MXPA98000222A - An electroquirurg instrument - Google Patents

Abstract

An electrosurgical instrument, which is used to treat tissue in the presence of an electrically conductive fluid (eg, "underwater surgery"), comprises an instrument shaft and an electrode assembly at one end of the shaft. The electrode assembly comprises a tissue treatment electrode (11) and a return electrode (12) which is electrically wound from the tissue treatment electrode by an insulating member (15). The tissue treatment electrode (11) is exposed at the terminal distal end of the instrument, and the return electrode (12) has a contact surface with the fluid separated from the end of the tissue treatment electrode by an insulating member (15). ). The instrument further comprises feeding elements (17) for feeding the electrically conductive fluid to the exposed end region of the tissue treatment electrode (11) so as to define, during use, a conductive fluid path that completes an electrical circuit between the tissue treatment electrode and the return electrode (1

Description

AN ELECTROOUROPING INSTRUMENT The invention relates to an electrosurgical instrument for the treatment of tissue in the presence of a fluid electrically conductive medium, to an electrosurgical apparatus including that instrument, and to an electrode unit for use in that instrument. Endoscopic electrosurgery is useful for treating tissue in the body cavities, and is normally performed in the presence of a distention medium. When the distension medium is a liquid, the technique is commonly referred to as under-water electrosurgery, which in turn denotes electrosurgery in which living tissue is treated using an electrosurgical instrument with an electrode or treatment electrodes submerged in liquid at the site of operation. A gaseous medium is commonly used when performing endoscopic surgery in a distensible body cavity of larger potential volume, in which a liquid medium would be inadequate, as is often the case with laparoscopy or gastroenterological surgery. Underwater surgery is commonly performed using endoscopic techniques, in which the same endoscope can provide a conduit (commonly referred to as a working channel) for the passage of an electrode. Alternatively, the endoscope can be specifically adapted (as in a resectoscope) to include elements for mounting an electrode, or the electrode can be introduced into a body cavity via a separate access element at an angle to the endoscope - a technique which is commonly referred to as triangulation. These variations in the technique can be subdivided by surgical specialty, where one or the other of the techniques has particular advantages given the access route for the specific body cavity. Endoscopes with integral working channels, or those characterized as resectoscopes, are usually used where the body cavity can be accessed through a natural opening - such as the cervical canal to access the endometrial cavity of the uterus, or the urethra to have access to the prostate gland and the bladder. Endoscopes designed specifically for use in the endometrial cavity are referred to as hysteroscopes, and those designed for use in the urinary tract include cytoscopes, urethroscopes and resectoscopes. Procedures for transurethral resection or vaporization of the prostate gland are known as TURP and EVAP, respectively. When there is no natural bodily opening through which an endoscope can be passed, the triangulation technique is commonly employed. Triangulation is commonly used during endoscopic underwater surgery in joint cavities such as the knee and shoulder. The endoscope used in these procedures is commonly referred to as an arthroscope. Electrosurgery is usually carried out using either a monopolar instrument or a bipolar instrument. With monopolar electrosurgery, an active electrode is used in the region of operation, and a return plate is secured to the patient's skin at a position remote from the site of operation. With this arrangement, the current passes from the active electrode through the patient's tissues to the external return plate. Since the patient represents a significant portion of the circuit, the energy input levels have to be high (typically 150 to 250 watts), to compensate for the limiting resistive current of the patient's tissues, and in the case of electrosurgery under the water, the energy losses due to the fluid medium that becomes partially conductive due to the presence of blood or other bodily fluids. Using high energy with a monopolar array is also risky, because tissue heating occurs on the return plate, which can cause severe skin burns. There is also the risk of capacitive coupling between the instrument and the patient's tissues at the entry point into the body cavity. When surgery is performed in the body cavities, vital structures are often in close proximity to the application site, and these structures can be damaged by the collateral scattering of the electrosurgical effect. Also relative to when monopolar electrosurgery is used is that the operating voltage rises to overcome the limiting resistive current of the patient's tissues or to overcome the carbonization of the application electrode at the entry point. Arcing by direct coupling to adjacent structures, or through cuts in the insulation, can cause accidental tissue damage outside the narrow field of view of the endoscope. There is also a risk of capacitive coupling between the instrument and the patient's tissues at the point of entry into the body cavity so that the electrosurgical energy can be coupled to the entry point. This coupled energy can sometimes be enough to cause burns. These risks of using monopolar electrosurgery during endoscopic procedures are now well recognized, and have led to a shift towards the adoption of bipolar surgery. With bipolar electrosurgery, a pair of electrodes (an active electrode and a return electrode) are used together at the tissue application site. This arrangement has advantages from the point of view of safety, due to the relative proximity of the two electrodes, so that the radiofrequency currents are limited to the region between the electrodes. However, the depth of the effect is directly related to the distance between the electrodes, and, during applications that require very small electrodes, the separation between electrodes becomes very small, thus limiting the effect on the tissue and the energy of the electrodes. departure. Further separating the electrodes would often obscure the vision of the application site, and would require a modification in the surgical technique to ensure the correct contact of both electrodes with the tissue. There are many variations to the basic design of the bipolar probe. For example, U.S. Patent Specification Number: 4706667 describes one of the design fundamentals, i.e., the ratio of the contact areas of the return electrode and the active electrode is greater than 7: 1 and less than 20: 1 for cutting purposes. This range relates only to the cutting electrode configurations. When a bipolar instrument is used for desiccation or coagulation, the radius of the contact areas of the two electrodes can be reduced to approximately 1: 1 to avoid the differential electrical tensions that occur at the contact between the tissue and the electrodes. The electrical conjunction between the return electrode and the tissue can be supported by wetting the tissue by a conductive solution such as normal saline solution. Both monopolar and bipolar probe arrays often provide a suction and irrigation element. who mainly intend to wash the operation site. In that case, the active electrode is retracted into the irrigation cover to allow direct contact of the cover with the tissue without the risk of mechanical damage to the tissue by the exposed electrode. A surgical effect can not be produced with the electrode retracted, or during the passage of the saline solution. As a secondary benefit, this arrangement allows tissue moistening to reduce contact impedance. In bipolar needle arrays, one of the obvious limitations is that the active electrode must be completely buried in the tissue to allow the return electrode to complete the circuit. Another problem is of orientation, a change even if it is relatively small in the application angle from the ideal perpendicular