Anaesthesia and surgery All patients will be premedicated with oral midazolam 7.5 mg and they will receive a loading dose of lactate-ringer solution (5 ml.kg-1) intravenously after arrival in the operating theatre. The standard anaesthetic monitoring will comprise non-invasive blood pressure, ECG, pulsed oxygen saturation and end-tidal carbon dioxide. Processed EEG parameters will be acquired with a BIS monitor, using surface electrodes, with impedance maintained at less than 5kΩ to ensure adequate signal quality. Raw EEG data from two channels (F7-CZ and F8-CZ) will be processed by company proprietary software and the BIS values (calculated for each 4-sec epoch) will be continuously displayed along with the trend line.