction lumen to confine the electric currents therein.

[0085] Referring to FIG. 10, another embodiment of the present invention incorporates an aspiration electrode 160 within the aspiration lumen 162 of the probe. As shown, the electrode 160 is positioned just proximal of distal opening 209 so that the tissue fragments are ablated as they enter lumen 162. In the representation embodiment, the aspiration electrode 160 comprises a loop electrode that stretches across the aspiration lumen 162. However, it will be recognized that many other configurations are possible. In this embodiment, the return electrode 164 is located outside of the probe as in the previously embodiments. Alternatively, the return electrode(s) may be located within the aspiration lumen 162 with the aspiration electrode 160. For example, the inner insulating coating 163 may be exposed at portions within the lumen 162 to provide a conductive path between this exposed portion of return electrode 164 and the aspiration electrode 160. The latter embodiment has the advantage of confining the electric currents to within the aspiration lumen. In addition, in dry fields in which the conductive fluid is delivered to the target site, it is usually easier to maintain a conductive fluid path between the active and return electrodes in the latter embodiment because the conductive fluid is aspirated through the aspiration lumen 162 along with the tissue fragments.

[0086] Referring to FIG. 9, another embodiment of the present invention incorporates a wire mesh electrode 600 extending across the distal portion of aspiration lumen 162. As shown, mesh electrode 600 includes a plurality of openings 602 to allow fluids and tissue fragments to flow through into aspiration lumen 162. The size of the openings 602 will vary depending on a variety of factors. The mesh electrode may be coupled to the distal or proximal surfaces of ceramic support member 102. Wire mesh electrode 600 comprises a conductive material, such as titanium, tantalum, steel, stainless steel, tungsten, copper, gold or the like. In the representative embodiment, wire mesh electrode 600 comprises a different material having a different electric potential than the active electrode terminal(s) 104. Preferably, mesh electrode 600 comprises steel and electrode terminal(s) comprises tungsten. Applicant has found that a slight variance in the electrochemical potential of mesh electrode 600 and electrode terminal(s) 104 improves the performance of the device. Of course, it will be recognized that the mesh electrode may be electrically insulated from active electrode terminal(s) as in previous embodiments

[0087] Referring now to FIGS. 11A-11C, an alternative embodiment incorporating a metal screen 610 is illustrated. As shown, metal screen 610 has a plurality of peripheral openings 612 for receiving electrode terminals 104, and a plurality of inner openings 614 for allowing aspiration of fluid and tissue through opening 609 of the aspiration lumen. As shown, screen 610 is press fitted over electrode terminals 104 and then adhered to shaft 100 of probe 20. Similar to the mesh electrode embodiment, metal screen 610 may comprise a variety of conductive metals, such as titanium, tantalum, steel, stainless steel, tungsten, copper, gold or the like. In the representative embodiment, metal screen 610 is coupled directly to, or integral with, active electrode terminal(s) 104. In this embodiment, the active electrode terminal(s) 104 and the metal screen 610 are electrically coupled to each other.

[0088] In other embodiments (now shown), the aspiration lumen may be formed on the perimeter of the shaft 100 (e.g., an annular or semi-annular lumen) rather than in the center, as described above. In these embodiments, the aspiration lumen is preferably set back proximally from the electrode terminals 104 by a distance of about 0.2 mm to 10 cm, preferably about 0.5 mm to 1 cm. In these embodiments, the aspiration lumen may also include one or more aspiration electrode(s) for reducing clogging as described above. One of the advantages of this configuration is that the suction of conductive fluid into the aspiration lumen does not interfere with the plasma layer formed at the tips of the electrode terminal(s). This allows the surgeon to provide a relatively large suction force, while still maintaining the requisite conditions for formation of the vapor layer and subsequent molecular dissociation of tissue.