contact with respect to the surface of the tissue, will change the proportion of the contact area of the electrode, so that a surgical effect can occur in the tissue that is in contact with the return electrode. Applicants have developed a bipolar instrument suitable for underwater electrosurgery using a liquid or gaseous conductive medium. This electrosurgical instrument for the treatment of tissue in the presence of a fluid medium, comprises an instrument body having a handpiece and an instrument shaft and an assembly of electrodes, at one end of the shaft. The electrode assembly comprises an electrode for the treatment of tissues that is exposed at the extreme distal end of the instrument, and a return electrode that is electrically isolated from the tissue treatment electrode and has a contact surface with the fluid separated proximally from the tissue. the exposed part of the tissue treatment electrode. During the use of the instrument, the tissue treatment electrode is applied to the tissue to be treated while the return electrode, being proximally separated from the exposed part of the tissue treatment electrode, is normally separated from the tissue and serves to completing a cycle of electrosurgical current from the tissue treatment electrode through the tissue and the fluid medium. This electrosurgical instrument is described in the applicants specification British Patent Application No. 9512889.8. The electrode structure of this instrument, in combination with a means of conductive distention, greatly avoids the problems experienced with monopolar or bipolar electrosurgery. In particular, the input energy levels are much lower than those generally needed, with a monopolar array (typically 100 watts). Moreover, due to the relatively large separation between their electrodes, an increased depth of effect is obtained compared to conventional bipolar arrays. This type of electrosurgical instrument was first designed for use in a saline environment, so it can not be used outdoors or in environments that operate gas filled. The goal of the invention is to provide an irrigated bipolar electrosurgical instrument that can be used outdoors or in gas filled environments, in body fluids, or by insertion into the tissue by creating a conductive fluid environment around the tip of the body. instrument. The present invention provides an electrosurgical instrument for the treatment of tissue in the presence of an electrically conductive fluid, the instrument comprises an axis of the instrument and an assembly of electrodes at one end of the shaft, the electrode assembly comprising an electrode for the treatment of tissues and a return electrode that is electrically isolated from the tissue treatment electrode by means of an insulating member, the tissue treatment electrode is exposed at the distal end of the instrument, and the return electrode has a contact surface with the fluid separated from the exposed end of the tissue treatment electrode by the isolation member, wherein the instrument further comprises feeding elements for feeding the electrically conductive fluid to the region of the exposed end of the tissue treatment electrode in such a manner as to define a conductive fluid path that completes, during use, an electrical circuit between the tissue treatment electrode and return electrode. In this way, it is possible to create a local conductive fluid environment around the tip of an electrosurgical instrument by sending the fluid through the instrument in such a way that the return electrode can be placed away from the tissue treatment electrode on or within the axis of the instrument. The structure of this instrument thus simulates a monopolar configuration with an active electrode (tissue treatment) and a remote return electrode, the return electrode being placed on the axis of the instrument to provide all the advantages of bipolar safety of electrosurgery without the disadvantages. The separation of the two electrodes is supported by the supply of the conductive medium, and allows the higher energies to be delivered compared to conventional bipolar electrosurgery, but still at lower energy levels than in conventional monopolar electrosurgery. The arrangement can also produce a tissue contact vaporization comparable to that of laser surgery. The return electrode is separated from the tissue treatment electrode so that, during use, it does not come into contact with the tissue to be treated, and in this way the simple electrical circuit is completed by the conductive fluid, and not simply by the arching between the electrodes. Undoubtedly, the arrangement is such that arching between the adjacent parts of the electrode assembly is avoided, thereby ensuring that the tissue treatment electrode can be wrapped in a vapor pocket so that the tissue that is introduced into the The steam bag becomes the preferred path for the flow to flow back to the return electrode via the conductive fluid. The electrosurgical instrument of the invention is useful for tissue dissection, resection, vaporization, drying and coagulation and combinations of these functions with particular application in laparoscopy, colposcopy (including vaginal speculum) and open surgical procedures in the female genital tract and related related diseases. . Laparoscopic operative procedures may include removal of subserosal and pedunculated fibroids, ablation of ectopic endometrium, ovarian cystectomy and ovarian piercing procedures, oophorectomy, salpingo-oophorectomy, subtotal hysterectomy, and laparoscopically assisted vaginal hysterectomy (LAVH) as may be performed for benign or malignancies, laparoscopic uterosacral nerve ablation (LUNA); fallopian tube surgery as correction of ectopic pregnancy or complications arising from acquired obstructions, division of abdominal adhesions; and hemostasis. The electrosurgical instrument of the invention is also useful in the lower female genital tract, including treatment of the cervix, vagina and external genitalia when accessed directly or using instrumentation generally comprising speculum and colposcopes. These applications include vaginal hysterectomy and other pelvic procedures using vaginal access; LLETZ / LEEP procedure (large cycle excision of the transformation zone) or excision of the transformation zone of the endocervix, removal of cystic or septic lesions, ablation of venereal warts, excision of benign and malignant lesions; cosmetic and surgical repairs including vaginal prolapse, excision of diseased tissue, and hemostasis. The electrosurgical instrument of the invention is also useful for the dissection, resection, vaporization, drying and coagulation of tissue and combinations of these functions with particular application in surgery of the ear, nose and throat (ENT) and more particularly procedures performed in oropharynx, nasopharynx and breasts. These procedures can be performed through the mouth or nose using a speculum or gag or using endoscopic techniques such as functional endoscopic sinus surgery (FESS). Functional endoscopic sinus procedures may include the removal of mucosal coatings, polyps, and neoplasms of the various chronically diseased, inflamed, and hypertrophic skull anatomical sinuses, excision of diseased tissue, and hemostasis. Procedures in the nasopharynx may include the removal of mucosal, polyps and neoplasm coatings from chronically diseased, inflamed or hypertrophic turbinates and nasal passages; Resection of the nasal septum, excision of diseased tissue, and hemostasis. Procedures in the oropharynx may include removal of hypertrophic, chronically diseased or inflamed tissue, polyps and neoplasms particularly as this occurs related to the tonsils, adenoids, and epiglotic and supraglottic regions, and salivary glands, as an alternative method to perform the procedure commonly known as laser-assisted uvulopalatoplasty (LAUP); excision of diseased tissue and hemostasis. It is evident from the scope of the applications of the invention that it has other additional applications for the dissection, resection, vaporization, drying and coagulation of tissue and combinations of these functions in general laparoscopic, thoracoscopic and neurosurgical procedures, being particularly useful for the removal of diseased tissue and neoplastic disease whether benign or malignant.

