This prospective, single-center, randomized interventional study aims to investigate the effects of commonly used adjunct anesthetic drugs on the Bispectral Index (BIS) and electroencephalographic (EEG) activity during total intravenous anesthesia.

BIS monitoring is widely used to estimate the depth of anesthesia. However, previous studies suggest that certain anesthetic drugs, particularly dexmedetomidine and esketamine, may alter BIS values independently of the patient's actual level of consciousness. As a result, BIS readings may not always accurately reflect anesthetic depth when multiple drugs are administered together.

Adult patients undergoing elective laparoscopic cholecystectomy under standardized propofol-remifentanil anesthesia will be randomly assigned to receive one of the following adjunct drugs: midazolam, dexmedetomidine, esketamine, or no additional study drug (control group). Continuous BIS values and raw EEG signals will be recorded throughout the study period.

The primary objective is to compare changes in BIS values among different adjunct anesthetic drugs under otherwise similar anesthetic conditions. The study will also explore corresponding EEG characteristics associated with these changes. The findings are expected to improve understanding of drug-related differences in processed EEG monitoring and provide data for future development of more accurate anesthesia depth assessment methods.

Inclusion Criteria:

1. ASA physical status I-II;
2. BMI 18-28 kg/m²;
3. Scheduled for elective laparoscopic cholecystectomy, with an expected surgical duration from skin incision to completion of wound closure of ≥45 min;
4. Planned to receive propofol-remifentanil total intravenous anesthesia, with routine intraoperative BIS monitoring and simultaneous acquisition of raw EEG signals;
5. Voluntarily agrees to participate in this study, has signed the informed consent form, and is able to cooperate with the intervention and assessment procedures.

Exclusion Criteria:

1. A confirmed history of psychiatric or neurological disorders, or use of antipsychotics, antidepressants, benzodiazepines, or other sedative-hypnotic drugs within 4 weeks before surgery;
2. Cognitive impairment identified by Mini-Cog screening;
3. Poorly controlled or untreated hypertension, sinus bradycardia, or severe cardiac conduction block;
4. Acute angle-closure glaucoma;
5. Known allergy to any required anesthetic drug;
6. Difficulty in electrode placement or any condition that may interfere with EEG monitoring.