Abstract: Abstract: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/m2 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 anesthesia induction, and then a rate of 0.5 μg·kg-1·h-1 was continuously infused. Dexmedetomidine 0.5 μg/kg was infused in group D2 after anesthesia induction, and then a rate of 0.3 μg·kg-1·h-1 was continuously infused. Group C was received the equal volume of normal saline. Anesthesia was main⁃ tained with propofol-remifentanil and intermittent iv boluses of rocuronium. Arterial and jugular venous blood samples were collected before anesthesia induction (T0), at 15 min after two-lung ventilation (T1), at 5 min (T2) and 30 min (T3) of OLV for blood gas analysis. Value of Qs/Qt was calculated and SctO2 was recorded at the same time. Results Compared with group C and group D2, Qs/Qt was decreased at T2 in group D1 (P < 0.05). Qs/Qt was lower at T3 in group D1 and D2 than that of group C, and which was lower in group D1 than that of group D2 (P < 0.05). In group C and group D1 a significant de⁃ crease in SctO2 was observed at T2 and T3 compared to that at T0 and T1 (P < 0.05). SctO2 was significantly higher at T2 and T3 in group D2 than that in group C and group D1 (P < 0.05). Conclusion Dexmedetomidine given during OLV undergoing thoracotomy can improve oxygenation, decrease pulmonary shunt fraction and reduce the occurrence of low SctO2

Key words: one-lung ventilation, Dexmedetomidine, cerebral oxygen saturation, pulmonary shunt fraction