System and method for measuring initial tissue impedance

1. An electrosurgical system comprising:

an electrosurgical generator adapted to supply electrosurgical energy to tissue, the generator further adapted to supply an electrical signal having at least one substantially constant value to tissue to determine initial tissue impedance response, the initial tissue impedance being used to determine an amount of the electrosurgical energy to tissue prior to tissue treatment, the generator including:

sensor circuitry adapted to continuously monitor initial tissue impedance response, wherein the initial tissue impedance response includes at least one of an initial impedance, an impedance drop, an impedance minimum and a first impedance rise; and

a microprocessor adapted to generate at least one tissue treatment parameter as a function of the initial tissue impedance response, including the at least one of initial impedance, the impedance drop, the impedance minimum and the first impedance rise, the microprocessor being in electrical communication with a memory to continuously store collected impedance and tissue information, the memory including at least a look up table for storing collected impedance values from a plurality of uses of the electrosurgical system; and

an electrosurgical instrument including at least one active electrode adapted to apply electrosurgical energy to tissue for treatment, wherein the electrosurgical instrument is an electrosurgical forceps for sealing tissue, the forceps comprising:

at least one shaft member having an end effector assembly disposed at a distal end thereof; the end effector assembly including jaw members movable from a first position in spaced relation relative to one another to at least one subsequent position wherein the jaw members cooperate to grasp tissue therebetween; and

a sealing plate attached to each of the jaw members in opposing relation thereto, said sealing plates adapted to connect to the electrosurgical generator such that said sealing plates communicate electrosurgical energy through tissue held therebetween;

wherein a tissue impedance profile during an entire tissue sealing procedure varies in a non-linear manner, such that in a first phase the initial tissue impedance drops to reach a minimum impedance, in a second phase rises at a first rate, and in a third phase rises at a second rate, the second rate being less than the first rate and the second rate stabilizing over a period of time.

2. An electro surgical system as in claim 1 , wherein the microprocessor is further adapted to adjust output of the electrosurgical generator based on the at least one tissue parameter.

3. An electrosurgical system as in claim 1 , wherein the at least one tissue parameter is selected from the group consisting of pressure to be applied to tissue, duration of energy application, amount of energy to be supplied and target impedance trajectory.

4. An electrosurgical system as in claim 1 , wherein the constant value of the electrical signal is selected from the group consisting of constant voltage, constant current, constant power and constant energy.

5. A method for performing electrosurgical procedures comprising:

supplying an electrosurgical generator for providing an electrical signal having at least one substantially constant value to tissue to determine an initial tissue impedance response, the initial tissue impedance being used to determine an amount of electrosurgical energy to tissue prior to tissue treatment, said initial tissue response including at least one of an initial impedance, an impedance drop, an impedance minimum and a first impedance rise;

continuously monitoring said initial tissue impedance response;

generating, via a microprocessor, at least one tissue treatment parameter as a function of the initial tissue impedance response, including the at least one of initial impedance, the impedance drop, the impedance minimum and the first impedance rise, the microprocessor being in electrical communication with a memory to continuously store collected impedance and tissue information, the memory including at least a look up table for storing collected impedance values from the electrosurgical procedures performed; and

providing an electrosurgical instrument including at least one active electrode for applying the electrosurgical energy to tissue,

wherein the step of providing an electrosurgical instrument further includes providing an electrosurgical forceps for sealing tissue, the forceps comprising:

at least one shaft member having an end effector assembly disposed at a distal end thereof, the end effector assembly including jaw members movable from a first position in spaced relation relative to one another to at least one subsequent position wherein the jaw members cooperate to grasp tissue therebetween; and

a sealing plate attached to each of the jaw members in opposing relation thereto, said sealing plates adapted to connect to the electrosurgical generator such that said sealing plates communicate electrosurgical energy through tissue held therebetween;

wherein a tissue impedance profile during an entire tissue sealing procedure varies in a nonlinear manner, such that in a first phase the initial tissue impedance drops to reach a minimum impedance, in a second phase rises at a first rate, and in a third phase rises at a second rate, the second rate being less than the first rate and the second rate stabilizing over a period of time.

6. A method as in claim 5 , further comprising the step of:

adjusting the output of the electrosurgical generator based on the at least one tissue parameter.

7. A method as in claim 6 , wherein the at least one tissue parameter is selected from the group consisting of pressure to be applied to tissue, duration of energy application, amount of energy to be supplied and target impedance trajectory.

8. A method as in claim 5 , wherein the constant value of the electrical signal is selected from the group consisting of constant voltage, constant current, constant power and constant energy.

9. An electrosurgical system adapted to supply electrosurgical energy to tissue comprising an electrosurgical generator having:

an RF output stage adapted to supply electrosurgical energy to tissue and further adapted to supply an electrical signal having at least one substantially constant value to tissue to determine an initial tissue impedance response, the initial tissue impedance being used to determine an amount of the electrosurgical energy to tissue prior to tissue treatment;

a sensor circuitry adapted to continuously monitor the initial tissue impedance response, wherein the initial tissue impedance response includes at least one of an initial impedance, an impedance drop, an impedance minimum and a first impedance rise; and

a microprocessor adapted to generate at least one tissue treatment parameter as a function of the initial tissue impedance response, including the at least one of initial impedance, the impedance drop, the impedance minimum and the first impedance rise, the microprocessor being in electrical communication with a memory to continuously store collected impedance and tissue information, the memory including at least a look up table for storing collected impedance values from a plurality of uses of an electrosurgical instrument;

wherein the electrosurgical instrument is an electrosurgical forceps for sealing tissue, the forceps comprising:

at least one shaft member having an end effector assembly disposed at a distal end thereof, the end effector assembly including jaw members movable from a first position in spaced relation relative to one another to at least one subsequent position wherein the jaw members cooperate to grasp tissue therebetween; and

a sealing plate attached to each of the jaw members in opposing relation thereto, said sealing plates adapted to connect to the electrosurgical generator such that said sealing plates communicate electrosurgical energy through tissue held therebetween;

wherein a tissue impedance profile during an entire tissue sealing procedure varies in a non-linear manner, such that in a first phase the initial tissue impedance drops to reach a minimum impedance, in a second phase rises at a first rate, and in a third phase rises at a second rate, the second rate being less than the first rate and the second rate stabilizing over a period of time.

10. An electrosurgical generator as in claim 9 , wherein the microprocessor is further adapted to adjust output of the electrosurgical generator based on the at least one tissue parameter.

11. An electrosurgical generator as in claim 9 , wherein the at least one tissue treatment parameter is selected from the group consisting of pressure to be applied to tissue, duration of energy application, amount of energy to be supplied and target impedance trajectory.

12. An electrosurgical generator as in claim 9 , wherein the electrosurgical generator is connected to an electrosurgical instrument including at least one active electrode adapted to apply electrosurgical energy to tissue.

13. An electrosurgical generator as in claim 9 , wherein the constant value of the electrical signal is selected from the group consisting of constant voltage, constant current, constant power and constant energy.