James L Crow

US Patent:

44374640, Mar 20, 1984

Filed:

Nov 9, 1981

Appl. No.:

6/319423

Inventors:

James J. Crow - Englewood CO

Assignee:

C.R. Bard, Inc. - Murray Hill NJ

International Classification:

A61B 1739

US Classification:

12830314

Abstract:

Leakage cancelling apparatus suitable for use in electrosurgery apparatus to prevent electrical burns is disclosed. The apparatus comprises a transformer which is connected in the electrical circuit between the electrosurgical source and the patient. The transformer has a primary winding connected in series with the active surgical electrode and a secondary winding connected in series with the return path to the electrosurgical generator. The connections to the windings are polarized so that during normal operation the magnetic fields in the transformer core generated by current flow are almost completely cancelled. Consequently, the transformer windings present very small impedances in series with the electrosurgical circuit. If a break occurs in the return lead of the electrosurgical circuit and the patient becomes ungrounded, a condition which would normally result in a high risk of a burn, the currents in the primary and secondary windings of the transformer become unequal, the magnetic fields in the transformer core do not cancel and the transformer windings present a significant impedance to the flow of electrosurgical current which reduces the occurence of electrosurgical burns. In addition, the uncanceled inductance presented by the transformer windings during a break situation may be chosen to resonate with the leakage capacitance of the electrosurgical circuit, further reducing the current flow and preventing burns.