This study will investigate the incidence of postoperative POD in patients undergoing non cardiac surgery under general anesthesia with and without the implementation of the BIS monitoring.T

This study will compare the incidence of POD after elective non cardiac surgery conducted under general anesthesia before and after the implementation of BIS monitoring in our University Hospital.

The POD will be evaluated with the CAM and Nu-DESC tools, which have been adapted for the greek population.

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)