[0089] FIG. 5 illustrates the electrical connections 250 within handle 204 for coupling electrode terminals 104 and return electrode 112 to the power supply 28. As shown, a plurality of wires 252 extend through shaft 100 to couple terminals 104 to a plurality of pins 254, which are plugged into a connector block 256 for coupling to a connecting cable 22 (FIG. 1). Similarly, return electrode 112 is coupled to connector block 256 via a wire 258 and a plug 260.

[0090] In some embodiments of the present invention, the probe 20 further includes an identification element that is characteristic of the particular electrode assembly so that the same power supply 28 can be used for different electrosurgical operations. In one embodiment, for example, the probe 20 includes a voltage reduction element or a voltage reduction circuit for reducing the voltage applied between the electrode terminals 104 and the return electrode 112. The voltage reduction element serves to reduce the voltage applied by the power supply so that the voltage between the electrode terminals and the return electrode is low enough to avoid excessive power dissipation into the electrically conducting medium and/or ablation of the soft tissue at the target site. The voltage reduction element primarily allows the electrosurgical probe 20 to be compatible with other ArthroCare generators that are adapted to apply higher voltages for ablation or vaporization of tissue. For contraction of tissue, for example, the voltage reduction element will serve to reduce a voltage of about 100 to 135 volts rms (which is a setting of 1 on the ArthroCare Model 970 and 980 (i.e., 2000) Generators) to about 45 to 60 volts rms, which is a suitable voltage for contraction of tissue without ablation (e.g., molecular dissociation) of the tissue.

[0091] Of course, for some procedures, the probe will typically not require a voltage reduction element. Alternatively, the probe may include a voltage increasing element or circuit, if desired.

[0092] In the representative embodiment, the voltage reduction element is a dropping capacitor 262 which has first leg 264 coupled to the return electrode wire 258 and a second leg 266 coupled to connector block 256. Of course, the capacitor may be located in other places within the system, such as in, or distributed along the length of, the cable, the generator, the connector, etc. In addition, it will be recognized that other voltage reduction elements, such as diodes, transistors, inductors, resistors, capacitors or combinations thereof, may be used in conjunction with the present invention. For example, the probe 90 may include a coded resistor (not shown) that is constructed to lower the voltage applied between return electrode 112 and electrode terminals 104 to a suitable level for contraction of tissue. In addition, electrical circuits may be employed for this purpose.

[0093] Alternatively or additionally, the cable 22 that couples the power supply 10 to the probe 90 may be used as a voltage reduction element. The cable has an inherent capacitance that can be used to reduce the power supply voltage if the cable is placed into the electrical circuit between the power supply, the electrode terminals and the return electrode. In this embodiment, the cable 22 may be used alone, or in combination with one of the voltage reduction elements discussed above, e.g., a capacitor.

[0094] In some embodiments, the probe 20 will further include a switch (not shown) or other input that allows the surgeon to couple and decouple the identification element to the rest of the electronics in the probe 20. For example, if the surgeon would like to use the same probe for ablation of tissue and contraction of tissue in the same procedure, this can be accomplished by manipulating the switch. Thus, for ablation of tissue, the surgeon will decouple the voltage reduction element from the electronics so that the full voltage applied by the power source is applied to the electrodes on the probe. When the surgeon desires to reduce the voltage to a suitable level for contraction of tissue, he/she couples the voltage reduction element to the electronics to reduce the voltage applied by the power supply to the electrode terminals.

[0095] Further, it should be noted that the present invention can be used with a power supply that is adapted to apply a voltage within the selected range for treatment of tissue. In this embodiment, a voltage reduction element or circuitry may not be desired.

[0096] The power supply may also includes one or more current sensors (not shown) for detecting the output current. The sensor is designed for use with coding resistors in electrosurgical probes to limit the amount of voltage applied to the probe according to its design limits. The design limits are revealed by the internal coding resistor, which is typically contained in the handle portion of the disposable probe. This feature allows the power supply to be used with a wide variety of probes and in a wide variety of surgical procedures. In addition, this sensing capability can be used to detect whether electrically conductive fluid is present adjacent the electrode terminals to prevent energizing the probe if the appropriate amount of fluid is not present. The generator may also include a voltage threshold detector for setting peak RF output voltage limits.

