IlllllllllllllllIllllIlllllllllllllllllllIllllI||||lllllllllllllllllllllll
`US005540684A
`
`United States Patent
`
`[19]
`
`{in Patent Number:
`
`5,540,684
`
`Hassler, Jr.
`
`[451 Date of Patent:
`
`Jul. 30, 1996
`
`[54] METHOD AND APPARATUS FOR
`ELECTROSURGICALLY TREATING TISSUE
`
`Inventor: William L. Hassler, Jr., c/o Ethicon
`Endo—Surgery, 4545 Creek Rd.,
`Cincinnati, Ohio 45242—2839
`
`Appl. No.: 282,522
`
`Filed:
`
`Jul. 28, 1994
`
`Int. Cl.“ ....................................... .. A61B 17/39
`U.S. Cl. ...................... 606/40; 606/38; 606/51
`Field of Search .................................. 606/37-40, 51,
`606/52
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`.
`
`3/1972 1-lildebrandt et al.
`3,651,811
`11/ 1980 Herczog .
`4,232,676
`2/1981 1-lerczog et al. .
`4,248,231
`10/1984 Koch.
`4,474,179
`3/1987 Chang ct al. .
`4,651,280
`4/1987 Harris ct :11.
`.
`4,658,819
`8/1987 Koch et al.
`4,685,459
`2/1990 Stasz et al.
`4,903,696
`7/1990 Ensslin .
`4,938,761
`10/1991 Rink.
`5,057,099
`606/40
`6/1992 Lennox
`5,122,137
`606/40
`8/1994 Nardella
`5,342,357
`............................... 606/40
`4/1995 Yates et al.
`5,403,312
`FOREIGN PATENT DOCUMENTS
`2573301
`5/1986
`France .
`
`,
`.
`
`2455171
`2213381
`94/10925
`95/09576
`
`8/1976
`8/1989
`5/1994
`4/1995
`
`Germany .
`United Kingdom .
`WIPO .
`WIPO .
`
`Primary Examiner—Lee S. Cohen
`
`[57]
`
`ABSTRACT
`
`Tissuc impedance or tissue impedance in combination with
`tissue temperature is used to control electrosurgical tissue
`treatment. Tissue impedance alone provides better control of
`electrosurgical treatment by determining an initial maxi-
`mum tissue impedance, a minimum tissue impedance select-
`ing a point between the maximum and minimum imped-
`ances, preferably the average, as an impedance threshold,
`and turning off rf power to the electrosurgical instrument
`when the impedance reaches the threshold as it rises from
`the minimum. Control may also be by the combination of
`tissue impedance and temperature. Temperature is con-
`trolled to maintain a selected preferred temperature and a
`maximum temperature is also selected so that if the tissue
`reaches the maximum temperature, power is turned off.
`Impedance control is combined with temperature control so
`that the temperature of the instrument is maintained at a
`selected preferred temperature unless a maximum tempera-
`ture is exceeded, which normally will not happen. The
`impedance is also monitored with maximum and minimum
`values being determined as well as a threshold impedance
`between the max and the min. When the threshold, prefer-
`ably the average impedance, is reached, power is removed
`from the instrument.
`
`15 Claims, 7 Drawing Sheets
`
`CONT/YDLLE/7
`
`.L
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`lrltrrel
`. _. _ .1
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`\\ 1340
`/343
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`/37
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`ETHICON ENDO-SURGERY, INC.
