Abstract:
A design and method of manufacture is disclosed for an insulated electrode used during surgical procedures. The electrode includes a durable electrical insulation element that can withstand the range of temperatures generated during an electrosurgical procedure. Such insulation characteristics include resistance to meltback and manufacturability to ensure the device is biocompatible and non-toxic so as to prevent adverse reactions in both patients and users of the device. The insulated electrode further includes properties that reduce the incidence of scope damage caused by the intensity of heat generated during the cutting and coagulation cycles.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an insulated electrode used during surgical procedures and a method of assembling an insulated electrode. The present invention particularly relates to electrode insulators and methods of insulating an electrode that reduce meltback of the insulation and the incidence of scope damage due to high temperatures generated during the cutting or coagulation cycle. 
     BACKGROUND OF THE INVENTION 
     Resectoscopes are commonly used to cut and coagulate tissue of a patient during a surgical procedure. The typical resectoscope includes an optical component for illuminating and viewing a target tissue, valves for controlling irrigating fluids, an active element, such as a loop electrode, for cutting tissue and sealing blood vessels, and a handle assembly for connecting electrosurgical current from a generator to the loop electrode. During the surgical procedure, radio frequency (RF) electrical energy passes through the electrode, into the target tissue and causes heating of the target tissue. The amount of heat applied to the tissue controls the cutting and coagulation process. 
     An example of a surgical procedure utilizing a resectoscope is transurethral resection of the prostate (TURP). TURP is used to treat benign prostatic hyperplasia (BPH), a medical condition causing urinary tract obstruction commonly experienced by men over fifty years old. During the surgical procedure, the surgeon uses a loop electrode to remove the obstructing tissue one piece at a time. Tissue pieces are washed into the bladder using irrigating fluids and subsequently flushed out at the end of the procedure. Various instruments for performing surgical cutting and coagulation procedures such as TURP are known in the art. 
     An example of such a device may be found in U.S. Pat. No. 5,658,280, which discloses an electrode assembly for a resectoscope. The electrode assembly includes a cutting electrode and a coagulation electrode, with insulation surrounding at least a portion of both the cutting and coagulation electrodes. A support frame connects the cutting and coagulation electrodes to an energy source for supplying energy to the electrodes. The coagulation electrode provides tissue coagulation simultaneously while the cutting electrode cuts tissue. 
     A further example may be found in U.S. Pat. No. 5,702,387, which discloses an electrosurgical electrode which resists buildup of eschar. The electrode includes a coating of silicone elastomer, applied by dipping, molding or electrostatically spraying the silicone onto the electrode, which improves the ease of cleaning any tissue buildup, such as eschar. The coating is thin or nonexistent at the electrode blade edges and tip. A function of this particular silicone coating configuration is to concentrate the current at the edges and tip of the electrode, resulting in improved eschar removal. 
     Yet still a further example is found in U.S. Pat. No. 5,810,764, which discloses an electrosurgical probe with an active electrode coupled to a high frequency voltage source. In one aspect of the invention, the active electrode includes a “non-active” portion or surface that selectively reduces undesirable current flow from the non-active portion into tissue or surrounding electrically conducting liquids. The “non-active” electrode portion is coated with an electrically insulating material which is applied to the electrode by plasma deposition, evaporative or sputtering techniques, or dip coating processes. 
     The above-described electrodes used. during an electrosurgical procedure (and other similar devices not specifically described) offer many advantages to potential users, including effectiveness, safety and convenience. However, it has been discovered that an obstacle or disadvantage to such devices is the susceptibility to meltback of currently used insulation materials and insulation designs. This is due to a variety of factors, including high temperatures generated during the cutting cycle. When the insulation is compromised due to meltback, there is the likelihood that the adjoining components of the resectoscope may also be damaged by the high temperatures. Further, the additional exposed surface area of the active portion of the electrode may destroy surrounding non-target tissue and cause patient injury. 
     There are a number of causes of current meltback problems. For example, insulators made from Fluoronated Ethylene Propylene (FEP) or Tetra Fluoro Ethylene (TFE) do not closely conform to the external diameter of the electrode wire and therefore lead to concentrated contact points which, due to the somewhat low melting point of FEP and TFE, makes. these contact points more susceptible to meltdown. In addition, the insulators such as sputtered silicone coatings similarly do not provide the uniformity of insulation, thus leading to uneven heat concentration. Moreover, the sputtering process is expensive and difficult to perform reliably. 