[0097] Referring to FIG. 20, the power output signal is coupled to a plurality of current limiting elements 96, which are preferably located on a daughter board since the current limiting elements may vary depending on the application. FIG. 20 illustrates an arrangement that may be used in arthroscopic procedures with a multi-electrode probe. As shown, a high frequency power supply 28 comprises a voltage source 98 which is connected to a multiplicity of current limiting elements 96a, 96b, . . . 96z, typically being inductors having an inductance in the range of about 100 to 5000 microhenries, with the particular value depending on the electrode terminal dimensions, the desired ablation rates, and the like. Capacitors having capacitance values in the range of about 200 to 10,000 picofarads may also be used as the current limiting elements. It would also be possible to use resistors as current limiting elements. The current limiting elements any also be part of a resonant circuit structure, as described in detail in PCT/US94/05168.

[0098] FIGS. 12-14 illustrate a method for treating nasal or sinus blockages, e.g., chronic sinusitis, according to the present invention. In these procedures, the polyps, turbinates or other sinus tissue may be ablated or reduced (e.g., by tissue contraction) to clear the blockage and/or enlarge the sinus cavity to reestablish normal sinus function. For example, in chronic rhinitis, which is a collective term for chronic irritation or inflammation of the nasal mucosa with hypertrophy of the nasal mucosa, the inferior turbinate may be reduced by ablation or contraction. Alternatively, a turbinectomy or mucotomy may be performed by removing a strip of tissue from the lower edge of the inferior turbinate to reduce the volume of the turbinate. For treating nasal polypi, which comprises benign pedicled or sessile masses of nasal or sinus mucosa caused by inflammation, the nasal polypi may be contracted or shrunk, or ablated by the method of the present invention. For treating severe sinusitis, a frontal sinus operation may be performed to introduce the electrosurgical probe to the site of blockage. The present invention may also be used to treat diseases of the septum, e.g., ablating or resecting portions of the septum for removal, straightening or reimplantation of the septum.

[0099] The present invention is particularly useful in functional endoscopic sinus surgery (FESS) in the treatment of sinus disease. In contrast to prior art microdebriders, the electrosurgical probe of the present invention effects hemostasis of severed blood vessels, and allows the surgeon to precisely remove tissue with minimal or no damage to surrounding tissue, bone, cartilage or nerves. By way of example and not limitation, the present invention may be used for the following procedures: (1) uncinectomy or medial displacement or removal of portions of the middle turbinate; (2) maxillary, sphenoid or ethmoid sinusotomies or enlargement of the natural ostium of the maxillary, sphenoid, or ethmoid sinuses, respectively; (3) frontal recess dissections, in which polypoid or granulation tissue are removed; (4) polypectomies, wherein polypoid tissue is removed in the case of severe nasal polyposis; (5) concha bullosa resections or the thinning of polypoid middle turbinate; (6) septoplasty; and the like.

[0100] FIGS. 12-14 schematically illustrate an endoscopic sinus surgery (FESS) procedure according to the present invention. As shown in FIG. 12, an endoscope 300 is first introduced through one of the nasal passages 301 to allow the surgeon to view the target site, e.g., the sinus cavities. As shown, the endoscope 300 will usually comprise a thin metal tube 302 with a lens (not shown) at the distal end 304, and an eyepiece 306 at the proximal end 308. As shown in FIG. 3, the probe shaft 100 (not shown in FIG. 12) has a bend 101 to facilitate use of both the endoscope and the probe 90 in the same nasal passage (i.e., the handles of the two instruments do not interfere with each other in this embodiment). Alternatively, the endoscope may be introduced transorally through the inferior soft palate to view the nasopharynx. Suitable nasal endoscopes for use with the present invention are described in U.S. Pat. Nos. 4,517,962, 4,844,052, 4,881,523 and 5,167,220, the complete disclosures of which are incorporated herein by reference for all purposes.