Surgical procedures using the electrosurgical instrument of the invention include introducing the electrode assembly into the surgical site where by means of an artificial (cannula) or natural conduit that can be in an anatomical body cavity or a surgically created space either using the same instrument or by another technique. The cavity or space can be distended during the procedure using a fluid, or it can be kept open by anatomical structures. The surgical site can be washed in a continuous flow of conductive fluid, such as a saline solution, to create a locally irrigated environment around the tip of the electrode assembly in a gas filled cavity or an external body surface or other tissue surfaces. thus exposed during part of a surgical procedure. Irrigation fluid can be aspirated from the surgical site to remove the products created by the application of radiofrequency energy, tissue waste and blood. The procedures may include simultaneous visualization of the site via an endoscope or using an indirect display element. In a preferred embodiment, the instrument further comprises a removal element for removing the electrically conductive fluid from the region of the exposed end of the tissue treatment electrode. The removal element is par- ticularly important when the conductive fluid is a liquid such as a saline solution, such as saline solution heated by the electrosurgical output needs to be removed to avoid the risk of tissue collateral damage. By continuously feeding electrically conductive fluid such as saline to the tissue treatment (active) electrode region, and continuously removing fluid from this region, it is possible to create a local fluid field in the active electrode. Moreover, since the fluid is constantly filling this region, the temperature of the active electrode can be maintained at a desired level. Conveniently, the removal element is constituted by a fluid return channel formed within the axis of the instrument, and by an element for applying suction to the proximal end of the fluid return channel, and the supply element is constituted by a Fluid feed channel formed inside the axis of the instrument. The fluid feed channel can be placed around the fluid return channel. In a preferred embodiment, the return electrode is a tubular member that is coated with an insulating cover, the coated return electrode constituting the axis of the instrument. Conveniently, the inner surface of the tubular member constitutes the return electrode. Preferably, the tubular member is made of stainless steel. In this case, the tissue treatment electrode may be supported centrally within the tubular member by an insulating spacer. Conveniently, the insulating separator is made of ceramic material, silicone rubber or glass. The instrument may also comprise a tube that extends proximally of the spacer. Preferably, the feeding channel is constituted by the annular space between the return electrode and the tube, and the return channel is constituted by the interior of the tube and the opening element extending through the spacer. Alternatively, the instrument may further comprise a second return electrode constituted by a second tubular stainless steel member concentrically positioned within the aforementioned tubular stainless steel member. In this case, the supply channel can be constituted by the annular space between the two return electrodes, and the return channel is constituted by the annular space between the second return electrode and the tube. The invention also provides an electrosurgical apparatus comprising a radiofrequency generator and an electrosurgical instrument for the treatment of tissue in the presence of an electrically conductive fluid medium., where the electrosurgical instrument is as defined above. Conveniently, the radio frequency generator includes a control element for varying the output energy supplied to the electrodes, the control element being suitable for providing output power in a first and a second output range, the first range being output to provide energy to the electrosurgical instrument for tissue desiccation, and being the second output range to provide energy to the electrosurgical instrument for tissue removal by cutting or vaporization. Preferably, the first output range is from about 150 volts to 200 volts, and the second output range is from about 250 volts to 600 volts, the voltages being peak voltages. The invention further provides a method for operating an electrosurgical apparatus having at least one tissue desiccation mode and one tissue vaporization mode, the apparatus having a radiofrequency generator coupled to an electrode assembly for tissue treatment in the presence of of a fluid electrically conductive medium, the electrode assembly comprising an electrode for the treatment of tissues and a return electrode which is electrically isolated from the tissue treatment electrode by means of an insulating member, the tissue treatment electrode being exposed to the distal end of the assembly, and the return electrode having a fluid contact surface separated from the exposed end of the tissue treatment electrode by the insulating member, the method comprises the steps of: feeding the electrically conductive fluid to the end region exposed of the tissue treatment electrode two, and control the output energy of the radio frequency generator to be within a first output range for the tissue drying mode and to be within a second range for the tissue vaporization mode, being the first output range such that the energy supplied to the electrode assembly maintains the conductive fluid adjacent to the tissue treatment electrode substantially at the boiling point for tissue desiccation without creating a vapor pocket surrounding the tissue treatment electrode, and the second range The output is such that the output energy supplied to the electrode assembly for tissue vaporization is such as to maintain a vapor pocket around the tissue treatment electrode. Conveniently, the method further comprises an electrosurgical tissue desiccation method comprising the steps of: providing an electrosurgical apparatus comprising a radiofrequency generator coupled to an electrode assembly comprising a tissue treatment electrode and a return electrode , the tissue treatment electrode having a distal end exposed; and introducing the electrode assembly at a selected operating site with the tissue treatment electrode adjacent to the tissue to be treated; feeding electrically conductive fluid to the region of the exposed end of the tissue treatment electrode; activating the generator, and applying sufficient radiofrequency energy to the electrode assembly to vaporize the electrically conductive fluid surrounding the tissue treatment electrode to maintain a vapor pocket surrounding the tissue treatment electrode. Conveniently, the return electrode is separated proximally with respect to the tissue treatment electrode, and the electrode assembly is introduced into the selected operating site so that the treatment electrode is positioned at least adjacent to the tissue being removed. to be treated, with the vapor bag in contact with the tissue, and with the return electrode in contact with the electrically conductive fluid, the electrode structure being manipulated to at least achieve vaporization of the tissue. The invention will now be described in greater detail, by way of example, with reference to the drawings, in which: Figure 1 is a diagram showing an electrosurgical apparatus constructed in accordance with the invention. Figure 2 is a schematic longitudinal sectional view of the distal end of a first form of electrosurgical instrument for use with the apparatus of Figure 1; and Figure 3 is a schematic longitudinal sectional view of a second form of electrosurgical instrument for use with the apparatus of Figure 1. Each of the electrosurgical instruments described below is intended to be used with a conductive medium such as normal saline or argon. Each instrument has a dual electrode structure, with the conductive medium acting as a conductor between the tissue being treated and one of the electrodes, hereinafter referred to as the return electrode. The other electrode is applied directly, or immediately adjacent, to the tissue, and is hereinafter referred to as the (active) tissue treatment electrode. In many cases, the use of a liquid medium is preferable, since it avoids the excessive temperature of the electrode in most circumstances, and greatly eliminates the sticking of tissue. Referring to the drawings, Figure 1 shows the electrosurgical apparatus including a generator 1 having an output hub 2 that provides a radio frequency (RF) output for an instrument in the form of a hand piece 3 via a connecting cord 4. Activation of the generator 1 can be performed from the hand piece 3 via a control connection on the cord 4, or by means of a pedal switch unit 5, as shown, connected separately to the rear part of the generator 1 by means of a connecting cord of the foot switch 6. In the illustrated embodiment the foot switch unit 5 has two foot switches 5a and 5b for selecting a desiccation mode or a vaporization mode of the generator 1, respectively. The front panel of the generator has oppression buttons 7a and 7b to respectively set the drying and vaporization energy levels, which are indicated in a visual display 8. The depressed buttons 9a are provided as alternative elements for the selection between the drying modes and vaporization. The hand piece 3 assembles a removable electrosurgical instrument E, such as the electrode units El and E2 which are described below.

