Controlling impedance rise in electrosurgical medical devices

1. An electrosurgical system for providing an electrosurgical signal to a patient, the system comprising:

a control circuit programmed to:

for a first application period during a coagulation cycle, apply the electrosurgical signal to first and second electrodes according to a first mode, wherein in the first mode, the control circuit is configured to:

limit the electrosurgical signal to a first first-mode maximum power when an impedance between the first and second electrodes is less than a first mode threshold; and

limit the electrosurgical signal to a second first-mode maximum power when the impedance between the first and second electrodes exceeds the first mode threshold, wherein the first first-mode maximum power is greater than the second first-mode maximum power; and

for a second application period after the first application period during the coagulation cycle, apply the electrosurgical signal according to a second mode, wherein in the second mode, the control circuit is configured to:

limit the electrosurgical signal to a first second-mode maximum power when the impedance between the first and second electrodes is less than a second mode threshold; and

limit the electrosurgical signal to a second second-mode maximum power when the impedance between the first and second electrodes exceeds the second mode threshold, wherein the first second-mode maximum power is greater than the second second-mode maximum power,

wherein the second second-mode maximum power is greater than the second first-mode maximum power.

2. The electrosurgical system of claim 1 , wherein the first mode threshold is less than the second mode threshold.

3. The electrosurgical system of claim 1 , wherein the control circuit is further programmed to:

for a third application period after the second application period during the coagulation cycle, apply the electrosurgical signal according to a third mode, wherein in the third mode, the control circuit is configured to:

limit the electrosurgical signal to a first third-mode maximum power when the impedance between the first and second electrodes is less than a third mode threshold; and

limit the electrosurgical signal to a second third-mode maximum power when the impedance between the first and second electrodes exceeds the third mode threshold.

4. The electrosurgical system of claim 3 , wherein in the third mode, the control circuit is configured to limit the electrosurgical signal to the second third-mode maximum power when the impedance between the first and second electrodes exceeds the third mode threshold during an application period of a first sub-mode, and wherein the control circuit is further programmed to:

for a fourth application period after the third application period during the coagulation cycle, apply the electrosurgical signal according to a second sub-mode, wherein in the second sub-mode, the control circuit is configured to:

limit the electrosurgical signal to a first second-sub-mode maximum power when the impedance between the first and second electrodes is less than the third mode threshold; and

limit the electrosurgical signal to a second second-sub-mode maximum power when the impedance between the first and second electrodes exceeds the third mode threshold, wherein the second second-sub-mode maximum power is greater than the second third-mode maximum power.

5. The electrosurgical system of claim 4 , wherein the control circuit is further programmed to:

for a fifth application period after the fourth application period during the coagulation cycle, apply the electrosurgical signal according to a third sub-mode, wherein in the third sub-mode, the control circuit is configured to limit the electrosurgical signal to a third-sub-mode maximum power when the impedance between the first and second electrodes exceeds the third mode threshold, wherein the third-sub-mode maximum power is greater than the second second-sub-mode maximum power.

6. The electrosurgical system of claim 3 , wherein the control circuit is programmed to continue the third application period until the impedance between the first and second electrodes reaches a terminal threshold.

7. The electrosurgical system of claim 1 , wherein the control circuit is configured to limit the electrosurgical signal to the second first-mode maximum power by limiting the electrosurgical signal to a first maximum voltage.

8. The electrosurgical system of claim 1 , wherein in the first mode, the control circuit is also configured to limit the electrosurgical signal to a third first-mode maximum power when the impedance between the first and second electrodes exceeds a second first-mode threshold.

9. The electrosurgical system of claim 1 , wherein the control circuit is further programmed to apply the electrosurgical signal during the first mode as a plurality of pulses.

10. The electrosurgical system of claim 1 , wherein the control circuit is further programmed to:

after the first and second application periods, determine whether a new tissue bite has been initiated; and

upon determining that a new tissue bite has been initiated, apply the electrosurgical signal to the first and second electrodes according to the first mode.

11. The electrosurgical system of claim 1 , wherein the second application period is longer than the first application period.

12. The electrosurgical system of claim 11 , wherein the first application period is about 1.4 seconds and the second application period is about 4 to 5.4 seconds.