Electrosurgical mode conversion system Number:7,175,621 from the United States Patent and Trademark Office (PTO) owispatent

Title: Electrosurgical mode conversion system

Abstract: A surgical system that applies electrical energy to obtain predetermined surgical effects while improving the control of the application of the energy that is supplied by electrosurgical generators. In one embodiment, a surgical assembly interfaces with and receives power from an electrosurgical generator for executing a first electrosurgical procedure. This surgical assembly may employ a shunt circuit between its power and return lines for providing in effect a voltage limitation and/or to allow a constant power electrosurgical generator to execute an at least substantially constant voltage electrosurgical technique. The electrosurgical assembly may also include a return coupler for directing energy from the patient back to the electrosurgical generator, which in turn may include a dielectric material which interfaces with the patient and which at least initially conveys the return energy via one or more electric fields versus conduction.

Patent Number: 7,175,621 Issued on 02/13/2007 to Heim,   et al.

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Inventors:	Heim; Warren P. (Boulder, CO), Brassell; James L. (Boulder, CO), Olichney; Michael D. (Lyons, CO)
Assignee:	Surginetics, LLC (Boulder, CO)
Appl. No.:	10/723,320
Filed:	November 25, 2003

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Related U.S. Patent Documents

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	Application Number	Filing Date	Patent Number	Issue Date
	09619919	Jul., 2000	6692489
	60144946	Jul., 1999

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Current U.S. Class:	606/48 ; 606/34
Current International Class:	A61B 18/18 (20060101)
Field of Search:	606/32-34,41,48-50

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References Cited [Referenced By]

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U.S. Patent Documents

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Foreign Patent Documents

	98477436		Oct., 1998		WO

Other References

Serway, Raymond; Physics for Scientists and Engineers, pp. 746-755. cited by other . U.S. Appl. No. 09/619,919, filed Jul. 20, 2000, Heim et al. cited by other.

Primary Examiner: Peffley; Michael
Attorney, Agent or Firm: Hansen Huang Tech Law Group LLP

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Parent Case Text

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RELATED APPLICATIONS

This patent application claims priority under 35 U.S.C. .sctn.119(e) to U.S. patent application Ser. No. 60/144,946, that was filed on Jul. 21, 1999, that is entitled "SURGICAL MODE CONVERSION SYSTEM," the entire disclosure of which is incorporated by reference in its entirety herein, and further is a divisional of, and claims priority under 35 U.S.C. .sctn.120 to, U.S. patent application Ser. No. 09/619,919, that was filed on Jul. 20, 2000 now U.S. Pat. No. 6,692,489, that is entitled "ELECTROSURGICAL MODE CONVERSION SYSTEM," and the entire disclosure of which is also incorporated by reference in its entirety herein.

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Claims

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What is claimed is:

1. An electrosurgical assembly which interfaces with a generator for executing a first electrosurgical procedure and which comprises: an output assembly which is at least operatively interconnectable with said generator; an active electrosurgical element which is operatively interconnected with said output assembly and which interacts with a first portion of a patient during said first electrosurgical procedure; a return path element which interacts with a second portion of said patient during said first electrosurgical procedure and which is mechanically interconnected with said active electrosurgical element to define a bipolar configuration, wherein said first and second portions are different, and wherein said return path element comprises a first dielectric component which interfaces with said patient; and a return assembly which is operatively interconnected with said return path element and further which is at least operatively interconnectable with said generator, wherein said return path element further comprises a first return conductor which interfaces with said first dielectric component in such a manner that energy is returned to said generator first through said first dielectric component and then to said first return conductor, wherein said first dielectric component is defined by a first tube, wherein said first return conductor is defined by a second tube, and wherein said first and second tubes are disposed in end-to-end relation.

2. An electrosurgical assembly, as claimed in claim 1, wherein: said generator comprises an outlet connector and a return connector, said output assembly comprises an output plug which is detachably interconnectable with said output connector and an output line which is disposed between said output plug and said active electrosurgical element, and said return assembly comprises a return plug which is detachably interconnectable with said return connector and a return line which is disposed between said return plug and said return path element.

3. An electrosurgical assembly, as claimed in claim 1, wherein: said active electrosurgical element comprises at least one active electrode, wherein each said electrode has at least one patient interface surface, and wherein each said patient interface surface is selected from the group consisting of a curved surface and a flat surface.

4. An electrosurgical assembly, as claimed in claim 1, wherein: said active electrosurgical element is selected from the group consisting of one or more blades, hooks, balls, spatulas, loops, pins, wireforms, tubes, and tubes with fluid passageways.

5. An electrosurgical assembly, as claimed in claim 1, wherein: said first dielectric component comprises a first material having a dielectric product greater than about 2,000, wherein said dielectric product is a dielectric constant of said first material, multiplied by a dielectric strength of said first material.

6. An electrosurgical assembly, as claimed in claim 5, wherein: said first material is selected from the group consisting of alumina, diamond, boron nitride, polyimide, polyester, parylene, barium titanate, titanium dioxide, Teflon, and polycarbonate.

7. An electrosurgical assembly, as claimed in claim 1, wherein: said first dielectric component comprises a first material having a dielectric product greater than about 4,000, wherein said dielectric product is a dielectric constant of said first material, multiplied by a dielectric strength of said first material.