     In view of the above, it is apparent that there is a need to provide an electrode such as those described above with a more durable and reliable insulation element and insulator design that can withstand the range of temperatures generated during an electrosurgical procedure. There is also a need to provide a method of manufacturing such an improved insulator that is efficient, easy to implement and cost effective. Such insulation characteristics include electrical insulation resistance to meltback and efficient manufacturability to ensure the device is biocompatible and non-toxic so as to prevent adverse reactions in both patients and users of the device. It further includes properties that reduce the incidence of scope damage caused by electrical discharge and the intensity of heat generated during the cutting and coagulation cycles. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     In view of the foregoing, it is an object of the present invention to provide an insulated electrode assembly that addresses the. obstacles and disadvantages associated with the current problems of insulation meltback and inadvertent electrical discharge due to a variety of factors, including generation of high temperatures and arcing to the resectoscope during surgical procedures. 
     A further object of the present invention is to provide an insulated electrode assembly that reduces the incidence of scope damage due to the high temperatures generated during cutting and coagulation cycles and inadvertent electrical discharge caused by arcing to the resectoscope. 
     A further object of the present invention is to provide an insulated electrode assembly that reduces insulation meltback caused by high heat intensities. 
     A further object of the present invention is to provide an insulated electrode assembly that prevents the destruction of surrounding non-target tissue and reduces potential patient injury. 
     A further object of the present invention is to provide an insulated electrode assembly that includes uniform insulation thickness and surface contact between the insulation and the electrode. 
     These and other objects not specifically enumerated herein are believed to be addressed by the present invention which contemplates an electrode assembly that includes an elongated wire and an insulation tube located on a portion of the wire, wherein the insulation tube in an undeformed state may have an internal diameter smaller than the external diameter of the elongated wire. The insulation tube or element that is disposed on the active portion of the electrode forms a non-active section. 
     The present invention also contemplates a method of assembling insulation onto an electrode which may include the steps of sliding one end of an insulation tube over an assembly tool tip and securing the insulation tube to the tool. The next steps may include positioning one end of the electrode into the other end of the insulation tube and introducing a flow of fluid through the insulation tube. The following step would include inserting the electrode into the insulation tube during the flow of fluid causing the insulation tube to float over the electrode. The final step would likely include discontinuing the flow of fluid so that the insulation surface uniformly contacts the electrode. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of the present invention will be seen as the following description of particular embodiments progresses in conjunction with the drawings, in which: 
     FIG. 1 is a perspective view of an electrode assembly in accordance with the present invention; 
     FIG. 2 is a top perspective view of a portion of an electrode assembly in accordance with the present invention; 
     FIG. 3 is a front perspective view of an electrode assembly in accordance with the present invention; 
     FIG. 4 is a side perspective view of an electrode assembly in accordance with the present invention; 
     FIG. 5 is a cross-sectional top view of an electrode assembly in accordance with the present invention; 
     FIG. 6 is a cross-sectional side view of an insulation tube, illustrating its inner diameter, and a wire element, illustrating its outer diameter, in accordance with the present invention; 
     FIG. 7 is a perspective view of a method of positioning one end of a wire element adjacent to one end of an insulation tube; and 
     FIG. 8 is a perspective view of a method of inserting a wire element into an insulation tube. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, an embodiment of an electrode assembly  10  for use with a resectoscope or other similar device in accordance with the present invention includes a support tube  12  and an active element  14  for cutting tissue and sealing blood vessels. A portion of the distal end of the active element  14  is surrounded by an insulation tube  16 . The insulation tube  16  is non-active and protects adjacent tissues and blood vessels. Additionally, the non-active insulation tube  16  allows the surgeon to selectively cut and coagulate tissue only at the target site. An outer tube  18  and a stem tube  20  are located along a segment of the electrode assembly  10 . The outer tube  18  provides structural support for the electrode assembly  10  when affixed to a resectoscope or similar device. The stem tube  20  provides a layer of insulation for the active element  16  as it extends along the length of the electrode assembly  10 . A power contact  22 ′attached to the proximal end of the active element  14  electrically couples the active element  14  to a power supply (not shown) to provide power to the electrode assembly  10 . 
