GB2154881A - Electrosurgical unit - Google Patents

Abstract

An electrosurgical unit for use in surgical diathermy and comprising a micro-computer (1) for controlling the output of the unit. The micro-computer is connected for: (a) address by one or more signals from: a user interface (3a-j; 4a; 4b; 5a-c) for selection of a desired output from the electrosurgical unit, and means (13) for sampling at one or more locations, the electrical state of the electrosurgical unit; and (b) delivery of one or more command signals to a power generator circuit (9, 10, 7m, 7b, 11) for producing the output power of the electrosurgical unit, and one or more devices (14a-c; 15a-h; 16a-c, 18) for conveying information as to the state of the electrosurgical unit to the user. <IMAGE>

Description

SPECIFICATION Electrosurgical unit The present invention relates to an electrosurgical unit for use in surgical diathermy.

Surgical diathermy is a process by which heat is employed to cut tissue and coagulate blood. This heat is developed by the passage of high frequency electric current which, in monopolar electrosurgery passes through the body of the patient from the site of cutting or coagulation. This high frequency current, which is typically of the order of 500 KHz to 1 1 MHz with a power delivery of several hundred Watts, is supplied by an electrosurgical unit. The surgical effect obtained, that is, cutting or coagulation, is determined by the waveform of the output current employed.

In monopolar electrosur ery, the electrosurgical unit is connected to both an "active" and a "plate" electrode. The active electrode has a very small surface area and is used for cutting and/or the coagulation of blood. The plate electrode which is generally strapped to the patient's thigh, has a much larger surface area and returns the active current to the electrosurgical unit.

In view of the high power levels employed in such electrosurgery, the patient may receive severe burns should the plate electrode not be in good electrical contact with the skin or should the electrical connection between this electrode and the electrosurgical unit be poor or broken.

Thus, it is extremely important that the circuit formed by these two electrodes, and in particular, that the plate electrode be constantly and reliably monitored and that the electrosurgical unit be provided with suitable safety cut-outs responsive to this monitoring.

Circuits which monitor the connection between the plate electrode and the electrosurgical unit are known and widely used, as are those which monitor the contact between the patient and the plate electrode. To this end, such circuits generally monitor the current flow and/or the voltage on the plate electrode.

In addition, the electrosurgical unit should in itself be as fail safe as possible, providing automatic cut-outs should any electrical /electronic defect arise. To this end, the unit must be self monitoring.

Up till now, those control and monitoring functions available in electrosurgical units have been provided by electrical/electronic circuits using valves, relays, transistors and solid state integrated circuits in conjunction with discrete components. The resulting units are complex and expensive to produce and are not readily adapted to the increasing demand for safety and flexibility.

In addition, the electrical output of the electrosurgical units presently available is limited both in form and level. The operating voltage waveforms which are employed today have been selected on the basis of crude and subjective observation of this limited range of waveform options. However, it is believed that the optimum level and waveform composition may well vary not only from operation to operation but also during an individual cutting or coagulation procedure. Thus, there is the desire for a unit capable of producing a wide variety of output waveforms for investigation and eventual adoption of improved surgical diathermy techniques.

An object of the present invention is to provide an electrosurgical unit which is both economical to produce and will accommodate more flexible safety monitoring and control functions and the delivery of a variety of outputs.

Accordingly, the present invention provides an electrosurgical unit for use in surgical diathermy, the unit comprising a micro-computer for controlling the output of the unit which micro-computer is connected for: (a) address by one or more signals from: a user interface for selection of a desired output from the electrosurgical unit, and means for sampling at one or more locations, the electrical state of the electrosurgical unit, and (b) delivery of one or more command signals to: a power generator circuit for producing the output power of the elctrosurgical unit, and one or more devices for conveying information as to the state of the electrosurgical unit to the user.

In a preferred embodiment, the electrosurgical unit is adapted to produce both monopolar and bipolar outputs for selection by the user.

In an embodiment in which the electrosurgical unit has a monopolar output, a safety circuit is provided for monitoring a plate electrode circuit, the micro-computer being connected to and addressable by signals from this circuit.

The safety circuit preferably monitors the connection between a plate electrode and the electrosurgical unit, the voltage on the plate electrode with respect to earth and the electrical contact between this electrode and the patient's body.

The waveform of the electrosurgical unit output is preferably generated by the microcomputer.

