High Frequency Electrosurgical Apparatus

Abstract

Electrosurgical apparatus including electrodes powered by high frequency electric current, wherein the amplitude of the current flowing through the circuit is monitored and compared with a reference amplitude so that the current source can be regulated to transmit power of a desired amplitude. Further, the waveform of the current can be selectively switched from a sinusoidal waveform to a pulsed waveform. Also, there is provided an indifferent or return electrode whose conductivity controls the operation of the power source.

Description

BACKGROUND OF THE INVENTION

This invention pertains to electrosurgical apparatus and more particularly, to such apparatus which is powered by high frequency current for cutting tissue, coagulating blood vessels and fulguration of growths.

Known electrosurgical apparatus generates a high frequency electric current which is fed to an active electrode. An indifferent electrode is placed in contact with the patient to supply a return path for the current. When the active electrode is applied to tissue of the patient at the operating site, a circuit is closed and the high frequency power emitted by the active electrode generates heat at the site. The resultant heat implements the desired operative procedure.

The amplitude of the current flowing between the electrodes is a function of the electrical resistance of the tissue current path between the electrodes. If the current generator is set to transmit a current of a given amplitude, such amplitude will be effectively related to a given load resistance. If the resistance decreases, the current amplitude increases; and vice versa.

During an operation, the impedance of the tissue changes as the active electrode moves through different types of tissue. Accordingly, a selected initial setting of the current generator at the start of an operation may not produce the desired current conditions as the operation proceeds.

It is a general object of this invention to provide electrosurgical apparatus wherein the power delivered to the active electrode as the same engages the tissue, is maintained at a constant desired level during the entire operational procedure.

Another object of this invention is to provide in apparatus of the character described, means for monitoring the amplitude of the power flow to the electrodes of the apparatus and controlling the output of the high frequency generator to maintain a desired or selected power amplitude.

Essentially, the electrosurgical apparatus of the instant invention comprises a pair of electrodes applicable to biological tissue; the electrodes being powered from a high frequency generator operative to controllably vary the power amplitude. The apparatus further includes reference means to establish a desired power amplitude in respect to the operating current passing through the biological tissue; together with means for sensing the amplitude of the power passing through the tissue and control means for comparing the amplitudes of the desired and actual power; the control means being responsive to such amplitude comparison to regulate the operation of the generator so that the generator will transmit power having an amplitude substantially equal to the desired power amplitude.

It is known in the art that different operative procedures require differing high frequency current waveforms. Thus, a cutting operation calls for a continuous wave or sinusoidal radio frequency oscillation of the current; whereas a coagulating procedure requires an oscillating current of the type provided by a spark gap oscillator. Such a spark gap oscillator generates a spectrum of frequencies between 0.5 mHz. and 1.5 mHz. This noise spectrum is distinguished by high voltage "spikes" with low average power values. Such a signal when impressed by way of the electrode on tissue, has a drying effect which leads to a coagulating action in respect to such tissue, with very little tissue separation or cutting.

It is believed that any waveform which spreads the signal over a reasonable frequency spectrum, will produce the same effect.

Accordingly, the instant invention comprises a high frequency current generator which can be selectively controlled to operate in a continuous wave mode or a pulsed wave mode with the amplitudes of the signals being held at predetermined values.

In electrosurgical procedures the input current is applied to the tissue by way of an active electrode of very small cross section so as to obtain high current densities at the operation site. These high current densities provide the desired heating effects. However the return or indifferent electrode must be in contact over a substantial area of the tissue so that the return current has a low density, which prevents burning or scarring of the tissue in contact with the indifferent electrode.

If for any reason, the indifferent electrode or its connection to the current source is broken or faulty, the low current density is not achieved and the tissue at the situs where the high frequency currents leave, will be burned or scarred.

With the apparatus of the instant invention, the conductive state of the indifferent electrode and its connection to the current generator is monitored and the generator made inoperative when the conductive state falls below a given value.

