The goal of this clinical trial is to compare the efficacy of patient-controlled sedation (PCS) versus clinician-controlled sedation (CCS) using remimazolam in adult patients undergoing primary hip arthroplasty under spinal anesthesia.

The main questions it aims to answer are:

• Does patient-controlled sedation significantly reduce the total consumption of remimazolam compared to clinician-controlled sedation?
• Are there differences in secondary outcomes, such as sedation depth , sedation-related adverse events, frequency of airway interventions, and patient/surgeon satisfaction?

Researchers will compare the PCS group to the CCS group to see if the patient-controlled method leads to a reduction in total remimazolam consumption while maintaining effective sedation.

Participants will:

• Be randomly assigned to either the PCS group or the CCS group.
• In the PCS group: Receive an initial 0.05 mg/kg remimazolam dose over 1 minute. If deeper sedation is desired, the patient can self-administer a 1 mg bolus of remimazolam via a button press, which has a 1-minute lockout interval.
• In the CCS group: Receive an initial 0.05 mg/kg remimazolam dose over 1 minute, followed by a continuous infusion starting at 0.3 mg/kg/h. The clinician will assess the MOAA/S score every 10 minutes and adjust the infusion rate to maintain a target MOAA/S score of 3.

Inclusion Criteria:

• Patients aged 19 to 70 years with an ASA (American Society of Anesthesiologists) physical status of I or II who are undergoing primary hip arthroplasty under spinal anesthesia.

Exclusion Criteria:

• Refusal to participate in the study
• Patients with contraindications to spinal anesthesia
• Patients who do not consent to intraoperative sedation
• Patients with contraindications to remimazolam
• Patients with a history of allergy or hypersensitivity to remimazolam
• Patients with a baseline MOAA/S (Modified Observer's Assessment of Alertness/Sedation) score of 4 or lower
• Pregnant women