During anaesthesia induction, the patients will breath an air-oxygen mixture through a face mask. The target effect-site concentration of propofol will first be set at 0.5 ng.ml-1 and it will be increased by 0.2 ng.ml-1 every 2 min until the clinical endpoint will be achieved (loss of consciousness and unresponsiveness). Then, ventilation will be assisted manually and the trachea will be intubated after the intravenous administration of fentanyl (100 mcg) and rocuronium (0.7 mg.kg-1).