The micro-computer may be connectable with an external computer via, for example, a telephone line. This permits the external computer to acquire operational data stored in the micro-computer and also to reprogramme this micro-computer. Operational data obtained in this way from a large number of electrosurgical units may thus be collated and analysed centrally to obtain data regarding the optimum output for the electrosurgical unit under different conditions. This data may then be used in the reprogramming and hence updat ing of the operation of these same electrosurgical units.

In a preferred embodiment of the invention, the micro-computer is programmable directly by the user, permitting tailoring of the outputs available from the unit to the user and/or to the surgical procedure to be employed. This, reprogramming of the micro-computer is preferably achieved by replacement of a "plug in" pre-programmed memory device.

In a further embodiment, the micro-computer is programmed so that the electrosurgical unit will perform a self-diagnostic circuit test routine at "switch on" and/or when instructed to do so by activation of a manually operable switch. This facility provides considerable advantages as regards overall unit safety and fault location.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 shows a block diagram illustrating the operation of an embodiment of an electrosurgical unit according to the present invention; Fig. 2 is a block diagram illustrating a preferred embodiment of the present invention; Fig. 3 is a block digram illustrating an embodiment of a monopolar power controller and amplifier circuit, and Fig. 4 is a block diagram illustrating an embodiment of a bipolar power amplifier circuit.

In Figure 1, the electrosurgical unit comprises a micro-computer 1 which is addressable by instruction signals A from a user interface, signals B generated by safety monitoring circuitry and signals C originating from other parts of the electrosurgical unit, which indicate the state of those parts. The microcomputer processes the signals received and produces command signals D to control the type, form and level of the output power of the electrosurgical unit and to switch this output on and off, and signals E to control visual displays and audible devices which convey information about the state of the electrosurgical unit to the user.

Figure 2 shows an electrosurgical unit which is adapted to supply both a monopolar and a bipolar output waveform at a respective output. Unlike the monopolar modes of "cutting" and "coagulation", bipolar electrosurgery does not employ a large area plate electrode. In this case, the diathermy current is formed between two prongs of a pair of forceps. This is used for the coagulation of blood vessels and has particular application in delicate procedures which need localized and precisely controlled coagulation such as neurosurgery, plastic surgery and laparoscopic sterilization. Bipolar electrosurgery requires only low power outputs in the region of 50 Watts as compared with the 400 Watts generally employed in monopolar electrosurgery and therefore, unlike monopolar electrosurgery, does not in itself represent any great potential hazard to the patient.

In this embodiment, the micro-computer 1 comprises a pulse pattern generator 2 in addition to those devices such as, a micro-processor, programme and data memories, address decoders, a clock, bus drivers, a watch dog timer and other peripheral devices, which commonly constitute a micro-computer. The programme memory contains the programme instructions and data for the overall operation of the micro-processor, whereas the data memory provides for the temporary storage of data relating to the status of various parts of the electrosurgical unit. In this embodiment, the microcomputer is constituted by the NSC 800 family of micro-chips.

The pulse pattern generator 2 is a timer whose output is determined by the microprocessor in accordance with preset waveforms for monopolar and bipolar operation, stored in the programme memory. The output of this generator 2 determines the waveform obtained at the respective outputs of the unit, as will be described in more detail below. In this embodiment, the generator 2 is constituted by counter-timer chips.

The micro-computer 1 is programmed to receive 1-bit binary input signals from ten, two-position switches 3a to 3j for selection of operational modes via suitable interface devices, such as, for example, Schmitt Triggers, potential dividers and low pass filters. Of these, three finger switches are provided for selection of a respective one of three principle modes of operation, namely, "cutting", ''coagulation'' and "bipolar". Three electrical contact foot switches respectively duplicate the action of these finger switches, and a further pneumatically operated foot switch provides an additional means for selection of bipolar operation.

Three further two-position switches are provided on the electrosurgical unit. An interlock switch 3j permits the interlocking of the three bipolar selection switches 3c, 3d and 3g so that an operator may employ any or all of these switches during a single procedure.

Switch 3h allows selection of monopolar operation without specifying either "cut" or "coagulation" mode, and switch 3i permits a change-over from monopolar to bipolar operation or vice versa.

The micro-computer 1 also receives 1-bit binary signals from two other switches 4a and 4b provided on the electrosurgical unit for selection of certain secondary modes of operation. Switch 4a is a two-position switch which provides for selection of either of two voltage levels, high and low, for bipolar operation.

