The Effect of Reversal of Remimazolam Sedation With Flumazenil on Cognitive Function in Patients Undergoing Hip Arthroplasty Under Spinal Anesthesia

This clinical trial aims to establish whether reversing remimazolam sedation with flumazenil can prevent postoperative neurocognitive disorders in patients undergoing total hip replacement surgery. The main questions it aims to answer are: * Does administering flumazenil after surgery lead to an improvement in cognitive function (measured by the MoCA scale) at 24 hours post-operation compared to a placebo? * Does this intervention reduce the incidence of postoperative delirium within the first 48 hours? Researchers will compare flumazenil to a placebo (0.9% saline solution) to see if actively reversing sedation leads to better cognitive outcomes and a lower incidence of delirium. Participants will: * Undergo a planned total hip replacement surgery under spinal anesthesia. * Receive sedation with remimazolam during the operation. * At the end of the surgery, receive an intravenous injection of the study drug (flumazenil) or a placebo. * Undergo assessments for cognitive function (using the MoCA scale) and delirium (using the 4AT scale) before and at multiple time points after the surgery. * Complete a questionnaire about their quality of recovery (QoR-15).