Electrosurgery system
An electrosurgery system includes an electrosurgical generator (10) coupled to or part of an electrosurgical instrument, the generator being operable to generate electrosurgical power in low frequency (typically at 1 MHz) and high frequency bands (typically at 2.45 GHz) either simultaneously or individually. The generator includes a load-responsive control circuit which, in one mode, causes power to be generated predominantly at 1 MHz when the load impedance is high and predominantly at 2.45 MHz when it is low. This allows automatic switching between cutting and coagulation operation. In one embodiment, the instrument includes a gas plasma generator operating such that an ionisable gas is energised in a gas supply passage by the 2.45 GHz component to form a plasma stream which acts as a conductor for delivering the 1 MHz component to a tissue treatment outlet of the passage.
Latest Gyrus Medical Limited Patents:
This application is a Continuation of U.S. patent application Ser. No. 10/374,097, filed Feb. 27, 2003, which is a Continuation of U.S. patent application Ser. No. 09/517,631, filed Mar. 3, 2000, which claims priority of U.S. Provisional Patent Application No. 60/141,261, filed Jun. 30, 1999, and UK Patent Application No. 9905211.0, filed Mar. 5, 1999. The disclosures of the prior applications are hereby incorporated by reference in their entirety.
This invention relates to a radio frequency electrosurgery system and a method of operating an electrosurgical instrument at UHF frequencies.
It is known to use a needle or narrow rod electrode for cutting tissue in monopolar electrosurgery at frequencies in the range of 300 kHz to 3 MHz. An electrosurgical signal in this frequency range is applied to the electrode, and the electrical current path is completed by conduction through tissue to an earthing plate secured to the patient's body elsewhere. The voltage applied to the electrode must be sufficiently high to cause arcing and consequent thermal rupture so that tissue adjacent the needle is ablated or vaporised.
At lower power levels, coagulation of the tissue can be achieved, i.e. without arcing, due to thermal dissipation of energy in the tissue adjacent the electrode. However, with a narrow electrode as commonly used for tissue cutting, desiccation of the tissue immediately adjacent the electrode and build-up of desiccated material on the electrode itself constitutes a high-impedance barrier to further coagulation. Spatula-shaped electrodes have been produced to overcome the difficulty in providing a dual-purpose electrode, i.e. one suitable for both cutting and coagulation. The designees intention is that the edge of the electrode is used for cutting, whereas the flat surface is used for coagulation. However, coagulation with such an electrode tends to be imprecise due to the size of the flat surface, with the result that a large thermal margin is produced.
It is an object of the invention to provide a means of achieving both tissue cutting and coagulation with a single electrode assembly.
According to this invention, there is provided an electrosurgery system comprising an electrosurgical generator, a feed structure and an electrode assembly, the electrode assembly having at least one active electrode and at least one adjacent return electrode each of which is coupled to the generator via the feed structure, wherein the generator and feed structure are capable of delivering radio frequency (r.f.) power to the active and return electrodes in lower and upper frequency rant the upper range containing frequencies at least three times the frequencies of the lower frequency range. The lower frequency range may extend from 100 kHz to 100 MHz, preferably 300 kHz to 40 MHz, and the upper frequency range may extend from 300 MHz to 10 GHz, preferably above 1 GHz, with operating frequencies in the upper and lower ranges having a frequency ratio of 5:1 or greater. Typically, the generator is arranged such that the r.f. power delivered in the upper frequency range is at a fixed frequency which is at least ten times the frequency of power delivered in the lower frequency range. Indeed, a fixed frequency of 2.45 (3 Hz in the upper frequency range is preferred.
The preferred system allows simultaneous delivery of lower and upper frequency range components to the electrodes to provide a combination of medium or low frequency tissue cutting, vaporisation or ablation together with coagulation of surrounding tissue to a degree dependent upon the amplitude of the component in the upper frequency range.