Switch 4b is provided on the unit and has four positions for the selection of any one of four preprogrammed waveforms contained in the programme memory. Again, these binary signals are supplied to the micro-computer 1 via suitable interface devices.

The micro-computer 1 is also addressable by an 8-bit binary coded signal from three digital power level control switcbes 5a to 5c, which are respectively provided for preselection by the user of the power level of each of the three principle modes of operation.

As mentioned previously, the output waveform of the electrosurgical unit is controlled by means of the pulse pattern generator 2.

On command from the micro-processor, this generator supplies two 1-bit signals to two lines 19, one of which is connected to two power amplifiers 7m and 7b and the other of which is connected to power amplifier 7m alone, for controlling the pulse pattern of the output current waveform.

Monopolar or bipolar output selection is achieved by means of a signal sent by the micro-processor on one of two inhibit lines 8m and 8b connected to a "monopolar" power controller 10 and the "bipolar" amplifier 7b, respectively. This signal inhibits supply of power to that output not selected by the user.

To generate a monopolar output, the microcomputer 1 supplies an 8-bit signal via a digital to analogue converter 9 to set the output voltage of the high power controller 10 which supplies the monopolar amplifier 7m.

This controller 10 provides a continuously variable power supply at a set voltage dictated by the voltage level signal supplied by the micro-computer. In the present embodiment, this voltage may take any value between 0 and 1 50 V.

The controller 10 is constituted by a switch mode regulator such regulators are well known and in this embodiment, as illustrated in Fig. 3, comprises a high voltage (200V) MOSFET switch transistor FET1 which charges a capacitor C1 through aninductor L1. A diode D2 maintains current flow through the inductor L1 during periods when transistor FET1 is not conducting. A voltage feed back circuit consisting of a power control amplifier 22 and associated components including a switch mode controller 25, ensures that the output voltage of the controller 10 follows the input of the power control amplifier 22. This input is derived from the microprocessor via the analogue to digital converter 9. The entire switch mode regulator is fed from a conventional DC power supply 21.

The voltage output of the controller 10 is fed directly to the monopolar power amplifier 7m. As shown in Fig. 3, this circuit comprises two MOSFET high power switches FET2 and FET3 arranged so as to work in push-pull mode and connected to one end of each of two parallel primary windings of an output transformer TM, the other ends being connected to the output of the power controller 10. The pulse pattern derived from the microcomputer is interfaced with the gates of the MOSFET switches FET2, FET3 through suitable high gain buffer circuits forming a pulse generator circuit 24 of known type, to ensure fast switching with a rise time of less than 100 nanoseconds.In the Cut Mode this generator circuit provides pulses of constant width and interval in response to a signal from the pulse pattern generator 2, whereas in Blend and Coagulation Modes, this circuit provides a waveform which has a pulse group pattern generated by the generator 2. This combination of voltage and pulse pattern control permits the generation of any desired pulse pattern at any voltage level up to about 3kV peak to peak on the secondary winding of the transformer TM.

In order to protect the power generator circuit 24 against overloads and excessive current, the voltage across each transistor FET2 and FET3 is measured during the conduction period. This voltage is transferred via diodes D5 and D8 to a current limit trigger circuit 23. If the voltage at the input to the circuit 23 exceeds a predetermined value, a signal is fed to the pulse generator so as to cause the pulse interval to increase to several hundred times its normal value. This ensures that excessive currents cannot be passed through transistors FET2 and FET3.

The bipolar amplifier 7b is connected to a fixed voltage rail, and voltage level selection between "high" and "low" is achieved by means of a 1-bit signal supplied by the microprocessor via line 11 connected to the bipolar amplifier 7b. Fine control of the output power level of the bipolar amplifier 7b is achieved by means of pulse group modulation as dictated by the micro-computer via the output of the pulse pattern generator 2, in response to the setting of the bipolar power level control switch 5c.

As illustrated in Fig. 4, the bipolar power amplifier 7b comprises two medium power MOSFET switches FET4 and FETS working in push-pull mode and connected to one end of each of two parallel primary windings of an output transformer TB. The pulse pattern derived from the micro-computer is interfaced with the gates of the MOSFET switches FET4, FETS by means of suitable high gain buffer circuits forming a pulse group generator 20 to ensure fast switching with a rise time of less than 100 nanoseconds. The "high"/"low" voltage level is applied to the other ends of the primary windings of the transformer TB.