`
`EX. 1014
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`1
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`

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`U.S. Patent
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`"
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`Jul. 30, 1996
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`Sheet 1 of 7
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`5,540,684
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`2
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`U.S. Patent
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`11]. 30, 1996
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`Sheet 2 of7
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`5,540,684
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`3
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`U.S. Patent
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`Jul. 30, 1996
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`Sheet 3 of 7
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`5,540,684
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`/35
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`/34
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`/4! ‘L /43
`T ‘ "1
`I
`-..l :5’?-75*-?:
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`CONTROLLER
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`J fiji
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`I340
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`/37
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`4
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`U.S. Patent
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`Jul. 30, 1996
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`Sheet 4 of 7
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`5,540,684
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`TURN ON
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`RF POWER
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`NO
`
`RF
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`POWER ON
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`7
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`/50
`
`YES
`
`MEASURE
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`IRF 8 VRF
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`CALCULAT
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`Z
`
`TO
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`FROM
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`FIG -5
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`F/G -5
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`5
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`

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`U.S. Patent
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`Jul. 30, 1996
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`Sheet 5 of 7
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`5,540,684
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`F
`_
`ROM FIG 4
`
`To
`FIG-4
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`ZMIN=Z/
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`ZAVG=
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`ZMAX-1» ZMIN
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`2
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`SET
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`ZAVG FLAG
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`6
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`U.S. Patent
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`Jul. 30, 1996
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`Sheet 6 of 7
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`5,540,684
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`_' DRIVER
`I
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`/37
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`7
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`U.S. Patent
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`Jul. 30, 1996
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`Sheet 7 of 7
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`5,540,684
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`IMPEDANCE
`
`ZMAX
`
`T
`
`Zfh
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`l
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`8
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`

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`5,540,684
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`1
`METHOD AND APPARATUS FOR
`ELECTROSURGICALLY TREATING TISSUE
`
`BACKGROUND OF THE INVENTION
`
`The present invention relates in general to electrosurgical
`treatment of tissue and, more particularly, to a method and
`apparatus
`for electrosurgical
`treatment wherein tissue
`impedance or tissue impedance in combination with tissue
`temperature are used to control the electrosurgical treatment.
`Many available radio frequency (rf) generators for use in
`the medical field for surgical purposes including cauteriza-
`tion, dissection, transection,
`tissue welding and the like,
`generally do not effectively regulate the electrical power
`supplied to an clcctrosurgical instrument. Typically such
`generators control the voltage such that a selected power
`level
`is approximately delivered and a maximum power
`level is not exceeded. When such rf generators are used, the
`primary control
`is the experience of the surgeon who
`responds to what is observed as happening to the tissue
`being treated using the if energy. Often, particularly for
`endoscopic procedures, surgeons can not see what is hap-
`pening to the tissue and may not be able to react quickly
`enough even if good observation is possible.
`A variety of instrument and rf energy generator control
`arrangements have been proposed. For example, tempera-
`ture sensors have been incorporated into rf forceps to sense
`the temperatures of the contact faces of the forceps with the
`rfpower applied to the forceps being controlled based on the
`temperature of one or both of the contact faces or the
`temperature difference between the contact faces.
`Rf power has been controlled in accordance with me
`square of the impedance over the range of increasing tissue
`impedance. The differential quotient of tissue impedance has
`also been considered with regard to determining the initial
`power level and the time for switching off rf power applied
`to tissue.
`
`Notwithstanding these control arrangements, there is a
`continuing need in the art for different approaches and
`techniques for the control of rf energy powered surgical
`instruments to better assist surgeons and improve treatment
`using rf energy.
`
`SUMMARY OF THE INVENTION
`
`This need is met by the invention of the present applica-
`tion wherein tissue impedance or tissue impedance in com-
`bination with tissue temperature is used to control electro-
`surgical tissue treatment. Tissue impedance can be used by
`itself for better control of eleetrosurgical treatment by deter-
`mining an initial tissue impedance which is a maximum
`impedance for the tissue, a minimum impedance for the
`tissue which signals the end of the initial tissue heating and
`the onset of tissue desiccation, selecting a point between the
`maximum and minimum impedances as a threshold, and
`turning olI power to the electrosurgical instrument when the
`impedance reaches the threshold as it rises from the mini-
`mum after falling from the maximum to the minimum.
`Preferably, the threshold is selected as the average between
`the maximum and minimum impedance values.
`Further and more precise control is effected by the com-
`bination of tissue impedance and temperature to control
`clectrosurgical treatment. The temperature is controlled to
`maintain a selected preferred temperature for the electrosur-
`gical procedure being performed. A maximum temperature
`is also selected such that if the tissue reaches the maximum
`
`2
`temperature the power is turned elf to the electrosurgical
`instrument. Impedance control is combined with tempera-
`ture control by incorporating the previously described
`impedance control of the instrument with the temperature
`control. Thus, the temperature of the instrument is main-
`tained at a selected preferred temperature unless a maximum
`temperature is exceeded, which normally will not happen.
`The impedance is also monitored with maximum and mini-
`mum valucs being determined as well as a threshold imped-
`ance between the maximum and the minimum. When the
`threshold, preferably the average impedance,
`is reached,
`power is removed from the instrument.
