Electrosurgical medical system and method

• US 20090088736A1
• Filed: 08/27/2008
• Published: 04/02/2009
• Est. Priority Date: 12/28/2000
• Status: Active Grant

• Current Assignee: Senorx Incorporated (Becton, Dickinson & Co)
• Original Assignee: Senorx Incorporated (Becton, Dickinson & Co)
• Inventors: Daw, Derek, Dabney, James Huntington
• Granted Patent: US 7,976,540 B2
• Time in Patent Office: Days
• US Class Current: 606/33
• CPC Class Codes: A61B 18/1206 Generators therefor
• CPC Class Codes: A61B 18/1402 Probes for open surgery
• CPC Class Codes: A61B 18/18 by applying electromagnetic radiation, e.g. microwaves radiation therapy A61N5/00
• CPC Class Codes: A61B 2018/00601 Cutting
• CPC Class Codes: A61B 2018/00702 Power or energy
• CPC Class Codes: A61B 2018/00726 Duty cycle
• CPC Class Codes: A61B 2018/00755 Resistance or impedance
• CPC Class Codes: A61B 2018/00875 Resistance or impedance
• CPC Class Codes: A61B 2018/00946 slidable
• CPC Class Codes: A61B 2018/1286 having a specific transformer

Abstract

A medical device system and method provide an RF electrosurgical generator coupled to an electrosurgical electrode via a patient box disposed in close proximity to the patient. An RF signal is delivered from the generator to the patient box where signal power is increased and the RF signal delivered to the electrosurgical electrode. The patient box is coupled to the electrosurgical electrode by a short cable capable of carrying an HV, high frequency 5 MHz signal without leakage. An electrical characteristic associated with the electrosurgical electrode is monitored and a desired RF power output and duty cycle maintained by adjusting DC input voltage applied to an RF amplifier, responsive to the monitoring. The system determines when the electrosurgical cutting electrode has started cutting and switches from a start mode to a run mode having a different RF duty cycle and a reduced RF power output controlled by a servo system.

Claims

1. -5. (canceled)

6. A method for controlling an electrosurgical electrode of a medical device comprising:

delivering energy from an RF generator to an electrosurgical electrode, said RF generator including an RF amplifier;

monitoring an electrical characteristic associated with said electrosurgical electrode; and

controlling the output of the RF generator based upon the monitored electrical characteristic associated with the electrosurgical electrode.

7. The method as in claim 6, further comprising selecting said desired RF duty cycle.

8. The method as in claim 7, wherein said selecting comprises selecting a run RF duty cycle for a run mode and further comprising a start mode preceding said run mode and which includes a pre-programmed start RF duty cycle.

9. The method as in claim 6, wherein said maintaining a desired RF power output and a desired RF duty cycle includes maintaining a constant duty cycle and adjusting at least one of RF output voltage and RF output current during a cutting mode during which said electrosurgical electrode is cutting.

10. The method as in claim 9, wherein said electrical characteristic comprises output load impedance and said monitoring comprises calculating said output load impedance by detecting at least one of an output voltage, an output current and a phase angle between a waveform representing said output voltage and a waveform representing said output current.

11. The method as in claim 10, wherein said detecting includes measuring at a point of said output load and also at an output of an RF combiner disposed within said RF generator.

12. The method as in claim 6, wherein said electrical characteristic comprises output load impedance and said maintaining a desired RF power output and a desired RF duty cycle by adjusting DC input voltage occurs during a tissue cutting mode.

13. The method as in claim 12, wherein said output load impedance comprises tissue impedance of tissue being acted on by said electrosurgical electrode.

14. The method as in claim 6, wherein said adjusting is responsive to changes in tissue impedance of tissue being acted on by said electrosurgical electrode.

15. The method as in claim 6, further comprising automatically switching from a start mode to a run mode when said electrosurgical electrode begins cutting tissue and wherein said maintaining a desired RF power output and a desired RF duty cycle takes place during both said start mode and said run mode and includes maintaining a lower RF power output in said run mode than in said start mode.

16. The method as in claim 15, further comprising maintaining a different duty cycle in said run mode than in said start mode.

17. The method as in claim 15, wherein said switching occurs responsive to detecting a plasma at said electrosurgical electrode.

18. The method as in claim 15, wherein said switching occurs responsive to detecting a DC voltage across said electrosurgical electrode and a return electrode.

19. The method as in claim 6, wherein said maintaining a desired RF power output and a desired RF duty cycle takes place during both said start mode and said run mode and comprises using a matching network during said start mode and using a servo system during said cut mode, said start mode comprising an initiation of cutting.

20. The method as in claim 6, wherein

said delivering energy includes said RF generator producing an RF power output signal;

and

maintaining a desired RF power output includes monitoring said RF output power by sending an RF signal from said RF amplifier to a transformer with at least a primary winding and a secondary winding and symmetrically tapping said secondary winding of said transformer to produce a voltage signal having a voltage proportional to a voltage of said RF power output signal.

21. The method as in claim 20 further comprising sending said voltage signal through an isolation transformer.

22. The method as in claim 6, further comprising using a DC current servo to limit said RF power output by monitoring and controlling root mean square (RMS) current provided to said RF amplifier.

23. The method as in claim 6, wherein said DC input voltage is adjusted using a voltage servo during a cutting operation.

24. The method as in claim 6, further comprising matching an impedance of said RF amplifier to a load impedance of tissue being acted on by said electrosurgical electrode.

