Currently used drugs for monitored general anesthesia include propofol, midazolam, and dexmedetomidine. Each drug has different advantages and disadvantages. Remimazolam causes a relatively small decrease in blood pressure, and it has no injection pain. In addition, remimazolam has a very short onset time, and even after the continuous infusion, the onset of remimazolam is fast, and even after continuous injection, the effect disappeared very quickly due to the short context-sensitive half time. and through continuous infusion, the patient's depth of anesthesia can be maintained constant. In addition, the short duration of action and the ability to quickly reverse the effect of flumazenil suggest that remimazolam can be used effectively under general anesthesia as well as under general anesthesia. Remimazolam can be used as a continuous infusion for general anesthesia. However, it has also been reported to be used for sedation by continuous infusion or divided intravenous infusion. However, the effective infusion dose of remimazolam for supervised general anesthesia without mechanical ventilation has not been established.

In this study, the ED90 of the maintenance dose that maintain loss of consciousness in patients when supervised general anesthesia is performed through continuous infusion of remimazolam after spinal anesthesia is obtained.

Inclusion Criteria:

• ASA PS 1-3
• Patients undergoing lower extremity surgery under spinal anesthesia and sedation using remimazolam

Exclusion Criteria:

• Patients who refuse to participate in this study
• Patients with hypersensitivity to benzodiazepine or flumazenil
• Patients with severe renal/hepatic disease
• Patients with drug/alcohol abuse
• Patients who take antidepressants, anticonvulsants, psychoactive drugs chronically
• Patients with difficulty in communication
• Patients with severe obstructive sleep apnea or other airway problems
• Patients contraindicated to regional anesthesia
• Patients judged to be inappropriate for this study