     In a preferred embodiment, the distal end of the active element  14  has a loop geometry as shown in FIGS. 1,  2  and  3 . Appropriate active element  14  geometries include, but are not limited to, radial, circular, elliptical, curved, rounded, bowed, arc, arch, crescent, semicircle, malleable, roller cylinder and roller ball. When configured in a loop geometry, the active element  14  has a preferred loop diameter of approximately 24 French (8 mm). However, the loop diameter of the active element  14  can range from 22 to 28 French (7.33 to 9.33 mm), or any suitable size that enables the electrode assembly  10  to fit into a resectoscope or similar device. Further, when configured in a loop geometry, the distal end of the active element  10  forms a pair of spaced semi-parallel arm sections  24 ,  26  which angle forwardly and upwardly and are connected by the loop. 
     The active element  14  is typically a wire that transfers energy from a generator or power. source (not shown) to. a tissue target area. The cross-sectional outline of the active element  14  may encompass a variety of shapes including, but not limited to, circular, oval, rectangular, square, triangular, C-shaped or combinations of the above. In addition, in a preferred embodiment, the cross-sectional diameter of the active element  14  is approximately 0.51 mm (0.020 in). 
     As shown in FIGS. 1,  2  and  4 , the distal end  22  of the active element  14  can include grooves or slots of a variety of shapes that promote high electric field intensities and enhance tissue cutting capabilities of the active element  16 . A variety of electrical conductive materials maybe used to fabricate the active element  14 . These material&#39;s include, but are not limited to, tungsten, its alloys, stainless steel and the like. A preferred material is Molybdenum. 
     As shown in FIG. 5, the electrode assembly  10  further includes an insulation tube  16  that extends along and shields a. portion of the active element  14 . For the electrode assembly  10  shown in FIG. 5, two separate sections of insulation tube  16  are, required to adequately surround the active element  14  of the electrode assembly  10 . In a preferred embodiment, the insulation tube  16  is made of a non-active, elastic electrical insulation material, such as silicone, that is capable of being easily stretched or expanded and resuming its former shape. The preferred insulation material is silicone because of its good electrically insulating properties, biocompatibility and high melting point and it conforms very well to mating surfaces. 
     Referring to FIG. 6, preferably in its unmounted or undeformed state, the inner diameter of the insulation tube  16  is either less than or very nearly equal to the outer diameter of the active element  14 . This relative sizing of the tube  16  to the active element  14  ensures that there is a snug and conforming fit and contact between the tube  16  and the element  14 , particularly in view of the elastically stretchable and expandable properties of the insulation tube  16 . It also enables the use of an insulation tube of maximum thickness thus ensuring that the dielectric strength and the insulating properties of the device are maximized. In this connection, it is desired that the tube material be in tension, even if it is minimal tension, when the tube  16  is mounted on the element  14 . This desirable configuration is achieved when the diameter of the tube  16  is either less than or very nearly equal to the outer diameter of the active element. 
     In a preferred embodiment of the invention, the insulation tube  16  has a manufacturing specification of 0.5080 mm+/−0.0508 mm (0.020 in +/−0.002 in) for its inner diameter and 0.9906 mm+/−0.0508 mm (0.039 in+/−0.002 in) for its outside diameter and the active element  14  has a manufacturing specification of 0.5080 mm+/−0.0203 mm (0.020 in +/−0.0008 in) for its outside diameter. An insulation tube  16  and an active element  14  manufactured according to these specifications achieves the aforedescribed mounting characteristics of the insulation tube  16 . 
     Another aspect of the insulation tube  16  that is advantageous to achieving the goals of the invention is the use of a material that has a high coefficient of friction relative to the metal comprising the active. element  14 . The use of such a material better ensures secure and conforming mounting and adherence of the tube  16  to the element  14 . In a preferred embodiment, the insulation tube  16  is made of silicone which has a coefficient of friction against a steel or Molybdenum surface of approximately 0.80 (dry). This may be contrasted with conventional insulation materials such as FEP or TFE, which typically have a lower coefficient of friction, such as 0.04 (dry). 
