Electrosurgical safety circuit

In an electrosurgical device used in an environment having a system ground and having a radio-frequency generator coupled to chassis ground, an active electrode for performing electrosurgery on a patient, an active lead connecting the radio-frequency generator to the active electrode for carrying current from the radio-frequency generator to the active electrode, a dispersive electrode for receiving current which passes from the active lead and through the patient, and a return lead connecting the dispersive electrode to the radio-frequency generator for carrying current from the dispersive electrode back to the radio-frequency generator, an electrosurgical safety circuit, comprising:

• a first monitor means for sensing the flow of current in the active lead;
• a second monitor means for sensing the flow of current in the return lead;
• means responsive to said first monitor means sensing a predetermined greater level of current than said second monitor means for actuating an alarm;
• a first low impedance alternate current path coupled between chassis ground and the return lead so as to hold the dispersive electrode near ground potential and to provide a current path from chassis ground to the radio-frequency generator;
• a third monitor means for sensing a predetermined current flow in said first alternate current path and for actuating an alarm;
• a second alternate current path coupled between system ground and chassis ground so as to establish a return path from system ground to the radio-frequency generator via the first and second alternate current paths;
• and
• a fourth monitor means for sensing a predetermined current flow in said second alternate current path and for actuating an alarm,
• whereby radio-frequency current flowing from the patient to a ground results in an alarm generated by said first and second monitor means by virtue of a greater level of current flowing in the active lead than in the return lead irrespective of the operability of said third or fourth monitor means, said first alternate path holds the dispersive electrode near ground potential to prevent the dispersive electrode from floating to a hazardous potential, said third monitor means causes an alarm to be actuated irrespective of the operability of said first, second or fourth monitor means when current flows between chassis ground and the return lead, and said fourth monitor means causes an alarm to be activated irrespective of the operability of said first, second or third monitor means when current flows to system ground.