Surgical electrically shielded radiotranslucent cannula for r.f. patient protection

Abstract: A device for dissipating electrical energy from a surgical device is provided. The electrical energy is induced on the surgical device when a charge-inducing instrument, e.g. an unipolar electrocautery device, is energized in proximity thereto. The induced energy is dissipated by conveying the energy along an electrically conductive element 34 to an energy dissipation region. In a preferred embodiment of the invention, the surgical device is a cannula 26 fabricated from a dielectric material, e.g., fiberglass, and induced electrical energy is dissipated by contacting the energy dissipation 36 region, e.g., a conductive band 36 around the periphery of the cannula, with the body wall of the patient. An alternative means for grounding is achieved by providing an electrical fitting on a cannula housing which remains external to the patient's body, and securing a grounding wire thereto.

Description: Technical Field The present invention relates to a device for dissipating electrical energy during a surgical procedure and, more particularly, to an energy dissipation device having application in endoscopic surgical procedures. Background of the Invention Endoscopic procedures have been practiced for many years. Initially endoscopic procedures Were primarily diagnostic in nature, i.e., involving the introduction of laparoscopes and like devices to view internal organs. Laparoscopic sterilizations have also been performed for some time. More recently, surgeons have begun to perform complex and innovative endoscopic surgical procedures. For example, endoscopic cholecystectomy has become a preferred modality for gall bladder removal in just the last two years. Endoscopic procedures are typically performed through trocar sleeves or cannulas. Prior to introducing the cannula through the body wall, the surgeon generally insufflates the body cavity with carbon dioxide, e.g., through a Verres needle or like device. Insufflation creates a free area between internal body organs and the body wall. The surgeon then introduces one or more trocars through the body wall into the insufflated body cavity. Trocars are sharp pointed instruments which include a trocar shaft or obturator with a piercing tip located at the distal end thereof. The trocar is positioned within a cannula for introduction of both into the body cavity. After introduction, the trocar is removed from the cannula and endoscopic instrumentation may be introduced through the cannula to effect diagnostic and/or surgical procedures. The cannula is typically provided with an internal flapper or trumpet valve to prevent gas release from the body cavity and generally measures from 3 to 12 min in diameter. Safety trocars which include a spring-loaded safety shield surrounding the obturator are also known. See U.S. Patent No. 4,601,710 to Moll et al. A wide range of accessory instrumentation finds application in endoscopic surgical procedures. For example, graspers, dissectors, clip appliers, lasers and electrocautery devices are routinely employed. It is also common to perform a cholangiogram by introducing a catheter into the cystic duct during an endoscopic cholecystectomy. To obtain high quality imaging, radiolucent (rather than stainless steel) cannulas are typically employed in the region of the cholangiogram. Tissue gripping devices have also been developed for deployment on the exterior of the cannula, either permanently or removably, to prevent the cannula from working out of the body wall as a result of instrument manipulation therethrough. Surgeons have long employed cautery to destroy or vaporize tissue and to cut and coagulate vessels and tissue through the application of electricity, heat or corrosive chemicals. Electrocautery (or galvanocautery) is routinely used to achieve hemostasis, both in endoscopic (closed) and non-endoscopic (open) surgical procedures. Electrocautery operates by taking advantage of the resistance to the flow of electrical current through tissue, such resistance resulting in heat generation as current attempts to pass therethrough. The degree of resistance to electrical current flow for tissue depends primarily on its vascularity and water content, with bone and fat having a higher resistance to current flow than skin and muscle. Electrocautery instrumentation is typically either unipolar or bipolar. In unipolar applications, electrical energy is supplied from a generator to the end of an electrical conductor, e.g., cauterization wire, which is pressed against or placed adjacent the desired surgical site. A grounding plate is typically located below the patient so that the electrical current delivered by the cauterization wire passes through the patient to the plate, thereby completing the electrocautery circuit. In bipolar electrocautery, by contrast, a grounding wire is part of the instrumentation placed adjacent the surgical site and the electrical current passes directly from the cauterization wire, through the tissue at the surgical site, and to the grounding wire. Electrical burns constitute the most common electrical hazard in the operating room, the majority of which are associated with the use of electrosurgery or cautery units. A radiofrequency generator supplies alternating current to the active electrode tip at frequencies between 300 thousand and 2 million hertz (cycles/second). Higher frequency devices are preferred to minimize the likelihood of muscle and nerve stimulation, i.e. electrical shock. The