Patent ID: 8657817

Claim:
A high frequency (HF) cutting and coagulating surgical instrument for cutting and coagulating biological tissue by means of an HF current, comprising: a cutting electrode; an HF generator for supplying an HF current to said cutting electrode; and at least one control device for interrupting an HF current circuit, comprising: a current monitoring device, adapted to detect the amplitude of the HF current and to generate a first switch-off signal when as a first switch-off criterion at least one of the following occurs: (a) the HF current decreases over a defined period of time; and (b) the HF current falls below a threshold value characterizing a state of the treated tissue, an arc monitoring device, adapted to generate a second switch-off signal when as a second switch-off criterion an arc is formed between the cutting electrode and the tissue, and a timer to delay either the first or second switch-off signals for a time period after they have been detected, wherein the control device being designed to detect an incipient cutting action during a vapor phase of a tissue treatment procedure by detecting whether the first switch-off criterion is reached and if the first switch-off criterion is not reached, the second switch-off criterion is verified by the arc monitoring device, so that the HF circuit is interrupted in response to the first switch-off signal or the second switch-off signal after the time period to allow cutting action by the HF circuit.