Apparatus and method for creating, maintaining, and controlling a virtual electrode used for the ablation of tissue

A method for treating tissue by ablation with a virtual electrode, the method comprising:

• (a) placing an RF power delivery electrode in contact with target tissue of a patient;
• (b) providing the tissue with a super-cooled fluid to cause a temporary cessation of cellular or electrical activity;
• (c) evaluating the effect of the distributed super-cooled fluid, including whether the providing of the super-cooled fluid to the target tissue causes a temporary cessation of cellular activity or electrical activity indicative of the disorder or tumor, or a temporary cessation of cellular activity or electrical activity indicative of a temporary adverse side effect;
• (d) providing the tissue with a conductive fluid to create a virtual electrode;
• (e) applying RF current to the tissue through the virtual electrode while continuing to provide conductive fluid to the tissue;
• (f) monitoring an impedance of the tissue;
• (g) determining a rate of change of the tissue impedance within a predetermined time interval;
• and
• (h) increasing a size of the virtual electrode when the determined rate of change of tissue impedance exceeds a predetermined value by increasing a flow rate of the conductive fluid.

A system for producing, maintaining, and controlling a virtual electrode for a provision of RF current therapy through the virtual electrode to a target tissue of a patient, the system providing a conductive fluid and an RF current via at least one surgical instrument to the target tissue to create the virtual electrode, the apparatus comprising:

• a) at least one source of super-cooled fluid for selectively providing super-cooled fluid to the target tissue to cause a temporary cessation of cellular or electrical activity;
• b) at least one source of conductive fluid for selectively providing conductive fluid to the target tissue;
• c) a surgical instrument including an electrode for delivery of the RF current to the virtual electrode;
• d) a generator of RF current, the generator supplying the RF current to the virtual electrode via the surgical instrument;
• e) means for detecting an electrical arc;
• f) means for measuring the impedance of the body of the patient to the passage of the RF current;
• g) at least one primary temperature sensor for sensing the temperature at at least a first predetermined location in the body of the patient;
• h) means for controlling a rate of application of the super-cooled fluid and a rate of application of the conductive fluid to the target tissue and for controlling a power level of the RF current, the means for controlling receiving arc detection signals from the arc detection means, impedance measurement signals from the impedance measuring means, and temperature measurement signals from the at least one temperature sensor, the rate of super-cooled fluid flow controlled in response to the sensed temperature, the power level of the RF current and the rate of conductive fluid flow controlled by the controlling means in response to changes in the measured impedance and the sensed temperature, the means for controlling discontinuing the application of RF current for a predetermined period of time upon receiving signals indicating a detection of an electrical arc.