Method and system for controlling output of RF medical generator

1. An electrosurgical system comprising:

an electrosurgical generator adapted to supply electrosurgical energy to tissue;

a microprocessor configured to generate a target impedance trajectory having at least one slope, wherein the target impedance trajectory includes a plurality of target impedance values, the microprocessor also configured to drive tissue impedance along the target impedance trajectory by adjusting the output level to substantially match tissue impedance to a corresponding target impedance value, the microprocessor further configured to compare tissue impedance to a threshold impedance value and adjust output of the electrosurgical generator when the tissue impedance is equal to or greater than the threshold impedance; and

an electrosurgical instrument including at least one active electrode adapted to apply electrosurgical energy to tissue, such that the tissue impedance is monitored in real-time in one or more closed loop control configurations by at least one control module that regulates the electrosurgical energy received from the generator, the one or more closed loop control configurations being an inner control loop configuration for controlling a first set of variables, the first set of variables selectively used to derive a second set of variables and an outer control loop configuration for providing additional control of a subset of at least one of the first and second sets of variables of the inner control loop.

2. An electrosurgical system as in claim 1 , wherein the microprocessor is further configured to generate the threshold impedance value as a function of an offset impedance value and an ending impedance value.

3. An electrosurgical system as in claim 2 , wherein the offset impedance value is selected from the group consisting of an impedance value corresponding to maximum current value, a minimum impedance value and an initial impedance value.

4. An electrosurgical system as in claim 1 , wherein the microprocessor is further configured to compare duration of a reaction period to a reaction timer value and adjust output of the electrosurgical generator when the duration of the reaction period is equal to or greater than the reaction timer value.

5. An electrosurgical system as in claim 4 , wherein the microprocessor is further configured to compare duration of the reaction period to a sum of the reaction timer value and a time offset period and adjust output of the electrosurgical generator when the duration of the reaction period is equal to or greater than the sum of the reaction timer value and the time offset period.

6. A method for performing an electrosurgical procedure comprising the steps of:

applying electrosurgical energy at an output level to tissue from an electrosurgical generator;

generating a target impedance trajectory, wherein the target impedance trajectory includes a plurality of target impedance values;

driving tissue impedance along the target impedance trajectory by adjusting the output level to match tissue impedance to a corresponding target impedance value; and

comparing tissue impedance to a threshold impedance value and adjusting output of the electrosurgical generator when the tissue impedance is equal to or greater than the threshold impedance, such that the tissue impedance is monitored in real-time in one or more closed loop control configurations by at least one control module that regulates the electrosurgical energy received from the generator, the one or more closed loop control configurations being an inner control loop configuration for controlling a first set of variables, the first set of variables selectively used to derive a second set of variables and an outer control loop configuration for providing additional control of a subset of at least one of the first and second sets of variables of the inner control loop.

7. A method as in claim 6 , further comprising the step of generating the threshold impedance value as a function of an offset impedance value and an ending impedance value.

8. A method as in claim 7 , wherein the step of generating the threshold impedance value further includes the step of selecting the offset impedance value from the group consisting of an impedance value corresponding to maximum current value, a minimum impedance value and an initial impedance value.

9. A method as in claim 6 , further comprising the step of comparing duration of a reaction period to a reaction timer value and adjusting the output of the electrosurgical generator when the duration of the reaction period is equal to or greater than the reaction timer value.

10. A method as in claim 9 , wherein the step of comparing duration of a reaction period further includes the step of comparing duration of the reaction period to a sum of the reaction timer value and a time offset period and adjusting the output of the electrosurgical generator when the duration of the reaction period is equal to or greater than the sum of the reaction timer value and the time offset period.

11. A method according to claim 6 , wherein the step of generating the target impedance trajectory further includes the step of:

generating a positively sloping impedance trajectory.

12. A method according to claim 6 , wherein the step of generating the target impedance trajectory further includes the step of:

generating a negatively sloping impedance trajectory.

13. A method according to claim 6 , wherein the step of generating a target impedance trajectory further includes the step of:

generating the slope of the target impedance trajectory to be at least one of a linear, quasi-linear, and non-linear trajectory.

14. An electrosurgical generator comprising:

an RF output stage adapted to supply electrosurgical energy to tissue; and

a microprocessor configured to generate a target impedance trajectory having at least one slope, wherein the target impedance trajectory includes a plurality of target impedance values, the microprocessor also configured to drive tissue impedance along the target impedance trajectory by adjusting the output level to substantially match tissue impedance to a corresponding target impedance value, the microprocessor further configured to compare tissue impedance to a threshold impedance value and adjust output of the electrosurgical generator when the tissue impedance is equal to or greater than the threshold impedance, such that the tissue impedance is monitored in real-time in one or more closed loop control configurations by at least one control module that regulates the electrosurgical energy received from the generator, the one or more closed loop control configurations being an inner control loop configuration for controlling a first set of variables, the first set of variables selectively used to derive a second set of variables and an outer control loop configuration for providing additional control of a subset of at least one of the first and second sets of variables of the inner control loop.

15. An electrosurgical generator as in claim 14 , wherein the microprocessor is further configured to generate the threshold impedance value as a function of an offset impedance value and an ending impedance value.

16. An electrosurgical generator as in claim 15 , wherein the offset impedance value is selected from the group consisting of an impedance value corresponding to maximum current value, a minimum impedance value and an initial impedance value.

17. An electrosurgical generator as in claim 14 , wherein the microprocessor is further configured to compare duration of a reaction period to a reaction timer value and adjust output of the electrosurgical generator when the duration of the reaction period is equal to or greater than the reaction timer value.

18. An electrosurgical generator as in claim 17 , wherein the microprocessor is further configured to compare duration of the reaction period to a sum of the reaction timer value and a time offset period and adjust output of the electrosurgical generator when the duration of the reaction period is equal to or greater than the sum of the reaction timer value and the time offset period.