Dexmedetomodine Used In Total Intravenous Anaesthesia : A Randomized Control Observation Abstract Objective: Dexmedetomodine is a kind of selectivityα2 adrenergic receptor agonist. There are seldom Observation about its using in minor operation under total intravenous anaesthesia .the Objective of this study is to use Dexmedetomodine in minor operation ,observe its influence on hemodynamics during the operation and during the extubation, the time cost for analepsia，the and another objective is to find the optimal dose for clinical use. Method: There were 40 patients(ASAⅠ-Ⅱ) scheduled for thyreoidectomy under intravenous anaesthesia were included. Patients were divided into 2 groups randomly, Dexmedetomodine gtoup(D) and control group(N), 20 patients for each. Midazolam, fentanyl, etomidate and cis-atracurium were used for rapid intravenous induction and remifentanyl, propfol, cis-atracurium were used for maintenance. We used dexmedetomodine in group D, 0.8µg·kg-1 lasting 10 mins as a bolus, and 0.4µg·kg-1·h-1 pumping untile 10 mins before the end of the operation as a maintenace. The same volum of normal saline were given in the the same manner in group N. We recorded the patient’s blood presser(BP) and heart rate(HR) at these points: on arriving the operateing room, before awaking ,during extubation, and 1,5,10,30 mins after extubation. At these times , we calculated the value of rate pressure product (RPP, RPP=HR×SBP), recovery time, extubation grade ,and complications were also recorded. Statistical analysis were carried out using the SPSS17.0. statistical significance was accepted as P＜0.05. Result：1. There was no statistical significance on the general state of health of 2 groups (P＞0.05). 2. During the bolus , patients in group D express a significant decrease in HR, ( P＜0.05＝.3. During the maintenance , both groups had a steady circulation. 4. Significant difference was observed in BP and HR in both groups during extubation (P＜0.05＝，but in group D, the SBP had a less raise than those in group N (P＜0.05＝. 5. The raise in RPP was much lower in group D then in group N at the time of extubation, which demonstrate a lower myocardium oxygen consumption.6. there was no significant difference in recovery time, extubation grade and complications（P＞0.05）. Conclusion: 1. Dexmedetomodine used in minor operation under intravenous anaesthesia can diminished the fluctuation in circulation , provide a lower RPP which indicate a lower myocardium oxygen consumption ,without significant influence in recovery time, extubation grade and complications. 2.It was suitable for dexmedetomodine used in minor operation under intravenous anaesthesia. The method that 0.8µg·kg-1as a blous , continued with 4µg·kg-1·h-1 as a maintenace was suitable.