ObjectiveTo investigate the effect of dexmedetomidine on systemic vascular resistance in patients undergoing cardiopulmonary bypass. MethodsThirty-one patients undergoing cardiac surgery with cardiopulmonary bypass from January to April, 2012 were randomized into experimental group (n=16) and control group (n=15). The flow rate was kept at 2.4 L/(min·m2) and moderate hypothermia was maintained. Equivalent dexmedetomidine and 0.9% sodium chloride solution were pumped for the experimental group and control group, respectively. The mean artery pressure (MAP), systemic vascular resistance (SVR), Cortisol, epinephrine and norepinephrine were determined before (T0) and at 10 and 20 minutes (T1,T2) after dexmedetomidine administration. ResultsCompared with T0, there were significant decreases in MAP and SVR at T1 and T2 (P<0.05). MAP and SVR were significantly lower in the experimental group than in the control group at T1 and T2, respectively (P<0.05); cortisol, epinephrine and norepinephrine were significantly lower in the experimental group than in the control group at T1 and T2, respectively (P<0.05). ConclusionDexmedetomidine reduces SVR and causes decrease in MAP. It can effectively inhibit the stress reaction in patients undergoing cardiopulmonary bypass.