This combination of pulse pattern control and "high" /"Iow" voltage level permits the generation of any desired pulse pattern at either 400 V peak to peak ("High" power) or 200 V peak to peak ("Low" power) at the secondary winding of the transformer TD; the variation of pulse pattern controlling the total power deliv ered.

The output of the amplifiers 7m and 7b is supplied to the corresponding output of the unit via the respective transformer TM, TB and isolating capacitors Cm, Cb.

A safety circuit 12 is provided which monitors the plate electrode when the electrosurgical unit is employed in monopolar mode. In the event of a failure in the connection between the plate and electrosurgical unit, a 1 - bit binary signal is sent to the micro-computer 1 which in turn sends out signals to inhibit an output from the monopolar amplifier 7m and operates alarm signals. During surgical operation, the safety circuit monitors the votlage on the plate electrode relative to earth, compares this with a voltage reference level and if its value exceeds a "safe" margin, sends a 1-bit signal to the micro-computer which operates to switch off the amplifier 7m and/or switch on alarm signals. The safety circuit also monitors the patient's isolation by measuring the impedance between the plate circuit and earth.Again, if the impedance detected indicates the possibility of excessive conduction through the patient to earth, a 1-bit signal is sent to the micro-computer to inhibit power output and switch on alarm signals.

Operational conditions of the electrosurgical unit itself are also monitored. A 1-bit signal indicative of excessive output voltage provided at the output of the power controller 10 is fed to the microcomputer 1 via a power detector line 13 and the micro-processor operates to switch off the power output as appropriate and activate the alarm signals.

The programming of the computer ensures that an "unsafe" or unavailable" combination of selected parameters is not relayed to the remainder of the unit and that an alarm condition is indicated as appropriate.

In the present embodiment, the amplifier circuits 7m and 7b are inherently protected against over-current and this obviates the need for a thermostat to monitor the temperature attained by these amplifiers.

The electrosurgical unit is provided with various audio and visual displays which are connected to respective outputs of the microcomputer for relaying information to the user as to the state of the unit and providing alarm signals. In the unit shown in Figure 2, the micro-computer 1 supplies a 1-bit output signal via respective current buffers to switch on a a respective one of three visual display devices 1 4a to 1 4c to indicate which of the three principle modes is operating.

Nine light emitting diodes 1 5a to 1 5h indicate which of the available secondary modes of operation has been selected and other unit status information, in response to a respective 1-bit signal from the microcomputer.

The power output setting selected by means of the power level switches 5a to 5c, is read by the micro-computer 1 and displayed by a respective one of three bar display devices 1 6a to 1 6c. Each bar display is operated by an 8-bit signal from the micro-computer 1 via a respective digital to analogue converter 1 7a to 17c.

The micro-computer is also programmed to communicate to the user via the visual display devices those operating parameters available prior to selection. Accordingly, at each stage of the units setting up procedure, the appropriate one(s) of a respective set of visual displays 14a to c, 15ato 15hand 16a to 16c are caused to flash so as to indicate those selection options available and hence guide the user to appropriate combination.

In a fault or alarm condition, the microcomputer sends a 1-bit signal simultaneously to an audio and visual indicator device 18 via a current buffer and via both inhibit lines 8m, 8b to switch off supply to both the monopolar and bipolar output.

In a further embodiment, when a fault or alarm condition occurs, the micro-computer 1 also sends out an 8-bit signal to the visual alarm code display device to indicate the type of fault/alarm condition detected.

In a still further embodiment of the present invention, the 8-bit binary signal indicative of the type of alarm or fault condition which has arisen is supplied by the microcomputer 1 to an integrated circuit for synthesizing speech to provide the appropriate information audibly to the user.

As an alternative to the bar display devices 1 6a-c, the unit may comprise a seven segment digital display for display of the power level selected.

In another embodiment, the micro-computer is programmed so that the unit performs a self diagnostic test routine at switch-on and/or when instructed to do so by the activation of a manual switch. In this routine, for example, all the visual and audible indicators (14a-c; 1 5a-h; 1 6a-c and 18) are activated in a prespecified sequence and failure of any one of the components or sub-systems of the unit which may convey information to the user, may be recognised before the electrosurgical unit is used.

In yet another embodiment, the voltage between the active and plate electrodes is monitored periodically by the micro-computer together with the output current and the actual power delivered by the unit is calculated and compared with the output power selected by the user. Should there be a discrepancy between these values which exceeds a predetermined limit, the micro-computer then actuates alarm signals and/or switches off the power output.

