Apparatus for leakage control and method for its use

• US 5,372,596 A
• Filed: 07/27/1993
• Issued: 12/13/1994
• Est. Priority Date: 07/27/1993
• Status: Expired due to Term

• Current Assignee: Covidien AG (Medtronic Plc)
• Original Assignee: Valleylab Inc. (Medtronic Plc)
• Inventors: Paterson, William G., Klicek, Michael S.
• Primary Examiner(s): Pellegrino, Stephen C.
• Assistant Examiner(s): PEFFLEY, MICHAEL F
• Application Number:
  US08/097,737
• Time in Patent Office: 504 Days
• Field of Search: 606/32-35, 606/37-40
• US Class Current: 606/35
• CPC Class Codes: A61B 18/12 by passing a current through the tissue to be heated, e.g. high-frequency current
• CPC Class Codes: A61B 18/1206 Generators therefor
• CPC Class Codes: A61B 18/1233 with circuits for assuring patient safety
• CPC Class Codes: A61B 2018/00083 low, i.e. electrically insulating
• CPC Class Codes: A61B 2018/0075 Phase

Abstract

Apparatus and method find leakage due to tissue load or transients and has active and return electrodes for RF energy sensed by transformers for a circuit that finds leakage at more than two thousand times per second or a frequency dependent on the phase shift between voltage and current. Software and feedback manage V_rms to reduce the voltage or increase the crest factor, which is V_rms divided by peak voltage, by pulse width modulation of the RF drive. Voltage and current phase shift changes, angle θ, are compared to a threshold, and when greater, the frequency at which the differences between the active and return current signals are examined is increased. The differences between the active and return currents are examined and when greater than maximum leakage while in coagulation mode, the RF drive pulse width is reduced to maintain voltage wave peaks at a preset value and reduce V_rms thereby reducing leakage to the allowable maximum. Reducing the duty cycle or the pulse width of the output wave increases the crest factor. When the differences between active and return currents are greater than a maximum for leakage while in cut or bipolar mode, the V_rms is reduced to limit leakage to a maximum level. When the phase angle θ is less than a threshold, the frequency with which leakage is examined is reduced.

Claims

1. An apparatus for controlling leakage in a radio frequency electrosurgical system including changes in the load as a function of tissue being electrosurgically treated or transient conditions such as the initiation or termination of an electrosurgical effect wherein an active electrode not in electrical contact with the patient'"'"'s tissue transmits energy from an electrosurgical unit to a tip of the active electrode comprising:

an electrosurgical unit for providing radio frequency energy at an active output thereof and for controlling the flow of the energy through the active output, the electrosurgical unit having a return input;

an electrode connected to the active output for transmitting electrosurgical radio frequency energy to a patient in an electrosurgical procedure such as cutting, coagulating or a blending thereof;

a return electrode adapted to be connected to the patient for receiving radio frequency energy supplied to the patient during the electrosurgical procedure and connected to the return input for returning it to the return input of the electrosurgical unit;

an inductive transformer connected to and responsive to the active output for providing a signal of active energy flow;

an inductive transformer connected to and responsive to the return input for providing a signal of return energy flow;

a connection between the inductive transformers and the active output and return input, and

a comparison circuit connected to receive the active and return signals as a measure of leakage, the comparison circuit having means for determining instantaneous differences at rates of a speed sufficient to handle transient conditions, the comparison circuit having means for examining the differences at a frequency dependent on the phase shift between the output voltage and current of the electrosurgical unit.

2. The apparatus for controlling leakage of claim 1 wherein the electrosurgical unit includes a microprocessor therein, the microprocessor having software programmed with one or more algorithms, the microprocessor software algorithm or algorithms for determining the differences between the active and return current signals and the microprocessor software algorithm or algorithms for examining the differences between the active and return current signals at a frequency dependent on the phase shift between the proportional output voltage and proportional current of the electrosurgical unit.

3. The apparatus for controlling leakage of claim 2 wherein the algorithm for determining the differences between the active and return current signals and for examining the differences ascertains the phase shift between the radio frequency voltage and current at the peaks thereof respectively.

4. The apparatus for controlling leakage of claim 3 wherein the algorithm is the Cosine of the phase angle θ

is ((V_max)² +(I_max)² -(V-I)_max²) divided by 2(V_max *I_max).

5. The apparatus for controlling leakage of claim 4 wherein the phase angle θ

is compared in the microprocessor to a threshold and if greater then the frequency at which the differences between the active and return current signals are examined is increased accordingly.

6. The apparatus for controlling leakage of claim 4 wherein the differences between the active and return current signals are examined in the feedback loop of comparison circuit in combination with the microprocessor and if greater than a maximum for leakage while the mode selected is coagulation then the pulse width of the radio frequency drive is reduced to maintain voltage wave-form peaks at a predetermined value while the RMS voltage is reduced to lower the leakage to a maximum allowed level.

7. The apparatus for controlling leakage of claim 4 wherein the differences between the active and return current signals are examined in the feedback loop of the comparison circuit in combination with the microprocessor and if greater than a maximum for leakage while the mode selected is coagulation then the frequency at which the leakage current is calculated is increased in the feedback loop of the comparison circuit so a maximum allowed level is maintained until the phase angle θ

is smaller than the threshold.

8. The apparatus for controlling leakage of claim 4 wherein the differences between the active and return current signals are examined in the feedback loop of the comparison circuit in combination with the microprocessor and if greater than a maximum for leakage while the mode selected is cut or bipolar then the V_rms is reduced by lowering the electrosurgical unit radio frequency stage voltage until the differences lower the leakage to a maximum allowed level.

