Electrosurgical Generator With Adaptive Power Control

Abstract

An electrosurgical generator has an output power control system that causes the impedance of tissue to rise and fall in a cyclic pattern until the tissue is desiccated. The advantage of the power control system is that thermal spread and charring are reduced. In addition, the power control system offers improved performance for electrosurgical vessel sealing and tissue welding. The output power is applied cyclically by a control system with tissue impedance feedback. The impedance of the tissue follows the cyclic pattern of the output power several times, depending on the state of the tissue, until the tissue becomes fully desiccated. High power is applied to cause the tissue to reach a high impedance, and then the power is reduced to allow the impedance to fall. Thermal energy is allowed to dissipate during the low power cycle. The control system is adaptive to tissue in the sense that output power is modulated in response to the impedance of the tissue.

1 . An electrosurgical generator for applying output power to tissue, the electrosurgical generator comprising:
 a tissue impedance measurement circuit configured to measure tissue impedance; and   a controller coupled to the tissue impedance measurement circuit, the controller adapted to cycle output power from the electrosurgical generator to cause a cycling of the tissue impedance by applying the output power to tissue and then adjusting the output power to at least one of a lower output value and termination of output power, the controller further adapted to re-apply the output power to tissue if measured tissue impedance does not indicate tissue desiccation and to terminate output power when the measured tissue impedance indicates tissue desiccation.   
   
   
       2 . The generator according to  claim 1 , wherein the controller changes the output voltage to cycle the output power. 
   
   
       3 . The generator according to  claim 1 , wherein the controller changes the output current to cycle the output power. 
   
   
       4 . The generator according to  claim 1 , wherein the output voltage is cycled by lowering the output voltage once the output voltage reaches a predetermined maximum and raising the output voltage if the rise in measured tissue impedance does not indicate tissue desiccation. 
   
   
       5 . The generator according to  claim 1 , wherein the output power is cycled at a frequency that is from about 1 Hz to about 20 Hz. 
   
   
       6 . The generator according to  claim 1 , wherein the output voltage does not exceed 120 volts. 
   
   
       7 . The generator according to  claim 1 , further comprising a comparator and wherein the measured tissue impedance value is compared to a first signal representative of a desired tissue impedance value by the comparator to produce a difference signal. 
   
   
       8 . The generator according to  claim 7 , wherein the difference signal is input into the controller which generates a signal to adjust the power. 
   
   
       9 . The generator according to  claim 7 , wherein the first signal has a cyclic pattern. 
   
   
       10 . The generator according to  claim 9 , wherein the first signal is a sine wave. 
   
   
       11 . An electrosurgical generator for treating tissue by applying energy, the electrosurgical generator comprising:
 a desiccation detector configured to determine completeness of tissue desiccation; and   a controller coupled to the desiccation detector, the controller adapted to cycle output power to cause a cycling of tissue impedance in response to the degree of tissue desiccation, the controller further adapted to re-apply the output power to tissue if the desiccation detector does not indicate tissue desiccation.   
   
   
       12 . The generator according to  claim 11 , wherein the output power is terminated by the controller upon detection of desiccated tissue. 
   
   
       13 . The generator according to  claim 12 , wherein the desiccation detector further comprises impedance measuring circuitry adapted to measure tissue impedance and to determine degree of tissue desiccation based on the measured tissue impedance. 
   
   
       14 . The generator according to  claim 13 , wherein the impedance measuring circuitry adjusts the output power by adjusting the output voltage within a predetermined voltage range. 
   
   
       15 . The generator according to  claim 11 , wherein the output power is repeatedly increased and decreased by the circuitry at a frequency from about 1 Hz to about 20 Hz. 
   
   
       16 . A method for applying electrosurgical energy to tissue to treat tissue, the method comprising:
 a) cycling output power from an electrosurgical generator to cause a cycling of tissue impedance by applying output power to tissue and then adjusting output power to at least one of a lower output value and termination of output power;   b) re-applying output power to tissue if tissue impedance does not indicate tissue desiccation;   c) allowing the tissue impedance to fall to a predetermined minimum value and then raising the output power to cause an increase in tissue impedance; and   d) repeating steps b and c until tissue impedance at least reaches a predetermined value that corresponds to tissue desiccation.   
   
   
       17 . The method according to  claim 16 , further comprising the step of:
 lowering the output voltage once the output voltage reaches a predetermined maximum and raising the output voltage if the rise in measured tissue impedance does not indicate tissue desiccation.   
   
   
       18 . The generator according to  claim 1 , wherein the cycling of the output power is accomplished at a frequency from about 1 Hz to about 20 Hz.