Electrosurgical instrument

An electrosurgical instrument for the treatment of tissue in the presence of an electrically conductive fluid medium, comprising an instrument shaft and an electrode assembly at a distal end of the shaft, wherein the electrode assembly comprises:

• a single active electrode fixedly positioned in the electrode assembly and having an exposed tissue treatment portion,
• a return electrode having an exposed fluid contact surface, and
• an insulating member positioned between and electrically insulating the active electrode and the return electrode and axially spacing apart the exposed treatment portion of the active electrode and the exposed fluid contact portion of the return electrode such that, when the treatment portion is brought adjacent to a tissue surface immersed in the fluid medium, the fluid medium completes a conduction path between the active electrode and the return electrode,
• and wherein the exposed treatment portion is dimensioned and configured in relation to the exposed fluid contact surface and the insulation member such that, when the electrode assembly is immersed in the conductive fluid medium the ratio of (i) the length of the shortest conduction path (P.sub.1) through the fluid medium between the exposed fluid contact surface and that part of the exposed treatment portion which is furthest from the exposed fluid contact surface, to (ii) the length of the shortest conduction path (P.sub.2) through the fluid medium between the exposed fluid contact surface and the exposed treatment portion, is less than or equal to 2 to 1, but greater than or equal to 1.25 to 1.

An electrosurgical system comprising an electrosurgical instrument for the treatment of tissue in the presence of an electrically conductive fluid medium comprising an instrument shaft and an electrode assembly at a distal end of the shaft and an electrosurgical generator for supplying radio frequency power to the instrument,

• the electrode assembly comprising:
• a single active electrode fixedly positioned in the electrode assembly and having an exposed tissue treatment portion,
• a return electrode having an exposed fluid contact surface, and
• an insulating member positioned between and electrically insulating the active electrode and the return electrode and axially spacing apart the exposed treatment portion of the active electrode and the exposed fluid contact portion of the return electrode such that, when the treatment portion is brought adjacent to a tissue surface immersed in the fluid medium, the fluid medium completes a conduction path between the active electrode and the return electrode,
• and wherein the exposed treatment portion is dimensioned and configured in relation to the exposed fluid contact surface and the insulation member such that, when the electrode assembly is immersed in the conductive fluid medium the ratio of (i) the length of the shortest conduction path (P.sub.1) through the fluid medium between the exposed fluid contact surface and that part of the exposed treatment portion which is furthest from the exposed fluid contact surface, to (ii) the length of the shortest conduction path (P.sub.2) through the fluid medium between the exposed fluid contact surface and the exposed treatment portion, is less than or equal to 2 to 1, but greater than or equal to 1.25 to 1,
• the generator including an output stage having an output voltage applied to output connections connected respectively to the active electrode and the return electrode of the instrument, a sensing circuit for deriving a sensing signal representative of the peak radio frequency output voltage developed between the output connection, and a power adjustment circuit for automatically causing a reduction in delivered output power when the sensing signal is indicative of a predetermined peak radio frequency output voltage having been reached.

An electrosurgical apparatus for the treatment of tissue in the presence of an electrically conductive fluid medium, comprising an electrosurgical instrument and an electrosurgical generator, the electrosurgical instrument comprising an instrument shaft and an electrode assembly at a distal end of the shaft, wherein the electrode assembly comprises:

