An electromagnetic surgical ablation system having a generator adapted to selectively provide surgical ablation energy to an ablation probe, and methods of operating same, are disclosed. The system includes a controller operatively coupled to the generator, and at least one tissue sensor probe operatively coupled to the controller. The at least one tissue sensor provides a tissue impedance measurement to the controller. A sensor probe may be designated a threshold probe adapted to sense when tissue is sufficiently ablated, or, a critical structure probe adapted to protect an adjacent anatomical structure from undesired ablation. During an electromagnetic tissue ablation procedure, the controller monitors tissue impedance to determine tissue status, to activate an indicator associated therewith, and, additionally or alternatively, to activate and deactivate the generator accordingly.