In known electrosurgical apparatus, the indifferent electrode takes the form of a stainless steel plate which is placed under the patient and a conductive fluid is spread thereover to increase the contact area. Such an electrode must be sterilized before each use thereof and must be prewet with conductive fluid. This procedure may lead to omissions and inexact applications of fluid.

In the apparatus of the instant invention there is provided an inexpensive, prepackaged disposable indifferent electrode which is presterilized and prewet with conductive fluid. Such an electrode facilitates monitoring its conductive state and thus avoids tissue burns or scars.

Other objects of this invention will in part be obvious and in part hereinafter pointed out.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram for electrosurgical apparatus embodying the invention;

FIG. 2 is a top plan view of the indifferent electrode, forming part of the apparatus;

FIG. 3 is a sectional view taken on the line 3-3 of FIG. 2;

FIG. 4 is an enlarged, partial sectional view of a portion of said electrode;

FIG. 5 is a top plan view showing a connector for the electrode of FIG. 2;

FIG. 6 is a sectional view taken on the line 6-6 of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in the drawings, and particularly FIG. 1, electrosurgical apparatus embodying the invention is indicated at 10, for operative application to selected tissue portions of a patient indicated at 12. The apparatus 10 comprises a high frequency current generating system including an R.F. oscillator 14 which drives a gain controlled power amplifier 16. The power amplifier 16 is coupled via step-up transformer 18 and coupling capacitors 20, 22 to active electrode 24 and an indifferent electrode 100, respectively.

During normal operation, when on/off switch 28 is in its closed position, the output of oscillator 14 is amplified by power amplifier 16 and transformer 18 to provide a alternating current which flows via capacitor 20 and active electrode 24 to the selected tissue area in contact therewith. The current passes through the body of patient 12 to the indifferent electrode 100 where it is returned via lead 30 and capacitor 22 to transformer 18.

The power output in the form of the square of the amplitude of the alternating current must be set at a selected, desired level and maintained at such level for the desired operating procedure. Such desired levels are attained by adjusting one of the two calibrated power level setting potentiometers 32, 34. The operation of the respective potentiometers 32, 34 will be hereinafter described.

It is assumed that a voltage indicating the desired square law power amplitude level is present on lead 36 which feeds one input of difference amplifier 38. The other input of difference amplifier 38 is a voltage on lead 40 from square-law detector 42. The inputs of detector 42 are connected to a winding 44 of a magnetic core toroid 46 through which passes lead 30 connecting indifferent electrode 100 to capacitor 22. The combination of lead 30, toroid 46 and winding 44 provides in effect a transformer acting as a current sensor.

As the alternating current flows through lead 30, it will induce an alternating current in winding 44 which is detected in detector 42 to thereby generate a DC voltage having an amplitude proportional to the square of the AC current in lead 30. Difference amplifier 38 compares the DC voltage on line 40 with the DC voltage on line 36 and transmits a signal on line 48 to gain control amplifier 50 which amplifies the signal and transmits the same by lead 52 to a gain control terminal of power amplifier 16.

The relationship of the signals is such that if the amplitude of the current in lead 30 is greater than the desired amplitude as represented by the DC voltage on line 36, the signal on line 52 has a value to decrease the gain of amplifier 16. A similar effect occurs in the opposite direction when the actual current amplitude is less than the desired amplitude. Thus, amplifier 16 and the elements connected to its output comprise a servo system with the current sensor, square law detector, difference amplifier and gain control amplifier being the feedback loop; the signal on line 52 being the error signal and the signal on line 36 being the reference signal.

When the indicated surgical procedure involves a cutting operation, cutting switch 54 is closed to energize relay 56 which causes transfer contact 56A to connect potentiometer 32 to lead 36, and transfer contact 56B to connect with fixed contact 56C. In this case, oscillator 14 transmits a continuous wave of AC signal, as will be hereinafter described, and lead 36 transmits a DC voltage related to the desired amplitude of the alternating current for the cutting operation.

