ELECTROSURGICAL SYSTEM EMPLOYING MULTIPLE ELECTRODES AND METHOD THEREOF

• US 20090054891A1
• Filed: 08/29/2008
• Published: 02/26/2009
• Est. Priority Date: 10/08/2004
• Status: Active Grant

• Current Assignee: Covidien AG (Medtronic Plc)
• Original Assignee: Covidien AG (Medtronic Plc)
• Inventors: Heard, David N., Buysse, Steven P., McPherson, James W., Gay, Brandon, Dobbins, Gary
• Granted Patent: US 7,699,842 B2
• Time in Patent Office: Days
• US Class Current: 606/34
• CPC Class Codes: A61B 18/1206 Generators therefor
• CPC Class Codes: A61B 18/1477 Needle-like probes
• CPC Class Codes: A61B 2018/00011 with fluids
• CPC Class Codes: A61B 2018/00797 measured by multiple temperature sensors
• CPC Class Codes: A61B 2018/00827 Current
• CPC Class Codes: A61B 2018/00875 Resistance or impedance
• CPC Class Codes: A61B 2018/124 switching the output to different electrodes, e.g. sequentially
• CPC Class Codes: A61B 2018/1425 Needle
• CPC Class Codes: A61B 2018/143 multiple needles

Abstract

A system and method for heat ablation of tissue in which energy is sequentially applied to at least two electrodes inserted into tissue. The system is comprised of a radiofrequency (RF) source for supplying RF energy, at least two electrodes configured to apply RF energy to tissue, at least one return electrode for returning the RF energy to the RF source, and a controller configured to sequentially apply the RF energy to each of the at least two electrodes. The sequential delivery of energy is determined by the measured current and voltage, the calculated impedance at each of the electrodes and the timing for each electrode. An internal load may be activated with the previously activated channel and remain on until the next channel is activated to avoid the generator from having an open circuit.

Claims

1. A method for heat ablation of tissue in a patient, the method comprising the steps of:

inserting at least two electrodes into the tissue;

placing at least one return electrode in contact with the patient;

sequentially applying energy to each of said at least two electrodes for a pre-determinable period of time, wherein said pre-determinable period of time is determined by the procedure and the number of selected electrodes.

2. The method as in claim 1, further comprising the steps of:

determining a parameter at the energized electrode wherein the parameter is selected from a group consisting of impedance, temperature or time and any combination thereof; and

switching the applied energy to a next electrode if the parameter is above a predetermined limit.

3. The method as in claim 2, further comprising the steps of:

determining an off time of a next electrode in sequence;

comparing the off time to a predetermined minimum off time, wherein the predetermined minimum off time is determined by a number of electrodes selected; and

if the off time is less than the minimum off time, skipping over the next electrode in sequence.

4. The method as in claim 2, further comprising the steps of:

determining an off time of a next electrode in sequence;

comparing the off time to a predetermined minimum off time, wherein the predetermined minimum off time is determined by a number of electrodes selected; and

if the off time is greater than the minimum off time, switching the applied energy to the next electrode.

5. The method as in claim 2, further comprising the steps of:

determining an off time of the next electrode;

comparing the off time to a predetermined minimum off time, wherein the predetermined minimum off time is determined by a number of electrodes selected; and

if the off time is less than the minimum off time, switching the applied energy to a load for dissipating the energy.

6. The method as in claim 2, wherein a selected parameter is impedance and the predetermined impedance limit is a measured baseline impedance and a predetermined differential impedance.

7. The method as in claim 6, further comprising the steps of:

applying energy to an individual electrode for a predetermined period of time;

measuring the impedance at the individual electrode; and

setting the measured baseline impedance to a measured impedance.

8. The method as in claim 7, wherein if the measured baseline impedance is less than 100 ohms, setting the predetermined impedance limit to the baseline measured impedance plus 30 ohms.

9. The method as in claim 7, wherein if the measured baseline

impedance is greater than 100 ohms, setting the predetermined impedance limit to the baseline measured impedance plus 30% of the measured baseline impedance.

10. The method as in claim 1, further comprising the step of continuously cooling the at least two electrodes.

11. The method as in claim 1, wherein the at least two electrodes are inserted into a single tumor.

12. The method as in claim 1, wherein electrodes are inserted into at least two different tumors.

13. The method as in claim 1, further comprising the steps of:

sequentially withdrawing each of the at least two electrodes; and

applying energy to an individual electrode being withdrawn to maintain a predetermined temperature at the individual electrode.