25. The method as in claim 24, wherein said matching is accomplished using a Class D amplifier with a 350 ohm transformer during cutting by said electrosurgical electrode.

26. The method as in claim 6, wherein said delivering energy comprises delivering up to 1200 Watts power but having a total output not greater than 400 Watt-second.

27. The method as in claim 6, further comprising:

providing said RF generator in a generator housing and a patient box in a patient box housing, said patient box housing disposed in close proximity to a patient and said generator housing disposed further from said patient than said patient box housing;

delivering an RF signal with a first RF power level from said RF generator to said patient box;

increasing said RF power level of said RF signal in said patient box; and

delivering said RF signal with an increased RF power level to said electrosurgical electrode as an RF output,

wherein said patient box is coupled to said electrosurgical electrode by a cable not greater than 2 meters long.

28. The method as in claim 6, further comprising:

delivering an RF signal from said RF generator to said electrosurgical electrode by way of a patient box; and

detecting a leakage current by inducing a test signal in said patient box by directing said RF signal through an RF transformer in said patient box, coupling a series of two capacitors between ground and a center tap of a winding in said RF transformer, and inducing said test signal onto RF output leads of said patient box by passing said RF signal through a common mode transformer, said test signal having a frequency of about 500 KHz and said patient box and said RF generator disposed in separate housings.

29. The method as in claim 28, further comprising monitoring said RF signal after passing through said RF transformer, using a plurality of current sense transformers.

30. The method as in claim 29, further comprising an analog circuit driving a leakage path detection drive transformer and monitoring an output of said current sense transformers.

31. The method as in claim 28, further comprising converting said test signal to a DC level proportional to said leakage current and determining if said leakage current exceeds a setpoint.

32. The method as in claim 6, wherein said delivering energy comprises delivering an RF signal from said RF generator to said electrosurgical electrode by way of a patient box, said patient box and said RF generator disposed in separate housings, and further comprising:

providing a balanced and symmetrical shielded transmission line coupling said RF generator to said patient box that includes a transformer;

providing a common mode choke in said patient box, said common mode choke including an output winding and a return winding, each wound about a ferrite core, said output winding and said return winding spaced apart and in parallel to maintain a desired impedance, said output winding comprising a wire carrying said RF signal and said return winding comprising a duality of intertwined wires, each winding including adjacent ribs spaced apart and said windings wound in opposite directions; and

directing a common mode signal from said RF signal to said common mode choke thereby blocking said common mode signal while allowing said output signal to be applied substantially unaltered to a patient.

33. -43. (canceled)

44. A system for controlling an electrosurgical electrode of a medical device comprising:

an RF generator coupled to an electrosurgical electrode, said RF generator including an RF amplifier;

means for delivering energy from said RF generator to said electrosurgical electrode;

means for monitoring an electrical characteristic associated with said electrosurgical electrode; and

means for maintaining a desired RF power output and a desired RF duty cycle by adjusting DC input voltage applied to an output stage of said RF amplifier based on said monitoring.

45. The system as in claim 44, further comprising

a patient box coupled between said RF generator and said electrosurgical electrode, said patient box and said electrosurgical generator disposed in separate housings;

an RF signal delivering said energy from said RF electrosurgical generator to said electrosurgical electrode by way of said patient box;

a balanced and symmetrical shielded transmission line coupling said electrosurgical generator to a transformer of said patient box;

a common mode choke in said patient box, said common mode choke including an output winding and a return winding, each wound about a ferrite core, said output winding and said return winding spaced apart and in parallel to maintain a desired impedance, said output winding comprising a wire carrying said RF signal and said return winding comprising a duality of intertwined wires, each winding including adjacent ribs spaced apart; and

means for directing a common mode signal from said RF signal to said common mode choke thereby blocking said common mode signal while allowing said output signal to be applied substantially unaltered to a patient.

46. A medical device comprising:

an electrosurgical cutting electrode;

an RF generator configured to provide a start mode with a relatively high RF power output and a first RF duty cycle and a run mode with an RF power output lower than the RF power output of the start mode and a second RF duty cycle;

means for delivering energy from said RF generator to said electrosurgical cutting electrode;

means for determining when said electrosurgical cutting electrode has started cutting tissue; and

a switch for switching the RF generator from the start mode to the run mode in response to the means for determining when the electrosurgical cutting electrode has started to cut tissue

said start mode controlled by a matching unit and including a relatively high RF power output and a first RF duty cycle, and said run mode controlled by a servo system and having a second RF duty cycle and a reduced RF power output.

47. A system for mitigating leakage in an RF electrosurgical generator, comprising:

an RF electrosurgical generator coupled to a patient box coupled to an electrosurgical electrode;

a return electrode coupled to said patient box;

a balanced and symmetrical shielded transmission line coupling said RF electrosurgical generator disposed in a first housing to said patient box disposed in a second, different housing;

a common mode choke disposed in said patient box, said common mode choke including an output winding and a return winding, each winding wound about a ferrite core, said output winding and said return winding spaced apart and in parallel to maintain a desired impedance, said output winding comprising a wire carrying an RF output signal and said return winding comprising a duality of intertwined wires carrying a return signal from said return electrode, each winding having adjacent ribs spaced apart and said windings wound in opposite directions;

means for delivering an RF signal from said RF electrosurgical generator to said electrosurgical electrode by way of said patient box; and

means for directing a common mode signal from said RF signal to said common mode choke thereby blocking said common mode signal.