8. An electrosurgical assembly, as claimed in claim 1, wherein: said first dielectric component comprises a first material having a dielectric product greater than about 8,000, wherein said dielectric product is a dielectric constant of said first material, multiplied by a dielectric strength of said first material.

9. An electrosurgical assembly, as claimed in claim 1, wherein: said first dielectric component comprises a first material having a dielectric constant greater than about 10.

10. An electrosurgical assembly, as claimed in claim 9, wherein: said first material is selected from the group consisting of ceramics, alumina, titanium dioxide, barium nitrate, and any combination thereof.

11. An electrosurgical assembly, as claimed in claim 1, wherein: said first dielectric component comprises a first material having a dielectric constant greater than about 20.

12. An electrosurgical assembly, as claimed in claim 1, wherein: said first dielectric component comprises a first material having a dielectric constant greater than about 50.

13. An electrosurgical assembly, as claimed in claim 1, wherein: said first dielectric component comprises a mixture of first and second materials.

14. An electrosurgical assembly, as claimed in claim 1, wherein: an impedance of said return path element is less than about 800 ohms.

15. An electrosurgical assembly, as claimed in claim 1, wherein: an impedance of said return path element is less than about 500 ohms.

16. An electrosurgical assembly, as claimed in claim 1, wherein: an impedance of said return path element is less than about 300 ohms.

17. An electrosurgical assembly, as claimed in claim 1, wherein: an impedance of said return path element is less than about 200 ohms.

18. An electrosurgical assembly, as claimed in claim 1, wherein: said return path element further comprises a first return conductor which interfaces with said first dielectric component in such a manner that energy is returned to said generator first through said first dielectric component and then to said first return conductor, and wherein a wall thickness of said first dielectric component is less than about 0.025 inches.

19. An electrosurgical assembly, as claimed in claim 1, wherein: said return path element further comprises a first return conductor which interfaces with said first dielectric component in such a manner that energy is returned to said generator first through said first dielectric component and then to said first return conductor, and wherein a wall thickness of said first dielectric component is no more than about 0.010 inches.

20. An electrosurgical assembly, as claimed in claim 1, wherein: said return path element further comprises a first return conductor which interfaces with said first dielectric component in such a manner that energy is returned to said generator first through said first dielectric component and then to said first return conductor, and wherein a wall thickness of said first dielectric component is no more than about 0.005 inches.

21. An electrosurgical assembly, as claimed in claim 1, wherein: said first dielectric component withstands voltages exceeding 1,000 volts peak to peak.

22. An electrosurgical assembly, as claimed in claim 1, wherein: said first dielectric component withstands voltages exceeding 2,000 volts peak to peak.

23. An electrosurgical assembly, as claimed in claim 1, wherein: said first dielectric component withstands voltages exceeding 5,000 volts peak to peak.

24. An electrosurgical assembly, as claimed in claim 1, wherein: said return path element comprises a capacitor.

25. An electrosurgical assembly, as claimed in claim 1, further comprising: an inductor disposed in series with said return path element.

26. An electrosurgical assembly, as claimed in claim 1, further comprising: means for offsetting an impedance of said return path element.

27. An electrosurgical assembly, as claimed in claim 1, further comprising: means for allowing energy transfer from said patient to said electrosurgical generator by electric fields, wherein said means for allowing comprises said return path element.

28. An electrosurgical assembly, as claimed in claim 1, wherein: said second portion of said patient is selected from the group consisting of body tissue and at least one conductive liquid.

29. An electrosurgical assembly, as claimed in claim 1, wherein: said electrosurgical assembly comprises a probe, wherein said probe comprises first and second longitudinal segments, wherein said active electrosurgical element is disposed within said first longitudinal segment and said return path element is disposed within said second longitudinal segment, wherein said active electrosurgical element is electrically isolated from said return path element, and wherein said first dielectric component defines a perimeter of said probe along said second longitudinal segment.

30. An electrosurgical assembly, as claimed in claim 1, wherein: a configuration of said electrosurgical assembly allows said first electrosurgical procedure to be selected from the group consisting of cutting, coagulation, desiccation, fulguration, ablation, and tissue shrinkage.

31. An electrosurgical assembly, as claimed in claim 1, further comprising: a shunt circuit between said output and return assemblies.

32. An electrosurgical assembly, as claimed in claim 1, wherein: said first dielectric component comprises at least about 50 wt % barium titanate.

33. An electrosurgical assembly, as claimed in claim 1, wherein: said first tube has a wall thickness of no more than about 0.25 inches and a surface area which is within a range of about 0.007 in.sup.2 to about 1 in.sup.2.

34. An electrosurgical assembly, as claimed in claim 1, wherein: said first tube has a minimum wall thickness that is at least about 0.0005 inch.

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Description

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FIELD OF THE INVENTION

The present invention relates to surgical methods and assemblies employing the application of electrical energy to tissue to achieve a predetermined surgical effect, and, more particularly, to achieve such effect with reduced likelihood of inadvertent tissue damage and with better control of energy application to tissues.

BACKGROUND OF THE INVENTION

The potential uses and recognized advantages of employing electrical energy for surgical purposes are ever-increasing. In particular, for example, electrosurgery techniques are now being widely employed to provide significant localized control advantages in both open and laparoscopic, including arthroscopic, applications relative to prior traditional surgical approaches.

