The purpose of this study is to compare midazolam-dexmedetomidine with dexmedetomidine alone for hemodynamic stability and quality of sedation in elderly patients under spinal anesthesia.

Inclusion Criteria:

• aged ≥ 65 years
• ASA physical status class I-II
• the patients who want sedation during elective lower limb surgery under spinal anesthesia

Exclusion Criteria:

• contraindication to spinal anesthesia
• neurologic or cognitive dysfunction
• severe cardiovascular or pulmonary disease
• refusal to participation