Effect of Esketamine on Postoperative Sleep in Postmenopausal Women

Inclusion Criteria: 1. American Society of Anesthesiologists (ASA) physical status I-III. 2. Aged ≥ 45 years. 3. Women with natural menopause (aged ≥ 45 years and postmenopause for more than 12 months without surgical or medical intervention) . 4. Scheduled to undergo elective lower-limb fracture surgery with an expected duration of more than 60 min under general anesthesia. 5. Body Mass Index (BMI) between 18 and 28 kg/m². Exclusion Criteria: 1. Presence of preoperative sleep-related disorders, such as obstructive sleep apnea or restless legs syndrome. 2. History of drug or alcohol abuse or dependence. 3. Known contraindications or allergies to esketamine or other anesthetic agents. 4. Use of psychotropic medications or sex hormones within the past 3 months. 5. Shift work or taking medications affecting melatonin. 6. Severe comorbid conditions, including but not limited to uncontrolled hypertension, coronary artery disease, cardiac insufficiency, pulmonary hypertension, intracranial hypertension or elevated intraocular pressure, hyperthyroidism, severe hepatic or renal dysfunction. 7. History of cerebral infarction, intracerebral hemorrhage, or residual central nervous system deficits. 8. Impairments of language, hearing, vision, or cognitive function that would prevent completion of questionnaires or cooperation with sleep monitoring. 9. Active oral pathologies. 10. Transfer to ICU postoperatively.