Electrosurgical techniques use an instrument with working surfaces that contact tissue, such as a tissue ablation or cutting device, a source of radio frequency (RF) electrical energy, and a return path device, commonly in the form of a return electrode pad. The working surfaces that contact the patient in the region where the surgical effect is to occur are commonly called the active electrode or electrodes. The return path device contacts the patient either directly on the tissue or indirectly through, for example, a conductive liquid such as blood or normal saline. The return path device provides a return electrical path from the patient's tissues. Both the instrument and the return path device are connected using electrically conductive wires to the source of the radio frequency electrical energy which serves as both the source and the sink for the electrical energy to produce a complete electrical circuit. When the instrument and the return path device are separate devices the technique is termed monopolar. In some cases the instrument contains working surfaces that both supply the electrical energy and provide the return path. In these cases the technique is termed bipolar.

FIG. 3 illustrates a schematic of an electrosurgical system generally of the above-described type which includes an electrosurgical generator 1 with the generator electronics 2 (including the radio frequency (RF) electrical energy source, controls, and power supply being included in the electronics), as well as an electrosurgical accessory or instrument 100 and a return system 110 which is mechanically separated from the accessory 100. As such, the configuration of FIG. 3 is of the monopolar type. An output connector plug 3 and a return connector plug 4 of the accessory 100 connect to the output connector 5 and the return connector 6 that are part of the generator 1. The output connector plug 3 and a return connector plug 4 typically are molded plastic parts with metallic prongs (not shown) or receptacles (not shown). One or more of the metallic prongs in the output connector plug 3 connect to the output line 7 of the accessory 100, which typically consists of one or more conductive metal wires covered with an insulating coating. The output line 7 passes from the distal end of the output connector plug 3 and has a length suited to have the handle 8 of the accessory 100 a comfortable distance from the generator 1. The output line 7 passes into the proximal end of the accessory handle 8. The output line 7 is routed through the accessory handle 8 and may connect to a variety of internal conductors (not shown) that eventually make electrical contact with the active element 9 of the accessory 100, such as a blade. The accessory active element 9 may be in either direct or indirect contact with the patient 10. Electrosurgical energy passes from the active element 9 to the patient 10. The electrical return path is provided by the return system 110, which again is separate from the accessory 100 in the illustrated monopolar configuration of FIG. 3. The return system 110 consists of the return line 11 which typically connects with one or more metallic receptacles (not shown) that are molded into the housing of the return connector plug 4 and that, in turn, connect to the return connector 6 that is part of the generator 1. The return line 11 typically consists of one or more conductive metal wires covered with an insulated coating. The return line 11 exits the distal end of the return connector plug 4 and connects to the return path device 12 of the return system 110, which is usually a return electrode pad when monopolar procedures are used and as contemplated by the configuration of FIG. 3.

A variation of the accessory 100 from FIG. 3 is presented in FIG. 4 in the form of a schematic of an electrosurgical accessory 100'. In this case a supplemental return line 13 of the return system 110' extends from the return connector plug 4 to the output connector plug 3 where it interfaces with the return line 11. The supplemental return line 13 will be long enough to span the distance between the output connector 5 and the return connector 6 and allow the user enough slack to conveniently connect the output connector plug 3 and the return connector plug 4 to the generator 1. This length will typically be between 6 and 18 inches. The length should not be longer than necessary to avoid producing confusing clutter.

The output line 7 and the return line 11 may leave the output plug 3 separately or joined together in a cable in the case of either of the configurations presented in FIGS. 3 4. Although this is appropriate for the monopolar configurations presented in FIGS. 3 4, joining the lines together is particularly advantageous when they both go to an accessory which is of the bipolar type, and one embodiment of which is schematically presented in FIG. 5. In this case, the accessory handle 8 of the accessory 150 provides electrical continuity from both the output line 7 and the return line 11 to the active element 9 and the return path device 12 (e.g., return electrode), respectively. In bipolar accessories in general, the active element 9 and the return path device 12 are often joined together mechanically, but not electrically, using an accessory electrode housing 14. The accessory electrode housing 14 can be of many forms, of which an insulated shaft is an example. The common feature of the various forms of the accessory electrode housing 14 is that it allows both the active element 9 and the return path device 12 to contact simultaneously the patient 10. Such contact may be either direct or indirect.

One embodiment of a prior art bipolar configuration is more particularly illustrated in FIG. 15, which is used in conductive liquid environments. The accessory 200 operatively interfaces with an electrosurgical generator (not shown) via an output connector 5 on the generator and a return connector 6 on the generator. The accessory 200 has a supplemental return line 13 passing from the return connector 4 to the output connector 3. The accessory 200 illustrated in FIG. 15 is a bipolar electrosurgical accessory that uses a return electrode and it will be compared to later figures to illustrate distinctive features of the subject invention. The device 200 illustrated in FIG. 15 includes a probe assembly 27 that has a probe handle 28 and a probe shaft 29. The output line 7 and the return line 11 are of a length needed to allow the surgeon to conveniently place the electrosurgical generator. The probe shaft 29 is coated with probe shaft insulation 30 that extends almost the complete length of the probe shaft 29. The probe shaft 29 is typically made of either a polymer, which may be flexible, or, more commonly, of metal. One or more channels (not shown) may pass through the probe shaft 29 to allow irrigation solution, aspirated materials, tools, light sources, or visualization equipment to pass into the patient. At the distal tip of the probe shaft 29 is the active electrode assembly 31 which includes the active electrode 32. The output line 7 may continue through the length of the probe assembly 27 and electrically connect to the active electrode 32. If the output line 7 does not directly connect to the active electrode, then one or more conductive elements (not shown) form a conductive path to the active electrode 32. The probe shaft 29 is electrically connected to the return line 11. A section of the probe shaft 29 is left uninsulated to be the return electrode 33. The illustrated device shows a probe shaft 29 made only from metal. If a polymeric or other insulating material forms the probe shaft 29, then the shaft 29 is not insulated and a conductive metal element is attached to form the return electrode 33. The active electrode assembly 31 is insulated from the return electrode 33 by an active electrode standoff insulator 34.

