A total of 126 patients undergoing elective thoracoscopic surgery under general anesthesia were randomly divided into three groups: normal saline group (Group C), dexmedetomidine group (Group D), and esketamine group (Group E),with 42 patients in each group.In Group C,an equal volume of normal saline was continuously infused. In Group D,a loading dose of dexmedetomidine (1 μg/kg) was administered 10 min before induction of anesthesia, followed by a continuous infusion at a rate of 0.4 μg·kg-1·h-1 until 30 minutes before the end of the surgery. In Group E, 0.2mg/kg esketamine was infused intravenously before the induction of anesthesia for 10 min, and then maintained at 0.15 mg·kg-1·h-1 until 30 minutes before the end of the surgery. The primary outcome measures of this study were the oxygenation index (OI) at the following time points: before one-lung ventilation (OLV) (T1), 30 minutes after OLV initiation (T2), and 60 minutes after OLV initiation (T3). The secondary outcome measures included: (1)The duration of OLV, blood loss, fluid infusion volume, the dosages of propofol, remifentanil and vasoactive drugs(ephedrine and atropine) were recorded in each group.(2)Heart rate (HR) and mean arterial pressure (MAP) were recorded at the following time points: upon entering the operating room (T0), before OLV (T1), 30 minutes after OLV initiation (T2), 60 minutes after OLV initiation (T3), before extubation (T4), and 5 minutes after extubation (T5).(3)Blood gas anlaysis parameters,airway plateau pressure,tidal volume and positive end-expiratory pressure were recorded from T1 to T3，and dynamic lung compliance and intrapulmonary shunt fraction were calculated.(4) White blood cell counts, neutrophil percentage,and C-reactive protein (CRP) levels were recorded preoperatively and 24 hours postoperatively.(5)Postoperative pain was evaluated using the visual analogue score (VAS) at 2, 6, 12, and 24 hours after surgery, and the number of patients requiring rescue analgesia in each group was recorded. The occurrence of postoperative adverse reactions and postoperative pulmonary complications (PCCs) within one week after surgery were recorded. The postoperative quality of recovery was evaluated using the QOR-15 scale at 24 and 48 hours after surgery,and the postoperative hospital stay was recorded.