• a single active electrode having an exposed tissue treatment portion,
• a return electrode having an exposed fluid contact surface, and
• an insulating member positioned between and electrically insulating the active electrode and the return electrode and axially spacing apart the exposed treatment portion of the active electrode and the exposed fluid contact surface of the return electrode such that, when the treatment portion is brought adjacent to a tissue surface immersed in the fluid medium, the fluid medium completes a conduction path between the active electrode and the return electrode,
• the generator applying sufficient radio frequency output power to the active and return electrodes in a first voltage range to increase the temperature of the conductive fluid adjacent the active electrode treatment portion to near boiling without creating a vapour pocket surrounding the treatment portion when the electrosurgical instrument is used for desiccation and in a second voltage range to thermally evaporate conductive fluid adjacent the active electrode treatment portion to create a vapour pocket surround the treatment portion when the electrosurgical instrument is used for cutting or ablation;
• and
• wherein the exposed treatment portion is dimensioned and configured in a fixed relationship to the exposed fluid contact surface and the insulation member, such that, when the electrode assembly is immersed in the conductive fluid medium, the ratio of (i) the length of the shortest conduction path (P.sub.1) through the fluid medium between the exposed fluid contact surface and that part of the exposed treatment portion which is furthest from the exposed fluid contact surface, to (ii) the length of the shortest conduction path (P.sub.2) through the fluid medium between the exposed fluid contact surface and the exposed treatment portion, is less than or equal to 2 to 1, but greater than or equal to 1.25 to 1.

An electrosurgical instrument for the treatment of tissue in the presence of an electrically conductive fluid medium, comprising an electrosurgical instrument and an electrosurgical generator, the electrosurgical instrument comprising an instrument shaft and an electrode assembly at a distal end of the shaft, wherein the electrode assembly comprises:

• a single active electrode having an exposed tissue treatment portion,
• a return electrode having an exposed fluid contact surface, and
• an insulating member positioned between and electrically insulating the active electrode and the return electrode axially spacing apart the exposed treatment portion of the active electrode and the exposed fluid contact surface of the return electrode such that, when the treatment portion is brought adjacent to a tissue surface immersed in the fluid medium, the fluid medium completes a conduction path between the active electrode and the return electrode,
• the generator applying sufficient radio frequency output power to the active and return electrodes in a first voltage range to increase the temperature of the conductive fluid adjacent the active electrode treatment portion to near boiling without creating a vapour pocket surrounding the treatment portion when the electrosurgical instrument is used for desiccation and in a second voltage range to thermally evaporate conductive fluid adjacent the active electrode treatment portion to create a vapour pocket when the electrosurgical instrument is used for cutting or ablation and;
• wherein the exposed treatment portion is dimensioned and configured in a fixed relationship to the exposed fluid contact surface and the insulation member, such that, when the electrode assembly is immersed in the conductive fluid medium, the length of the shortest conduction path through the fluid medium between the exposed fluid contact surface and the exposed treatment portion is large enough to prevent direct arcing between the exposed treatment portion and the fluid contact surface of the return electrode, and
• wherein the ratio of (i) the length of the shortest conduction path (P.sub.1) through the fluid medium between the exposed fluid contact surface and that part of the exposed treatment portion which is furthest from the exposed fluid contact surface, to (ii) the length of the shortest conduction path (P.sub.2) through the fluid medium between the exposed fluid contact surface and the exposed treatment portion, is less than or equal to 2 to 1, but greater than or equal to 1.25 to 1.

A method of desiccating tissue using a bipolar electrode assembly, the assembly including a active electrode and a return electrode, the active electrode having an exposed treatment portion, and the return electrode having an exposed fluid contact surface spaced and set back axially from the exposed treatment portion, the exposed treatment portion being dimensioned and configured in a fixed relationship to the exposed fluid contact surface, such that, when the electrode assembly is immersed in a conductive fluid medium the ratio of (i) the length of the shortest conduction path (P.sub.1) through the fluid medium, between the exposed fluid contact surface and that part of the exposed treatment portion which is furthest from the exposed fluid contact surface, to (ii) the length of the shortest conduction path (P.sub.2) through the fluid medium between the exposed fluid contact surface and the exposed treatment portion, is greater than or equal to a ratio of 1.25 to 1, but less than or equal to a ratio of 2 to 1 to ensure that power applied to the exposed treatment portion is controlled without the formation of a vapor pocket surrounding the exposed treatment portion, the method comprising the steps of:

• (a) introducing the electrode assembly into a selected operation site;
• (b) surrounding the electrode assembly with a conductive fluid so that the conductive fluid defines an electrical path between the active and return electrodes;
• (c) applying sufficient radio frequency output power to the electrode assembly to increase the temperature of the conductive fluid adjacent the active electrode treatment portion without creating a vapour pocket surrounding the treatment portion, said output power being subsequently reduced by at least 50% within a predetermined period of time to maintain a desiccating mode of operation;
• and
• (d) contacting the treatment portion to tissue while maintaining the return electrode fluid contact surface out of contact with the tissue.

A method of vaporising tissue using a bipolar electrode assembly, the bipolar electrode assembly including an active electrode fixedly mounted in the electrode assembly and a return electrode axially spaced from the active electrode, the active electrode having an exposed treatment portion, and the return electrode having an exposed fluid contact surface, the exposed treatment portion being dimensioned and configured in relation to the exposed fluid contact surface such that, when the electrode assembly is immersed in a conductive fluid medium, the ratio of (i) the length of the shortest conduction path (P.sub.1) through the fluid medium between the exposed fluid contact surface and that part of the exposed treatment portion which is furthest from the exposed fluid contact surface, to (ii) the length of the shortest conduction path (P.sub.2) through the fluid medium between the exposed fluid contact surface and the exposed treatment portion, is less than or equal to a ratio of 2 to 1, but greater than or equal to a ratio of 1.25 to 1 to ensure that the exposed treatment portion is enveloped in a vapor pocket, the method comprising the steps of:

• (a) introducing the electrode assembly into a selected operation site;
• (b) surrounding the electrode assembly with a conductive fluid;
• (c) applying sufficient radio frequency output power to the electrode assembly to vaporise the conductive fluid adjacent the active electrode treatment portion to create a vapour pocket surrounding the treatment portion, said output power being reduced by at least 50% with a predetermined period of time to maintain a vaporising mode of operation;
• and
• (d) positioning the treatment portion of the active electrode adjacent the tissue with the vapour pocket in contact with the tissue while maintaining the return electrode out of contact with the tissue.

A method of desiccating tissue using a bipolar electrode assembly, the assembly including an active electrode and a return electrode, the active electrode having an exposed treatment portion, and the return electrode having an exposed fluid contact surface radially spaced and axially set back from the exposed treatment portion, the active electrode and return electrode being in a fixed relationship during use, such that, when the electrode assembly is immersed in a conductive fluid medium the ratio of (i) the length of the shortest conduction path (P.sub.1) through the fluid medium between the exposed fluid contact surface and that part of the exposed treatment portion which is furthest from the exposed fluid contact surface, to (ii) the length of the shortest conduction path (P.sub.2) through the fluid medium between the exposed fluid contact surface and the exposed treatment portion, is less than or equal to 2 to 1, but greater than or equal to 1.25 to 1, the method comprising the steps of:

• (a) introducing the electrode assembly into a selected operation site;
• (b) surrounding the electrode assembly with a conductive fluid so that the conductive fluid defines an electrical path between the active and return electrodes;
• (c) applying sufficient radio frequency output power to the electrode assembly to increase the temperature of the conductive fluid adjacent the active electrode treatment portion without creating a vapour pocket surrounding the treatment portion;
• (d) contacting the treatment portion to tissue while maintaining the return electrode fluid contact surface out of contact with the tissue.

