Surgery – Instruments – Electrical application
Reexamination Certificate
1998-10-16
2002-04-02
Shay, David M. (Department: 3739)
Surgery
Instruments
Electrical application
C606S039000, C606S040000
Reexamination Certificate
active
06364877
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an electrosurgical generator for delivering an electrosurgical current particularly but not exclusively in intracavitary endoscopic electrosurgery. The invention also relates to an electrosurgical system comprising the combination of a generator and an electrode assembly. The term “intracavitary” is used in this specification to denote electrosurgery in which living tissue is treated by least invasive surgical access to a body cavity. This may involve “underwater electrosurgery”, a term denoting that the surgery is performed using an electrosurgical instrument with a treatment electrode or electrodes immersed in liquid at the operation site. The invention has particular application in the fields of urology, hysteroscopy and arthroscopy.
BACKGROUND OF THE INVENTION
Intracavitary endoscopic electrosurgery is useful for treating tissue in anatomical or surgically created cavities of the body which can be accessed by methods involving minimal trauma to the patient, be this through a natural body passage or one created artificially. The cavity is distended to provide space for gaining access to the operation site to improve visualisation and to allow for manipulation of instruments. In low volume body cavities, particularly where it is desirable to distend the cavity under higher pressure, liquid rather than gas is more commonly used due to better optical characteristics and because it washes blood away from the operative site. Conventionally, a non-electrolyte solution such as glycine is used as the fluid distension medium when electrosurgery is being used, glycine being electrically non-conductive.
The limited surgical access encountered during intracavitary endoscopic procedures makes the removal of tissue pieces derived from a typical electrosurgical loop cutting electrode both difficult and time consuming. Vaporisation of tissue whereby the tissue is reduced to smoke and water vapour is a preferable technique in these situations, rather than the piecemeal removal of tissue. The products of vaporisation may be removed following dissolution within a liquid irrigating medium.
With regard to underwater endoscopic electrosurgery, the applicants have found that it is possible to use a conductive liquid medium such as normal saline in place of glycine. Normal saline is the preferred distension medium in underwater endoscopic surgery when electrosurgery is not contemplated or a non-electrical tissue effect such as laser treatment is being used. Although normal saline (0.9% w/v; 150 mmol/l) has an electrical conductivity somewhat greater than that of most body tissue, it has the advantage that displacement by absorption or extravasation from the operative site produces little physiological effect and the so-called water intoxication effects of glycine are avoided.
Effective electrosurgical treatment of tissue which is totally immersed in liquid at the application site is difficult to achieve because the heat generated by the flow of electrical currents in both the tissue being treated and surrounding conductive liquid tends to cause boiling of the liquid. The operating electrode is intermittently surrounded by water vapour rather than liquid, with consequent large variations in the electrical impedance of the load presented to the generator supplying the electrosurgical power to the electrode. Whilst this variation is mitigated by use of a non-conductive liquid, it cannot be eliminated entirely due to the release of body fluids at the operative site which elevates the electrical conductance of the liquid. Changes in tissue type also alter the load impedance. These effects result in difficulty in controlling the electrosurgical output to produce consistent effects on the tissue being treated. As a result, high powers are commonly employed to overcome this performance variation.
SUMMARY OF THE INVENTION
According to a first aspect of this invention, an electrosurgical generator for supplying radio frequency power to an electrical instrument, comprises a radio frequency output stage having at least a pair of electrosurgical output connections for the delivery of radio frequency power to the instrument, a power supply coupled to the output stage for supplying power to the output stage, and control circuitry including sensing means for deriving a sensing signal representative of the radio frequency peak output voltage developed across the output connections, wherein the output stage comprises a resonant output circuit coupled to the output connections and a switching device coupled to the resonant output circuit, and wherein the control circuitry is operable to actuate the switching device to reduce the delivered radio frequency power. The switching device is preferably connected between the resonant output circuit and one of a pair of supply rails of the power supply means, and connected so as to switch current repeatedly through the resonant output circuit at its resonant frequency. In order to cause a control overshoot, in terms of the degree to which the delivered power is reduced when the output voltage reaches the predetermined threshold, the control circuitry is so arranged and coupled to the switching device that it is capable of reducing the “on” time of the switching device during individual radio frequency switching cycles sufficiently rapidly to cause a 50% reduction in delivered output power within 100 &mgr;s of the predetermined threshold having been reached. This allows surgery to be performed in a conductive fluid field, in particular in a saline solution. Large and rapid changes in load impedance can occur substantially without causing unwanted electrosurgical effects. For example, when it is desired to produce electrosurgical desiccation, any increase in impedance due to vaporisation of surrounding saline in the region of an electrode of the instrument which might otherwise lead to unwanted arcing at the required power level for effective desiccation can be largely prevented. When electrosurgical tissue cutting or tissue vaporisation is required, output voltage limitation can be used to prevent electrode burning and/or excessive tissue vaporisation.
The control circuitry may include a control line feeding a first power reduction control signal to the radio frequency output stage. The output stage, which may be a radio frequency power oscillator, typically has as the oscillating element a radio frequency power device, and in the preferred embodiment, the control circuitry is arranged such that at least a 50% reduction in output power is brought about in a period of less than 20 &mgr;s after the output voltage reaches the predetermined threshold by reducing the period of conduction of the device during individual cycles of the radio frequency output signal. Such alteration in the period of conduction is advantageously achieved independently of any variation in supply voltage to the radio frequency power device. In practice, the reduction in output power is brought about using a single control variable, i.e. the peak output voltage or peak-to-peak output voltage, independently of supply voltage and independently of the delivered output power which varies according to the load impedance and the supply voltage. Thus, triggering of a power reduction occurs at the same preset output voltage threshold but at different output power and load impedance values, according to circumstances.
As an adjunct to direct control of the radio frequency output stage, the means for causing a reduction in output power may include a further control line which is coupled to the power supply means, the control circuitry being arranged such that a second power reduction signal is fed to the power supply means to effect a reduction in the average power supply voltage supplied to the output stage. Typically, the rate of reduction of power due to lowering of the power supply voltage is comparatively slow, but the combination of two means of control can produce a larger range of available output power levels.
Thus, according to a second aspect of the inven
Goble Colin Charles Owen
Goble Nigel Mark
Gyrus Medical Limited
Nixon & Vanderhye P.C.
Shay David M.
LandOfFree
Electrosurgical generator and 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 generator and system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrosurgical generator and system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2914215