The return electrode 33 is a conductor that contacts whatever liquid (not shown) may be surrounding it. A perforated shield (not shown) may surround the return electrode 33 as well, but the shield allows conductive liquid to contact the return electrode 33. The conductive liquid needs to contact the return electrode 33 to form an electrically conductive path.

The probe shaft insulation 30 is selected to insulate the probe shaft 29 from contacting patient tissues that may lead to inadvertent electrical return paths. The insulation 30 is not selected to allow energy transfer by electrical fields to the probe shaft 29, and such energy transfer is not required, nor can it occur, when the return electrode 33 has electrical continuity with surrounding conductive liquid to generate a current return path.

The waveforms produced by the radio frequency electrical source in an electrosurgical procedure are designed to produce a predetermined effect such as tissue ablation or coagulation when the energy is conveyed to the patient's tissue. The characteristics of the energy applied to the tissue, such as frequency and voltage, are selected to help achieve the desired tissue effect.

Electrosurgical procedures can experience inadvertent problems that lead to unintended tissue damage. During electrosurgical procedures the depth of the effect to the tissue depends upon tissue properties, which change during the application of energy. It is desirable to not have the tissue effects change so rapidly that the surgeon has difficulty controlling the surgical result. During some procedures, such as minimally invasive surgical (MIS) procedures wherein surgical instruments are passed through small openings in the patient's tissue, energy can enter a patient's tissue at a location other than where the active electrode is positioned. Such inadvertent energy application can lead to burns or other complications. When surgical instruments are being inserted or withdrawn from patients during MIS procedures, concern exists for inadvertent activation of the RF energy source and tissue damage that could occur from such an event. One aspect of this problem occurs when the return path device is positioned such that it causes high current flux through tissue adjacent to it. High current flux can cause tissue burns or other damage. It would be desirable for the devices used by surgeons to not allow such inadvertent high current fluxes to occur.

The source of RF energy (the generator) has an output power that depends upon the operating characteristics of its design, including the design of its internal circuitry. Typically the generator is set by the clinical user to a setting that represents the output power desired. When the generator operates, the output power typically depends upon the impedance of the load into which the generator is delivering power. In general, the various generators available operate in modes that approximate constant voltage devices, constant power devices, or some hybrid mode that lies between constant voltage and constant current. The modes approximate constant voltage or constant power output due to the variations inherent in electronic component performance. Modern general purpose generators commonly used in operating rooms typically operate in a constant power mode when power outputs other than low power are desired.

Generator supply companies have long recognized the desirability of using constant power for major surgical procedures such as open surgical procedures. Consequently, the modern generators in operating rooms use a constant power mode. Recently, procedures, such as arthroscopic surgical procedures (e.g., tissue ablation and capsular shrinkage), that benefit from using a constant voltage mode have become increasingly common and important. Special purpose generators have been developed for these constant voltage procedures. Surgical instruments connect to the constant voltage generator and the RF energy is conveyed to the working surfaces using conductors of various types.

Constant power can lead to runaway interactions between the RF energy and the tissue. During electrosurgical procedures the tissue impedance eventually increases as the tissue is affected by the energy imparted to it. In an attempt to continue delivering constant power, a constant power source will increase the output voltage to overcome the increased tissue impedance. This increased voltage will lead to continued changes in the tissue with corresponding increases in tissue impedance, which, in turn, cause the generator to increase the voltage further. The cycle of events usually occurs very rapidly, so rapidly that during some procedures it is beyond the user's ability to respond quickly and prevent undesired tissue effects such as charring or excessive tissue destruction.

Constant voltage automatically reduces the rate that energy is supplied to the tissue as the tissue impedance increases. When constant voltage is used, the current delivered to the tissue, and consequently the power delivered, decreases as tissue impedance increases. This inherent response can greatly reduce or eliminate runaway interactions between the tissue and the RF energy applied to it.

To date, the advantages of constant voltage cannot be easily obtained from constant power generators. It would be beneficial for users, when they so desire, to easily and economically be able to have constant power generators deliver constant voltage to a surgical site. In particular, it would be useful for users to achieve the benefits of constant voltage supply without needing to modify existing generators or attach special adapters to generators. In cases where single use, or limited use, disposable surgical accessories are used, it would be particularly beneficial if the accessory makes the conversion from constant power to constant voltage. For example, it would be beneficial if an arthroscopic instrument intended for ablating tissue could be plugged into a constant power generator and apply power that approximated constant voltage to the tissue.

