System and method for tissue sealing

1. An electrosurgical generator, comprising:

an RF output stage configured to supply electrosurgical energy to tissue via at least one active electrode configured to apply electrosurgical energy to tissue;

sensing circuitry configured to measure impedance of tissue and measure a phase between voltage and current waveforms of the electrosurgical energy delivered to tissue; and

a controller programmed to:

determine whether a tissue reaction has occurred as a function of a minimum impedance value and a predetermined rise in impedance, wherein tissue reaction corresponds to a boiling point of tissue fluid;

generate a target impedance trajectory as a function of measured impedance and a predetermined desired rate of change of impedance based on the tissue reaction determination, wherein the target impedance trajectory includes a plurality of target impedance values for each of a plurality of time-steps;

drive tissue impedance along the target impedance trajectory by adjusting the output level of the electrosurgical generator to substantially match tissue impedance to a corresponding target impedance value for at least a predetermined minimum time period;

determine an open circuit based on the phase being above an upper phase threshold; and

determine a short circuit based on the phase being below a lower phase threshold.

2. The electrosurgical system according to claim 1 , wherein the controller is further programmed to terminate delivery of electrosurgical energy in response to the phase being outside the lower and upper phase thresholds.

3. The electrosurgical system according to claim 1 , wherein the controller is further programmed to measure time for driving tissue impedance along the target impedance trajectory and comparing the measured time to the predetermined minimum time period.

4. The electrosurgical system according to claim 3 , wherein the controller is programmed to output at least one of an alarm or a signal to adjust output of the RF output stage in response to the measured time being less than the predetermined minimum time period.

5. The electrosurgical system according to claim 1 , wherein the controller is programmed to generate a threshold impedance value as a function of an offset impedance value and an ending impedance value, wherein the offset impedance value is obtained after an initial impedance measurement.

6. The electrosurgical system according to claim 5 , wherein the controller is programmed to determine whether tissue impedance is at least equal to the threshold impedance for a predetermined shutoff period.

7. The electrosurgical system according to claim 6 , wherein the controller is programmed to adjust output of the electrosurgical generator in response to the determination whether tissue impedance is at least equal to the threshold impedance for a predetermined shutoff period.

8. An electrosurgical system, comprising:

an RF output stage configured to supply electrosurgical energy to tissue;

sensing circuitry configured to measure impedance of tissue and a phase between voltage and current waveforms of the electrosurgical energy delivered to the tissue;

a controller programmed to:

determine whether a tissue reaction has occurred as a function of a minimum impedance value and a predetermined rise in impedance, wherein tissue reaction corresponds to a boiling point of tissue fluid;

generate a target impedance trajectory as a function of measured impedance and a predetermined desired rate of change of impedance based on the tissue reaction determination, wherein the target impedance trajectory includes a plurality of target impedance values for each of a plurality of time-steps;

drive tissue impedance along the target impedance trajectory by adjusting the output level of the electrosurgical generator to substantially match tissue impedance to a corresponding target impedance value for at least a predetermined minimum time period;

determine an open circuit based on the phase being above an upper phase threshold; and

determine a short circuit based on the phase being below a lower phase threshold; and

an electrosurgical instrument including at least one active electrode configured to apply electrosurgical energy to tissue.

9. The electrosurgical system according to claim 8 , wherein the controller is further programmed to terminate delivery of electrosurgical energy in response to the phase being outside the lower and upper phase thresholds.

10. The electrosurgical system according to claim 8 , wherein the controller is further programmed to measure time for driving tissue impedance along the target impedance trajectory and comparing the measured time to the predetermined minimum time period.

11. The electrosurgical system according to claim 8 , wherein the controller is programmed to output at least one of an alarm or a signal to adjust output of the RF output stage in response to the measured time being less than the predetermined minimum time period.

12. The electrosurgical system according to claim 8 , wherein the controller is programmed to generate a threshold impedance value as a function of an offset impedance value and an ending impedance value, wherein the offset impedance value is obtained after an initial impedance measurement.