[0101] Alternatively, the endoscope 300 may include a sheath (not shown) having an inner lumen for receiving the electrosurgical probe shaft 100. In this embodiment, the shaft 100 will extend through the inner lumen to a distal opening in the endoscope. The shaft will include suitable proximal controls for manipulation of its distal end during the surgical procedure.

[0102] As shown in FIG. 13, the distal end of probe 90 is introduced through nasal passage 301 into the nasal cavity 303 (endoscope 300 is not shown in FIG. 12). Depending on the location of the blockage, the electrode terminals 104 will be positioned adjacent the blockage in the nasal cavity 303, or in one of the paranasal sinuses 305, 307. Note that only the frontal sinus 305 and the sphenoidal sinus 307 are shown in FIG. 13, but the procedure is also applicable to the ethmoidal and maxillary sinuses. Once the surgeon has reached the point of major blockage, electrically conductive fluid is delivered through tube 233 and opening 237 to the tissue (see FIG. 3). The fluid flows past the return electrode 112 to the electrode terminals 104 at the distal end of the shaft. The rate of fluid flow is controlled with valve 17 (FIG. 2) such that the zone between the tissue and electrode support 102 is constantly immersed in the fluid. The power supply 28 is then turned on and adjusted such that a high frequency voltage difference is applied between electrode terminals 104 and return electrode 112. The electrically conductive fluid provides the conduction path (see current flux lines) between electrode terminals 104 and the return electrode 112.

[0103] FIG. 13 schematically illustrates the relative position of some of the major nerves within the nasal cavity. As shown, the fila of the olfactory nerve 309 extend downward into the nasal cavity 303, and the nasopalatine nerve 311 extends across the cavity toward the septum of the nose. The optic nerve (not shown) extends from the brain into the retina, and thus extends close to the outer boundary of the nasal cavity. In addition, other cranial nerves (not shown), such as the nasociliary nerve and the posterior superior nasal branches extend through the nasal cavity. These nerves can be difficult to visualize with conventional techniques and instruments. In addition, these nerves often extend through or around the target tissue. Accordingly, the present invention provides the distinct advantage of ablation or otherwise modifying tissue within the nasal cavity without significantly damaging or impairing the function of these cranial nerves.

[0104] FIGS. 14A and 14B illustrate the removal of sinus tissue in more detail As shown, the high frequency voltage is sufficient to convert the electrically conductive fluid (not shown) between the target tissue 302 and electrode terminal(s)104 into an ionized vapor layer 312 or plasma. As a result of the applied voltage difference between electrode terminal(s) 104 and the target tissue 302 (i.e., the voltage gradient across the plasma layer 2312), charged particles 315 in the plasma (viz., electrons) are accelerated towards the tissue. At sufficiently high voltage differences, these charged particles 315 gain sufficient energy to cause dissociation of the molecular bonds within tissue structures. This molecular dissociation is accompanied by the volumetric removal (i.e, ablative sublimation) of tissue and the production of low molecular weight gases 314, such as oxygen, nitrogen, carbon dioxide, hydrogen and methane. The short range of the accelerated charged particles 315 within the tissue confines the molecular dissociation process to the surface layer to minimize damage and necrosis to the underlying tissue 320.

[0105] During the process, the gases 314 will be aspirated through opening 209 and suction tube 211 to a vacuum source. In addition, excess electrically conductive fluid, and other fluids (e.g., blood) will be aspirated from the target site 300 to facilitate the surgeon's view. During ablation of the tissue, the residual heat generated by the current flux lines (typically less than 150° C.), will usually be sufficient to coagulate any severed blood vessels at the site. If not, the surgeon may switch the power supply 28 into the coagulation mode by lowering the voltage to a level below the threshold for fluid vaporization, as discussed above. This simultaneous hemostasis results in less bleeding and facilitates the surgeon's ability to perform the procedure. Once the blockage has been removed, aeration and drainage are reestablished to allow the sinuses to heal and return to their normal function.