`In accordance with one aspect of the present invention, an
`electrosurgical apparatus for coagulating tissue during a
`surgical procedure comprises first and second elements
`electrically insulated from one another and movable relative
`to one another for engaging tissue to be coagulated therebc-
`tween. A power controller responsive to a power control
`signal provides for controlling rf energy connected to the
`first and second elements. Impedance measurement circuitry
`coupled to the first and second elements measures the
`impedance of tissue between the first and second elements.
`The impedance measuring circuitry includes a first device
`for storing an initial impedance value which is a maximum
`impedance, and a second device for storing a minimum
`impedance value. A threshold determining circuit is coupled
`to the first and second devices for determining a threshold
`impedance value between the initial maximum impedance
`value and the minimum impedance value. A first comparator
`compares measured impedance values to the threshold
`impedance value and generates a power control signal to
`stop the power controller upon the measured impedance
`value exceeding the threshold impedance value.
`For use of commonly available rf power generators, the
`power controller includes at least one electrical switch for
`selectively applying rf energy to the first and second ele-
`ments for coagulating tissue positioned between the first and
`second elements. The threshold determining circuit com-
`prises an averaging circuit
`for determining an average
`impedance value approximately midway between the initial
`maximum impedance value and the minimum impedance
`value and setting the threshold impedance to the average
`impedance value.
`The electrosurgical apparatus may further comprise at
`least one temperature sensor coupled to the first element or
`at least one temperature sensor coupled to the first element
`and at least one temperature sensor coupled to the second
`element. A third device determines a maximum acceptable
`temperature for coagulating tissue. A second comparator
`compares the maximum acceptable temperature to a tissue
`temperature. The tissue temperature is derived from tem-
`peratures indicated by the at least one temperature sensor
`coupled to the first element or the temperature sensors
`coupled to the first and second elements. The second com-
`parator generates a control signal
`to enable the power
`controller as long as the tissue temperature does not exceed
`the maximum acceptable temperature and to disable the
`power controller upon a tissue temperature exceeding the
`maximum acceptable temperature.
`In accordance with another aspect of the present inven-
`tion, an apparatus for electrosurgically treating tissue during
`a surgical procedure comprises an instrument for applying rf
`energy to tissue to be electrosurgically treated. Impedance
`measurement circuitry is coupled to the instrument for
`measuring the impedance of tissue engaged by the instru-
`ment and for generating a representative impedance signal.
`Temperature measurement circuitry is coupled to the instru-
`
`9
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`5,540,684
`
`3
`ment for measuring the temperature of tissue engaged by the
`instrument and for generating a representative temperature
`signal. Control circuitry responsive to the impedance signal
`and the temperature signal is provided for controlling rf
`energy connected to the instrument.
`the instrument
`In one embodiment of the invention,
`comprises a pair of forceps for coagulating tissue during a
`surgical procedure. The impedance measurement circuitry
`comprises a first device for storing an initial maximum
`impedance value and a second device for storing a minimum
`impedance value. The control circuitry comprises a thresh-
`old determining circuit connected to the first and second
`devices
`for determining a threshold impedance value
`between the initial maximum impedance value and the
`minimum impedance value. A first comparator compares
`measured impedance values to the threshold impedance
`value and generates a control signal
`to stop the power
`controller upon the measured impedance value exceeding
`the threshold impedance value. For use of commonly avail-
`able rf power generators, the control circuitry includes at
`least one electrical switch for selectively applying rf energy
`to the instrument.
`
`In accordance with still another aspect of the present
`invention, a method of operating apparatus for electrosur-
`gieally treating tissue during a surgical procedure comprises
`the steps of: applying rf energy to tissue to be electrosurgi-
`cally treated by means of an electrosurgical
`instrument;
`measuring the impedance of tissue engaged by the electro-
`surgical instrument; generating an impedance signal repre-
`sentative of the impedance of the tissue; measuring the
`temperature of tissue engaged by the electrosurgical instru-
`ment; generating a temperature signal representative of the
`temperature of the tissue; and, controlling the rf energy
`applied to the electrosurgical instrument in response to the
`impedance signal and the temperature signal.
`The step of controlling the rf energy applied to the
`electrosurgical instrument may comprise the steps of: stor-
`ing an initial maximum impedance value; storing a mini-
`mum impedance value; determining a threshold impedance
`value between the initial maximum impedance value and the
`minimum impedance value; comparing measured imped-
`ance values to the threshold impedance value; and, gener-
`ating a control signal to stop the power controller upon the
`measured impedance value exceeding the threshold imped-
`ance value.
