The primary objective of this observational study is to evaluate the effectiveness of preoperative anaesthesia depth monitoring parameters in predicting postoperative cognitive functions in non-cardiac adult patients.

Participants will preoperatively perform cognitive tests such as the Nursing Delirium Screening Scale(Nu-DESC) and 4 'A's Test(4AT) to assess baseline cognitive performance. The same tests will be repeated twice daily until the postoperative 3rd day or discharge.

The primary objective of this observational study is to evaluate the effectiveness of preoperative anaesthesia depth monitoring parameters such as Bispectral Index(BIS), Spectral edge frequency(SEF) and Median frequency(MF) in predicting postoperative cognitive functions in non-cardiac adult patients.

Participants will preoperatively perform cognitive tests such as the Nursing Delirium Screening Scale(Nu-DESC) and 4 'A's Test(4AT) to assess baseline cognitive performance. Intraoperative haemodynamic and BIS parameters will be collected via manual data entry into printed forms. Also, a two-channel electroencephalogram(EEG) and BIS parameters(BIS Number, SEF, MF) will be collected digitally.

The cognitive tests will be repeated twice daily until the postoperative 3rd day or discharge.

Parameters such as mean intraoperative MF value and the ratio of MF over SEF will be compared against postoperative cognitive test scores.

Inclusion Criteria:

Adult patients (aged over 18 years), Patients undergoing elective surgeries, Patients consenting to participate in the study.

Exclusion Criteria:

Pediatric patients (aged under 18 years), Patients undergoing emergency surgeries, Patients requiring or anticipated to require postoperative intensive care for more than one day, Patients undergoing cardiac surgeries, Patients undergoing intracranial surgeries, Patients are undergoing endoscopic sinus or brain surgeries, Patients with pacemakers or implantable cardioverter-defibrillators (ICDs), Patients diagnosed with dementia (including Alzheimer's disease, Lewy body dementia, etc.), Patients with chronic opioid or benzodiazepine use, Patients with contraindications to Propofol, Remifentanil, or Fentanyl, Pregnant or breastfeeding women, Patients are not willing to participate in the study.

The research focuses on adults (≥18 years old) of any gender residing in Türkiye, scheduled for elective, non-cardiac surgeries.