[0106] Another advantage of the present invention is the ability to precisely ablate layers of sinus tissue without causing necrosis or thermal damage to the underlying and surrounding tissues or bone. In addition, the voltage can be controlled so that the energy directed to the target site is insufficient to ablate bone. In this manner, the surgeon can literally clean the tissue off the bone, without ablating or otherwise effecting significant damage to the bone.

[0107] Methods for treating air passage disorders according to the present invention will now be described. In these embodiments, an electrosurgical probe such as one described above can be used to ablate targeted masses including, but not limited to, the tongue, tonsils, turbinates, soft palate tissues (e.g., the uvula), hard tissue and mucosal tissue. In one embodiment, selected portions of the tongue 314 are removed to treat sleep apnea. In this method, the distal end of an electrosurgical probe 90 is introduced into the patient's mouth 310, as shown in FIG. 15. An endoscope (not shown), or other type of viewing device, may also be introduced, or partially introduced, into the mouth 310 to allow the surgeon to view the procedure (the viewing device may be integral with, or separate from, the electrosurgical probe). The electrode terminals 104 are positioned adjacent to or against the back surface 316 of the tongue 314, and electrically conductive fluid is delivered to the target site, as described above. The power supply 28 is then activated to remove selected portions of the back of the tongue 314, as described above, without damaging sensitive structures, such as nerves, and the bottom portion of the tongue 314.

[0108] In another embodiment, the electrosurgical probe of the present invention can be used to ablate and/or contract soft palate tissue to treat snoring disorders. In particular, the probe is used to ablate or shrink sections of the uvula 320 without causing unwanted tissue damage under and around the selected sections of tissue. For tissue contraction, a sufficient voltage difference is applied between the electrode terminals 104 and the return electrode 112 to elevate the uvula tissue temperature from normal body temperatures (e.g., 37° C.) to temperatures in the range of 45° C. to 90° C., preferably in the range from 60° C. to 70° C. This temperature elevation causes contraction of the collagen connective fibers within the uvula tissue.

[0109] FIG. 15 illustrates the hypoglossal nerve 351, which originates in the medulla oblongata, collects into the hypoglossal canal and extends into the tongue 314, where it functions as the motor nerve of the tongue 314. In procedures that require removal or contraction of tissue within the tongue 314, the present invention has a distinct advantage of being able to perform these procedures without causing significant damage to the hypoglossal nerve 351.

[0110] In one method of tissue contraction according to the present invention, an electrically conductive fluid is delivered to the target site as described above, and heated to a sufficient temperature to induce contraction or shrinkage of the collagen fibers in the target tissue. The electrically conducting fluid is heated to a temperature sufficient to substantially irreversibly contract the collagen fibers, which generally requires a tissue temperature in the range of about 45° C. to 90° C., usually about 60° C. to 70° C. The fluid is heated by applying high frequency electrical energy to the electrode terminal(s) in contact with the electrically conducting fluid. The current emanating from the electrode terminal(s) 104 heats the fluid and generates a jet or plume of heated fluid, which is directed towards the target tissue. The heated fluid elevates the temperature of the collagen sufficiently to cause hydrothermal shrinkage of the collagen fibers. The return electrode 112 draws the electric current away from the tissue site to limit the depth of penetration of the current into the tissue, thereby inhibiting molecular dissociation and breakdown of the collagen tissue and minimizing or completely avoiding damage to surrounding and underlying tissue structures beyond the target tissue site. In an exemplary embodiment, the electrode terminal(s) 104 are held away from the tissue a sufficient distance such that the RF current does not pass into the tissue at all, but rather passes through the electrically conducting fluid back to the return electrode. In this embodiment, the primary mechanism for imparting energy to the tissue is the heated fluid, rather than the electric current.

