US 4,094,320 AGranted

Electrosurgical safety circuit and method of using same

AssigneeValleylab, Inc.

InventorsDavid W. Newton, Frank A. Alford

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Abstract

An improved electrosurgical safety circuit where the currents in the active and patient leads are monitored, the monitored currents being respectively rectified and then subtracted from one another. Whenever the active current exceeds the patient or return current by an amount corresponding to a dynamically variable threshold, an appropriate measure is taken such as the sounding of an alarm and/or the de-energization of the electrosurgical generator. The dynamic threshold varies in accordance with the level of the signal applied to the patient and compensates for leakage current through stray capacitance from the active lead to ground. The patient lead is substantially grounded at radio frequencies through a frequency sensitive network. The frequency sensitive network may include a capacitor, the value of which is such as to provide the foregoing frequency response. Since as small a capacitor as possible must be used to provide a high impedance at low frequencies, and since the radio frequency voltage across the capacitor must be kept low to thereby keep the voltage patient low at radio frequencies, a further network is employed to enable the use of a small capacitor while at the same time decreasing the effective voltage thereacross whereby protection of the patient is enhanced.

Claims15

Dependent claims

An electrosurgical generator comprising

a radio frequency generator;
an electrosurgical instrument having an active electrode suitable for application to a patient;
an active lead connected between said generator and said active electrode for conducting current from said generator to said active electrode;
a patient electrode adapted for connection to said patient to provide a low impedance path for current from said active electrode;
a patient lead connected between said generator and said patient electrode for conducting current from said patient electrode back to said generator;
and
a safety circuit means for detecting only an excess of active lead current with respect to patient lead current to thereby indicate a discontinuity in a patient circuit including said patient electrode and said patient lead;
the level of the output signal from said radio frequency generator being adjustable and said safety circuit means detecting an excess of current in the active lead with respect to current in the return lead and including threshold means for indicating an alarm condition when the active lead current exceeds the patient lead current by a threshold level established by said threshold means, said threshold means including compensating means for dynamically varying said threshold level, said compensating means being responsive to adjustments in the output signal level of said generator to make said safety circuit means responsive to expected differences of said active and patient lead currents under normal conditions to thereby both provide a sensitive threshold in a variety of conditions and to offset the tendency of said signal adjustments to prematurely generate said alarm condition when there is no danger to said patient.

5 more elements

An electrosurgical generator comprising

a radio frequency generator, the level of the output signal of which is adjustable;
an electrosurgical instrument having an active electrode suitable for application to a patient;
an active lead connected between said generator and said active electrode for conducting current from said generator to said active electrode;
a patient electrode adapted for connection to said patient to provide a low impedance path for current from said active electrode;
a patient lead connected between said generator and said patient electrode for conducting current from said patient electrode back to said generator;
a safety circuit means for detecting an excess of current in the active lead with respect to current in the return lead including threshold means for indicating an alarm condition when the active lead current exceeds the patient lead current by a threshold level established by said threshold means;
and
said threshold means including compensating means for dynamically varying said threshold level, said compensating means being responsive to adjustments in the output signal level of said generator to offset the tendency of said signal adjustments to prematurely generate said alarm condition when there is no danger to said patient.

5 more elements

An electrosurgical method comprising the steps of

generating a radio frequency signal from a radio frequency generator;
applying an electrosurgical instrument having an active electrode to a patient;
conducting current from said generator to said active electrode through an active lead;
connecting a patient electrode to said patient to provide a low impedance path for current from said active electrode;
conducting current from said patient electrode back to said generator through a patient lead;
detecting an excess of active lead current with respect to patient lead current to thereby indicate a discontinuity in a patient circuit including said patient electrode and said patient lead;
the level of the signal from said radio frequency generator being adjustable and where detecting step detects an excess of current in the active lead with respect to current in the return lead and indicates an alarm condition when the active lead current exceeds the patient lead current by a threshold level, said method including the step of dynamically varying said threshold level to offset the tendency of adjustments in the level of the generated radio frequency signal to cause unwanted alarm conditions or increases in said threshold level.

4 more elements

Dependencies are inferred from the claim text.