For tissue, cutting, vaporisation or ablation the system preferably operates in a monopolar mode with a separate earthing electrode applied to the outside of the patient's body, whilst coagulation occurs in a quasi-bipolar mode whereby the return current path in the upper frequency range runs from the tissue adjacent the operation site to the return electrode of the electrode assembly due to capacitive coupling. It will be understood that the system may allow selection of power delivery either in the lower frequency range or the upper frequency range depending upon the kind of treatment requited. This selection may be performed manually by the surgeon or automatically in the manner to be described below. In addition, power may be supplied in both frequency ranges simultaneously to obtain a blended cutting and coagulation effect, the two components being linearly added or otherwise combined in a single signal feed structure.
In a particularly preferred embodiment of the invention, the generator includes a control circuit responsive to electrical load and operable to cause the delivered power to have a predominant frequency component in the lower frequency range when the load impedance is in an upper impedance range, and to have a predominant frequency component in the upper frequency range when the load impedance is in a lower impedance range. In this way, it is possible to cut, ablate or vaporise living tissue (i.e. causing cell rupture) with the lower frequency range component but also to bring about efficient coagulation when a very low load impedance is detected, indicating the presence of electrolytic fluid such as blood from a blood vessel, requiring coagulation. The system reverts to predominantly low frequency operation once the impedance has risen above a predetermined threshold following coagulation.
When electrical load impedance is used as the control stimulus, a signal representative of load impedance being compared with a reference signal, the reference signal may have different levels depending on whether the generator is to be switched from a predominant low frequency component to a predominant high frequency component or vice versa. In other words, different load impedance thresholds may be selected when operating in the lower frequency range or the upper frequency range respectively.
A composite signal having components from both frequency ranges may be produced by combining (e.g. adding) the signals from two generator stages, one operating in the region of, say, 1 MHz and the other operating at 2.45 GHz. Both generator stages may be in a single supply unit coupled to an electrosurgical instrument which consists of a handpiece mounting the electrode assembly so that, for instance, the two frequency components are fed from the supply unit to the handpiece by common delivery means such as a low loss flexible coaxial cable. Alternatively, the generator stage producing the UHF frequency component may be located in the handpiece to reduce transmission losses and radiated interference, the signal combination being performed within the handpiece as well.
For dual-purpose operation, i.e. cutting and coagulation, an electrode assembly having a needle-like active electrode is preferred.
Typically, the electrode assembly is at the distal end of a rigid or resilient coaxial feed forming the above-mentioned feed structure. To reduce extraneous UHF radiation, an isolating choke element in the form of a conductive quarter-wave stub or sleeve may be mounted to the outer supply conductor of the coaxial feed in the region of the distal end. As stated above, the active electrode may take the form of a rod or pin projecting from the coaxial feed distal end. The return electrode may be a conductive sleeve, plate or pad connected to the outer supply conductor at the feed distal end and extending proximally over the outer conductor but spaced from the latter so that the active electrode rod and the return electrode sleeve, plate or pad together form an axially oriented dipole at the operating frequency of the generator in the upper frequency range. Alternatively, the return electrode simply takes the form of a distal end portion of the feed outer conductor located distally of the choke. The return electrode may be covered with an electrically insulative layer in order that when the active electrode is applied to tissue, the return electrode, being set back from the active electrode so as normally to be spaced from the tissue, acts as a capacitive element forming pant of a capacitive return path between the treated tissue and the return supply conductor of the feed.
In an alternative embodiment in accordance with the invention, the electrode assembly includes a gas supply passage and the active electrode is located within the passage where it acts as a gas-ionising electrode. In this case, the active electrode acts as a low- to high-impedance transformer at the operating frequency of the generator in the upper frequency range, producing an intense electric field in the space between the distal end portion of the active electrode and the return electrode. Accordingly, when there is an ionisable gas in the passage the major part of the power delivered to the electrode assembly in the upper frequency range is dissipated in the passage. In the lower frequency range no transforming effect occurs and the frequency component in the lower frequency range is, instead, delivered to the tissue to be treated by the ionised gas plasma which, in effect, acts as a monopolar gaseous electrode. Use of a UHF frequency component as a plasma generator and a lower frequency component for electrosurgery allows independent control of plasma generation and electrosurgical power delivery, thereby avoiding the disadvantage of known single r.f. source gas plasma electrosurgery devices. Typically, in such a prior device the ability of the some to deliver current through the plasma is severely hampered due to the requirement for high peak voltages when using low frequencies (i.e. typically, less than 1 MHz).