[0111] In an alternative embodiment, the electrode terminal(s) 104 are brought into contact with, or close proximity to, the target tissue so that the electric current passes directly into the tissue to a selected depth. In this embodiment, the return electrode draws the electric current away from the tissue site to limit its depth of penetration into the tissue. Applicant has discovered that the depth of current penetration also can be varied with the electrosurgical system of the present invention by changing the frequency of the voltage applied to the electrode terminal and the return electrode. This is because the electrical impedance of tissue is known to decrease with increasing frequency due to the electrical properties of cell membranes which surround electrically conductive cellular fluid. At lower frequencies (e.g., less than 350 kHz), the higher tissue impedance, the presence of the return electrode and the electrode terminal configuration of the present invention (discussed in detail below) cause the current flux lines to penetrate less deeply resulting in a smaller depth of tissue heating. In an exemplary embodiment, an operating frequency of about 100 to 200 kHz is applied to the electrode terminal(s) to obtain shallow depths of collagen shrinkage (e.g., usually less than 1.5 mm and preferably less than 0.5 mm).

[0112] In another aspect of the invention, the size (e.g., diameter or principal dimension) of the electrode terminals employed for treating the tissue are selected according to the intended depth of tissue treatment. As described previously in copending patent application PCT International Application, U.S. National Phase Serial No.

[0113] PCT/US94/05168, the depth of current penetration into tissue increases with increasing dimensions of an individual active electrode (assuming other factors remain constant, such as the frequency of the electric current, the return electrode configuration, etc.). The depth of current penetration (which refers to the depth at which the current density is sufficient to effect a change in the tissue, such as collagen shrinkage, irreversible necrosis, etc.) is on the order of the active electrode diameter for the bipolar configuration of the present invention and operating at a frequency of about 100 kHz to about 200 kHz. Accordingly, for applications requiring a smaller depth of current penetration, one or more electrode terminals of smaller dimensions would be selected. Conversely, for applications requiring a greater depth of current penetration, one or more electrode terminals of larger dimensions would be selected.

[0114] In addition to the above procedures, the system and method of the present invention may be used for treating a variety of disorders in the mouth 310, pharynx 330, larynx 335, hypopharynx, trachea 340, esophagus 350 and the neck 360. For example, tonsillar hyperplasis or other tonsil disorders may be treated with a tonsillectomy by partially ablating the lymphoepithelial tissue. This procedure is usually carried out under intubation anesthesia with the head extended. An incision is made in the anterior faucial pillar, and the connective tissue layer between the tonsillar parenchyma and the pharyngeal constrictor muscles is demonstrated. The incision may be made with conventional scalpels, or with the electrosurgical probe of the present invention. The tonsil is then freed by ablating through the upper pole to the base of the tongue, preserving the faucial pillars. The probe ablates the tissue, while providing simultaneous hemostasis of severed blood vessels in the region. Similarly, adenoid hyperplasis, or nasal obstruction leading to mouth breathing difficulty, can be treated in an adenoidectomy by separating (e.g., resecting or ablating) the adenoid from the base of the nasopharynx.

[0115] Other pharyngeal disorders can be treated according to the present invention. For example, hypopharyngeal diverticulum involves small pouches that form within the esophagus immediately above the esophageal opening. The sac of the pouch may be removed endoscopically according to the present invention by introducing a rigid esophagoscope, and isolating the sac of the pouch. The cricopharyngeus muscle is then divided, and the pouch is ablated according to the present invention. Tumors within the mouth and pharynx, such as hemangionmas, lymphangiomas, papillomas, lingual thyroid tumors, or malignant tumors, may also be removed according to the present invention.

[0116] Other procedures of the present invention include removal of vocal cord polyps and lesions and partial or total laryngectomies. In the latter procedure, the entire larynx is removed from the base of the tongue to the trachea, if necessary with removal of parts of the tongue, the pharynx, the trachea and the thyroid gland.