A method of vaporising tissue using a bipolar electrode assembly, the assembly including an active electrode and a return electrode, the active electrode having an exposed treatment potion, and the return electrode having an exposed fluid contact surface radially spaced and axially set back from the exposed treatment portion, the active electrode and return electrode being in a fixed relationship during use, such that, when the electrode assembly is immersed in a conductive fluid medium the ratio of (i) the length of the shortest conduction path (P.sub.1) through the fluid medium between the exposed fluid contact surface and that part of the exposed treatment portion which is furthest from the exposed fluid contact surface, to (ii) the length of the shortest conduction path (P.sub.2) through the fluid medium between the exposed fluid contact surface and the exposed treatment portion, is less than or equal to 2 to 1, but greater than or equal to 1.25 to 1, the method comprising the steps of:

• (a) introducing the electrode assembly into a selected operation site;
• (b) surrounding the electrode assembly with a conductive fluid;
• (c) applying sufficient radio frequency output power to the electrode assembly to vaporise the conductive fluid adjacent the active electrode treatment portion to create a vapour pocket surrounding the treatment portion;
• (d) positioning the treatment portion of the active electrode adjacent the tissue with the vapour pocket in contact with the tissue while maintaining the return electrode out of contact with the tissue.

A method of operating a bipolar electrode assembly in two output voltage ranges, the assembly including an active electrode and a return electrode, the active electrode having an exposed treatment portion, and the return electrode having an exposed fluid contact surface radially spaced and axially set back from the exposed treatment option, the active electrode and return electrode being in a fixed relationship during use such that, when the electrode assembly is immersed in a conductive fluid medium the ratio of (i) the length of the shortest conduction path (P.sub.1) through the fluid medium between the exposed fluid contact surface and that part of the exposed treatment portion which is furthest from the exposed fluid contact surface, to (ii) the length of the shortest conduction path (P.sub.2) through the fluid medium between the exposed fluid contact surface and the exposed treatment portion, is less than or equal to 2 to 1, but greater than or equal to 1.25 to 1 the method comprising the steps of:

• (a) introducing the electrode assembly into a selected operation site;
• (b) surrounding the electrode assembly with a first fluid constituting a conductive liquid;
• (c) applying sufficient radio frequency output power in a first voltage range to the electrode assembly to thermally evaporate the first fluid adjacent the active electrode treatment portion to create a second fluid, the second fluid constituting a vapour pocket;
• (d) applying sufficient radio frequency output power in a second voltage range to the electrode assembly to maintain the second fluid adjacent the active electrode treatment portion without producing thermal disintegration of said active electrode;
• (e) positioning the treatment portion of the active electrode adjacent the tissue with the vapour pocket in contact with the tissue while maintaining the return electrode out of contact with the tissue.

A method of operating a bipolar electrode assembly in two output voltage ranges, the assembly including an active electrode and a return electrode, the active electrode having an exposed treatment portion, and the return electrode having an exposed fluid contact surface radially spaced and axially set back from the exposed treatment portion in a fixed relationship during use, such that, the length of the shortest conduction path through a fluid medium between the exposed fluid contact surface and the exposed treatment portion is large enough to prevent direct arcing between the exposed treatment portion and the fluid contact surface, and wherein the ratio of (i) the length of the shortest conduction path (P.sub.1) through the fluid medium between the exposed fluid contact surface and that part of the exposed treatment portion which is furthest f from the exposed fluid contact surface, to (ii) the length of the shortest conduction path (P.sub.2) through the fluid medium between the exposed fluid contact surface and the exposed treatment portion, is less than or equal to 2 to 1, but greater than or equal to 1.25 to 1, the method comprising the steps of:

• (a) introducing the electrode assembly into a selected operation site;
• (b) surrounding the electrode assembly with a first fluid constituting a conductive liquid;
• and either
• (c) applying sufficient radio frequency output power in a first voltage range to the electrode assembly to increase the temperature of the fluid adjacent the active electrode treatment portion to near boiling without creating a vapour pocket surrounding the treatment portion when the electrosurgical instrument is used for desiccation;
• or
• (d) applying sufficient radio frequency output power in a second voltage range to the electrode assembly to thermally evaporate the fluid adjacent the active electrode treatment portion to create a vapour pocket surrounding the treatment portion when the electrosurgical instrument is used for cutting or ablation.