`
`The step of applying rf energy to tissue to be electrosur-
`gieally treated by means of an electrosurgical instrument
`may comprise the step of selectively applying rl energy to
`the electrosurgical instrument.
`The step of controlling the rl energy applied to the
`electrosurgical instrument may also comprise the steps of:
`storing a maximum acceptable temperature for operation of
`the electrosurgical instrument; comparing temperature sig-
`nals and the maximum acceptable temperature; enabling the
`step of applying rf energy as long as temperature signals do
`not exceed the maximum acceptable temperature; and, dis-
`abling the step of applying rf energy for a temperature signal
`exceeding the maximum acceptable temperature.
`In accordance with yet another aspect of the present
`invention, a method of operating electrosurgical apparatus
`for coagulating tissue during a surgical procedure comprises
`the steps of: engaging tissue to be coagulated between first
`and second elements electrically insulated from one another
`and movable relative to one another; selectively controlling
`rf energy connected to the first and second elements for
`coagulating tissue positioned therebetween; measuring the
`
`4
`impedance of tissue positioned between the first and second
`elements; storing an initial maximum impedance value;
`storing a minimum impedance value; determining a thresh-
`old impedance value between the initial maximum imped-
`ance value and the minimum impedance value; comparing
`measured impedance values to the threshold impedance
`value; and, stopping the rf energy connected to the first and
`second elements upon the measured impedance value
`exceeding the threshold impedance Value.
`The step of selectively controlling rf energy connected to
`the first and second elements comprises the step of switching
`the rf energy on and off.
`The step of determining a threshold impedance value
`between the initial maximum impedance value and the
`minimum impedance value may comprise the steps of:
`determining an average impedance value between the initial
`maximum impedance value and the minimum impedance
`value; and, setting the threshold impedance to the average
`impedance value.
`The method may further comprise the steps of: coupling
`temperature sensors to the first and second elements; storing
`a maximum acceptable temperature for coagulating tissue;
`comparing temperatures from the temperature sensors and
`the maximum acceptable temperature; enabling the rf energy
`as long as a temperature of one of the temperature sensors
`does not exceed the maximum acceptable temperature; and,
`disabling the rf energy upon a temperature of one of the
`temperature sensors exceeding the maximum acceptable
`temperature.
`In accordance with still yet another aspect of the present
`invention, a method of operating apparatus for electrosur-
`gically treating tissue during a surgical procedure comprises
`the steps of: applying rf energy to tissue to be electrosurgi-
`cally treated by means of an electrosurgical
`instrument
`through an rf energy switch; measuring the temperature of
`tissue engaged by the electrosurgical instrument; generating
`a temperature signal representative of the temperature of the
`tissue; controlling the rf energy switch in response to the
`temperature signal to maintain a selected temperature for
`tissue engaged by the electrosurgical instrument; measuring
`the impedance of tissue engaged by the electrosurgical
`instrument; generating an impedance signal representative
`of the impedance of the tissue; and, controlling the rl energy
`switch in response to the impedance signal
`to stop the
`application of the rf energy to tissue engaged by the elec-
`trosurgical instrument.
`The step of controlling the rf energy switch in response to
`the impedance signal to stop the application of the rf energy
`to tissue engaged by the electrosurgical
`instrument may
`comprise the steps of: storing an initial maximum imped-
`ance value; storing a minimum impedance value; determin-
`ing a threshold impedance value between the initial maxi-
`mum impedance value and the minimum impedance value;
`comparing measured impedance values to the threshold
`impedance value; and, generating a control signal to stop the
`power controller upon the measured impedance value
`exceeding the threshold impedance value.
`The step of determining a threshold impedance value
`between the initial maximum impedance value and the
`minimum impedance value may comprise finding the mid-
`point between the initial maximum impedance value and the
`minimum impedance value.
`The method may further comprise the steps of: setting a
`maximum temperature of tissue engaged by the electrosur-
`gical instrument; comparing measured temperature values to
`the maximum temperature; and, generating a control signal
`
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`5,540,684
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`5
`to stop the power controller upon a measured temperature
`value exceeding the maximum temperature value.
`It is thus an object of the present invention to provide an
`improved method and apparatus for controlling electrosur-
`gical instrument control; to provide an improved method and
`apparatus for controlling electrosurgical instrument control
`wherein an impedance threshold between an initial maxi-
`mum impedancc and a minimum impedance is selected and
`used to shut off rf power to the instrument when the
`threshold is reached; and, to provide an improved method
`and apparatus for controlling electrosurgical instrument con-
`trol wherein both temperature and impedance measurements
`are used to control the instrument.