14. The method as in claim 13, wherein the applying energy step includes modulating the duty cycle of the energy to maintain the predetermined temperature at the individual electrode.

15. The method as in claim 14, further comprising the steps of:

measuring current at the individual electrode;

determining if the measured current is above a predetermined current limit; and

if the measured current is above the predetermined current limit, reducing the duty cycle of the energy.

16. The method as in claim 15, wherein the predetermined current limit is 2 amps.

17. The method as in claim 13, further comprising the steps of:

measuring an impedance at the individual electrode; and

if the measured impedance is above a predetermined impedance limit, stopping energy to the individual electrode.

18. The method as in claim 17, wherein the predetermined impedance limit is 700 ohms.

19. The method as in any of the claims 1, further comprising the steps of:

applying energy to an internal load prior to removing energy from the current electrode;

removing energy from said current electrode while maintaining the application of energy to said internal load;

applying energy to the next electrode while maintaining the application of the energy to said internal load;

removing energy from the internal load;

wherein the steps are repeated as the energy is sequentially applied to the said electrodes.

20. A system for heat ablation of tissue in a patient comprising:

a radiofrequency (RF) source for supplying RF energy;

at least two electrode configured to apply RF energy to tissue;

at least one return electrode for returning the RF energy to the RF source; and

a controller configured to sequentially apply the RF energy to each of the said at least two electrodes for a pre-determinable period of time, wherein said pre-determinable period of time is determined by at least a surgical procedure and the number of electrodes.

21. The system as in claim 20, further comprising:

current and voltage measuring circuitry at one of the at least two electrodes;

wherein the impedance is calculated based on the measured current and voltage.

22. The system as in claim 21, in which:

said controller determines the off time of the next electrode in sequence;

wherein said next electrode is skipped if the determined off time is less than the predetermined minimum off time;

wherein said predetermined minimum off time is determined by the number of electrodes selected.

23. The system as in claim 22, further comprising:

an internal load; and

circuitry configured to switch the RF energy to the internal load;

wherein the RF energy is switched to the internal load when the determined off time is less than the predetermined minimum off time.

24. The system as in claim 21, in which:

said controller determines the off time of the next electrode in sequence;

wherein the applied energy is switched to the next electrode when the determined off time is greater than the predetermined minimum off time;

wherein said predetermined minimum off time is determined by the number of electrodes selected.

25. The system as in claim 21, comprising:

circuitry which;

restricts the flow of RF energy to an electrode when the calculated impedance exceeds a threshold impedance; and

allows the flow of RF energy to an electrode when the calculated impedance does not exceed a threshold impedance;

wherein said threshold impedance relates to a baseline impedance and a pre-determined differential impedance.

26. The system as in claim 25, in which the baseline impedance comprises the lowest calculated impedance obtained in the initial about 10 seconds of RF energy delivery.

27. The system as in claim 25, in which the baseline impedance comprises the lowest average of consecutive calculated impedances obtained during the initial about 30 seconds of operation;

28. The system as in claim 25, in which the pre-determined differential impedance is about 30 ohms if the baseline impedance is less than about 100 ohms.

29. The system as in claim 25, in which the pre-determined differential impedance is about 30% of the baseline impedance if the baseline is greater than about 100 ohms.

30. The system in claim 25, comprising:

circuitry to sequence the delivery of RF energy between the at least two electrodes, wherein electrodes are skipped if the calculated impedance is above a predetermined threshold.

31. The system as in claim 25, further comprising:

an internal load; and

circuitry to direct the RF energy;

wherein the RF energy is directed to said internal load when the calculated impedance is above a predetermined threshold.

32. The system as in claim 20, further comprising:

an internal load; and

circuitry configured to switch the RF energy to said internal load;

wherein RF energy is applied simultaneously to said internal load and one of said at least two electrodes.

33. The system as in claim 20, further comprising a means to continuously cool an electrode.

34. The system as in claim 20, further comprising:

circuitry to measure current at the individual electrodes, wherein said controller reduces the duty cycle if said measured current exceeds a predetermined current limit.

35. The system as in claim 34, in which the predetermined current limit is about 2 amps.

36. The system as in claim 20, further comprising:

temperature measuring circuitry at one of the at least two electrodes;

wherein the applied energy at the current electrode is switched to the next electrode when the temperature at said current electrode is greater than a predetermined temperature.