[0117] Tracheal stenosis may also be treated according to the present invention. Acute and chronic stenoses within the wall of the trachea may cause coughing, cyanosis and choking.

[0118] The present invention is particularly useful in microendoscopic discectomy procedures, e.g., for decompressing a nerve root with a lumbar discectomy. As shown in FIGS. 16-19, a percutaneous penetration 270 is made in the patients' back 272 so that the superior lamina 274 can be accessed. Typically, a small needle (not shown) is used initially to localize the disc space level, and a guidewire (not shown) is inserted and advanced under lateral fluoroscopy to the inferior edge of the lamina 274. Sequential cannulated dilators 276 are inserted over the guide wire and each other to provide a hole from the incision 220 to the lamina 274. The first dilator may be used to “palpate” the lamina 274, assuring proper location of its tip between the spinous process and facet complex just above the inferior edge of the lamina 274. As shown in FIG. 17, a tubular retractor 278 is then passed over the largest dilator down to the lamina 274. The dilators 276 are removed, establishing an operating corridor within the tubular retractor 278.

[0119] As shown in FIG. 17, an endoscope 280 is then inserted into the tubular retractor 278 and a ring clamp 282 is used to secure the endoscope 280. Typically, the formation of the operating corridor within retractor 278 requires the removal of soft tissue, muscle or other types of tissue that were forced into this corridor as the dilators 276 and retractor 278 were advanced down to the lamina 274. This tissue is usually removed with mechanical instruments, such as pituitary rongeurs, curettes, graspers, cutters, drills, microdebriders and the like. Unfortunately, these mechanical instruments greatly lengthen and increase the complexity of the procedure. In addition, these instruments sever blood vessels within this tissue, usually causing profuse bleeding that obstructs the surgeon's view of the target site.

[0120] According to the present invention, an electrosurgical probe or catheter 284 as described above is introduced into the operating corridor within the retractor 278 to remove the soft tissue, muscle and other obstructions from this corridor so that the surgeon can easily access and visualization the lamina 274. Once the surgeon has reached has introduced the probe 284, electrically conductive fluid 285 is delivered through tube 233 and opening 237 to the tissue (see FIG. 3). The fluid flows past the return electrode 112 to the electrode terminals 104 at the distal end of the shaft. The rate of fluid flow is controlled with valve 17 (FIG. 2) such that the zone between the tissue and electrode support 102 is constantly immersed in the fluid. The power supply 28 is then turned on and adjusted such that a high frequency voltage difference is applied between electrode terminals 104 and return electrode 112. The electrically conductive fluid provides the conduction path (see current flux lines) between electrode terminals 104 and the return electrode 112.

[0121] The high frequency voltage is sufficient to convert the electrically conductive fluid (not shown) between the target tissue and electrode terminal(s)104 into an ionized vapor layer or plasma (not shown). As a result of the applied voltage difference between electrode terminal(s) 104 and the target tissue (i.e., the voltage gradient across the plasma layer), charged particles in the plasma (viz., electrons) are accelerated towards the tissue. At sufficiently high voltage differences, these charged particles gain sufficient energy to cause dissociation of the molecular bonds within tissue structures. This molecular dissociation is accompanied by the volumetric removal (i.e., ablative sublimation) of tissue and the production of low molecular weight gases, such as oxygen, nitrogen, carbon dioxide, hydrogen and methane. The short range of the accelerated charged particles within the tissue confines the molecular dissociation process to the surface layer to minimize damage and necrosis to the underlying tissue.

[0122] During the process, the gases will be aspirated through opening 209 and suction tube 211 to a vacuum source. In addition, excess electrically conductive fluid, and other fluids (e.g., blood) will be aspirated from the operating corridor to facilitate the surgeon's view. During ablation of the tissue, the residual heat generated by the current flux lines (typically less than 150° C.), will usually be sufficient to coagulate any severed blood vessels at the site. If not, the surgeon may switch the power supply 28 into the coagulation mode by lowering the voltage to a level below the threshold for fluid vaporization, as discussed above. This simultaneous hemostasis results in less bleeding and facilitates the surgeon's ability to perform the procedure.