Figure 2 shows the distal end of the first form of the electrosurgical instrument El. The instrument is formed with an electrode assembly at the distal end thereof, the electrode assembly comprising an (active) electrode for the treatment of tissues 11 and a tubular return electrode 12. The active electrode 11 is made of twisted noble metal (such as platinum / iridium or platinum / tungsten), and the return electrode is a stainless steel tube. The return electrode 12 is completely lined by a polyimide insulating cover 13. The electrode 12 extends to the total length of the electrosurgical instrument El, and constitutes the axis of the instrument. The electrodes 11 and 12 are provided with current from the radio frequency (RF) generator 1 (not shown in Figure 2), the return electrode 12 being directly connected to the generator and the electrode 11 is connected via a copper conductor 14. The generator 1 may be as described in the specification of our related British Patent Application number 9604770.9. The active electrode 11 is maintained centrally within the return electrode by means of a ceramic insulator / separator 15. The insulator / separator 15 has a generally cylindrical portion 15a surrounding the junction between the active electrode 11 and the conductor 14 and the adjacent regions of these two members and four equidistant wings 15b that extend radially and are in contact with the inner circumferential wall of the return electrode 12 to maintain the insulator / separator, and therefore the active electrode 11 centrally within the return electrode. A tube 16 made of an insulating material such as PTFE, is a friction fit around the proximal end of the cylindrical portion 15a of the insulator / spacer 15, and extends substantially along the entire length of the instrument. The tube 16 defines, together with the return electrode 12, a supply channel of coaxial salt solution 17, the interior of the tube defining a return channel of the saline solution 18. During use, the saline solution is fed into the channel 17. by gravity (no pumping is required), and the saline solution is removed via channel 18 and openings (not shown) in the cylindrical portion 15a of the insulator / separator 15 by means of a suction element.