9. The apparatus for controlling leakage of claim 4 wherein the differences between the active and return current signals are examined in the feedback loop of the comparison circuit in combination with the microprocessor and if greater than a maximum for leakage while the mode selected is cut or bipolar then the frequency at which the leakage current is calculated is increased in the feedback loop so the maximum allowed level remains high until the phase angle θ

is smaller than the threshold.

10. The apparatus for controlling leakage of claim 1 wherein the comparison circuit in combination with the microprocessor provides a closed loop feedback for monitoring and controlling the output RMS voltage by reducing the voltage of the output wave shaped therefrom or by increasing the crest factor, which is V_rms divided by peak voltage.

11. The apparatus for controlling leakage of claim 10 wherein in the electrosurgical unit, the microprocessor software algorithm or algorithms the crest factor is increased by pulse width modulation of the radio frequency drive.

12. The apparatus for controlling leakage claim 10 wherein the crest factor is increased by the microprocessor reducing the duty cycle or the pulse width of the output wave shape.

13. The apparatus for controlling leakage of claim 1 wherein the microprocessor analyzes the output of the comparison circuit to find the difference, I_lkg and if its is about 150 ma then the rate of monitoring is increased.

14. A method for controlling leakage in a radio frequency electrosurgical system during operation under varying tissue loads or through at least transient or open circuit conditions during the initiation or termination of an electrosurgical effect wherein an active electrode in or not in electrical contact with the patient'"'"'s tissue transmits energy to a tip thereof, having the following steps:

providing an electrosurgical unit having radio frequency energy at an active output thereof;

controlling the flow of the energy through the active output with the electrosurgical unit;

having a return input connected to the electrosurgical unit;

connecting an active electrode to the active output and transmitting electrosurgical radio frequency energy to a patient in an electrosurgical procedure such as cutting, coagulating or a blending thereof;

adapting a return electrode for connection to a patient and receiving radio frequency energy supplied to the patient during the electrosurgical procedure;

returning all but a preset maximum amount of radio frequency energy supplied to the return input of the electrosurgical unit;

providing an inductive transformer connected to and responsive to the active output for supplying a signal of active energy flow;

providing an inductive transformer connected to and responsive to the return input for supplying a signal of return energy flow, and

using a comparison circuit connected to receive the active and return signals to measure leakage and determine instantaneous differences at a rate of at least two thousand times per second between the active and return signals, and

examining the instantaneous differences at a frequency which is increased in accord with the phase shift between the output signals of proportional voltage and proportional current.

15. The method of claim 14 with the added step of including in the electrosurgical unit a microprocessor having software programmed with one or more algorithms, the microprocessor software algorithm or algorithms for calculating the differences between the active and return current signals and the microprocessor software algorithm or algorithms for examining the differences at a frequency dependent on the phase shift between the output energy of the electrosurgical unit.

16. The method of claim 15 with the added step of using the algorithms for calculating the differences between the active and return current signals and for examining the differences to ascertain the phase shift between the radio frequency proportional voltage and proportional current at the maximums thereof respectively.

17. The method of claim 15 with the added step of examining the differences between the active and return current signals in the feedback loop of the comparison circuit and if greater than the preset maximum of radio frequency energy supplied to the return input or leakage while the mode selected is coagulation then reducing the pulse width of the radio frequency drive to maintain voltage wave form peaks at a predetermined value as the RMS voltage is reduced to lower the leakage to the maximum allowed level.

18. The method of claim 15 with the added step of examining the differences between the active and return current signals in the feedback loop of the comparison circuit and if greater than the preset maximum amount of radio frequency energy supplied to the return input or leakage while the mode selected is coagulation then the frequency at which the leakage current is calculated is increased in the comparison circuit so a maximum allowed level is maintained until the phase angle θ

is smaller than the threshold.

19. The method of claim 15 with the added step of examining the differences between the active and return current signals are in the feedback loop of the comparison circuit and if greater than the preset maximum amount of radio frequency energy supplied to the return input or leakage while the mode selected is cut or bipolar then reducing the V_rms by lowering the electrosurgical unit radio frequency stage voltage until the differences produce the leakage lowered to the maximum allowed level.

20. The method of claim 15 with the added step of examining the differences between the active and return current signals in the feedback loop of the comparison circuit and if greater than the preset maximum amount of radio frequency energy supplied to the return input or leakage while the mode selected is cut or bipolar then maintaining the frequency at which the leakage current is calculated is increased in the feedback loop of the comparison circuit so the preset maximum amount of radio frequency energy supplied to the return input or leakage or allowed level is high until the phase angle θ

is smaller than the threshold.

21. The method of claim 15 with the added step of increasing the crest factor by reducing the duty cycle or the pulse width of the output wave shape.

22. The method of claim 16 with the added step of using the particular algorithm for calculating the Cosine of the phase angle θ

is ((V_max)² +(I_max)² -(V-I)_max²) divided by 2 V_max I_max.

23. The method of claim 22 with the added step of comparing the phase angle θ

to a threshold and if it is greater than the frequency at which the differences between the active and return current signals are examined is the frequency is increased accordingly.

24. The method of claim 14 with the added step of providing with the comparison circuit in combination with the microprocessor a closed loop feedback for monitoring and controlling the output RMS voltage by reducing the peak voltage of the output wave shaped therefrom or by increasing the crest factor.

25. The method of claim 24 with the added step of increasing by the electrosurgical unit, the microprocessor software algorithm or algorithms the crest factor by pulse width modulation of the radio frequency drive.