The invention will now be described by way of example and with reference to the drawings in which:—
The preferred embodiment of the present invention are applicable mainly to the performance of electrosurgery upon tissue in a gawk environment using a dual electrode instrument having active and return electrodes situated at the distal end of an instrument shaft. The active electrode is applied directly to the tissue. The return electrode does not contact the tissue being treed, but is normally adjacent the tissue surface where it is capacitively coupled to the tissue at UHF frequencies.
A system incorporating such an instrument is shown in
Instrument shaft 12B constitutes a feed structure for the electrode assembly 16 and takes the form of a rigid coaxial feed having an inner conductor and an outer supply conductor made with rigid material constructed as a resilient metal tube or as a plastics tube with a metallic coating. The distal end of the feed structure appears in
The return electrode is formed as a coaxial conductive sleeve 30 surrounding a distal end portion of the outer supply conductor 24 with an intervening annular space 31. An connection between the return electrode 30 and the outer supply conductor 24 is formed as an annular connection 30A at one end only, here the distal end, of the return electrode 30 such that the projecting prion of the active electrode 26 and the return electrode 30 together constitute an axially extending dipole with a feed point at the extreme distal end of the coaxial feed. This dipole 26, 30 is dimensioned to match the load represented by the tissue and air current path to the characteristic impedance of the feed at or near 2.45 GHz.
Located proximally of the electrode assembly formed by active electrode 26 and return electrode 30 is an isolating choke constituted by a second conductive sleeve 32 connected at one of its ends to the outer supply conductor 24 by an annular connection 32A. In this instance, the annular connection is at the proximal end of the sleeve. The sleeve itself has an electrical length which is a quarter-wavelength (λ/4) at 2.45 GHz or thereabouts, the sleeve thereby acting as an balun promoting at least an approximately balanced feed for the dipole 26, 30 at that frequency.
The projecting part of the active electrode 26 has a length in the region of 10 mm while the return electrode 30 is somewhat greater than 10 mm in length. The reason for this difference in length is that the relative dielectric constant of living tissue is higher than that of air, which tends to increase the electrical length of the active electrode for a given physical length. The electrode assembly 16 and choke 32 are configured to provide an electrical impedance match with the tissue being treated and, advantageously, a mismatch to the impedance of free space, so that power transmission from the electrode assembly is minimised when the active electrode is removed from tissue whilst an electrosurgical voltage is still being applied at 2.45 GHz.
Sleeve 32 has an important function insofar as it acts as an isolating trap isolating the outer supply conductor 24 of the feed structure from the return electrode 30, largely eliminating r.f. currents at 2.45 GHz on the outside of the outer supply conductor 24. This also has the effect of constraining the electric field which results from the application of a voltage at 2.45 GHz between the active electrode and the return electrode, as seen in
Referring back to
The ability to feed different voltage components at different frequencies from the supply unit to the handpiece in a single transmission line has advantages related to the main aspect of the present invention which is the provision of means for delivering r.f. power to the electrode assembly in lower and upper frequency ranges, the upper range containing frequencies at least five times the frequencies of the lower frequency range. Thus, the supply unit may include generator parts generating electrosurgical signals at, for instance, 1 MHz and 2.45 GHz respectively to suit different operation site conditions and surgical requirements. In the preferred embodiments of the invention, these different components are supplied simultaneously through cable 14 to the handpiece 12 and electrode assembly 16.
Details of the electrosurgical generator for delivering electrosurgical power in this way will now described with reference to FIGS. 4 to 9.
Referring to
At the output of the adder 54 a composite signal consisting principally of the two frequency components at 1 MHz and 2.45 GHz is delivered to the output socket 10S of the supply unit and thence via cable 14, which is typically in the region of three metres long, to the handheld instrument, represented in
Referring to
It will be understood that the filter/adder circuitry shown in
As will be seen from the graph of
Referring to
Thus, the signal at the output of buffer 90 is proportional to power, and is delivered to one input of an OR-gate formed by diodes 92, 94 which receives, at its other input, the voltage applied to input 80. Accordingly, the signal at the output 98 of the OR-gate is low only when both the delivered power at 1 MHz and the output voltage at 1 MHz are low, i.e. in accordance with the power and voltage characteristics shown in
The adder 54 is formed as a microstrip device, as shown in
The open circuit stubs 114, 116, 118 are transparent to the 1 MHz signal, whereas the series capacitor 111 and the short circuit stub 110 reactively attenuate the 1 MHz signal in order to isolate the UHF input port 104 at 1 MHz.