Preferably, the suction is carried out by a low noise pump (not shown) such as a mobile propeller pump or a diaphragm pump, instead of using a high speed propellant. As the tube leads to the pump intermittently it will contain small amounts of saline, a large vacuum is required (at least 500 mBar). However, the amount of gas and liquid to be removed is comparatively small, and this allows the use of a moving propeller or a diaphragm pump, although a large volume peristaltic pump could also be used. To circumvent the sterilization requirement of the pump, the pump operates via a disposable fluid trap (not shown) that incorporates a PTFE filter of 10 μm. This filter prevents both exhaust fluids and gas particles from being released by the pump and contaminating work areas and the surrounding environment. The instrument as described above is intended to be used outdoors or in gas-filled environments, in body fluids or by insertion into the tissue by the creation of a conductive fluid environment around the tip of the instrument, and is arranged in a manner that it is possible to create a local saline field at a distal end of the instrument. This instrument can, therefore, be used for laparoscopic applications. During use the saline is fed to the active electrode 11 via channel 17, the saline solution providing a conductive medium to act as a conductive path between the tissue being treated and the return electrode 12. Varying the output of the generator 1, the instrument can be used for the removal of tissue by vaporization, for cutting or drying. In each case, as the saline solution comes in contact with the active electrode 11, it is heated until it reaches an equilibrium temperature that depends on the energy output of the generator 1 and the flow rate of the saline solution. In equilibrium, as the new saline solution feeds via channel 17 to the active electrode ll, the outside temperature of the shaft is maintained at the same temperature as that of the surrounding saline solution. As the insulating cover 13 completely covers the external surface of the return electrode 12, accidental contact between the return electrode and the tissue is avoided. One of the advantages of using a low saline flow rate regimen is that the temperature of the saline solution can reach the boiling point. However, as there is a continuous flow of saline, there is a salient temperature gradient rise from the return electrode to the active electrode 11. This temperature gradient is important, since the hotter saline solution adjacent to the active electrode 11 reduces the energy threshold requirement to achieve vaporization, although the flow rate requirement can be calculated on the basis of the input power, the flexibility of generator 1 to maintain an optimum energy density means that the regime Flow is not critical. For example, if the generator is set for 100 W, then the maximum flow rate is calculated theoretically as follows: Flow rate = energy / specific heat capacity = 100 / 4.2 x 75 cc / s = 0.32 cc / s = 19 cc / min This assumes a temperature of the initial saline solution of 25 ° C, and a heating capacity of 4200 J / g / ° C. Although during the vaporization the saline solution is brought to the vapor state, the vapor is only stable around the active electrode 11. Thus, the energy absorbed by virtue of the latent heat of the vaporization can be ignored, since this energy is recovered by the new saline solution that arrives. Another important factor is that, due to the very short trajectory of the saline solution, the current can be considered to flow along several different trajectories, which, therefore, do not have the same energy density. Consequently, vaporization can occur at flow rates greater than the calculated maximum, due to unequal energy densities within the saline environment. However, the amount of vaporization that occurs along the length of the active electrode 11 will depend on the flow rate. As the saline solution is heated by the active electrode 11, it is potentially harmful to the tissues since it can cause thermal necrosis. It is important, therefore, that all heated saline solution recover and escape from the patient before coming into contact with the tissue adjacent to the application site. For this reason it is that there is suction from the active electrode 11 to an exhaust tank (not shown). However, assuring that the suction occurs in excess, saline can not escape from the region of the active electrode 11 other than the return channel path of saline solution 18. Any saline solution that escapes transversely beyond the outer shaft drops out of the ordinary path, and that's why it's not heated. The priority is, therefore, to ensure that the hottest saline solution is removed. As the thermal gradient is at a maximum adjacent to the active electrode 11 this is the most appropriate escape point for the saline solution. It is for this reason that the saline solution is drawn through the cylindrical portion 15a of the insulator / separator 15. Another important consideration in deciding the evacuation point of the saline solution is the potential for blocking the escape path. This could occur when tissue is cut or vaporized in such a way that small particles of tissue are released that could easily block the leak. The escape point, therefore, it is selected to be at the highest energy density point on the active electrode 11. This measure ensures that any tissue that approaches the point of escape instantaneously vaporizes within the solution, thereby avoiding the potential of blocking. Another significant advantage of ensuring a high degree of suction during tissue removal by vaporization, is that any smoke that has not been absorbed by the saline solution is also evacuated. This is important, because the smoke is capable of transmitting viable biological particles, and this can lead to infection. As mentioned above, the energy threshold for vaporization is not well defined. If the instrument El were operating in a static conductive medium, then the vaporization threshold would be well defined by an impedance switching point where the impedance of the electrode grows suddenly as a result of the vapor pockets that form around the active electrode. The threshold is usually dependent on the dissipation mechanism of the saline solution. In a static environment, the dissipation mechanism is predominantly by convection currents within the saline solution. Under these circumstances, the energy threshold for vaporization is defined by the input energy within the active region of the electrode being in excess of the dissipation from the saline solution. However, in the embodiment, described above, the saline solution around the active electrode 11 is continuously renewed. If it were not done, then only the dissipation mechanism would be by latent heat of vaporization, and the saline solution would evaporate rapidly. By providing a flow, the energy level of the threshold increases. However, the energy level of the threshold depends on the rate of renewal of the saline solution in the mere periphery of the active electrode 11. The rate of renewal in this boundary layer can be modified by altering the surface finish of the active electrode 11. For example , if the active electrode 11 has a smooth surface, then the saline solution would be rapidly renewed. If not, then the only dissipation mechanism would be by latent heating of vaporization, and the saline solution would evaporate rapidly, as a rapid flow regime was established. However, since the active electrode 11 has an uneven finish, the rate of bag renewal within the irregular surface decreases. Thus, the irregular surface traps the saline solution (or at least delays the renewal), and in this way absorbs more energy before it is replaced. In other words, the energy threshold is decreased by the surface of the irregular active electrode. This is a highly desirable property, since the energy requirement of the electrode drops substantially without adverse effects on tissue operation. The energy of the threshold is also reduced because the active electrode is constructed to provide a capillary action. Thus, even in the vaporized state, the active electrode 11 is wetted intermittently. Ensuring that this humidification humidifies the entire active electrode 11 by capillary action, there is a continuous source of vapor that minimizes intermittent wetting, and also reduces the demand for energy. To vaporize tissue, it is necessary for the saline solution to be fed from channel 17 to be in contact with the tissue, as well as with the active electrode 11. The saline solution, therefore, has to form a constant drip surrounding the electrode active 11. The tip of the active electrode 11, therefore, is designed so that the saline solution and the active electrode are brought into contact simultaneously with the tissue independently of the angle. If the flow of the saline solution from channel 17 to the active electrode was completely annular, the saline solution could flow from one side to the other, in which case the active electrode would only be partially wrapped. To avoid this, the annular channel 17 is segmented by the wings 15b in order to ensure a flow of saline solution in the uppermost part. This also improves the adhesion of the incoming saline solution by increasing the capillary action. When the tip of the active electrode 11 comes into contact with the tissue, the region that touches the tissue suddenly loses its ability to dissipate energy via the saline solution. While the return path is constituted by a flow of saline solution, the fabric does not have a mechanism for energy