In a further embodiment, the micro-computer derives the "crest factor" which is expressed by; Vpeak/VRMs from the voltage and current appearing on the active electrode and controls these to ensure a high crest factor and hence optimum coagulation rate.

In another embodiment, the micro-processor monitors the resistance at the active electrode during a cutting or coagulation procedure and controls the output current to ensure that this is at an optimum value throughout.

Since both the form and level of the output voltage of the electrosurgical unit can be directly controlled by the micro-computer, in all practical terms, an infinite number of such combinations is obtainable. This flexibility means that the unit is particularly suited for use as a research tool in the refining of surgical diathermy techniques.

Further, the unit of the present invention may be used in conjunction with additional devices for sensing the physiological condition of the patient and/or the tissue at the site of diathermy, the output of these devices being fed directly via an input, to the units microcomputer where it is collated and stored with the corresponding operational data for subsequent analysis. The micro-computer may also monitor this incoming physiological data for indications of undesirable physiological effects so that, where necessary, suitable signals can be sent out by the micro-processor to switch off the power output and/or active alarm signals.

As already explained, the overall operation of the micro-computer and hence the output of the unit is determined by the programme in the programme memory which may consist of, for example, a ROM, PROM, EPROM or similar device. Thus, simply by replacing the relevant integrated circuit(s), the operation of the electrosurgical unit can be customised.

Further, in a preferred embodiment, the unit is adapted so that the user can alter the operating programme himself by replacement of a pre-programmed memory device. This permits each user to adapt the output of an electrosurgical unit to provide a particular selection of output waveforms and power levels according to his preference and/or the surgical procedure to be performed.

In a still further embodiment, the microcomputer is connectable by means of a bus to an external computer for data acquisition and reprogramming of the electrosurgical unit by this computer.

Claims (14)

1. An electrosurgical unit for use in surgical diathermy, the unit comprising a micro-computer for controlling the output of the unit, which microcomputer is connected for: (a) address by one or more signals from: a user interface for selection of a desired output from the electrosurgical unit, and means for sampling at one or more locations, the electrical state of the electrosurgical unit; and (b) delivery of one or more command signals to: a power generator circuit for producing the output power of the electrosurgical unit, and one or more devices for conveying information as to the state of the electrosurgical unit to the user.

2. A unit as claimed in claim 1, wherein the waveform pattern of the output of the unit is generated by the micro-computer.

3. A unit as claimed in claim 2, wherein the waveform pattern is generated by means of counter timer chips.

4. A unit as claimed in any of claims 1 to 3, having a monopolar output, wherein said power generator circuit comprises a power controller, the output voltage of which is determined by the micro-computer, and a power amplifier circuit for supply of a selected output to said monopolar output and to which the output voltage of the power controller and a waveform pattern micro-computer is supplied.

5. A unit as claimed in any preceeding claim, having a monopolar output, wherein a safety circuit is provided for monitoring a plate electrode circuit connected to the monopolar output and has an output connected to the micro-computer.

6. A unit as claimed in any preceding claim, having a bipolar output, wherein said power generator circuit comprises a power amplifier circuit for supply of power to said bipolar output and to which a voltage and a waveform pattern determined by the microcomputer, are supplied at respective inputs.

7. A unit as claimed in any preceding claim, having a bipolar output, wherein control of the power supplied to this bipolar output is achieved by pulse group modulation.

8. A unit as claimed in any preceding claim, adapted to supply power to a selected one of a monopolar and a bipolar output, which monopolar and bipolar output power is generated in a respective one of two mutually isolated circuits.

9. A unit as claimed in claim 8, wherein means are provided to inhibit power supply to the monopolar output during bipolar power delivery and to the bipolar output during monopolar power delivery.

10. A unit according to claim 9, wherein should a signal or signals received by the micro-computer indicate a fault or alarm condition, the inhibit means are activated by the micro-computer to inhibit power delivery to at least said monopolar output.

11. A unit as claimed in any preceding claim, wherein the micro-computer is re-programmable.

12. A unit as claimed in any of claims 1 to 10, wherein tbe micro-computer has a programme memory in the form of a "plug in" pre-programmed device which is replaceable by the user.

13. A unit as claimed in any preceding claim, wherein the micro-computer is programmed to perform a self-diagnostic test routine.

14. An electrosurgical unit for use in surgical diathermy substantially as herein described with reference to Figure 1 with or without reference to any of Figures 2 to 4 of the accompanying drawings.