Objective To investigate the effects of different doses of dexmedetomidine on cerebral oxygen saturation and pulmonary shunt fraction in patients undergoing one-lung ventilation(OLV).Methods Sixty ASAⅠ-Ⅱ patients,aged 46-71 years,with body mass index(BMI)18-24 kg/m~2 and scheduled for thoracotomy were randomly divided into three groups(n=20 each):high dose dexmedetomidine group(group D1),low dose dexmedetomidine group(group D2) and control group(group C).Dexmedetomidine 1 μg/kg was infused in group D1 after...