To date, the primary means for delivering RF energy to tissue while employing constant voltage requires using a constant voltage generator. Constant voltage electrosurgical generator design is known art, such that described in U.S. Pat. No. 5,472,443. Constant voltage electrosurgical generators have outputs that are constant voltage and do not convert the output from a constant power generator to be constant voltage. U.S. Pat. No. 5,472,443 also presents a means for retrofitting selected generators to modify the output, however the circuit presented has considerable complexity and does not lend itself to use in disposable products. The U.S. Pat. No. 5,472,443 circuit is also intended for use with surgical instruments that cut using a sharp edge, rather than using electrosurgical energy to produce the cutting action. Other known electrosurgical generator art limits the current flow, such as described in U.S. Pat. Nos. 4,092,986, 5,267,997 and 5,318,563. The art described in these patents is incorporated into generators and does not convert the mode of a constant power generator into constant voltage. U.S. Pat. Nos. 4,114,623 and 5,891,095 describe current limiting means, as opposed to voltage limiting means. Electrosurgical systems may use temperature sensing to control the power applied to the tissue, such as described in U.S. Pat. No. 5,440,681.

SUMMARY OF THE INVENTION

The present invention generally relates a system/method for executing an electrosurgical procedure on a patient (e.g., cutting, coagulation, desiccation, fulguration, ablation, tissue shrinkage).

A first aspect of the present invention allows for limiting a maximum voltage which is applied to a patient during an electrosurgical procedure using an electrosurgical generator and an electrosurgical assembly which is separate from and interfaces with the generator. The electrosurgical generator and electrosurgical assembly are separate components and may be operatively interconnected at the desired time to affect the execution of desired electrosurgical procedure. One particularly desirable application of the subject first aspect is when the electrosurgical generator is of a constant power type configuration, or even more preferably when the electrosurgical generator is operating other than on a constant voltage basis. In this case, the electrosurgical assembly may include one or more relevant components to effectively allow the electrosurgical assembly to execute an at least substantially constant voltage electrosurgical procedure, or stated another way to allow the electrosurgical assembly to deliver voltage at least at substantially a constant magnitude to the patient. This is desirable for a number of reasons, including for reducing the potential for tissue damage.

The first aspect of the present invention is embodied in an electrosurgical assembly (e.g., an instrument or accessory) which interfaces with an electrosurgical generator. Components of the electrosurgical assembly of the subject first aspect include an output assembly which is at least operatively interconnectable with the generator and also which is operatively interconnected with an active electrosurgical element or electrode (e.g., one or more blades, hooks, balls, spatulas, loops, pins, wireforms, tubes, tubes with fluid passageways, members of forceps, graspers, scissors). Any such electrode may include one or more surfaces for interfacing with the patient, and each such surface may be either curved or flat. Power from the generator is provided to the active electrosurgical element through the output assembly of the electrosurgical assembly such that an interface between the active electrosurgical element and the patient (e.g., direct, indirect) may affect execution of the subject electrosurgical procedure. Typically the output assembly will include an output plug which detachably interconnects with an output connector on the generator, as well as an output or power line and/or one or more other appropriate electrical conductors which extend between the output plug and the active electrosurgical element.

Completion of the circuit between the patient and the electrosurgical generator is provided by a return path element which interfaces with the patient (e.g., tissue, one or more fluids and including conductive liquids), as well as a return assembly which is operatively interconnected with this return path element and further which is at least operatively interconnectable with the electrosurgical generator. Typically, the return assembly will include a return plug which detachably interconnects with a return connector on the generator, as well as a return line and/or one or more other appropriate electrical/energy transfer members which extend between the return plug and the return path element. In the case of the subject first aspect, a shunt circuit extends between and interconnects the output and return assemblies (e.g., between the output/power line and the return line).

Various refinements exist of the features noted in relation to the subject first aspect of the present invention. Further features may also be incorporated in the subject first aspect of present invention as well. These refinements and additional features may exist individually or in any combination. There are various ways in which the shunt circuit utilized by the subject first aspect may be characterized. Voltage regulation during a given electrosurgical procedure may be affected by the shunt circuit. Limitation of the maximum voltage transferred/applied to the patient from the interface with the electrosurgical assembly may also be provided by the shunt circuit. Yet another characterization is that a constant power electrosurgical generator may be used by the subject first aspect of the present invention to execute an at least substantially constant voltage electrosurgical procedure using the electrosurgical assembly in accordance with this first aspect of the present invention. In one embodiment where the assembly of the first aspect is used with a generator which delivers something other than a constant voltage output and including a constant power generator, a voltage variation of no more than about 15% is realized throughout the electrosurgical procedure by the inclusion of the shunt circuit in the electrosurgical assembly in accordance with the subject first aspect, particularly over/throughout a patient impedance range from about 500 ohms to about 2,000 ohms.

