The Impact of the Implementation of BIS on the Incidence of Postoperative Delirium

Inclusion Criteria: 1. adult patients over 60 years of age 2. an American Society of Anesthesiologists (ASA) physical status I to III 3. undergoing elective non cardiac surgery under general anaesthesia 4. native speakers of the Greek language 5. eligible to leave the post-anaesthesia care unit 6. an expected in-hospital stay at least 24 hours following surgery Exclusion Criteria: 1. refused to participate or sign the informed consent form 2. surgery or anaesthesia within the last 30 day 3. any prior or current history involving an affliction of the central nervous system 4. severe hearing or visual impairment 5. psychiatric disorders 6. a score less than 5 according the Geriatric Depression Scale (GDS-15) 7. a score less than 4 for females and less than 2 for males according to the Lawton-Brody Instrumental Activities of Daily Living Scale (I.A.D.L.) 8. alcohol consumption less than 35 units/week 9. drug dependence 10. previous neuropsychological testing 11. haemodynamical instability 12. peri-procedural desaturation (one or more events of SpO2\<80% for more than 2 minutes)