A Single-Center, Prospective Observational Cohort Study Comparing Perioperative Electroencephalographic Anesthesia Depth Parameters (Electroencephalographic Index, SE/RE Entropy, Burst Suppression Ratio) Between Patients With Preoperative Sleep Disorders and Those Without; To Identify the Independent Effects of Preoperative Sleep Disorders on the Speed of Electroencephalographic Recovery During Emergence, Electroencephalographic Status at Extubation, Intra-PACU Electroencephalographic Fluctuations, and Quality of Emergence.

Preoperative sleep disorder is a common perioperative comorbidity. It impairs central nervous system stability and anesthetic drug metabolism, delays postoperative recovery, and is strongly associated with delayed emergence from general anesthesia, emergence agitation, and postoperative cognitive decline. Electroencephalographic (EEG) monitoring enables continuous, quantitative assessment of anesthetic depth (including EEG index, entropy, and burst suppression ratio), which can reflect central nervous depression more sensitively than conventional vital sign monitoring. To date, there is a lack of evidence based on complete preoperative-intraoperative-postoperative continuous EEG data to clarify the correlations between sleep disorders, anesthetic depth, and emergence quality. This prospective cohort study will collect full-course EEG parameters throughout the perioperative period to identify the effects of preoperative sleep disorders on the stability of anesthetic depth, EEG recovery during emergence, and adverse emergence events, so as to provide evidence-based references for perioperative cerebral protection and precision anesthetic management.

Primary Outcome Measures Preoperative & Postoperative Polysomnography (PSG) indicators: Sleep Efficiency Index (SEI), Total Sleep Time (TST), Arousal Index (AI), and the proportional percentages of N1, N2, N3 stages within NREM sleep and REM sleep; assessments conducted on the night after surgery, postoperative Day 1 and postoperative Week 1.Intraoperative EEG parameters: mean value of EEG index, minimum EEG index value, cumulative duration when EEG index < 40, maximum Burst Suppression Ratio (BSR).Emergence-phase EEG indicators: recovery time of EEG index, EEG index at extubation, standard deviation of EEG fluctuation in Post-Anesthesia Care Unit (PACU).Emergence quality indicators: extubation time, PACU length of stay, incidence of emergence agitation.

Serum Brain-Derived Neurotrophic Factor (BDNF) levels collected at preoperative, intraoperative and postoperative time points.

Inclusion Criteria:

1. - Aged 18 to 65 years, with American Society of Anesthesiologists (ASA) physical status classification Ⅰ-Ⅲ;
2. Elective non-cardiac surgery with an expected operative duration longer than 2 hours;
3. Preoperative Mini-Mental State Examination (MMSE) score ≥ 24;
4. Completion of the Pittsburgh Sleep Quality Index (PSQI) assessment 1 day before surgery;
5. Absence of severe cardiac, hepatic, renal or cerebral diseases, and no history of psychiatric or neurological disorders;
6. Voluntary provision of written informed consent.

Exclusion Criteria:

1. Preoperative severe cognitive dysfunction, history of traumatic brain injury or stroke;
2. Long-term regular use of sedative-hypnotics, antidepressants or antipsychotics;
3. Intraoperative massive hemorrhage, cardiac arrest, or severe hypoxemia (SpO₂ < 90% lasting for more than 5 minutes);
4. Inability to cooperate with EEG monitoring or scale evaluation;
5. Pregnancy or breastfeeding status.

Drop-out Criteria :

1. Cancellation of scheduled surgery/anesthesia or postoperative admission to the intensive care unit (ICU);
2. Patient withdrawal of study participation;
3. Intraoperative massive hemorrhage, cardiac arrest, or severe hypoxemia (SpO₂ < 90% lasting for more than 5 minutes);
4. Development of severe postoperative complications;
5. Incomplete data collection or voluntary trial withdrawal.

Patients scheduled for elective non-cardiac surgery under general anesthesia at our hospital will be enrolled in this study.