Patients were enrolled according to predefined inclusion and exclusion criteria. Following surgical admission, standard monitoring was initiated, including continuous assessment of heart rate, blood pressure, electrocardiogram (ECG), and peripheral capillary oxygen saturation (SpO₂). A peripheral intravenous line was established. Bispectral index (BIS) monitoring was performed continuously using a BIS monitor to assess frontal lobe electroencephalographic activity. Based on the type of surgical procedure, regional nerve block was administered. Upon confirmation of adequate block efficacy, patients were assigned to treatment groups according to sealed envelope randomization, and corresponding intravenous sedative regimens were initiated. Sedative induction agents were administered as follows: Group A received remimazolam at 0.08 mg/kg; Group B received dexmedetomidine at 1 μg/kg over 10 minutes; Group C received midazolam at 0.05 mg/kg. Maintenance infusions were as follows: Group A received remimazolam at 1 mg/kg·h; Group B received dexmedetomidine at 0.2-0.7 μg/kg·h; for Group C, if consciousness was not sufficiently suppressed with the initial dose, midazolam was supplemented in increments of 0.01 mg/kg, not exceeding a total dose of 0.1 mg/kg. Following induction, sedation depth was assessed every 2 minutes using the Observer's Assessment of Alertness/Sedation (OAA/S) scale, with auditory stimulation applied every 30 seconds until the patient no longer responded. The time to loss of response to auditory stimuli and the time to loss of consciousness were recorded. Surgical intervention was then performed. Ten minutes prior to anticipated completion of surgery, sedative infusion was discontinued. Sedation depth was reassessed every 2 minutes using the OAA/S scale, with repeated auditory stimulation every 30 seconds to determine the time to return of response and time to recovery of consciousness. If the patient had not achieved an OAA/S score of 5 within 30 minutes after discontinuation of sedation, flumazenil was administered as a reversal agent. Once the OAA/S score reached 5 or spontaneous responses to auditory stimuli were observed-indicating transition back to a responsive state-and complete electroencephalographic data had been collected, no further intervention was required.

Inclusion Criteria:

• Age: 20 - 60 years old. BMI: 18 ≤ BMI ≤ 24 kg/m2. Right-handed. ASA classification: I - II. Patients scheduled for extremity surgery of upper and lower limbs and undergoing nerve block, those who understand and sign the informed consent form, and those receiving non-endotracheal general anesthesia with remimazolam or dexmedetomidine or midazolam, with Mallampati classification: I - II.

Exclusion Criteria:

• Skin infection at the site of nerve block puncture; history of smoking and alcohol abuse, history of brain surgery, history of cerebral infarction, mental and neurological disorders (MMSE < 18, 3D-CAM positive), history of taking any psychotropic or opioid drugs within 2 weeks, hearing impairment, cardiovascular disease, expected difficulty in airway management or sleep apnea syndrome, drug (including those with a history of allergic reaction to the test drug or contraindications for use) or food allergies, pregnant or lactating patients, patients or family members who refuse to participate, and those who refuse to undergo nerve block.

Patients undergoing elective orthopedic surgery under nerve block combined with intravenous anesthesia