total power output of such units typically ranges from 40 to 600 watts. The current density at the tip of the electrode is extremely high, allowing the surgeon to achieve local heating and coagulation. To minimize the risk of extraneous burns in endoscopic procedures, it has been suggested that low power electrosurgical units and bipolar grasping forceps be employed and that insulation of accessory instrumentation, the cannula and the laparoscope be undertaken. See "Principles and Hazards of Electrosurgery Including Laparoscopy," G.R. Neufield, Surgery, Gynecology & Obstetrics , Nov. 1978. It has been reported that conductive trocar sleeves (or cannulas) can result in internal bums, particularly where the operative portion of the electrocautery instrument is not advanced far enough beyond the end of the cannula. The suggested solution to this risk is the use of non-conductive cannulas, e.g., by placing a polyolefin heat-shrinkable tubing on the exterior of a conductive, stainless steel cannula. See "A Method for Preventing Abdominal Burns Caused by Electrocautery during Laparoscopy," J. M. Esposito, Am. J. Obstetr. Gynecol ., Vol. 114, No. 8, 1972, pages 1105-06. Specifically, DE-B-2535341 discloses a metal tube for guiding surgical instruments, which can be optical or electrical. At the proximal end of the tube is a prominent flange which extends radially outwards. Sheathing the metal tube on its exterior surface is an electrically- insulating sleeve. The flange may serve as an electrical connection. It has also been reported that endoscopic use of electrocautery devices can induce an electrical charge in or on the endoscope through which the electrocautery device is operated, despite the insulation of the electrocautery device. It will thus appear that high frequency current is leaking through the insulation, when in fact no electrons are passing therethrough. This phenomenon has been described as "capacitive coupling". See "Endoscopic Applications of Electrosurgery: A Review of Basic Principles," D. E. Barlow, Gastrointestinal Endoscopy , Vol. 28, No. 2, 1982, pages 73-76; "Safeguards in Laparoscopy: Education, Equipment Care, and Electron Control," R. M. Soderstrom, Contemporary OB/GYN , Vol. 11, March 1978, pages 95-107. The induction of electric charge has also been observed on the surface of non-conductive cannulas when used endoscopically with a unipolar cautery. The electrons passing through the unipolar cautery create an electromagnetic field which in turn creates and electric charge in the nearby cannula. The electric charge thus created is proportional to the frequency of the energy supplied to the cautery device. This electrical charge may be stored and released through a small area, such as the cannula touching the bowel, resulting in a burn. An electromagnetic field is not generally created when a biopolar cautery is used because electric currents run in both direction within the cannula, so that the net electromagnetic field is zero. In the case of unipolar cautery, unless this electrical energy is dissipated, contact between the "charged" cannula and an internal body organ or viscera may burn the organ or viscera. Thus, means are needed to ensure that any electrical energy induced in or in any way conveyed on to surrounding structures by the use of electrosurgical devices is controllably dissipated in a safe manner. Summary of the Invention In accordance with the present invention, a surgical device for receiving an electrical charge-inducing element is provided, which is adapted to dissipate electrical energy induced during a surgical procedure, e.g., through the endoscopic use of an electrocautery instrument. The surgical device of the present invention includes: (a) a tubular member defining a longitudinal axis, the tubular member being fabricated from a substantially dielectric material; (b) electrical conductive means on the exterior surface of the tubular member for conducting induced electrical charge along the longitudinal axis on the tubular member; and (c) energy dissipation means communicating electrically with the electrical conductive means, the energy dissipation means facilitating ground of the tubular member. In a preferred embodiment of the invention, the tubular member comprises a cannular fabricated from a substantially dielectric, i.e., substantially non-electrically conductive, material such as fibreglass. Suitable electrical conductive means include one or more conductive wires mounted to the exterior, and optionally also the interior, of the tubular member, electrically conductive materials interspersed within the tubular member, e.g., metal or carbon fiber particles, or an electrically conductive coating or surface treatment, e.g. a conductive ink or a surface deposition of aluminium or like material. The electrical conductive means is adapted to convey electrical energy to a region remote from internal body organs where electrical grounding may be safely and efficiently accomplished. For example, an electrically conductive band may extend around the periphery of the tubular member, thereby forming an energy dissipation region. Preferably, the energy dissipation region is configured and dimensioned to provide a relatively large grounding surface area, thereby minimising current density. A preferred mechanism for energy dissipation involves positioning the energy dissipation region so as to communicate electrically with the body wall of the patient. In this way, the tubular member may be continually grounded by the patient without risking electrical