Surgery – Instruments – Electrical application
Patent
1997-02-27
1999-03-23
Shay, David M.
Surgery
Instruments
Electrical application
606 41, 606 46, A61B 1736
Patent
active
058852778
DESCRIPTION:
BRIEF SUMMARY
This invention relates to endoscopic instruments of the species defined in the preamble of claim 1.
Such instruments allow surgery in arbitrary liquid-filled cavities such as the uterus or the intestine. Depending on the selected electrode and adjustment of the hf power, incisions may be made or bleeding be stopped by surface coagulation. Such instruments are used particularly in urology to operate on the bladder wall and especially for prostate resection.
The active electrode designed for cutting or for coagulation initially is placed in the liquid body or volume. Even if the hf generator is already turned on, current will not yet flow because the rinsing liquid is lean in electrolyte and is a poor electrical conductor. Current starts flowing when contact is made with the tissue which is rich in electrolyte and is a good conductor. The current then flows through the tissue to the neutral electrode.
In known instruments of the initially cited kind, the neutral electrode is mounted spaced from the body cavity, namely always on the body surface. In urological surgery, the neutral electrode frequently is wound around the thigh and on the skin.
This procedure has the drawback of a long and hence high-resistance current path through the body from the contact site of the active electrode with the tissue to the distant body surface zone in contact with the neutral electrode. There is danger of so-called stray currents which may lead to skin burns, for instance if the patient makes contact with a metallic object such as the operating table. Such stray currents lead to problems if the patient is making simultaneous contact with other metal conductors such as EKG electrodes and the like. Moreover, and in an exceedingly undesirable manner, the hf current also can jump through the endoscope optics toward the surgeon's eye. Many problems arise when the neutral electrode is poorly affixed. If such a neutral electrode makes contact only by a small area with the body surface, burns again are incurred.
Furthermore, the large penetration depth in the tissue underneath the active electrode is also a drawback. When the neutral electrode is connected to the body surface, the current flows from the contact site of the active electrode into the depths of the tissue and may still inflict thermal injury to the tissue far below those tissue layers where cutting is intended. As a result, undesired and very deep thermal injury is sustained, requiring long healing times and injuries which are susceptible to infection.
A so-called bipolar electrode system is known, wherein the neutral electrode is mounted in the vicinity of the active electrode and in contact with the body surface. The purpose of this configuration is to make the current between the two electrodes flow through the tissue along the shortest path. Illustratively, such an instrument is disclosed in German patent document 25 21 719 C2. However, it suffers from the drawback of design-entailed small contact area between body tissue and neutral electrode, causing high current density in the tissue.
An object of the present invention is to create instruments of the initially cited kind allowing elimination of the above cited drawbacks and hence permitting more reliable work with respect to the incision depth of influence and providing general electrical safety.
This problem is solved by the invention by the features of the characterizing part of claim 1.
In the invention, the neutral electrode is mounted a distance from the active electrode inside the same liquid volume and thereby also in the body cavity. Accordingly, current can only flow in the narrower zone of the body cavity. All safety problems raised by stray currents are thereby automatically eliminated. Moreover, the current's depth effect is substantially less when cutting or coagulating: the current does not flow depth-wise from the contact site between the active electrode and the tissue but preferentially sideways to spread in the body tissue--which is more conducting than the liquid volume--laterally on the surfa
REFERENCES:
patent: 4030502 (1977-06-01), Iglesias
patent: 4936301 (1990-06-01), Rexroth et al.
Farley Walter C.
Olympus Winter & Ibe GmbH
Shay David M.
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