The goal of this randomized controlled trial is to determine whether low-dose hyperbaric bupivacaine provides better hemodynamic stability and postoperative recovery compared with standard-dose hyperbaric bupivacaine in elderly patients undergoing lower limb orthopedic surgery under spinal anesthesia.

The main questions it aims to answer are:

• Does low-dose hyperbaric bupivacaine reduce the incidence of intraoperative hypotension and bradycardia compared with standard-dose hyperbaric bupivacaine?
• Does low-dose hyperbaric bupivacaine improve postoperative recovery profile compared with standard-dose hyperbaric bupivacaine?

Researchers will compare elderly patients receiving low-dose hyperbaric bupivacaine with those receiving standard-dose hyperbaric bupivacaine to determine whether a lower intrathecal dose improves cardiovascular stability and recovery without compromising the effectiveness of spinal anesthesia.

Participants will:

• Provide written informed consent before enrollment.
• Undergo elective lower limb orthopedic surgery under spinal anesthesia.
• Be randomly assigned to receive either low-dose or standard-dose hyperbaric bupivacaine.
• Have their blood pressure, heart rate, and other vital signs monitored throughout the surgical procedure.
• Be assessed for intraoperative hypotension and bradycardia according to predefined study criteria.
• Be evaluated for postoperative recovery parameters, including motor recovery and readiness for postoperative recovery and mobilization.

The information obtained from this study may help identify a safer and more effective spinal anesthetic technique for elderly patients undergoing orthopedic surgery.

Inclusion Criteria:

• Male or female patients aged 65 years and above.
• Patients scheduled for elective lower limb orthopedic surgery under spinal anesthesia.
• American Society of Anesthesiologists (ASA) physical status I-III.
• Patients willing to participate and provide written informed consent.

Exclusion Criteria:

• Refusal to participate in the study.
• Contraindications to spinal anesthesia (e.g., infection at puncture site, coagulopathy, severe hypovolemia, raised intracranial pressure).
• Known hypersensitivity or allergy to bupivacaine.
• Severe valvular heart disease.
• Significant cardiac arrhythmias.
• Uncontrolled hypertension.
• Severe hepatic or renal impairment.
• Pre-existing neurological disorders affecting lower limb motor or sensory function.
• Severe spinal deformity or previous lumbar spine surgery interfering with spinal anesthesia.
• Cognitive impairment or inability to provide informed consent.
• Emergency orthopedic procedures.

Individual participant data (IPD) collected during this study will not be made publicly available. Participant confidentiality and privacy will be maintained in accordance with institutional ethical guidelines and the approved study protocol. Aggregate study results may be published or presented, but individual-level data will not be shared outside the research team.

Participants will be unaware of the group allocation. Postoperative outcome assessment and data collection will be performed by an investigator blinded to treatment allocation. The anesthesiologist administering spinal anesthesia will not be blinded because of the preparation and administration of different doses of hyperbaric bupivacaine.