dissipation and therefore it heats up rapidly to the point where it evaporates. The effectiveness of the instrument for tissue vaporization depends on the proportion of the 'drip' and the length of the active electrode 11. A longer active electrode is the most demanding, since the ability to maintain a 'constant drip' is reduced. However, once the active electrode has vaporized a bag inside the tissue, so that the return electrode 12 is closer to the tissue surface, vaporization becomes easier, since there is a smaller voltage drop to through the saline solution, simply because it forms a minor part of the electrical circuit. By varying the output of generator 1, the instrument can also be used for drying (coagulation). In this case, the generator is controlled so that small bubbles of vapor are formed on the surface of the active electrode 11, but insufficient steam is produced to provide a vapor bubble (bag) surrounding the active tip of the electrode 1, essential being the vapor bubble for the removal of tissue by vaporization. The generator 1 is controlled in such a way that it has its respective output ranges for desiccation of tissue and for tissue removal by vaporization. The first range is 150 volts at 200 volts, and the last range is 250 volts at 600 volts, with voltages being peak voltages. In the vaporization mode, the generator 1 is controlled in such a way as to prevent the active electrode 11 from overheating. This requires a reduction in the output voltage of the generator 1 once a steam bag has been established. The generator 1 and its control elements are described in greater detail in the specification of our British patent application 9604770.9. The coagulation from this electrode is far superior to that of any conventional bipolar electrode. The reasons are double. First, the coagulation mechanism is not merely by the electric current in the tissue, but also due to the heated saline solution. Second, under normal circumstances, the weakest link to provide electrical energy to the tissue is the electrode / tissue interface, since this is the point of highest energy density, and thus imposes an energy limit. If a too high energy level is intended, the tissue at the interface quickly dries out, faster than the largest cross section of tissue that forms the remaining circuit. If a lower energy is selected, the interface can dissipate the temperature increase by means other than evaporation. Accordingly, the interface remains intact longer, and in this way energy can be supplied at a higher rate for a longer period, resulting in a depth of effect that is purely time and energy related. Figure 3 shows the distal end of the second form of electrosurgical instrument. This instrument is a modification of that shown in Figure 2, so that similar reference numerals will be used for equal parts, and only the modifications will be described in detail. The main modification is that the instrument of Figure 2 includes two tubular, coaxial, return electrodes 12 and 12 ', the return electrode 12 'being slightly shorter than the return electrode 12 and being placed inside it. The annular space between the two return electrodes 12 and 12 'constitute the feed channel of the saline solution 17, and the return channel of the saline solution 18 is constituted by the annular space between the return electrode 12' and the construction central constituted by the cylindrical portion 15a of the insulator / separator 15 and the tube 16. The tube 16 is also modified to form a friction fit around both proximal ends of the cylindrical portion 15a of the insulator / separator 15 and the active conductor 14. The advantage of the instrument of Figure 3 is that, when used to create vaporized pockets on a tissue surface (for example in a nested tumor) there is less chance that the return path of the saline solution to the return channel of the saline solution 18 is blocked. Thus, with the embodiment of Figure 2 when a vapor pocket is created, some saline solution forming the conduction path between the active electrode 11 and the return electrode 12 can escape due to the tissue obstructing the entrance to the channel. return 18. This saline solution may be of a high enough temperature to cause some peripheral tissue bleaching. As the fabric bleaching depends on the size of the instrument, the intrument of Figure 2 should have small dimensions, so that the amount of peripheral bleaching can be maintained at acceptable levels. With the embodiment of Figure 3, on the other hand, the return path of the saline solution from the active electrode 11 to the return channel 18 will then never be clogged with tissue. Moreover, when the conduction path between the active electrode 11 and the return electrode 12 becomes clogged, the portion of saline solution clogged from the active electrode 11 has a reduced energy dissipation. This reduced dissipation arises from the fact that both saline inlet and outlet solutions are connected to the return channel 18, so that the impedance is lower insofar as the majority of energy dissipation occurs then in the obstructing tissue. . The instrument of Figure 3 is, therefore, less suitable for miniaturization than that of Figure 2, due both to the extra tubing (the extra return electrode 12 ') and the aspect ratio of the tip (ie, the active electrode 11 can not protrude so much by diameter because the escape of the saline solution is being staggered back further). This exhaust has to be placed further back, as it passes through the second return electrode 12 '. If it were not so placed it would cause too large an energy distribution over the length of the active electrode 11. The saline exhaust solution from the instrument of Figure 3 may also contain tissue particles. As the escape path does not necessarily pass through the one vaporization region, this imposes a limit to the minimum size of this version of the instrument, due to the potential for blocking the escape path. The best vaporization performance for each instrument described above is when the active electrode 11 is designed to trap, or at least interrupt, the flow of the saline solution. The reason for this is very simple, or rather, the more the saline solution can be maintained in close proximity to the active electrode 11 and the more active energy and, therefore, the greater the propeneion to form a vapor. The wire or hollow forms of the active electrode are, therefore, the most effective. It would, for example, be possible to replace the twisted shape of the wire form of the active electrode with an active electrode in the form of an eepiral. It would also be possible to increase the vaporization by partially darkening the active electrode / saline interface by masking it with atomized ceramic, the atomized ceramic being deposited in a non-uniform particle coating. The instrument described above has advantages, namely: 1. Each provides an action similar to the monopolar with only one electrode (the active electrode 11) in direct contact with the tissue; 2. Each provides an immediate tissue de-bulge (vaporization) in a manner similar to that obtained with laser instruments; 3. The radiofrequency current is confined to the treatment area, thus reducing the collateral or deep thermal effects, and eliminating remote burns; 4. There is minimal smoke when it is cut or vaporized, due to cooling, condensation and the dissolving effects of the surrounding saline solution. Any smoke produced is rapidly removed due to suction adjacent to the active electrode 11; 5. As the path of the current within the electrode assembly is bidirectional, there is minimal capacitive coupling at any point of entry of the electrodes; 6. The saline solution provides an excellent active electrode interface / tissue interface that conserves current flow for a controlled depth of coagulation, this being purely dependent on energy and time of application. 7. The connection of the saline solution avoids the conditions of high impedance that could cause significant carbonization which is known to be detrimental to tissue sanitation, and increases the risk of adhesion formation. 8. The excellent low impedance of the active electrode / tissue interface allows the use of much higher energy for fast effects. This is particularly useful for rapid non-carbonizing coagulation; and 9. Much higher energy levels are supported than conventional bipolar electrosurgery. In practice, conventional bipolar electrosurgery is only effective up to a limit of 40W or 50W, since higher energy levels result in overheating and carbonization. With the electrode configuration of Figures 2 and 3, energy levels exceeding 200 can be supported. It will be apparent that modifications could be made to the instruments described above. Thus, the active electrode 11 could be of any other suitable shape, such as a needle electrode or a hollow, spherical perforated electrode partly made, for example, of platinum / iridium, and the insulator / separator 15 would be made of rubber from eilicon or glass. It would also be possible to replace the saline solution as the conductive medium with a conductive gas such as argon. In this case, the argon would need to be pumped to the region of the active electrode 11 through channel 17 and there would be no need to remove the argon via the return channel 18, there being no danger of collateral tissue damage by the hot argon. In this case a modified form of radio frequency generator would also be needed. The total electrode assembly could be constructed as a flexible or rigid assembly, and could also incorporate elements to direct or manipulate the active tip, or the insertion within the tissue.

