Surgery – Instruments – Electrical application
Reexamination Certificate
2001-02-02
2004-07-06
Bennett, Henry (Department: 3742)
Surgery
Instruments
Electrical application
C606S034000, C606S048000, C606S050000, C606S051000, C606S049000, C607S101000, C607S104000, C607S105000
Reexamination Certificate
active
06758846
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an electrosurgical instrument and an electrosurgery system including the instrument and a radio frequency generator system for treatment of tissue, wherein the operative site and distal portion of such an instrument are immersed in an aqueous solution during use to vaporise, coagulate, desiccate or otherwise thermally modify such tissues.
BACKGROUND OF THE INVENTION
Electrosurgery has been used in surgical practice for over fifty years and during that time has seen a number of improvements to enhance safety and performance in more challenging surgical environments. One such challenge has been the emerging use of minimal access or endoscopic techniques to perform an ever increasing range of surgical procedures.
Traditional monopolar and bipolar electrosurgical devices have been widely used in endoscopic surgery but have suffered from a number of technical disadvantages, particularly when the operative site is distended or irrigated with aqueous solutions. Such solutions are commonly employed to improve endoscopic visualisation and are usually introduced to the body cavity through a specific channel provided in the endoscope itself. The immersion of electrosurgical instruments in aqueous solutions introduces a number of technical hurdles in terms of insulation and preventing power dissipation to the solution rather than the target site.
Monopolar electrosurgery requires the aqueous solution to be non-conductive in order to operate efficiently. Despite use of solutions such as Dextrose, Sorbitol and Glycine which have very low values of electrical conductance, tissue and bodily fluids released during the operation can significantly increase the conductance of fluids bathing the target site. This usually necessitates increasing power output to overcome losses to the solution in order to maintain performance. Increasing power output increases the recognised risk of inadvertent burns to the patient or operator when using monopolar arrangements.
Burns associated with monopolar arrangements can be avoided, albeit in an instrument with limited power, by use of capacitive coupling in a return path between tissue adjacent the operative site and the conductive casing of a self-contained battery-powered instrument such as that disclosed in the applicant's International Application No. WO97/15237. This device has a single exposed electrode and with an integral generator inside a metallic handheld casing and is intended for dry field use at high frequencies. The casing, acts as a conductor capacitively coupled to its surroundings to provide a capacitive return path from tissue being treated to the generator within the casing. The impedance of the return path is widely variable due to the varying degree to which the instrument is capacitively coupled to the surgeon's hand and the variable juxtaposition of surrounding conductive masses. A thin plastics coating is provided over the casing to prevent direct electrical contact with conductive masses.
While a conventional bipolar electrosurgical instrument, in which the two poles of the electrosurgical output are mounted as neighbouring electrodes on the tip of the instrument and both are required to contact tissue in order to produce an effect, to a large extent eliminate the risks of burns, the output power will still preferentially pass through conductive fluid present at the application site rather than the tissue itself. Nonetheless, the heating of such fluid can produce secondary heating of the tissue and thereby produce coagulation or desiccation of the tissue. The problem is much more evident when trying to use a bipolar arrangement to cut or ablate tissue whereby the solution lowers the impedance of the output and prevents the output voltage reaching the levels necessary to induce vaporisation of the tissue, typically requiring a peak-to-peak voltage in excess of 500V.
U.S. Pat. No. 5,009,656, Reimels, describes a method of overcoming this problem in which the two electrodes of a bipolar pair are brought sufficiently close, such that the gap between them supports the production of water vapour and direct arcing between the two electrodes. Although the technique provides for a method of arcing during immersion in conductive fluid, the gap is so small that the tissue effect is very limited.
U.S. Pat. No. 4,116,198, Roos, describes a further technique of overcoming some of the problems associated with use of bipolar arrangements when immersed in electrically conductive solutions. This technique overcomes the limitations of Reimels by use of a return electrode which is set back from the active electrode such that a more protracted electrical circuit is completed by the solution and direct arcing between the two is avoided. By this means only one electrode of the bipolar pair is required to contact tissue and the electric field is sufficient to include the tissue at the application site. This technique was successfully employed in endoscopic surgical procedures involving transuretheral resection of the prostate gland, as described by Elsasser and Roos in an article entitled ‘Concerning an Instrument for Transuretheral Resection without Leakage of a Current’, published in the German magazine ‘Acta Medico Technica’ 1976 vol. 24 No. 4 pages 129-134.
The present applicants' co-pending patent applications relating to electrosurgery describe further improvements over the Roos prior art to control the dimensions of the active electrode relative to a complex interaction between the configuration of the active electrode, the power threshold to establish arcing at the active electrode and control features in the electrosurgical generator component of the system. The commercial embodiments of these inventions are now widely used in the fields of arthroscopic, hysteroscopic and urological surgery.
U.S. Pat. Nos. 5,366,443 and 5,697,909 in the names of Eggers and Thapliyal describe an alternative approach using an array of active electrodes which can be selectively activated, or current limited, in order to reduce power dissipation into the electrically conductive fluid.
The above arrangements tend to suffer from a number of problems and technical limitations during use. Carbon tracking is a problem wherein the carbon residue derived from tissue vaporisation forms a conductive track between active and return electrodes. Once established, the track has a negative temperature co-efficient of resistance so that the hotter the carbon becomes, the more conductive it becomes and the more current flows along the track between the electrodes. The temperature developed in the track places huge thermal stresses on the insulator separating the return and active electrodes, which may result in catastrophic failure. Similar failures can occur due to overheating of the electrode assembly without carbon track formation when only portions of the distal tip assembly are in contact with fluid such that current can still flow in the absence of sufficient fluid cooling of the assembly.
In these prior devices, the electric field becomes concentrated in the region representing the shortest conduction path through the fluid medium. The shortest paths occur between the most distal portion of the return electrode and the most proximal region of the active electrode exposed to the fluid. The effects of this are two-fold: firstly, the high current density may cause the return electrode to become “active”, particularly when the distal portion of the electrode is only partially immersed in fluid due to the accumulation of gaseous by-products produced during vaporisation; and, secondly, the depth of tissue effect is limited by the concentration of the electric field, particularly when a deeper coagulative effect is desirable.
When the active electrode is partially wetted and partially enveloped in vapour, very high powers are required to sustain what is, in effect, an unstable condition which usually results in intermittent collapse of the vapour pocket and variable surgical performance. The prior art describes certain ra
Goble Colin C. O.
Goble Nigel M
Bennett Henry
Dahbour Fadi H.
Gyrus Medical Limited
Nixon & Vanderhye P.C.
LandOfFree
Electrosurgical instrument and an electrosurgery system... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrosurgical instrument and an electrosurgery system..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrosurgical instrument and an electrosurgery system... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3217000