Method and apparatus for electrosurgically treating tissue

• US 5,540,684 A
• Filed: 07/28/1994
• Issued: 07/30/1996
• Est. Priority Date: 07/28/1994
• Status: Expired due to Term

• Current Assignee: Ethicon Endo-Surgery, Inc. (Johnson & Johnson)
• Original Assignee: Ethicon Endo-Surgery, Inc. (Johnson & Johnson)
• Inventors: Hassler, William L. Jr.
• Primary Examiner(s): Cohen, Lee S.
• Application Number:
  US08/282,522
• Time in Patent Office: 733 Days
• Field of Search: 606/37-40, 606/51, 606/52
• US Class Current: 606/40
• CPC Class Codes: A61B 18/1206 Generators therefor
• CPC Class Codes: A61B 18/1442 Probes having pivoting end effectors, e.g. forceps
• CPC Class Codes: A61B 2018/00666 using a threshold value
• CPC Class Codes: A61B 2018/00678 upper
• CPC Class Codes: A61B 2018/00702 Power or energy
• CPC Class Codes: A61B 2018/00708 switching the power on or off
• CPC Class Codes: A61B 2018/00791 Temperature
• CPC Class Codes: A61B 2018/00875 Resistance or impedance

Abstract

Tissue 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 maximum tissue impedance, a minimum tissue impedance selecting a point between the maximum and minimum impedances, 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 controlled 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 temperature 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, preferably the average impedance, is reached, power is removed from the instrument.

Claims

1. An electrosurgical apparatus for coagulating tissue during a surgical procedure, said apparatus comprising:

first and second elements electrically insulated from one another and movable relative to one another for engaging tissue to be coagulated therebetween;

a power controller responsive to a power control signal for controlling RF energy connected to said first and second elements;

impedance measurement circuitry coupled to said first and second elements for measuring the impedance of tissue between said first and second elements, said impedance measuring circuitry including;

a first device for storing an initial maximum impedance value; and

a second device for storing a minimum impedance value;

a threshold determining circuit coupled to said first and second devices for determining a threshold impedance value between said initial maximum impedance value and said minimum impedance value; and

a first comparator operatively associated with said threshold determining circuit for comparing measured impedance values to said threshold impedance value and generating a power control signal to stop said power controller upon said measured impedance value exceeding said threshold impedance value.

2. An electrosurgical apparatus for coagulating tissue during a surgical procedure as claimed in claim 1 wherein said power controller includes at least one electrical switch for selectively applying rf energy to said first and second elements for coagulating tissue positioned between said first and second elements.

3. An electrosurgical apparatus for coagulating tissue during a surgical procedure as claimed in claim 1 wherein said threshold determining circuit comprises an averaging circuit for determining an average impedance value approximately midway between said initial maximum impedance value and said minimum impedance value and setting said threshold impedance to said average impedance value.

4. An electrosurgical apparatus for coagulating tissue during a surgical procedure as claimed in claim 1 further comprising:

at least one temperature sensor coupled to said first element;

a third device for determining a maximum acceptable temperature for coagulating tissue; and

a second comparator operatively associated with said third device for comparing said maximum acceptable temperature to a tissue temperature derived from temperatures indicated by said at least one temperature sensor coupled to said first element and generating a control signal to enable said power controller as long as said tissue temperature does not exceed said maximum acceptable temperature and to disable said power controller upon a tissue temperature exceeding said maximum acceptable temperature.

5. An electrosurgical apparatus for coagulating tissue during a surgical procedure as claimed in claim 4 further comprising at least one temperature sensor coupled to said second element and wherein said tissue temperature is derived from temperatures indicated by said at least one temperature sensor coupled to said first element and said at least one temperature sensor coupled to said second element.

6. A method of operating electrosurgical apparatus for coagulating tissue during a surgical procedure, said method comprising 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 said first and second elements for coagulating tissue positioned therebetween;

measuring the impedance of tissue positioned between said first and second elements;

storing an initial maximum impedance value;

storing a minimum impedance value;

determining a threshold impedance value between said initial maximum impedance value and said minimum impedance value;

comparing a measured impedance value to said threshold impedance value; and

stopping said RF energy connected to said first and second elements upon said measured impedance value exceeding said threshold impedance value.

7. A method of operating electrosurgical apparatus for coagulating tissue during a surgical procedure as claimed in claim 6 wherein said step of selectively controlling rf energy connected to said first and second elements comprises the step of switching said rf energy on and off.

8. A method of operating electrosurgical apparatus for coagulating tissue during a surgical procedure as claimed in claim 6 wherein the step of determining a threshold impedance value between said initial maximum impedance value and said minimum impedance value comprises the steps of:

determining an average impedance value between said initial maximum impedance value and said minimum impedance value; and

setting said threshold impedance value to said average impedance value.