Claims (27)

1. An electrosurgical instrument for treating tissue in the presence of an electrically conductive fluid, the instrument comprising an instrument shaft and an electrode assembly at one end of the shaft, the electrode assembly comprising a tissue treatment electrode and an electrode of return that is electrically isolated from the tissue treatment electrode by an insulating member, the tissue treatment electrode being exposed at the distal end of the instrument, and the return electrode having a contact surface with the fluid separated from the exposed end of the electrode. tissue treatment electrode by the insulating member, wherein the instrument further comprises a feeding element for feeding electrically conductive fluid to the region of the exposed end of the tissue treatment electrode in such a way as to define, during use, a path of conductive fluid that completes a circuit or electrical between the tissue treatment electrode and the return electrode. An electrosurgical instrument, as claimed in claim 1, further comprising a removal element for removing the electrically conductive fluid from the exposed end region of the tissue treatment electrode. An electrosurgical instrument as claimed in claim 2, wherein the removal element is constituted by a fluid return channel formed within the axis of the instrument, and by an element for applying suction to the proximal end of the return channel of the instrument. fluid . 4. An electrosurgical instrument as claimed in any of claims 1 to 3, wherein the feeding element is constituted by a fluid feeding channel formed within the axis of the instrument. An electrosurgical instrument as claimed in claim 4, when dependent on claim 3, wherein the fluid supply channel is positioned around the fluid return channel. 6. An electrosurgical instrument as claimed in any of claims 1 to 5, wherein the return electrode is a tubular member that is coated with an insulating cover, the return electrode constituting the shaft of the instrument. 7. An electrosurgical instrument as claimed in claim 6, wherein the inner surface of the tubular member constitutes the return electrode. 8. An electrosurgical instrument as claimed in claim 6 or claim 7, wherein the tubular member is made of stainless steel. 9. An electrosurgical instrument as claimed in any of claims 6 to 8, wherein the tissue treatment electrode is supported centrally within the tubular member by an insulating spacer. 10. An electrosurgical instrument as claimed in claim 9, wherein the insulating separator is made of ceramic material, silicone rubber or glass. 11. An electrosurgical instrument as claimed in claim 9 or claim 10, further comprising a tube extending proximally from the separator. 1