The active electrosurgical element and return path element of the subject first aspect may be integrated with the electrosurgical assembly in a manner which provides a monopolar configuration/technique, as well as in a manner which provides a bipolar configuration/technique. A monopolar configuration/technique exists when the return path element is a separate device from that which carries the active electrosurgical element, whereas a bipolar configuration/technique exists when the active electrosurgical element and the return path element are incorporated in the same structure (e.g., both being positioned on a probe or the like). Although what may be characterized as "conventional" return path elements may be utilized in relation to the subject first aspect of the present invention (e.g., a return electrode pad for a monopolar configuration, conventional electrical conductors such as a metal tube or shaft with insulation disposed about all but an end portion thereof, which then interfaces with the patient, for a bipolar configuration), in one embodiment the return path element of the first aspect for a bipolar application includes a return coupler having a first dielectric body or component (e.g., one or more dielectric materials, alone or in combination with one or more non-dielectric materials). This first dielectric body or component directly interfaces with the patient during execution of the electrosurgical procedure (e.g., via tissue contact, via body fluid(s) contact), and also interfaces with an appropriate conductor of the return coupler (e.g., a hollow shaft, a solid shaft with one or more channels extending therethrough, at least some of which may be electrically conductive) in such a manner that energy from the patient first transfers, using nonconductive means, across the first dielectric body and then to the conductor when proceeding back to the generator via the return assembly. Stated another way, the return coupler effectively defines or is at least part of a capacitor in the return path to the generator, such that the energy from the patient is at least initially returned to the generator via electrical fields versus conduction. After transferring across the first dielectric body, conventional conduction structure/techniques may be employed.

The patient effectively has an impedance load associated therewith which may then be characterized as a patient impedance load. In one embodiment of the first aspect, the shunt circuit is disposed in parallel with this patient impedance load. Various types of shunt circuits may be utilized, preferably by being disposed in the noted electrically parallel relation to the patient. A single electronic element may define the shunt circuit, such as a capacitor. Appropriate electrical leads could then be used to electrically interconnect the capacitor with the output and return assemblies of the electrosurgical assembly. However, the shunt circuit may also include one or more electronic elements, and these electronic elements may be passive, active, or some combination of one or more passive and one or more active electrical components. Appropriate electronic components or elements for the shunt circuit of the subject first aspect include capacitors, inductors, resistors, transistors, diodes, and integrated circuits.

Options exist regarding the physical location of the shunt circuit associated with the first aspect of the present invention. In one embodiment, the shunt circuit may be positioned other than in a user handle which may be utilized by the electrosurgical assembly. This not only reduces the potential for an increased temperature of the handle or incorporating an appropriate cooling system within any such handle to address the heat buildup which will be caused by the shunt circuit, but also allows the existing space within any such handle to be used for other purposes (e.g., for certain electronics, for other systems such as suction/irrigation systems) or to allow the handle to continue to be of a desired size for providing an appealing physical interface with a user of the electrosurgical assembly (e.g., a surgeon). Appropriate locations for the shunt circuit include within an output plug of the electrosurgical assembly which again would detachably interconnect with an output connector on the generator, within a return plug of the electrosurgical assembly which again would detachably interconnect with a return connector on the electrosurgical generator, between portions of an output and return line which extend from an output plug of the electrosurgical assembly and a handle of the assembly or which otherwise extend to such a handle, or within an adapter of sorts which may be an in-line connector between the electrosurgical assembly of the subject first aspect and the electrosurgical generator. Notwithstanding the above-noted benefits of not including the shunt circuit within a handle which may be utilized by the electrosurgical assembly of the first aspect, one or more fundamental advantages associated with the first aspect may still be realized by having the shunt circuit within the handle, and therefore such is within the scope of the first aspect of the present invention.

A second aspect of the present invention also relates to a bipolar configuration of an electrosurgical assembly which receives power from an electrosurgical generator for executing an electrosurgical procedure on a patient. Components of the electrosurgical assembly include an output assembly which is at least operatively interconnectable with the generator and which is operatively interconnected with an active electrosurgical element or electrode (e.g., one or more blades, hooks, balls, spatulas, loops, pins, wireforms, tubes, tubes with fluid passageways, members of forceps, graspers, and scissors). Each active electrosurgical element may include one or more surfaces for interfacing with the patient, and such may either be flat or curved. Power from the generator is provided to the active electrosurgical element through the output assembly such that an interface between the active electrosurgical element and the patient (e.g., direct, indirect) may affect a particular electrosurgical procedure. Typically the output assembly will include an output plug which electrically interfaces with an output connector on the generator, as well as an output or power line and/or one or more other appropriate electrical conductors which extend between the output plug and the active electrosurgical element.

Completion of the circuit between the patient and the electrosurgical generator is provided by a return path element which interfaces with the patient (e.g., tissue, one or more fluids and including various body fluids) and which is mechanically interconnected with the above-noted active electrosurgical element to define a bipolar configuration (e.g., on a common probe). Another portion of this "return" to the generator is provided by a return assembly which is operatively interconnected with this return path element and further which is at least operatively interconnectable with the electrosurgical generator. Typically the return assembly will include a return plug which electrically interfaces with a return connector on the generator, as well as a return line and/or one or more other appropriate electrical/energy transfer members which extend between the return plug and the return path element. In the case of the subject second aspect, the return path element includes a first dielectric body or component (e.g., one or more dielectric materials, alone or in combination with one or more non-dielectric materials) which directly interfaces with the patient.

Energy from the patient is at least initially transferred through the return path element via a field effect or via one or more electrical fields in the case of the subject second aspect of the present invention, which again is limited to a bipolar application (e.g., by having the active electrosurgical element and return path element mounted on a common probe or the like). Known bipolar devices instead use conduction in this instance. During most electrosurgical procedures, and including minimally invasive procedures and open surgical procedures, there will be a liquid interface between the patient and the first dielectric body associated with the subject second aspect. Any appropriate conductive liquid may be utilized for this interface, including saline, lactated Ringers solution, as well as a combination of saline and one or more bodily fluids of the patient such as blood and/or perspiration.

