[en] An electrosurgical bipolar forceps for sealing is disposed. The forceps includes one or more shaft members having an end effector assembly disposed at the distal end. The end effector assembly includes two jaw members movable from a first position to a closed position wherein the jaw members cooperate to grasp tissue at constant pressure. Each of the jaw members includes an electrically conductive sealing plate connected to a first energy source which communicates electrosurgical energy through the tissue held therebetween. The electrically conductive sealing plates are operably connected to sensor circuitry which is configured to measure initial tissue impedance and transmit an initial impedance value to a controller. The controller determines the constant pressure to be applied to the tissue based on the initial impedance value.