energy build-up in or on the tubular member and burn injury to internal organs. In has been found according to the present invention that an improved accessory surgical device may be provided which includes: (a) a housing fabricated from a substantially dielectric material and adapted to be mounted to the exterior of a tubular member, the tubular member defining a longitudinal axis and in use accommodating an electrical charge-inducing element; (b) electrical conductive means on the exterior surface of the housing for conducting an induced electrical charge longitudinally along said housing; and (c) energy dissipation means communicating electrically with the electrical conductive means, the energy dissipation means facilitating grounding of the housing. Illustrative of the improved accessory devices of the preferred embodiment of the present invention is a guide tube positioning device of the type disclosed a commonly European patent application which published on February 20, 1991 under EPO Publication No. 0 413 493 A2 Such an accessory device may be removably secured to an electrically conductive, e.g., stainless steel, cannula. The electrical conductive means is adapted to convey induced energy from the cannula across the housing to energy dissipation means where grounding is accomplished. The accessory device may also form a distally-extending part of the cannula housing to which the cannula is mounted. In any case, the accessory device permits energy transfer to an energy dissipation region, thereby greatly minimizing the risk of burn injury to internal organs through contact with an energized cannula. Brief Description of the Drawings Fig. 1 is a top view, partially in section, of a trocar of a preferred embodiment of the present invention, the trocar including a cannula assembly and an obturator assembly; Fig. 2 is an exploded view of a cannula assembly; Fig. 3 is a side view, partially in section, of an alternative cannula assembly; Fig. 4 is a side perspective view of a surgical accessory of a preferred embodiment of the present invention; Fig. 5 is a front view of the surgical accessory of Fig 4; and Fig. 6 is a side perspective view of an alternative surgical accessory of a preferred embodiment of the invention. Detailed Description of the Illustrated Embodiment Referring to Figs. 1 and 2, trocar 10 includes a cannula assembly 12 and an obturator assembly 14. Obturator assembly 14 comprises an obturator housing 16, obturator shaft 18 with a pyramidal piercing tip 20 at its distal end, and a spring-loaded tubular clement 22 which shields piercing tip 20 in its spring-biased distal position. Cannula assembly 12 includes a cannula housing 24 (formed by top and bottom portions 24A and 24B, respectively) in which is pivotally mounted a flapper valve 23, and a cannula 26. Torsion spring 23 biases flapper valve 25 into engagement with gasket 30. Insufflation lever 29 permits manual manipulation of flapper valve 25. A stopcock 28 is mounted to cannula housing 24 to permit gas insufflation and desufflation through cannula assembly 12. A stabilizer plate 32 is mounted within cannula housing 24 proximal of gasket 30 which cooperates with proximally-facing valve member 27 of flapper valve 25 and accessory instrumentation (not pictured) introduced therethrough to provide a gas seal. Cannula assembly 12 is sized to receive obturator shaft 18 and tubular element 22 longitudinally therewithin. Thus, as shown in Fig. 1, tubular element 22 and obturator shaft 18, which form a subassembly, are removably received within cannula 26 and extend longitudinally therebeyond. When pressed against a body wall, tubular element 22 reciprocates proximally to expose piercing tip 20. Once the piercing tip enters the body cavity, tubular element 22 springs forward to shield piercing tip 20, thereby minimizing the likelihood of inadvertent injury to internal organs. It is to be recognized that trocars are also known that do not include a spring-loaded tubular element, and that such trocars may also be improved according to the present invention. After entry into the body cavity, the subassembly which comprises obturator assembly 14 is removed from cannula assembly 12 and cannula 26 remains extended through the body wall and into the body cavity. Cannula 26 thus provides a port of entry for accessory instrumentation. Cannulas for use in endoscopic procedures are typically fabricated from stainless steel or a radiolucent material, e.g., fiberglass. Radiolucent cannulas are preferred where the surgeon anticipates internal imaging, e.g., x-ray imaging of a radiopaque, dye-injected cystic duct, known as a cholangiogram. The materials used to fabricate radiolucent cannulas are substantially dielectric and they are not therefore capable of dissipating electrical energy induced thereon, e.g., when a unipolar cautery is operated therewithin. The present invention enables dielectric tubular member to be adapted to provide endoscopic access for electrical instrumentation, e.g., unipolar electrocautery devices, are provided with conductive means to facilitate conveyance of electrical energy to a grounding region. By dielectric material is meant a material which does not permit transfer of an electrical current at a rate and to a degree which will effectively dissipate an electrical charge and thereby obviate the danger of tissue burn through contact therewith. Fiberglass is an example of such a dielectric material. Referring again to Figs. 1 and 2, cannula 26 is fabricated from a dielectric material, and is provided