When a coagulating action is desired, switch 58 is closed, switch 54 being open, to energize relay 60 causing its transfer contact 60A to connect with fixed contact 60B; transfer contact 56A of relay 56 now connects lead 36 to potentiometer 34. In this case, oscillator 14 emits packets of alternating current, as later described, and lead 36 transmits a DC voltage related to the desired amplitude of the alternating current for a coagulating operation.

The indifferent electrode 100 requires an electrolyte to provide good conductive contact with patient 12. When the quantity of electrolyte falls below a certain level, poor contact results and the patient may suffer from burns. Accordingly, the electrolyte is monitored as to quantity and the oscillator 14 is rendered inoperative when the quantity falls below a given value.

To this end, a series circuit is established between voltage source V, lead 62, a terminal 102 of electrode 100, the electrolyte in the electrode, another terminal 104 of the electrode lead 64, switch 28, the coil of relay 66 and ground. If sufficient electrolyte is present when switch 28 is closed, relay 66 is energized, closing contact set 66A which supplies operating power to oscillator 14, and opening contact set 66B which breaks the series circuit from voltage source V via contact set 66B and neon bulb 68 and ground to deenergize bulb 68.

If the electrolyte is insufficient, relay 66 is not energized and oscillator 14 is made inoperative, while bulb 68 is energized to direct attention to the insufficiency of electrolyte in electrode 100.

The R.F. oscillator 14 comprises transistor T1 and transformer 70 whose primary winding is connected between the collector of the transistor and ground. The output winding of the transformer is connected to a voltage source V and the input of power amplifier 16. The feedback winding of the transformer has one end connected to the base of the transistor, the other end being connected to transfer contact 56B, and a center tap being connected to relay contact 60A. The emitter of the transistor T1 is connected via contact set 66A to operating voltage source V. A timing capacitor 72 connects the emitter to junction 74 which is connected to fixed contact 56C. Resistor 76 connects junction 74 to ground while resistor 78 connects junction 74 to contact 60B.

When relay 66 is energized, an operating voltage is applied to the transistor T1 by virtue of the closing of contact set 66A. Now, if relay 56 is energized, the feedback winding of transformer 70 is connected to the emitter of the transistor via capacitor 72 and the oscillator 14 operates in the continuous wave mode with a frequency determined by the constants of the transformer, the capacitor 72 and the load on the transformer. The frequency may thus be set at 1 mHz. However, when relay 60 is energized the center tap of transformer 70 is connected to junction 74. Now, as capacitor 72 charges via resistor 76, the oscillator is turned off until the base-emitter junction of the transistor is forward biased. At that time the oscillator oscillates at 1 mHz. for a period of time determined by the time required for capacitor 72 to discharge via resistor 78 to a value which again back biases the base-emitter junction. By a suitable choice of values for resistor 78 it is possible to cause the oscillator to block at a 100 kHz. rate.

The power amplifier 16 is conventional in form and whose gain is controlled by shifting its operating voltage which is supplied by line 52. Gain control amplifier 50, difference amplifier 38 and square-law detector 42 are known devices. Active electrode 24 takes the form of known electrosurgical probes regularly used in the art.

The indifferent electrode 100 is shown in detail in FIGS. 2--4; the same comprising a conductive base member 110 which may take the form of a sheet of plastic such as polyvinyl chloride (PVC) whose top surface is metallized as by depositing aluminum or the like thereon by known techniques. Tabs 112, 114 are affixed to the bottom surface of member 110 at the opposite ends thereof, in the form of adhesive tapes, for affixing the electrode to patient 12.

A porous sheet 116 of flexible spongy material such as sponge rubber, latex or polyurethane foam, or the like, is fixed to the top metallized surface of member 110 by an appropriate adhesive. The porous sheet 116 is impregnated with nontoxic electrolyte such as a saturated saline solution. The solution is preferably rendered somewhat viscous by adding gelatine thereto, to thereby reduce the evaporation of the same.