2. An electrosurgical instrument as claimed in claim 11, when dependent on claim 5, wherein the fluid supply channel is constituted by the annular space between the return electrode and the tube, and the return channel is constituted by the interior of the tube and an opening element extending through the separator. 1

3. An electrosurgical instrument as claimed in any of claims 5 to 11, further comprising a second return electrode, the second return electrode being constituted by a second tubular member concentrically positioned within said first tubular member. 1

4. An electrosurgical instrument as claimed in claim 13, when dependent on claim 5 and 11, wherein the feed channel is constituted by the annular space between the two return electrodes, and the return channel is constituted by the annular space between the second return electrode and the tube. 1

5. An electrosurgical apparatus comprising a radiofrequency generator and an electrosurgical instrument for the treatment of tissue in the presence of a fluid electrically conductive medium, wherein the electrosurgical instrument is as claimed in any of claims 1 to 14. 1

6. The apparatus as claimed in the claim 15, wherein the radio frequency generator includes a control element for varying the output energy supplied to the electrodes. The apparatus as claimed in claim 16, wherein the control element is such as to provide output power in a first and a second output range, the first output range being to energize the electrosurgical instrument for dewatering tissue, and being the second output range to give energy to the electrosurgical instrument for tissue removal by cutting or vaporization. 18. The apparatus as claimed in claim 17, wherein the first output range is from about 150 volts to 200 volts, and the second output range is from about 250 volts to 600 volts, with the voltage being the peak voltage. 19. A method for operating an electrosurgical apparatus having at least one tissue drying mode and one tissue vaporization mode, the apparatus having a radio frequency generator coupled to an electrode assembly for the treatment of tissue in the presence of a fluid electrically conductive medium, the electrode assembly comprises a tissue treatment electrode and a return electrode which is electrically isolated from the tissue treatment electrode by means of an insulating member, the tissue treatment electrode being exposed at the end distal end of the assembly, the return electrode has a fluid contact surface spaced from the exposed end of the tissue treatment electrode by the insulating member, the method comprising the steps of: feeding electrically conductive fluid to the region of the exposed end of the electrode of tissue treatment; and controlling the output energy of the radio frequency generator to be within a first output range for the tissue desiccation mode and to fall within a second range for the tissue vaporization mode, the first output range being such that the energy euminiected to the electrode assembly keeps the conductive fluid adjacent to the tissue treatment electrode suetancially at the boiling point for drying the tissue without creating a vapor pocket surrounding the tissue treatment electrode, and the second eevaluation range ee that the output energy supplied to the electrode assembly for vaporizing the tissue is such as to maintain a vapor pocket surrounding the tissue treatment electrode. 20. A method as claimed in claim 19, further comprising the step of removing the electrically conductive fluid from the region of the exposed end of the tissue treatment electrode. 21. A method as claimed in claim 19 or claim 20, wherein the first output range is from approximately 150 volts to 200 volts and the second output range is from approximately 250 volts to 600 volts, the voltages being peak voltages. 22. A tissue drying method comprising the steps of providing an electrosurgical apparatus comprising a radiofrequency generator coupled to an electrode assembly comprising a tissue treatment electrode and a return electrode, the treatment electrode having one end exposed distal introduce the electrode assembly into a selected operating site with the tissue treatment electrode adjacent to the tissue to be treated; feeding an electrically conductive fluid to the region of the exposed end of the tissue treatment electrode; activate the generator; and controlling the radiofrequency energy supplied to the electrode assembly by the generator to maintain the conductive fluid adjacent the tissue treatment electrode substantially at its boiling point without creating a vapor pocket surrounding the tissue treatment electrode. 23. A method as claimed in claim 22, wherein the return electrode is separated proximally from the tissue treatment electrode, and wherein the electrode assembly is introduced into the selected operating site so that the tissue treatment electrode is in contact with the tissue that it is to be treated, and the return electrode is immersed in the electrically conductive fluid, the electrode assembly being manipulated to cause heating and drying of the tissue in the required region adjacent to the tissue treatment electrode. 24. A method as claimed in claim 23, wherein the electrode assembly is manipulated by moving the tissue treatment electrode through the surface of the tissue to be treated in a side-by-side "painting" technique. . 25. An electrosurgical method comprising the step of: providing an electrosurgical apparatus comprising a radiofrequency generator coupled to an electrode assembly comprising a tissue treatment electrode and a return electrode, the tissue treatment electrode having one end exposed distal, - introduce the electrode assembly into a selected operating site with the contact electrode with the tissue adjacent to the tissue to be treated; feeding the electrically conductive fluid to the region of the exposed end of the tissue treatment electrode; activate the generator; and applying sufficient radiofrequency energy to the electrode assembly to vaporize the electrically conductive fluid surrounding the tissue treatment electrode. 26. A method as claimed in claim 25, further comprising the step of controlling the radiofrequency energy to prevent the tissue treatment electrode from overheating. 2

7. A method as claimed in claim 25 or claim 26, wherein the return electrode is separated proximally from the tissue treatment electrode, and wherein the electrode assembly is inserted into the selected operating site. so that the tissue treatment electrode is positioned at least adjacent to the tissue to be treated, with the vapor pocket in contact with the tissue, and with the return electrode in contact with the electrically conductive fluid, the structure of electrodes to reach when the vaporization of the tissue decreases.