It will be appreciated that the λ/4 components described above may, instead, have an electrical length which is any odd-number multiple of λ/4. Here, λ is the wavelength of the applied UHF (2.45 GHz) signal in the microstrip medium.
The 2.45 GHz synthesiser includes a power control circuit as shown in
It will be appreciated that electrosurgical power may be delivered from the supply unit 10 shown in
As described above, detection of low tissue impedance in these circumstances can be achieved by comparison of voltage and current amplitudes at the output of the 1 MHz source, prior to the adder 54 shown in
It should be noted that detection of low power delivery at 1 MHz as described above with reference to
In an alternative embodiment, not shown in the drawings, the UHF (2.45 GHz) synthesiser 52 shown in
It will be appreciated that losses at UHF are much reduced with this embodiment, to the extent that the power output of the UHF synthesiser may be reduced. Drawbacks include the additional bulk and weight of the handpiece and the possible need for forced fluid cooling of the UHF synthesiser, depending on the required power output. Such cooling could take place by evacuating air firm the operation site into a passage at the distal end of the electron shaft through a filter element to the UHF synthesiser, performing the dual functions of cooling the synthesiser and removing smoke or vapour from the operation site to enhance visibility.
The ability to supply electrosurgical voltages at widely spaced frequencies also has application in a further alternative embodiment making use of a gas plasma electrode, as will now be described with reference to
It is well known to use an inert gas such as argon, ionised using an r.f. voltage and fed via a nozzle, typically having a diameter in excess of 1 mm, to produce a hot plasma “beam”. Directing this gas plasma onto the tissue being treated causes coagulation through transfer of thermal energy.
The behaviour of the argon plasma depends upon the incident energy. The higher the temperature of the argon, the greater its electrical conductivity. Paradoxically, the more energy initially imparted to the plasma, the less is the energy absorbed by the plasma due to its lower electrical impedance.
Supplying upper and lower frequency components simultaneously to a plasma-generating electrode assembly has the advantage that formation of the plasma can be performed independently of the conduction of energy along the plasma beam. As described above with reference to FIGS. 1 to 9, the upper and lower components typically have frequencies of 2.45 GHz and 1 MHz respectively.
Referring to
Plated on the lateral exterior surface of the ceramic nozzle body 200 is a conductive return electrode 212 adjacent to the outer supply conductor 24 of the feed structure 12B and spaced from the supply conductor 24 by a gap 213.
Essentially then, the plasma generator comprises a whisker antenna within a ceramic tube having a metallised shroud. The capacitance between the whisker electrode 210 and the return electrode 212 is typically in the region of 0.5 to 5 pF. Clearly, this is a relatively low impedance at 2.45 GHz but a very high impedance at 1 MHz. This, coupled with the fact that the λ/4 length of the electrode 210 causes the electrode 210 to act as an impedance transformer producing a high voltage at the tip of the electrode, means that the 2.45 GHz component is dissipated within the plasma chamber when an ionisable gas is introduced via inlet 204 (causing plasma generation in bore 208) whereas the low frequency component at 1 MHz is conducted along the plasma beam to target tissue and to earth via the return pad attached to the patient (see
The plasma generator is highly efficient at UHF frequencies, which means that the plasma may be generated with sufficient flow to absorb as much as 100 watts. The ionised gas is pumped from the chamber 202 through bore 208 which may have a bore as small as 0.1 mms. Since the majority of the power is dissipated within the chamber, little or no power at UHF is conducted to the nozzle outlet by the plasma. Instead, the UHF current component flows from the whisker electrode 210 via capacitive coupling to the return electrode 212, and thence via further capacitive coupling to the outer conductor 24 of the feed structure 12B.
Using the UHF source alone, the plasma beam acts as a powerful tissue coagulation tool, the depth and area of the coagulation effect being determined by the dispersion of the gas beyond the nozzle which depends, in turn upon the distance the nozzle is held from the tissue surface. This is a purely thermal effect.
