Effects of Esketamine on Perioperative Plasma Metabolic Dynamics in Frail Elderly Patients: A Prospective Cohort and Nested Randomized Controlled Study

INTERVENTION: Weakness Group (Control Group):0.2 mg/kg saline solution;Non‐frail group (experimental group):0.2 mg/kg esclorazepam;Non‐frail group (control group):0.2 mg/kg saline solution;Weakness Group (Experimental Group):0.2 mg/kg esclorazepam; CONDITION: Patients undergoing elective orthopedic spinal decompression, spinal fusion, or hip/knee arthroplasty under general anesthesia. PRIMARY OUTCOME: QoR‐15 score on postoperative;Rockwood Frailty Index;Arterial blood metabolomic changes?; SECONDARY OUTCOME: Postoperative delirium assessment;Cognitive function;Fatigue assessment;Anxiety and depression assessment;Wake‐up Time;Changes in Laboratory Test Results (Liver and Kidney Function, Complete Blood Count);Incidence of Nausea and Vomiting;Vital Signs;Respiratory Depression;Adverse Reactions;Length of Hospital Stay; INCLUSION CRITERIA: 1) Fully understand and voluntarily participate in this study, and sign the informed consent form; 2) Patients scheduled to undergo elective orthopedic spinal decompression surgery, spinal fusion surgery, or hip or knee replacement surgery under general anesthesia; 3) Age >= 65 years; 4) Surgery duration >= 1 hour, with an expected postoperative hospital stay of >= 3 days.