Abstract: An electrosurgical feedback system for detecting the effects of electrosurgical energy on tissue. The feedback system can include an acoustical detection element that acoustically detects the effects of energy on tissue and then generates an acoustic output signal indicative of these energy effects. A power regulation element, in response to the acoustic output signal, regulates the electrosurgical energy supplied to the tissue. Alternatively, the feedback system can include an impedance determination circuit that determines the impedance of the tissue. The tissue determination stage can include a first and second differentiator circuit to determine the time-based derivative of the measured tissue impedance. The tissue determination stage generates an impedance output signal of either the first or second derivative of the tissue impedance, which is conveyed to the power regulation element. The regulation element regulates the amount of energy supplied to the tissue in response to the impedance output signal.