`
`Other objects and advantages of the invention will be
`apparent from the following description, the accompanying
`drawings and the appended claims.
`
`BRIEF DESCRIPTION OF THE INVENTION
`
`FIG. 1 is a perspective view of a pair of endoscopic
`bipolar electrosurgical forceps operable in accordance with
`the present invention;
`FIG. 2 is a perspective View of tissue gripping elements
`of the forceps of FIG. 1 shown on an enlarged scale to
`illustrate temperature sensors coupled to the tissue gripping
`elements;
`FIG. 3 is a schematic block diagram of apparatus for
`controlling the forceps of FIG. 1 for electrosurgically treat-
`ing tissue in accordance with the present invention;
`FIGS. 4 and 5 form a flow chart for operation of a
`microprocessor controller when used in the apparatus of
`FIG. 3;
`FIG. 6 is a schematic block diagram of an alternate
`embodiment of a controller for use in the apparatus of FIG.
`3; and
`FIG. 7 is a graph illustrating the change of impedance
`over time during application of electrosurgical energy to
`tissue.
`
`DETAILED DESCRIPTION OF TIIE
`INVENTION
`
`While the present invention is generally applicable to a
`variety of surgical instruments, both conventional and endo-
`scopic, it will be described herein with reference to a pair of
`endoscopic bipolar electrosurgical forceps for which the
`invention is initially being applied. As shown in FIG. 1, a
`pair of endoscopic bipolar electrosurgical forceps 100 oper-
`able in accordance with the present invention includes a
`proximal handle operating end 102 and first and second
`gripping elements 104, 106 at the distal end of the instru-
`ment. The gripping elements are electrically insulated from
`one another and movable relative to one another for engag-
`ing tissue to be coagulatcd therebetween.
`The distal gripping elements 104, 106 are separated from
`the proximal handle operating end 102 by a long tubular
`member 108. In terms of gripping tissue, the pair of endo-
`scopic bipolar electrosurgical forceps 100 are operated in a
`conventional well known manner by moving the forward
`handle portion 102A toward the rearward handle portion
`102B. Accordingly, description of the forceps will be made
`only to the extent necessary for understanding the present
`invention.
`
`For operation in accordance with the present invention,
`the gripping elements 104, 106 are modified to couple at
`least one temperature sensor to each of the gripping ele-
`
`6
`ments 104, 106. In the illustrated embodiment, a single
`resistive thermal device (RTD) 110 is coupled to the grip-
`ping element 104 and a single RTD 112 is coupled to the
`gripping element 106, see FIG. 2. While RTD’s secured to
`the outer back surfaces of the gripping elements 104, 106,
`are utilized in the illustrated embodiment,
`it should be
`apparent that other temperature sensors can be coupled to
`the gripping elements 104, 106 in a variety of ways, for
`example by embedding the sensors in the gripping elements
`104, 106.
`Two pairs of electrical conductors 114, 116 are provided
`for making electrical connections to the RTD’s 110, 112. The
`electrical conductors are housed in sheaths 114A, 116A
`which are routed through the long tubular member 108 and
`ultimately joined in a conductor protective sheath 117 which
`terminates in a four conductor connector 118 shown in FIG.
`1 for connection to temperature monitoring circuitry. A
`second two conductor connector 120 secured to the end of
`conductor protective sheath 122 provides for connection of
`radio frequency (rf) energy to the gripping members 104,
`106 to perform electrosurgical treatment using the endo-
`scopic bipolar electrosurgical forceps 100. Connection of
`these elements for operation of the present invention will
`now be described with reference to FIGS. 3-6.
`
`FIG. 3 is a schematic block diagram of apparatus for
`controlling the pair of endoscopic bipolar electrosurgical
`forceps of FIG. 1 for elcctrosurgically treating tissue in
`accordance with the present invention. The same identifica-
`tion numerals are used for corresponding elements from
`other drawings within the application. In FIG. 3, a section of
`tissue 124 comprising two layers of tissue 124A and 124B
`which are to be engaged by the gripping elements 104, 106
`and electrosurgically treated thereby are shown inserted
`between the gripping elements 104, 106. In the case of the
`pair of endoscopic bipolar electrosurgical forceps 100, the
`two layers of tissue 124A, 124B are to be welded together.