with an electrically conductive wire 34 which extends along the longitudinal axis thereof. Wire 34 provides a means for collecting and transferring electrical energy conveyed and/or induced on or in cannula 26. As shown, wire 34 extends substantially linearly along the length and at the outer surface of cannula 26. However, wire 34 may also be helically wound, oriented in a random pattern, or a variety of other configurations. Wire 34 connects with circumferential band 36 located toward the proximal end of cannula 26. Band 36 provides a means for grounding cannula assembly 12, and particularly cannula 26, preferably through contact with the body wall of the patient. Band 36 is sized and dimensioned to provide a relatively large area for contact with the body wall, thereby minimizing the current density at any given contact point along band 36 and reducing the likelihood of localized burns as grounding is accomplished. Alternatively, band 36 may be positioned on cannula assembly 12 so as to be outside the patient's body when cannula 26 is extended into the body cavity, and external grounding means may be secured to band 36. Band 36 may be fixedly secured to cannula 26, or longitudinally movable along the exterior of cannula 26. In instances where band 36 is longitudinally movable, a locking screw 38 may be provided to secure band 36 in a desired position. Regardless of the longitudinal positioning of band 36, wire 34 is adapted to transfer electrical energy thereto in a continuous, uninterrupted fashion. In use, cannula assembly 12 provides a port of entry for accessory instrumentation by way of cannula 26 extending into a body cavity. Band 36 is typically positioned so as to be in contact with the body wall and may optionally include a gripping mechanism, e.g., external threading, for maintaining cannula 26 in a fixed position relative to the body wall, despite manipulation of accessory instrumentation therethrough. When a surgeon introduces an accessory instrument with electrocautery capability through cannula 26, whether unipolar or bipolar, and energizes that instrument, an electrical charge may be induced in or on cannula 26. However, any risk of burn injury to internal organs or tissue through contact with cannula 26 is obviated through the transfer of such electrical energy along wire 34 to band 36. Through the uninterrupted contact of band 36 with the body wall (or an external grounding mechanism), safe and effective grounding of cannula 26 is achieved. An alternate embodiment is shown in Fig. 3. Cannula assembly 40 includes a cannula housing 42 and cannula 44. An electrically conductive ink 46 is applied to the exterior of cannula 44 in a substantially helical pattern. At the proximal end of cannula 44, conductive ink 46 electrically communicates with wire 48 which is mounted within cannula housing 42. Wire 48 is connected at its opposite end to electrical fitting 50 which is adapted to receive a grounding wire (not shown), The electrical circuitry of conductive ink 46, wire 48 and fitting 50 provides a means for grounding cannula assembly 40, and particularly cannula 44, external to a patient's body. In a further preferred embodiment of the present invention, an accessory device which is adapted to be associated with a cannula assembly is provided. For example, the accessory device may take the form of a gripping device for use in securing and maintaining the position of cannula assembly with respect to a patient's body wall. Referring to Figs. 4 and 5, accessory device 60 includes an outer housing 64 and an inner housing 66 which have axially aligned apertures to receive a cannula of the type shown in Figs. 1-3. Outer housing 64 is generally cylindrical with a central aperture 62 and includes a gripping portion 68 supporting gripping projections 70. Outer housing 64 also has an inwardly facing threaded section (not shown) to engage threaded section 74 of inner housing 66. A number of longitudinally extending gripping fingers 76 for frictionally gripping a cannula are provided as part of inner housing 66. Outer housing 64 includes an integral, distally extending sleeve 72 for surrounding a cannula. Sleeve 72 includes radially projecting ribs 78 which are shown in Fig. 4 as a helical coil extending radially from the, outer surface of sleeve 72. An electrically conductive wire 80 passes longitudinally along sleeve 72, connecting at its distal end with inwardly directed contact surface 86 and at its proximal end with distally directed grounding band 84 on forward face 82 of gripping portion 68. Contact surface 86 is adapted to electrically communicate with a cannula when accessory device 60 is mounted thereon. Grounding band 84 is adapted to transfer electrical energy to the body wall of the patient or to an external grounding mechanism, depending on the positioning of the carnnula assembly and/or accessory device 60 with respect to the body wall. The relatively large surface area of grounding band 84 minimizes the current density at any given point thereon as grounding takes place, thereby reducing the likelihood of localized burns as grounding is accomplished. Accessory device 60 acts to dissipate electrical energy induced or transferred to a cannula, regardless of the material from which the cannula is fabricated. In cases where the cannula is fabricated from stainless steel, electrical energy will easily pass along the cannula, through contact surface 86 and wire 80, to grounding band 84. However, in cases where the cannula is fabricated from a dielectric material, e.g., fiberglass, it