Subanesthetic Esketamine for Hemodynamic Stability and Recovery in Elderly Thoracic Surgery Patients

Inclusion Criteria: * Age 65-75 years * Scheduled for elective thoracic surgery (e.g., lobectomy, bullectomy) * ASA physical status I-III * Adequate cardiopulmonary function * Able to provide informed consent * Preoperative systolic blood pressure \<160 mmHg with stable control * No cognitive impairment Exclusion Criteria: * Severe cardiovascular disease (e.g., unstable angina, heart failure ≥ NYHA class III) * History of cerebrovascular disease * Uncontrolled hypertension (SBP \>180 mmHg) * Severe hepatic or renal dysfunction * Chronic psychiatric illness or long-term CNS-active drug use * Allergy to ketamine or its derivatives * Elevated intracranial or intraocular pressure * Use of monoamine oxidase inhibitors within 24 hours before surgery * History of substance abuse