To explore the sedative effect of remimazolam in patients undergoing spinal anesthesia without pain stimulation. Both the Modified Observer's Assessment of Alertness/Sedation (MOAA/S) and the Wavelet index (WLi) were used to monitor the depth of anesthesia of remimazolam, and exploring the correlation and consistency between MOAA/S score and WLi value at the same time.

Patients undergoing spinal anesthesia were received remimazolam besylate for sedation continuously. Both the Modified Observer's Assessment of Alertness/Sedation (MOAA/S) and the Wavelet index (WLi) were used to monitor the depth of anesthesia of remimazolam, and exploring the correlation and consistency between MOAA/S score and WLi value at the same time.

Inclusion Criteria:

• ASA was classified as I-III
• The operation time was less than 120 minutes
• Informed consent is signed by all study participants
• Elective lower extremity surgery under spinal anesthesia was performed

Exclusion Criteria:

• Pregnant or lactating women
• Patients with Difficult Airways
• History of severe neurological and muscular diseases and mental retardation
• Patients with severe respiratory and circulatory diseases, including acute heart failure. Unstable angina pectoris. Resting ECG heart rate <50 beats/min. QTc: ≥470ms in men and ≥480ms in women. Third degree atrioventricular block. Severe arrhythmia. Moderate to severe heart valve disease. Chronic obstructive pulmonary disease. A history of severe asthma.
• Abnormal liver and kidney function: ALT and/or AST exceeding 2.5 times the upper limit of the medical reference range
• Take diazole drugs and/or opioids in one month or nearly three months
• Patients who were allergic to or contraindicated to benzodiazepines, opioids, propofol, flumazenil, naloxone, etc
• Patients who could not monitor the depth of anesthesia for various reasons

This was an unrandomized, single-group study. The sample size was calculated using PASS 15™(NCSS, LLC. Kaysville, Utah, USA.) software. The degree of confidence (1-β) was set at 0.90, and the α value was set at 0.05. ρ0, the baseline correlation, was set to 0. The ρ1, alternating correlation, was set to 0.3 based on the expected minimum r value of 0.3 obtained in previous literature. Final calculations show that 112 pairs of data were needed to complete the experiments. Approximately 20 pairs of data were expected to be recorded per participant, and 30 participants were expected to be enrolled in this study. So, the sample size was adequate.