[0123] Another advantage of the present invention is the ability to precisely ablate soft tissue without causing necrosis or thermal damage to the underlying and surrounding tissues, nerves or bone. In addition, the voltage can be controlled so that the energy directed to the target site is insufficient to ablate the lamina 274 so that the surgeon can literally clean the tissue off the lamina 274, without ablating or otherwise effecting significant damage to the lamina.

[0124] Referring now to FIGS. 18 and 19, once the operating corridor is sufficiently cleared, a laminotomy and medial facetectomy is accomplished either with conventional techniques (e.g., Kerrison punch or a high speed drill) or with the electrosurgical probe 284 as discussed above. After the nerve root is identified, medical retraction can be achieved with a retractor 288, or the present invention can be used to ablate with precision the disc. If necessary, epidural veins are cauterized either automatically or with the coagulation mode of the present invention. If an annulotomy is necessary, it can be accomplished with a microknife or the ablation mechanism of the present invention while protecting the nerve root with the retractor 288. The herniated disc 290 is then removed with a pituitary rongeur in a standard fashion, or once again through ablation as described above.

[0125] As shown in FIG. 19, the nucleus pulposis 290 often impinges on the spinal nerve 275, which results in back pain. In order to remove or ablate the pulposis and relieve the pressure on the spinal nerve 275, the surgeon must operate extremely close to the nerve 275, which greatly enhances the risk of nerve damage or destruction, particularly in endoscopic procedures. The present invention provides the ability to remove this spinal tissue without damaging the spinal nerve.

[0126] In another embodiment, the electrosurgical probe of the present invention can be used to ablate and/or contract soft tissue within the disc 290 to allow the annulus 292 to repair itself to prevent reoccurrence of this procedure. For tissue contraction, a sufficient voltage difference is applied between the electrode terminals 104 and the return electrode 112 to elevate the tissue temperature from normal body temperatures (e.g., 37° C.) to temperatures in the range of 45° C. to 90° C., preferably in the range from 60° C. to 70° C., as discussed in detail above. This temperature elevation causes contraction of the collagen connective fibers within the disc tissue so that the disc 290 withdraws into the annulus 292.

[0127] The system and method of the present invention may also be useful to efficaciously ablate (i.e., disintegrate) cancer cells and tissue containing cancer cells, such as cancer on the surface of the epidermis, eye, colon, bladder, cervix, uterus and the like. The present invention's ability to completely disintegrate the target tissue can be advantageous in this application because simply vaporizing and fragmenting cancerous tissue may lead to spreading of viable cancer cells (i.e., seeding) to other portions of the patient's body or to the surgical team in close proximity to the target tissue. In addition, the cancerous tissue can be removed to a precise depth while minimizing necrosis of the underlying tissue.

[0128] Other modifications and variations can be made to disclose embodiments without departing from the subject invention as defined in the following claims. For example, it should be noted that the invention is not limited to an electrode array comprising a plurality of electrode terminals. The invention could utilize a plurality of return electrodes, e.g., in a bipolar array or the like. In addition, depending on other conditions, such as the peak-to-peak voltage, electrode diameter, etc., a single electrode terminal may be sufficient to contract collagen tissue, ablate tissue, or the like.

[0129] In addition, the active and return electrodes may both be located on a distal tissue treatment surface adjacent to each other. The active and return electrodes may be located in active/return electrode pairs, or one or more return electrodes may be located on the distal tip together with a plurality of electrically isolated electrode terminals. The proximal return electrode may or may not be employed in these embodiments. For example, if it is desired to maintain the current flux lines around the distal tip of the probe, the proximal return electrode will not be desired.