     The improved uniform surface contact achieved by the present invention, especially at the junction where the active element  14  is exposed from the insulation tube  16  at the distal end of the electrode assembly  10 , reduces the potential for tissue to adhere to the junction or fluid to wick between the insulation tube  16  and the active element  14 . It also better ensures uniform absorption of heat generated by the active element  14  thereby minimizing potential damage to surrounding tissues. 
     The outer surface of the insulation tube  16  is relatively smooth. In addition, the thickness of the insulation tube  16  is uniform along its entire length so as to adequately protect and shield the active element  14 . However, in an alternate embodiment, the thickness of the insulation tube  16  may be variable along its length depending on various desired electrical insulation characteristics or assembly constraints. 
     Referring to FIGS. 1 and 5, additional elements comprising the electrode assembly  10  include a support tube  12 , stem tube  20 , stiffener sleeve  28 , outer tube  18  and power contact  22 ′ (FIG. 1) or  26 ′ (FIG.  5 ). A support tube  12  circumscribes and extends along each arm section  24 ,  26  of the electrode assembly  10  to provide sufficient rigidity and structural support to the underlying sections of the active element  14  and insulation tube  16 . In a preferred embodiment, the support tube  12  is made of stainless steel, however other comparable materials which are corrosion resistant and easily formed, soldered and cleaned may also be used. 
     Surrounding the proximal section of the active element  14  and providing additional strength and durability is a non-conductive stem tube  20 . In a preferred embodiment, the stem tube  20  is made from FEP. Alternatively, the stem tube  20  may be fabricated from other materials such as TFE or Polyethylene. A stiffener sleeve  28  extends substantially along a portion of the insulation tube  16  and the entire length of the stem tube  20 , abutting the proximal end of the support tube  12  located on one arm section  24  of the electrode assembly  10 . The stiffener sleeve  28  insulates and seals a portion of the electrode assembly  10 , facilitating connection of the electrode assembly  10  into a resectoscope. 
     As shown in FIG. 5, an outer tube  18  is used to secure the proximal ends of the arm sections  24 ,  26  and provide additional structural support for the electrode assembly  10 . The outer tube  18 , like the support tube  12 , can be made of stainless steel or a similar corrosion resistant material. The distal end of the outer tube  18  is secured to the support tube  12  by soldering the support tube  12  into the outer tube  18 . The proximal end of the outer tube  18  is contained within a crimp so an edge is not created between the outer tube  18  and the stem tube  20 . 
     Located at the proximal end of the electrode assembly  10  is a power contact  26 ′. The power contact  26 ′ couples the active element  14  to a power supply to provide power to the electrode assembly  10 . The power contact  26 ′ is an electrically-conductive element formed from stainless steel or some other suitable conductive metal. 
     It should be understood that the invention is not limited to electrode assemblies comprising an active element that connects to a single power contact. For example, the active element may have two or more ends or terminals extending equal in length to the proximal end of the electrode assembly. Further, two or more power contacts may be used to connect the electrode assembly to the power source. 
     The electrode assembly  10  of the present invention can be used in both monopolar and bipolar devices. A monopolar device, as described above, directs electric current along a defined path from the exposed active element  14  of the electrode assembly  10  (i.e. the cutting electrode) through the patient&#39;s body and to a return electrode (not shown). The return electrode is externally attached to an appropriate area on the patient&#39;s body. 
     A bipolar device includes both the cutting electrode and return electrode on the same device. The cutting electrode and return electrode are configured adjacent to each other so that they simultaneously contact tissue, thereby directing current to flow along a path from the cutting electrode through the patient&#39;s tissue and to the return electrode. A portion of the return electrode in a bipolar device of the present invention is insulated, similar to the configuration of the insulation tube  16  located on the active element  14 . Preferably; the insulation is made of silicone, but other comparable materials previously described can also be used. The insulation, provides a layer of protection for surrounding tissues and aids in focusing the electric current on target tissues. 