is preferred that the cannula include energy conductive means of the type described above with respect to cannula 26 in Figs. 1 and 2. With the exception of wire 80, contact surface 86 and grounding band 84, accessory device 60 is typically constructed, such as by molding, of glass filled acetal or polycarbonate. One appropriate acetal material is available from LNP Division of ICI America Inc. under the trade specification KFL 4023. A suitable polycarbonate material is available from General Electric Company under the trade name LEXAN. In use, accessory instrument 60 is positioned on a cannula with inner housing 66 and outer housing 64 loosely engaged. Once located in the desired position on the cannula, inner and outer housing 66, 64 are rotatably threaded together so as to tighten gripping fingers 76 into engagement with the cannula. After penetration of the trocar through the body wall, sleeve 72 is brought into engagement therewith. Sleeve 72 may then be inserted into the incision by straight lateral force or by turning the cannula assembly to effectively "screw" sleeve 72 and helical ribs 78 into the body wall. Once inserted, the body wall surrounds sleeve 72 and extends into the recesses between ribs 78. The body wall is brought into engagement with and thereby acts to ground electrical energy from grounding band 84. In a further embodiment of the invention, wire 34 (first embodiment) or wire 48 (second embodiment) may be replaced in whole or in part by electrically conductive particles or materials. Thus, as shown in Fig. 6, electrically conductive particles 100 are interspersed within outer housing 64 and communicate electrically with grounding band 84. Particles 100 may be metallic or non-metallic, e.g., carbon fibers, and are included in an amount effective to transfer energy through accessory device 60 at a rate sufficient to obviate the risk of internal organ burns. For example, particles 100 may constitute from about 2 to 15% by weight of a cannula or accessory device, and may be randomly dispersed, oriented in a fixed pattern, or in fibrous form within the subject device. The claims which follow identify embodiments of the invention additional to those described in detail above.

Claims: A surgical device (12, 60) for receiving an electrical charge-inducing element and comprising: (a) a tubular member (26, 72) defining a longitudinal axis, said tubular member being fabricated from a substantially dielectric material; (b) electrical conductive means (34, 46, 80, 100) on the exterior surface of said tubular member for conducting induced electrical energy along the longitudinal axis of said tubular member; and (c) energy dissipation means (36, 84) communicating electrically with said electrical conductive means, said energy dissipation means facilitating grounding of said tubular member. A surgical device according to claim 1 wherein said tubular member is a cannula. A surgical device according to claim 1 or 2 wherein said charge-inducing element is an electrocautery device. A surgical device according to claim 1, 2 or 3 wherein said substantially dielectric material is radiolucent. A surgical device according to claim 4 wherein said radiolucent material comprises fibreglass. A surgical device according to any one of the preceding claims, wherein said electrical conductive means assumes a substantially helical configuration (46) as it extends along the longitudinal axis of said tubular member. A surgical device according to any one of the preceding claims wherein said energy dissipation means (36, 84) comprises an electrically conductive band mounted on the exterior surface of said tubular member. A surgical device according to claim 7 wherein said electrically conductive band (36) is movable along said tubular member A surgical device as claimed in any one of the preceding claims, which is a trocar (10) including a cannula, said cannula constituting the said tubular member. A trocar according to claim 9 wherein said cannula is fixedly secured to a cannula housing (42) and said energy dissipation means (48, 50) is associated with said cannula housing. A trocar according to claim 10 wherein said energy dissipation means is an electrical fitting (50) adapted to cooperate with a grounding wire. A trocar according to claim 9 wherein said energy dissipation means (36) is located on said cannula (26) so as to ground said cannula to a body wall of a patient when said cannula is introduced through said body wall. A surgical device as claimed in any one of claims 1 to 8, wherein the tubular member (72) is adapted to receive a cannula and the device is an accessory surgical device (60) for use with such a cannula. An accessory device according to claim 13 wherein said tubular member has adjustable means (76) to grip the exterior of said cannula. A surgical device according to any one of the preceding claims wherein said tubular member (26) is fixedly secured to a cannula housing (24). A surgical device according to any one of the preceding claims wherein said tubular member includes means (78) for engaging a body wall of a patient to retain said tubular member in position relative to said body wall. A surgical device according to claim 16 wherein said engaging means comprises helical gripping projections (78) extending radially outward from said tubular member.

Inventors: HENNING WALTER S, HENNING, WALTER S.
Applicants: UNITED STATES SURGICAL CORP, UNITED STATES SURGICAL CORPORATION
Application year: 1992
Main classification: A61B17
IPC codes: A61B17, A61M13, A61B19, A61B18