Objective To study the application of dexmedetomidine in patients with combined spinal epidural anesthesia and its effects on hemodynamics and renin angiotensin aldosterone system (RAAS).Methods96 patients with open surgery under combined spinal epidural anesthesia from Oct.2013 to Oct.2016 in our hospital were selected.Divided into two groups by randomly, the dexmedetomidine group(46 cases) was given dexmedetomidine before anesthesia, the control group(46 cases) was given sodium chloride solution.The operation condition, and the changed of mean arterial pressure (MAP), heart rate, plasma renin activity (PRA), angiotensin II (ANG-II) and aldosterone (ALD) at before anesthesia (T1), post anesthesia 10min (T2), end of the operation (T3) and end of the operation 30 min (T4) were compared.ResultsThere was no significant difference in the operation time, blood loss, intraoperative transfusion, and wake up time between the two groups;there was no significant difference in MAP and heart rate between the two groups at T1, at T2, T3, T4 point, control group MAP, heart rate were significantly changed(P<0.05), and there was no significant change in dexmedetomidine group, at T2,T3,T4 point, the levels of MAP, heart rate in the dexmedetomidine group were lower than the control group(P<0.05);there was no significant difference between the two groups in PRA, ANG-Ⅱ and ALD at T1, at T2 and T3 point, the PRA, ANG-Ⅱ and ALD in the two groups were increased, at T4 point down, there were significant differences compared with the same group at T1(P<0.05);but at T2,T3,T4, the levels of PRA,ANG-Ⅱ,ALD were lower than the control group(P<0.05).ConclusionIn the combined spinal epidural anesthesia with dexmedetomidine before anesthesia, which can Maintain hemodynamic stability, And inhibit the activation of RAAS.