Flow diagram of the study protocol. (1) Dexmedetomidine (DEX) group. The patients in the DEX group received an infusion of 0.5 μg/kg DEX within 10 min via a microinfusion pump after successful tracheal intubation. DEX at a dose of 0.5 μg/kg/h was then continuously infused until the operation was completed. (2) The control (Con) group. The patients in the Con group were administered normal saline in the same way and at the same dose. Arterial blood samples (3 mL) were collected in the Con and DEX groups at 5 min (T1) after tracheal intubation and 2 h (T2), 6 h (T3), and 24 h (T4) after surgery. ECG: electrocardiography; HR: heart rate; HR: heart rate; CPB: cardiopulmonary bypass; OLV: one-lung ventilation; IBP: invasive blood pressure; VT: tidal volume; TEE: transesophageal echocardiography.