Various refinements exist of the features noted in relation to the subject second aspect of the present invention. Further features may also be incorporated in the subject second aspect of present invention as well. These refinements and additional features may exist individually or in any combination. The first dielectric component may include a combination of materials (e.g., one or more dielectric materials in powder form, combined with a polymer or adhesive). In any case, the first dielectric component may include a first material which is subject to number of characterizations. This first material has a dielectric product which is greater than about 2,000 in one embodiment, greater than about 4,000 in another embodiment, and greater than about 8,000 in yet another embodiment. "Dielectric product" as used herein means the dielectric constant of the first material, multiplied by the dielectric strength of the first material. Materials having a dielectric product in accordance with the foregoing include alumina, diamond, boron nitride, polyimide, polyester, parylene, barium titanate, titanium dioxide, Teflon, and polycarbonate.

Another characterization of the first material which is at least part of the first dielectric component is that it may have a dielectric constant which is greater than about 10 in one embodiment, which is greater than about 20 in another embodiment, and which is greater than about 50 in yet another embodiment. Materials having a dielectric constant in accordance with the foregoing include ceramics, alumina, titanium dioxide, barium nitrate, and combinations thereof. The first dielectric component of the subject second aspect may be further characterized in relation to its wall thickness. The first dielectric component may have a wall thickness which is less than about 0.25 inches in one embodiment, which is less than about 0.10 inches in another embodiment, and which is less than about 0.01 inches in yet another embodiment.

Barium titanate is currently the preferred material to be the primary dielectric material for the first dielectric component of the return path element in accordance with the subject second aspect. The first dielectric component is at least about 50 wt % barium titanate in one embodiment, and is at least about 90 wt % barium titanate in another embodiment. Suitable energy transfer characteristics across the first dielectric component are realized when formed from barium titanate in the above-noted amounts, and further when: 1) the first dielectric component has a surface area of no larger than about 1 in.sup.2 in one embodiment, no smaller than about 0.2 in.sup.2 in another embodiment, and a surface area no smaller than about 0.007 in.sup.2 in yet another embodiment; and/or 2) when the first dielectric component is the form of a tube, which is any shaped material that has one or more openings into or through it, with a wall thickness of no more than about 0.5 inches in one embodiment, no more than about 0.1 inches in another embodiment, and about 0.020 inches in yet another embodiment, and being at least about 0.005 inches thick.

The return path element as a whole, which includes the first dielectric component, is also subject to a number of characterizations. The impedance of the return path element is less than about 800 ohms in one embodiment, is less than about 500 ohms in another embodiment, is less than about 300 ohms in another embodiment, and is less than about 200 ohms in yet another embodiment. Another characterization of the return path element is its voltage strength. The return path element is able to withstand a voltage exceeding 1,000 volts peak to peak in one embodiment, a voltage exceeding 2,000 volts peak to peak in another embodiment, and exceeding 5,000 volts peak to peak in yet another embodiment.

One configuration which may be utilized for the subject second aspect is a probe with a handle attached thereto. The probe may be characterized as including first and second longitudinal segments. The active electrosurgical element may be part of the first longitudinal segment and the return path element may be part of the second longitudinal segment. In any case, the first dielectric component may be in the form of a layer or the like which is disposed about an electrically conductive return tube or shaft of the return coupler, which in turn may be electrically interconnected with the return assembly (e.g., a return line having a return plug disposed on an opposite end thereof which detachably engages with a return connector on the generator). Another option is to provide the first dielectric component itself with a tubular construction (i.e., separately formed), and to interface/interconnect the same with an electrically conductive return tube or shaft of the above-noted type by disposing the first dielectric component over an end portion of the electrically conductive tube/shaft.

Additional components may be utilized by the subject second aspect of the present invention. One such component is an inductor that may be disposed in series with the return path element. This inductor may be characterized as affecting an offset of the impedance which may be associated with the return path element. The shunt circuit noted above in relation to the first aspect of the present invention may also be utilized in the subject second aspect of the present invention as well.

Based upon the foregoing, it should be appreciated that one primary objective of the present invention may be characterized as providing a surgical method and assembly which employ electrical energy to achieve a desired surgical effect while using the disposable or electrosurgical assembly/accessory to alter the output mode of the generator and thus improve control of the energy application to reduce the opportunity for inadvertent tissue damage. To achieve this objective, a surgical method associated with the present invention may include the steps of using surgical instruments that contain one or more elements of predetermined types to influence the manner in which energy transfers and thereby alter how RF energy is applied to the tissue. In particular, at least certain aspects of the present invention can be used to effectively limit the maximum voltage applied to the tissue during the electrosurgical process to reduce the interactions with tissue that lead to the aforementioned shortcomings associated with using constant power RF energy.

