Rocuronium. a curarizing agent, has been shown to decrease Bispectral Index (BIS) in awake volunteers.~However, correlation between Trend of Four (TOF) values after a bolus of rocuronium and BIS values during general anaesthesia for breast surgery has not been defined yet.~Investigators want to analyze this correlation during general anaesthesia conducted using Propofol and remifentanil. All of these drugs will be delivered with Targeted-Controlled Infusion pumps (in particular Eleveld for Propofol, Minto for Remifentanil), commonly used to deliver general anaesthesia. At stable anaesthesia maintenance, if requested for surgical (ie more muscle relaxation) or anesthesiological reasons (i.e. avoid air insufflation) a standard Rocuronium bolus (0.6 mg/kg) was given. In these case, with rocuronium bolus justified by clinical reasons, authors will observationally record the BIS values and the TOF values.
Aim of this trial is to define if Trend of Four (TOF) values after a bolus of rocuronium is correlated with Bispectral Index BIS values during standard general anaesthesia for breast surgery.