As described above, when both lower and upper frequency components are supplied, the lower frequency component at medium frequencies such as 1 MHz (a range of 100 kHz to 5 MHz is applicable in this instance) results in power being conducted along the plasma beam to the target tissue and thence to earth, vaporising the tissue.
Since the 1 MHz component is not coupled in plasma generation, its voltage can be comparatively low, at typically 300 volts to 1000 volts rms. It follows that the ability of the low frequency source to support significant current delivery at low power superior to that achievable in known prior systems.
The ionising ability of the UHF source is such that gases other than argon may be used. Argon has tended to be used in the prior art because it has a low ionisation potential, it is an inert gas, and it is the most abundant of the noble inert gases and consequently the cheapest. However, when using the described electrode assembly, with the plasma beam acting as an active electrode conveying electrosurgical tissue vaporising power at 1 MHz, a significant amount of residual carbon can be produced. This is the result of vaporising the tissue in an oxygen-free environment.
Use of an oxidising gas plasma by supplying oxygen or an oxide of nitrogen, gases which are both readily available in an operating theatre, counters the formation of carbon. Such gases have a considerably higher ionisation potential than argon with the result that considerably higher temperatures are attained with sufficiently conductive plasma streams, to the extent that the gas delivery rate has to be correspondingly reduced. An oxidising gas can be mixed with the argon before plasma generation, and introduced directly via inlet 204. Alternatively, the oxidising gas may be mixed with the argon plasma using an electrode assembly having a second gas inlet, as shown in
The whisker electrode 210 is preferably tungsten or tantalum due to the high melting point of these metals. Where an oxidising gas is introduced into the plasma generating chamber, a platinum or platinum-coated electrode is more appropriate, in order to avoid electrode oxidisation. The electrode may also be constructed from a thoriated alloy such as a thorium-toungsten alloy to improve electron emission and to promote predictable ionisation.
Dual frequency operation of a gas plasma electrode assembly as described above avoids the difficulties created by generating the plasma and the tissue effects from the same electrical source. Consequently, the difficulty in generating a plasma from a voltage which varies due to large variations in load impedance is avoided, and the lower frequency r.f. source can be used to deliver current though the plasma without relatively high peak voltages when using low frequencies, which places high power demands upon the r.f. generator.
Narrow jet diameters, as disclosed above, as allowed by high excitation voltages and low impedance, result in higher current density upon tissue contact, giving the opportunity to perform rapid but fine tissue vaporisation.
Claims
1. An electrosurgery system comprising an electrosurgical generator, a feed structure and an electrode assembly, the electrode assembly having at least one active electrode and at least one adjacent return electrode, each of which is coupled to the generator via the feed structure, wherein the feed structure comprises an adder, the generator and feed structure are capable of delivering radio frequency (r.f.) power to the active and return electrodes in lower and upper frequency ranges, the upper range containing frequencies at least three times the frequencies of the lower frequency range, and the adder linearly adds the lower and upper frequency ranges such that the generator and feed structure deliver r.f. power to the electrodes in the lower and upper frequency ranges simultaneously.
2. A system according to claim 1, wherein the lower frequency range is 100 kHz to 100 MHz and the upper frequency range is 300 MHz to 10 GHz.
3. A system according to claim 2, wherein upper frequency range is above 1 GHz and the operating frequencies in the said upper and lower ranges have a frequency ratio of 5:1 or greater.
4. A system according to claim 2, wherein the generator is arranged such that the r.f. power delivered in the upper frequency range is at a fixed frequency which is at least ten times the frequency of r.f. power delivered in the lower frequency range.
5. A system according to claim 4, wherein the fixed frequency is fixed to the extent that it remains within 50 MHz of 2.45 GHz.
6. A system according to claim 1, comprising a supply unit, a handpiece, and a cable connecting the handpiece to the supply unit, wherein:
- the electrode assembly is mounted in the handpiece,
- the generator has first and second stages for generating power in the lower and upper frequency ranges respectively, both stages being contained in the supply unit, and
- the supply unit and the cable are configured such that power is supplied to the handpiece in both the lower and the upper frequency range via the cable.