`Since tissue welding is not very well understood in the art
`at the present time,
`tissue welding is defined herein as
`bringing two pieces of tissue together and joining them
`together. The welding operation is believed to be performed
`by causing collagen molecules in the tissue to be mobilized
`by severing the disulfide cross linkages. The collagen mol-
`ecules then diffuse across the interface between the two
`pieces of tissue. Finally, new disulfide linkages are formed
`across the interface between the two pieces of tissue thereby
`causing the interface to disappear.
`While temperature and impedance have been used sepa-
`rately to control electrosurgical instruments, the two can be
`advantageously combined to provide an optimum control of
`such instruments. Tissue temperature defines the level of
`activation energy available for the chemical reaction noted
`above for tissue welding; and, the impedance defines the rate
`at which the reaction takes place. By utilizing both tissue
`temperature and impedance, optimum control can be
`attained as will be described.
`
`FIG. 7 graphically illustrates the change of impedance
`over time during application of electrosurgical energy to
`tissue. In FIG. 7, the onset of electrosurgical energy to the
`tissue occurs at time t1. Time t2 is believed to correspond to
`the end of the tissue heating phase and beginning of tissue
`desiccation. It is further believed that tissue desiccation is
`almost completed by time 13, and that tissue carbonization
`begins at time t4.
`While optimum control is attained by utilizing both tissue
`temperature and impedance as will be described, the present
`invention also provides improved control of an electrosur-
`
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`5,540,684
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`7
`
`instrument by means of impedance measurement
`gical
`alone. In accordance with this aspect of the present invention
`an initial tissue impedance, a maximum impedance for the
`tissue, Zmax,
`is determined (for example at time t1). A
`minimum impedance for the tissue, Zrnin, which is believed
`to signal the approximate end of the initial tissue heating and
`the onset of tissue desiccation, is determined (for example at
`time t2a). An impedance between the maximum and mini-
`mum impedances, Zth, is selected as a threshold, and rf
`power to the electrosurgical instrument is turned off when
`the impedance reaches the threshold as it rises from the
`minimum. Preferably, the threshold is selected as the aver-
`age between the maximum and minimum impedance values.
`This
`impedance control
`arrangement will be further
`described with reference to the combined tissue impedance
`temperature control.
`As shown in FIG. 3, the RTD’s 110, 112 are connected to
`a controller circuit 126 through preprocessing amplifiers
`represented by a pair of amplifiers 128, 130. The output
`signals from the amplifiers 128, 130 are passed to the
`controller circuit 126 via conductors 131. The output signals
`from the amplifiers 128, 130 are representative of the
`temperatures of the gripping elements 104, 106 and, accord-
`ingly, the temperature of the section of tissue 124 gripped
`between the gripping elements such that
`the controller
`circuit 126 can monitor the temperatures of the gripping
`elements 104, 106 and thereby the temperature of the section
`of tissue 124.
`
`An rf generator 132 provides rf energy to the gripping
`elements 104, 106 through a power controller 134, imped-
`ance measurement circuitry 136 and the connector 120. The
`power controller 134 is responsive to a power control signal
`generated by the controller circuit 126 for controlling rf
`energy connected to the gripping elements 104, 106. The
`impedance measurement circuitry 136 is coupled to the
`gripping elements 104, 106 for measuring the impedance of
`the tissue 124 gripped therebetween.
`the power
`In the illustrative embodiment of FIG. 3,
`controller 134 comprises a pair of normally open relay
`contacts 134A and 134B (indicated by an X) which are
`opened and closed by an associated relay coil 134C which
`receives control signals over conductors 137. Of course,
`other electromechanical and solid state switching devices
`can be used in the invention of the present application.
`The impedance measurement circuitry 136 comprises a
`low impedance current monitoring device 138 connected in
`series with the rf generator 132; and, a high impedance
`voltage monitoring device 140 connected in parallel across
`the rf generator 132. A noise filter 141 may also be inserted
`between the current and voltage monitoring devices 138,
`140 and the controller circuit 126 to filter noise out of the
`signals generated by the current and voltage monitoring
`devices 138, 140 which are past to the controller circuit 126
`over conductors 143.