The beneficial effects of reduced inadvertent tissue damage further manifest themselves when the return path device uses one or more electric fields to couple return energy flow from the tissue to the generator which itself is another aspect of the present invention. Such a return path device may be characterized as a return coupler as noted above. This return coupler may include a dielectric insulating material that completely insulates an inner conductive element (e.g., the dielectric insulating material may be part of a capacitor in which one capacitor electrode is defined by the inner conductive element, and in which the other electrode is defined by conductive liquid and/or bodily tissue). The inner conductive element is part of the conductive electrical path that extends to the generator. The inner conductive element is insulated from surrounding conductive liquids and the patient tissue by insulation and/or dielectric materials that surround the inner conductive element. The insulation prevents the inner conductive element from contacting the tissue, including both direct and indirect tissue contact via a conductive liquid (e.g., normal saline). The inner conductive element is surrounded by one or more insulating materials and the inner conductive element may be composed of one or more materials that are regarded as electrically conductive, such as any of copper, silver, or aluminum or an alloy of such a material. Another suitable material for the inner conductive element is stainless steel. The inner conductive element will commonly be a tube, in which case a power line for the active electrode may be directed through the hollow interior thereof so as to electrically isolate this power line from the inner conductive element. In any case, the inner conductive element will typically be electrically connected via a suitable means, such a wire connected at or near its proximal end which extends to a return plug (possibly via the output plug), and then to the return connection on the generator. The inner conductive element with its surrounding insulation will typically have a handle attached to it at the proximal end where the return wire exits. The return coupler is suited for use as the return path device with instruments having an active electrode and may be attached to the device to form a bipolar configuration. The distal tip of the instrument could be the location of the return coupler and is an example of a location where an active electrode assembly could also be located.

The dielectric insulating material for the noted return coupler preferably has a combination of thickness, dielectric constant, dielectric strength and area such that it withstands the electric field voltages without breaking down and has a low enough impedance to allow adequate energy flow. The exposed area of the surrounding insulation will also affect the impedance of the return coupler. When a properly insulated inner conductive element is partially or wholly submerged in a conductive liquid, an electric field forms that transfers energy. The energy transfer is significantly more efficient when the return coupler contacts conductive liquid than when it contacts tissue. Consequently, the impedance increases when the return coupler does not completely contact liquid, such as when it is contacting tissue as the device is withdrawn from a patient. If the energy source is a constant voltage source, then the total energy delivered decreases as the impedance increases. The result is a reduced possibility of inadvertent tissue damage. However, if the energy source is a constant power source and in the case of an increase of the impedance of the patient's tissue, higher voltages would be provided by the generator, and thereby increased power. Use of the shunt circuit discussed above in relation to the first aspect of the present invention, and which is also discussed in more detail below as well, may be utilized to in effect limit the maximum voltage output of the surgical instrument for these cases.

Proper insulating materials for the noted return coupler consist of one or more substances that, when applied to the inner conductive element, withstand the voltage across the insulation and lead to a low enough impedance for the area selected to be the return coupler. A combination of high dielectric constant and high dielectric strength is desired for the return coupler. The impedance of the return coupler increases with increasing insulation thickness and the ability to withstand voltage also increases with insulation thickness. Therefore, a tradeoff exists between having low impedance and having high voltage withstand strength. A high dielectric constant allows a material to have increased thickness while reducing the penalty of increasing impedance. A high dielectric strength material allows thinner insulation, which decreases impedance, while reducing the impact that thinner coatings have on decreased voltage withstand strength. The properties of dielectric constant and dielectric strength can be combined into one variable, the dielectric product (DP) as noted above and again where:

DP=(dielectric constant).times.(dielectric strength).

Dielectric constant is a dimensionless quantity and dielectric strength is measured in Volts/mil, where mil= 1/1000 of an inch. A material with a large DP will have a lower impedance at a given insulation thickness than a material with a lower DP will have. Therefore, large DPs are desirable for the substances used in the insulation coating the inner conductive element of a return coupler. DPs greater than 2,000 are preferred, and DPs greater than 4,000 and even 8,000 are even more preferred. Materials with large DPs include alumina, diamond and similar coatings, boron nitride, polyimide, polyester, parylene, barium titanate, titanium dioxide (including the rutile, anatase, and brookite forms), Teflon, polycarbonate, and inorganic and organic substances that are similar to these or that contain significant amounts (greater than about 30 percent) of these or similar materials.

To obtain the mixture of properties needed for manufacturing return couplers it is likely that materials with more than one DP will be used for the insulating material thereof. An example would be mixing a large DP material such as extremely fine (particles measured in microns) powders of barium titanate or titanium dioxide with binders, adhesives, or polymers such as epoxies, urethanes, or polyester. In some cases the large DP material could be blended into a polymer that is formed into tube, such as shrink tubing.

High dielectric constant materials are beneficial substances to use to make the insulating material for the return couplers. High dielectric constant materials have dielectric constants greater than about 10 [dimensionless]. Preferably, materials with dielectric constants greater than 20 or even 50 are used in conjunction with other substances, such as binders or adhesives. Examples of high dielectric constant materials include ceramics, and more particularly alumina, titanium dioxide (including rutile, anatase, and brookite forms), and barium titanate.

The insulating substance or substances for the noted return coupler may be applied using chemical or physical deposition means, such as chemically forming a layer, coating, wrapping, or vapor phase deposition. Shrink wrap tubing may be loaded with high dielectric materials. The insulating coating will beneficially be less than about 0.025 inches thick and even more beneficially if it is equal to less than about 0.010 or even 0.005 inches thick.

A separate component, such as a preformed hollow bead, made from one or more materials with a large DP may be used as well. For example, a hollow tube with a suitable length may be slipped over the end of the inner conductive element and placed in electrical c