7. A system according to claim 1, comprising a supply unit, a handpiece, and a cable connecting the handpiece supply unit, wherein
- the electrode assembly is mounted in the handpiece, and
- the generator has first and second stages for generating power in the lower and upper frequency ranges respectively, the first stage being contained in the supply unit and the second stage being contained in the combination of the handpiece and the electrode assembly.
8. A system according to claim 1, wherein the feed structure comprises:
- a rigid or resilient coaxial feed supporting the electrodes at a distal end, the coaxial feed having an inner supply conductor and an outer supply conductor, and
- an isolating choke element in the form of a conductive sleeve connected to the outer supply conductor in the region of the said distal end, and having an axial length which is an odd number multiple (1, 3, 5,... ) of a quarter wavelength at an operating frequency of the generator in the upper frequency band.
9. A system according to claim 1, wherein the return electrode comprises a conductive sleeve.
10. A system according to claim 9, wherein:
- the active electrode comprises a rod projecting from the conductive sleeve;
- the feed structure comprises a rigid or resilient coaxial feed; and
- the active electrode and the return electrode are connected to the inner and outer conductors respectively of the feed at its distal end, and extend respectively distally and proximally with respect to the said connection to form a dipole at an operating frequency of the generator in the upper frequency range.
11. A system according to claim 1, wherein the return electrode is covered with a electrically insulative layer.
12. A system according to claim 1, wherein the electrode assembly includes a gas supply passage and the active electrode is located in the passage to act as a gas ionising electrode.
13. A system according to claim 12, wherein the active electrode is capacitively coupled to the return electrode.
14. A system according to claim 1, wherein the electrode assembly includes a gas supply passage and the active electrode is located in the passage to act as a gas ionising electrode, and wherein the active electrode is an elongate conductor having an electrical length in the region of a quarter wavelength at the operating frequency of the generator in the upper frequency range.
15. A system according to claim 1, wherein:
- the adder comprises a low frequency input that inputs the r.f. power in the low frequency range to the adder, a high frequency input that inputs the r.f. power in the high frequency range to the adder, and an output that delivers the r.f. power from the adder to the electrodes in the lower and upper frequency ranges simultaneously;
- the adder isolates the input r.f. power in the low frequency range from the high frequency input; and
- the adder isolates the input r.f. power in the high frequency range from the low frequency input.
16. A dual frequency electrosurgical system configured to perform electrosurgical cutting or vaporisation at a first frequency within a lower frequency range and electrosurgical coagulation at a second frequency within an upper frequency UHF range, wherein the electrosurgical system comprises an adder that linearly adds the lower and upper frequency ranges to deliver r.f. power to electrodes in the lower and upper frequency ranges simultaneously.
17. A system according to claim 16, wherein the first frequency is within the range of from 100 kHz to 5 MHz and the second frequency is within the range of from 300 MHz to 10 GHz.
18. An electrosurgical system comprising an electrode assembly with at least a pair of electrodes for receiving radio-frequency electrosurgical power, and a gas supply passage containing at least one of the said electrodes, the arrangement of the electrodes and the passage being such that when the electrodes are energised with sufficient radio frequency power at an upper frequency in the range of from 300 MHz to 10 GHz, and when an ionisable gas is passed through the passage, a gas plasma is formed in the passage, the electrosurgical system comprises an adder that linearly adds the lower and upper frequency ranges to deliver r.f. power to electrodes in the lower and upper frequency ranges simultaneously.
19. A system according to claim 18, wherein the passage terminates in a distal nozzle downstream of the said at least one electrode.
20. A system according to claim 18, wherein the electrode assembly is part of a sterilised electrosurgical device.
21. A system according to claim 18, including a generator coupled to the electrodes and operable to generate electrosurgical power at a frequency in the range of from 300 MHz to 10 GHz.
Type: Application
Filed: May 16, 2007
Publication Date: Sep 27, 2007
Applicant: Gyrus Medical Limited (Cardiff)
Inventors: Colin Goble (Penarth), Francis Amoah (Cardiff), Nigel Goble (Cardiff)
Application Number: 11/798,738
International Classification: A61B 18/18 (20060101);