`
`In a working embodiment of the present invention, cur-
`rent and voltage monitoring transformers were used for the
`current and voltage monitoring devices 138, 140. The cur-
`rent monitoring transformer was constructed on a toroidal
`iron ferrite core manufactured by Micrometals and having a
`one inch outer diameter. The current monitoring transformer
`was wound with 2 primary turns and 25 secondary turns,
`both primary and secondary being 24 gauge wire. The
`voltage monitoring transformer was constructed using the
`same type core and 24 gauge wire but was wound with 32
`primary windings and 2 secondary windings. Of course,
`other current and voltage monitoring devices can be used in
`
`8
`the invention of the present application. In any event, current
`and voltage signals representative of the rf current flowing
`through the section of tissue 124 and the rf voltage con-
`nected across the section of tissue 124 are passed to the
`controller circuit 126 which converts the current and voltage
`signals tissue impedance values.
`A start switch 142 is connected to the controller circuit
`126 via a conductor 145 to generate a start signal to thereby
`initiate application of rf energy or power to the gripping
`elements 104, 106. The rf power is then controlled in
`accordance with the present invention such that consistent
`tissue welding is performed using the pair of endoscopic
`bipolar electrosurgical forceps 100. In particular,
`in the
`illustrated embodiment, the temperature and impedance of
`the section of tissue 124 are monitored and the temperature
`maintained at a selected temperature until either an imped-
`ance threshold is exceeded or, in the event of some problem,
`a maximum temperature is exceeded at which time the rf
`power is removed until the start switch 142 is once again
`operated. The start switch 142 should not be operated again
`until the surgeon controlling the pair of endoscopic bipolar
`electrosurgical forceps 100 has repositioned the forceps and
`is ready to electrosurgically treat the tissue which has then
`been engaged.
`The controller circuit 126 can take the form of a proces-
`sor, such as a microprocessor, in which case, the processor
`may be programmed to operate in accordance with the flow
`chart shown in FIGS. 4 and 5. Alternately, the controller
`circuit 126 can be a dedicated circuit for example as shown
`in FIG. 6. Operation of a processor controlled system will
`now be described with reference to FIGS. 4 and 5.
`
`Initially referring to FIG. 4, once the system has been
`activated, the processor will search for a new start signal as
`generated by activation of the start switch 142, see block
`144. Upon receipt of a start signal from the start switch 142,
`the coil 134c is activated to turn on rf power to the pair of
`endoscopic bipolar electrosurgical forceps 100, see block
`146.
`
`The temperatures, T1 and T2, of the gripping elements
`104, 106, respectively, are taken and an average temperature
`TAVG is calculated as being representative of the tempera-
`ture of the section of tissue 124, see blocks 148, 150. Of
`course, the temperatures T1 and T2 could be individually
`utilized if desired.
`A maximum temperature TMAX is selected which should
`never be reached in a properly operating system. Above
`TMAX, rf power is removed from the gripping elements
`104, 106 until the next operation of the start switch 142.
`While TMAX should never be reached during proper opera-
`tion of the system, it serves as a safety valve to ensure
`removal of rf power in the event of a problem. TMAX may
`be set for example between 85° C. and 100° C. In any event,
`TAVG is compared to TMAX: if TAVG is greater than
`TMAX, the rf power is turned off by deactivating the coil
`134C, a flag indicating the determination of ZAVG is cleared
`and the processor returns to the block 144 to search for a new
`start signal as generated by activation of the start switch 142,
`see blocks 152, 154, the determination of ZAVG and cor-
`responding flag will be described with reference to FIG. 5;
`if TAVG is not greater than TMAX, TAVG is compared to
`TSET, a desired operating temperature for the gripping
`elements 104, 106, see blocks 152, 156.
`If TAVG is greater than TSET, the if power is turned oil"
`by deactivating the coil 134C, see blocks 156, 158. This
`enters the temperature control loop including blocks 148,
`150, 152, 156 and 158. The processor continues to loop,
`
`12
`
`

`
`5,540,684
`
`9
`providedTAVG does not exceed TMAX, which it should not
`since rf power has been removed from the gripping elements
`104, 106, until TAVG is not greater than TSET. At this point,
`the processor determines whether rf power is on or not, see
`block 160. If the rf power is not on, it is turned on by
`returning to the block 146. If rf power is turned on, the rf
`current IRF and rf voltage VRF are measured by reading the
`output signals from the current and voltage monitoring
`devices 138, 140 and the impedance Z is calculated, sec
`blocks 162, 164.
`Referring now to FIG. 5, the flag indicating the determi-
`nation of ZAVG is checked, see block 166. If the flag is set
`indicating that ZAVG has b