9. A method of operating electrosurgical apparatus for coagulating tissue during a surgical procedure as claimed in claim 6 further comprising the steps of:

coupling at least one temperature sensor to said first element;

determining a maximum acceptable temperature;

comparing temperatures from said temperature sensor and said maximum acceptable temperature;

enabling said RF energy as long as a temperature of said temperature sensor does not exceed said maximum acceptable temperature; and

disabling said RF energy upon a temperature of said temperature sensor exceeding said maximum acceptable temperature.

10. A method of operating electrosurgical apparatus for coagulating tissue during a surgical procedure as claimed in claim 6 further comprising the steps of:

coupling at least one temperature sensor to said first and second elements;

storing a maximum acceptable temperature for coagulating tissue;

comparing temperatures from at least one of said temperature sensors and said maximum acceptable temperature;

enabling said rf energy as long as a temperature of one of said temperature sensors does not exceed said maximum acceptable temperature; and

disabling said rf energy upon a temperature of one of said temperature sensors exceeding said maximum acceptable temperature.

11. An apparatus for electrosurgically treating tissue during a surgical procedure, said apparatus comprising:

an instrument for applying RF energy to tissue to be electrosurgically treated;

impedance measurement circuitry coupled to said instrument for measuring the impedance of tissue engaged by said instrument and for generating a representative impedance signal wherein said impedance measurement circuitry comprises;

a first device for storing an initial maximum impedance value; and

a second device for storing a minimum impedance value;

temperature measurement circuitry coupled to said instrument for measuring the temperature of tissue engaged by said instrument and for generating a representative temperature signal; and

control circuitry operatively associated with said impedance circuitry and said temperature measurement circuitry and responsive to said impedance signal and said temperature signal for controlling RF energy connected to said instrument, wherein said control circuitry comprises;

a threshold determining circuit connected to said first and second devices for determining a threshold impedance value between said initial maximum impedance value and said minimum impedance value; and

a first comparator operatively associated with said threshold determining circuit for comparing a measured impedance value to said threshold impedance value and generating a control signal upon said measured impedance value exceeding said threshold impedance value.

12. A method of operating apparatus for electrosurgically treating tissue during a surgical procedure, said method comprising the steps of:

applying RF energy to tissue to be electrosurgically treated by means of an electrosurgical instrument;

measuring the impedance of tissue engaged by said electrosurgical instrument;

generating an impedance signal representative of the impedance of said tissue;

measuring the temperature of tissue engaged by said electrosurgical instrument;

generating a temperature signal representative of the temperature of said tissue; and

controlling the RF energy applied to said electrosurgical instrument in response to said impedance signal and said temperature signal wherein said step of controlling the RF energy applied to said electrosurgical instrument comprises the steps of;

storing an initial maximum impedance value;

storing a minimum impedance value;

determining a threshold impedance value between said initial maximum impedance value and said minimum impedance value;

comparing a measured impedance value to said threshold impedance value; and

generating a control signal upon said measured impedance value exceeding said threshold impedance value.

13. A method of operating apparatus for electrosurgically treating tissue during a surgical procedure as claimed in claim 12 wherein the step of determining a threshold impedance value between said initial maximum impedance value and said minimum impedance value comprises finding the midpoint between said initial maximum impedance value and said minimum impedance value.

14. A method of operating apparatus for electrosurgically treating tissue during a surgical procedure as claimed in claim 26 further comprising the steps of:

setting a maximum temperature of tissue engaged by said electrosurgical instrument;

comparing measured temperature values to said maximum temperature; and

generating a control signal upon a measured temperature value exceeding said maximum temperature value.

15. A method of operating apparatus for electrosurgically treating tissue during a surgical procedure, said method comprising the steps of:

applying RF energy to tissue to be electrosurgically treated by means of an electrosurgical instrument through an RF energy switch;

measuring the temperature of tissue engaged by said electrosurgical instrument;

generating a temperature signal representative of the temperature of said tissue;

controlling said RF energy switch in response to said temperature signal to maintain a selected temperature for tissue engaged by said electrosurgical instrument;

measuring the impedance of tissue engaged by said electrosurgical instrument;

generating an impedance signal representative of the impedance of said tissue; and

controlling the RF energy switch in response to said impedance signal to stop the application of said RF energy to tissue engaged by said electrosurgical instrument wherein said step of controlling the RF energy switch in response to said impedance signal to stop the application of said RF energy to tissue engaged by said electrosurgical instrument comprises the steps of;

storing an initial maximum impedance value;

storing a minimum impedance value;

determining a threshold impedance value between said initial maximum impedance value and said minimum impedance value;

comparing a measured impedance value to said threshold impedance value; and

generating a control signal to stop the application of RF energy to said tissue upon said measured impedance value exceeding said threshold impedance value.