The goal of this clinical trial is to compare the effect of remimazolam and dexmedetomidine on the incidence of hypotension during spinal anesthesia in adult patients.

Sedation during spinal anesthesia can reduce the patient's anxiety and increase satisfaction, but sedatives such as dexmedetomidine and midazolam may cause hemodynamic instability such as hypotension and bradycardia. In previous studies , hypotension occurred in about 33% and bradycardia in about 13% during spinal anesthesia, which is related to reduced cardiac output due to sympathetic blockade and relative activation of the parasympathetic nerve.

In the study comparing remimazolam and dexmedetomidine in patients with delirium after orthopedic surgery, the incidence of hypotension was lower in the remimazolam group (10.8%) than in the dexmedetomidine group (39.5%) (p=0.007) and there was no significant difference between the remimazolam group (2.7%) and the dexmedetomidine group (13.2%) in the incidence of bradycardia (p=0.200).

However, the effect of remimazolam on the incidence of hypotension during spinal anesthesia has not been revealed. Therefore, this study is designed to compare the effect of remimazolam and dexmedetomidine on the incidence of hypotension during spinal anesthesia in adults patients.

Inclusion Criteria:

- Patient scheduled for surgery under spinal anesthesia, aged 19-79, of ASA class I, II, or III

Exclusion Criteria:

• Patient refusal
• Contraindications to regional or neuraxial anesthesia (patient refusal, increased intracranial pressure, infection at puncture site, underlying neurologic disease, severe hypovolemia, severe aortic or mitral stenosis, thrombocytopenia or coagulopathy, sepsis)
• Contraindications or allergy to dexmedetomidine or remimazolam administration
• Emergency surgery
• Pregnancy