Abstract:Objective To investigate the effects of different doses of dexmedetomidine(DEX) on cognitive function and stress response in patients undergoing cardiopulmonary bypass (CBP).? Methods A total of 90 patients who intended to receive cardiac surgery under CBP from January 2015 to September 2016 were selected and was divided into low dose group (group A) in which intravenous infusion of 0.5 μg/kg DEX was given before anesthesia induction with 0.1 μg·kg^-1·h^-1 to the end of operation, medium dose group (group B)in which intravenous infusion of 0.8 μg/kg DEX was administered before anesthesia induction with 0.2 μg·kg^-1·h^-1 to the end of operation and high-dose group (group C)in which intravenous infusion of 1.0 μg/kg DEX was given before anesthesia induction with 0.3 μg·kg^-1·h^-1 to the end of surgery(n=30, each). The cognitive function and stress status in each group were compared at different time points of T₀ (before operation after anesthesia ), T₁(30 min after CPB beginning ), T₂(30 min after CPB ending), T₃(6 hours after operation) and T₄(24 hours after operation).? Results At T₀ time point, there were no significant differences in the serum levels of tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), S100 beta protein concentration, complement C3 and C4 among three groups (all P>0.05). At T₁ to T₄ time points, the levels of TNF-α, IL-6, complement C3 and C4 in group A were significantly higher than those in group B and group C (all P<0.05), and the concentration of S100β protein in group A and B was significantly lower than that in group C (all P<0.05). At one day before operation, there were no significant differences in mini-mental state examination(MMSE)scores among three groups (P> 0.05). At postoperative 1- and 4- day, MMSE scores in group A and B were significantly higher than those in group C (all P<0.05), and the incidence of adverse reactions in group C was significantly higher than that in group A (P<0.05).? Conclusion Intravenous infusion of 0.8 μg/kg DEX with 0.2 μg·kg^-1·h^-1 to the end of operation in patients undergoing cardiovascular surgery under CBP can effectively relieve the stress reaction state, cognitive dysfunction and reduce the incidence of adverse reactions.