Placebo group received an equivalent volume of 0.9% saline.

Following Anesthesia induction, dexmedetomidine (DEX) Low Dose group received a DEX loading dose (0.5 µg/kg over 10 min), followed by continuous infusions of 0.3 µg/kg/h, respectively, until 30 minutes before the end of the operation.

Following Anesthesia induction, dexmedetomidine (DEX) high dose group received a DEX loading dose (0.5 µg/kg over 10 min), followed by continuous infusions of 0.5 µg/kg/h, respectively, until 30 minutes before the end of the operation.

Following Anesthesia induction, dexmedetomidine (DEX) Low Dose group received a DEX loading dose (0.5 µg/kg over 10 min), followed by continuous infusions of 0.3 µg/kg/h, respectively, until 30 minutes before the end of the operation.

AQP1 expression, serving as an indicator of pulmonary interstitial water permeability, was assessed by immunohistochemistry (IHC) on lung tissue samples. Two histologically normal specimens (1×1×1 cm³ each) were collected per patient: 1) Before one-lung ventilation: ≥ 5 cm from tumor margin in planned resection area; 2) Immediately after lobectomy: ≥ 5 cm from margin in isolated lung. Tissues were fixed in 10% neutral buffered formalin (24 hours), paraffin-embedded, and sectioned (3 μm). Five random high-power fields (HPF, 400x) per section were evaluated. The percentage of positive cells (0: 0-25%; 1: 26-50%; 2: 51-75%; 3: 76-100%) and staining intensity (0: none; 1: light yellow; 2: brown; 3: dark brown) were scored. The total IHC score (range 0-9) was calculated as (percentage score x intensity score); specimens were classified as low (≤ 4) or high (> 4) AQP1 expression.

Radial arterial blood samples were drawn for blood gas analysis at the specified time points. Dynamic lung compliance (Cdyn) was recorded from the anesthesia machine.