Study aim: To compare warmed versus room-temperature intravenous fluid co-loading on spinal anesthesia-induced hypotension in elderly hypertensive patients undergoing orthopedic surgery. Design: Randomized, double-blind, parallel-group clinical trial. Sample size 70 (35 per group). Block randomization with sealed envelopes. Single center. Settings and conduct: Conducting at Al-Karkh Teaching Hospital, Baghdad, Iraq. Elderly hypertensive patients undergoing elective lower limb orthopedic surgery under spinal anesthesia are enrolled after informed consent and randomized to warmed or room-temperature Ringer's lactate co-loading. Standard monitoring includes electrocardiography, pulse oximetry, and non-invasive blood pressure. Participants, anesthesiologist, outcome assessor, and data analyst are blinded; fluids are prepared by a non-blinded nurse and covered with opaque materials. Participants/Inclusion and exclusion criteria: Inclusion: age ≥65, hypertension on medication, ASA II/III, elective lower limb orthopedic surgery under spinal anesthesia. Exclusion: severe hyperkalemia, severe hepatic impairment, lactic acidosis, inability to cooperate. Intervention groups: Group W: Ringer's lactate warmed to 37-38°C. Group R: Ringer's lactate at room temperature (20-24°C). Both co-loaded 10-15 mL/kg over 15-20 minutes after spinal block. Main outcome variables: Primary: incidence of spinal anesthesia-induced hypotension (systolic blood pressure drop ≥20% or <90 mmHg) within 30-45 minutes. Secondary: number of hypotensive episodes, vasopressor requirement, time to first episode.