A protective plastic film bag 118 encloses the electrode 100 including the saturated sheet 116 and the exposed adhesive surfaces of tabs 112, 114. Bag 118 provides a leakproof container for the electrolyte contained in sheet 116, while the same is in storage. When electrode 100 is to be used, no additional electrolyte need be added to sheet 116. Also, bag 118 serves as a germproof shield for its contents and need be sterilized but once when the same is filled. The bag protects the adhesive areas of the tabs 112, 114 until ready for use in applying the electrode in place.

At the time of use of electrode 100, the bag 118 is opened to expose sheet 116 and tabs 112, 114. The top of sheet 116 is placed against the patient and held in place by adhesive tabs 112, 114. A terminal connector is clipped to the electrode.

A terminal connector 120 for attachment to electrode 100, is shown in FIGS. 5, 6. Connector 120 comprises a pair of plates 122, 124 which are hingedly interconnected by ear portions extending toward each other at the side edges thereof, as at 126, 128. Plates 122, 124 are formed of Nylon or the like to be resistant to sterilizing temperatures. A spring 130 biases the forward jawlike portions of plates 122, 124 toward each other.

A pair of stainless steel terminal blocks 102, 104 are suitably affixed to the underside of top plate 122 and signal leads 62, 64 are respectively connected to said blocks. To clip the connector 120 to electrode 100, the rear portions of plates 122, 124 are pinched together to open the jaw portions to receive the edge portion of electrode 100 therebetween. The terminal blocks 102, 104 will then embed themselves in the porous sheet 116 to make good contact therewith. Terminal blocks 102, 104 are electrically interconnected only when sheet 116 is saturated with electrolyte and a measurement of the conductivity between the terminal blocks will determine the presence or absence of electrolyte.

The on/off switch 28 may be of the conventional foot pedal operated type. Alternatively such switch may be finger operated and mounted on the active electrode 24. Also the switch may be of the reed type which has a magnet to operate the same. Obviously, the foot operated and finger operated switches may be connected in parallel to afford a maximum of convenience in operation.

Claims

I claim:

1. High frequency electrosurgical apparatus for operating on electrically conductive tissue comprising first and second electrodes, each of said electrodes being adapted for electrically contacting tissue whereby an electric current path is established between said electrodes via said tissue, means for generating a high frequency electric current having a controllably varying amplitude, means for connecting said generating means to said electrodes, reference means for establishing a desired amplitude for the current passing through the tissue, sensing means for sensing the amplitude of the actual current passing through the tissue, and control means responsive to said reference means and said sensing means for controlling said generating means to generate a high frequency electric current having an amplitude substantially equal to said desired amplitude.

2. Apparatus as in claim 1 wherein said generating means includes means for selectively operating said generating means to operate in a first mode to generate a continuous alternating current, or in a second mode to generate time-spaced packets of alternating current.

3. Apparatus as in claim 2 wherein said reference means comprises means for establishing a first desired amplitude for electric current related to said continuous alternating current generated by said generating means and a second desired amplitude for electric current related to said time-spaced packets of alternating current generated by said generating means, and further comprising selection means for simultaneously controlling the mode of operation of said generating means and controlling which desired amplitude of electric current is received by said control means for controlling said generating means.

4. The apparatus of claim 1 wherein said first electrode is an active electrode and said second electrode is an indifferent electrode, and means for rendering said generating means inoperative when an open circuit exists in the electrical circuit including the tissue, said indifferent electrode and said generating means.

5. High frequency electrosurgical apparatus for operating on electrically conductive tissue comprising: a controllably operable generating means for generating a high frequency electric current; an active electrode adapted to be applied to tissue at the situs of the operation; an indifferent electrode for contact with tissue at the situs of the operation, said indifferent electrode comprising a sheet of porous material, adhesive means connected to said sheet of material for removably affixing said indifferent electrode to tissue, and a pair of spaced electrical terminals in contact with said porous material; circuit means for connecting said active electrode and said terminals of said indifferent electrode to said generating means; and control means for rendering said generating means inoperative when the conductivity in a circuit including the tissue, said indifferent electrode and said circuit means connecting said indifferent electrode to said generating means is less than a given value.