Study on the Effective Dose and Safety of Esketamine in Hysteroscopic Surgery Under Monitored Anesthesia Care

Inclusion Criteria: * Aged 18 - 55 years; * ASA physical status Ⅰ or Ⅱ; * Body mass index (BMI) 18 - 28 kg∙m-2; * Scheduled for elective diagnostic/therapeutic hysteroscopy. Exclusion Criteria: (i) Pharmacological contraindications: * Known hypersensitivity to study medications (esketamine, remifentanil, dexmedetomidine); * Opioid or benzodiazepine medications dependence; * Analgesic/psychotropic medication use within 48 hours preoperatively; * Participation in any other drug clinical trial within the preceding three months. (ii) Comorbidities: * Significant cardiopulmonary dysfunction (NYHA III-IV, FEV₁/FVC \<70%); * Hepatic impairment (Child-Pugh B/C); * Uncontrolled hypertension, intracranial hypertension, intraocular hypertension or hyperthyroidism; * Neurological/psychiatric conditions (epilepsy, schizophrenia, depression); * Active gastroesophageal reflux disease (GERD-Q score ≥8). (iii) Airway/Perioperative Risks: * Anticipated difficult airway (Mallampati III-IV, thyromental distance \<6 cm) or airway stenosis; * Non-fasted status (solids \<8h, clear fluids \<2h preoperatively).