     Method of Assembly 
     The present invention also contemplates a method of assembling the insulation tube  16  onto the active element  14  of the electrode assembly  10 , as shown in FIGS. 7 and 8. The first step of assembling the insulation tube  16  onto the active element  14  includes attaching one end of the insulation tube  16  to an appropriately sized needle  30  of a pressurized fluid source  32 . Although a preferred embodiment of the present invention utilizes a pressurized fluid source  32 , similar fluid compression devices may be substituted. A variety of fluids used with these devices include, but are not limited to, air, liquid and gas. The pressure regulator (not shown) of the pressurized fluid source  32  is set to 100 psi. It should be noted that alternative pressures may be used dependent upon the durometer, tensile strength and other material characteristics of the insulation tube  16 . 
     The next steps involve securing the insulation tube  16  onto the needle  30  of the pressurized fluid source  32  and positioning one non-loop end of the active element  14  in the open end of the insulation tube  16 . A clip  34  or other similar attachment device can be used to secure the insulation tube  16  onto the needle  30 . The attachment device should sufficiently clamp the insulation tube  16  to prevent the insulation tube  16  from slipping off the needle  30  when fluid is introduced. 
     The following steps include introducing fluid into the insulation tube  16  and inserting the active element  14  into the insulation tube  16 . Due to the insulating material&#39;s high coefficient of friction and its inner diameter relative to the outer diameter of the active element  14 , the insulation tube  16  cannot simply slide over the active element  14 . Therefore, fluid is slowly introduced into the insulation tube  16  via the needle  30 . of the pressurized fluid source  32 . As fluid-flows through the insulation tube  16  the pressure causes the insulation tube  16  to expand in a radially outwardly direction. As a result, the inner diameter of the insulation tube  16  increases in size. When the inner diameter of the insulation tube  16  becomes sufficiently greater than the outer diameter of the active element  14 , the active element  14  is inserted into the insulation tube  16  until the insulation tube  16  is tight against the loop of the active element  14 . 
     The final assembly step would likely include discontinuing the flow of fluid so that the inner surface of the insulation tube  16  uniformly contacts the outer surface of the active element  14 . Due to the elastomeric properties of the insulation tube  16 , the diameter and shape of the insulation tube  16  return to a configuration constrained only by the shape of the now-inserted wire when fluid no longer flows through the insulation tube  16 . That is, since the original inner diameter of the insulation tube  16  may be smaller than the outer diameter of the active element  14 , the inner surface of the insulation tube  16  uniformly contacts the outer surface of the active element  14 . 
     An alternate method of assembly includes soaking the insulation tube in freon, acetone, xylene and the like. Over a period of time, these chemicals permeate and subsequently expand the structure of the insulation tube  16 . When the insulation tube  16  is in this expanded state, the active element  14  may be manually inserted into the insulation tube  16 . After the insulation tube  16  is positioned on the active element  14 , the structure of the insulation tube  16  will revert to its original configuration when the chemicals naturally vaporize out of the insulation tube  16 . 
     Various processes well known in the art may be used to enhance the elastomeric properties of the insulation tube  16  prior to its assembly onto the active element  14 . The material properties of the insulation tube  16  can be enhanced via a post-cure process after the material has been extruded. The post-cure process involves the steps of positioning various lengths of insulation tube  16  into a stainless steel pan and placing them into an oven or similar device set at an appropriate temperature for a suitable length of time. In the preferred embodiment, the oven is set at 166° C.±5° C. and the post-cure continues for a duration of approximately 2 to 3 hours. However, based upon the material type, the post cure process may be performed at various temperatures and time durations. 
     Another aspect of the present invention involves the addition of colorant to the material that comprises the insulation tube  16 . As a convenience to the user, colorant is added to the insulation tube  16  material prior to performing the extrusion process. Each of the various colors of insulation tube corresponds to a unique loop size of the active element  14 . For example, a yellow insulation tube  16  corresponds to a 24 French size loop, likewise a white insulation tube  16  corresponds to a 26 French size loop, and so on. This aids the user of the device in easily and conveniently selecting the appropriate loop size of the active element  14  for the particular procedure to be performed. 
     Although the invention has been described in terms of particular embodiments and applications, one of ordinary skill in the art, in light of this teaching, can generate additional embodiments and modifications without departing from the spirit of or exceeding the scope of the claimed invention. Accordingly, it is to be understood that the drawings and descriptions herein are proffered by way of example to facilitate comprehension of the invention and should not be construed to limit the scope thereof.