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Objective To investigate the sedative effect of propofol combined with different doses of midazolam in patients undergoing long-time microsurgeries.Methods Forty ASA(American Society of Anesthesiologists)Ⅰ～Ⅱ patients were randomly divided into 4 groups.Normal saline(NS) 2 mL was administered in groupⅠ,while midazolam 0.01,0.02 and 0.04 mg/kg was administered in groupⅡ,Ⅲ,Ⅳ respectively.one min later,propofol was infused at a rate of 5～10 mg/kg?h combined with midazolam based on the abovementioned dosage per hour for groupⅡ,Ⅲ,Ⅳ respectively.Taking auditory evoked potential index(AAI) as a parameter,after it decreased to 40,the infusion rate of propofol was adjusted to keep AAI at the level of 30～45,and maintained the level by infusing propofol and midazolam for 5 hours.The dosage of propofol required for induction and maintenance was recorded.The emergence time and whether patients had awareness during the operation were recorded after the infusion stopped.Results At the target sedative level of AAI 30～45,the Observer's Assessment of alertness/sedation(OAA/S) score of all patients in the four groups reached 0～1.The induction period was obviously shortened and the propofol dosage was dramatically reduced in group Ⅱ～Ⅳ as compared with groupⅠ.At the stage of maintenance of sedation,the dosages of propofol in both groupⅠandⅡ were larger than those in group Ⅲ and Ⅳ.The emergence time in group Ⅳ was dramatically longer than the other groups(P
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B,Hb and Hct significantly increased in group B at t_2.3.PH increased in group B at t_1,furthermore exceeded the normal value,but gradually returned to the baseline at t_2;BE slightly increased at t_1 within the normal value;HCO~ - _3 unchanged before and after AHH.Lactic acid increased both in group A and group B at t_2.4.CaO_2、CcvO_2 decreased at t_1,but returned to the baseline at t_2 in group B;ERO_2 unchanged in group A,but slightly increased in group B after AHH.5.Na~+、K~+、BUN unchanged in both groups;Cl~ - decreased in group B at t_1,but returned to the baseline at t_2;Glu increased in both groups at t_2.Conclusion:The effect of rapid plasma Volume expansion with crystalloid or colloid on prevention of hypotension during induction of general anesthesia is similar.Vouven and Plasmalyte A were both safe and effective during induction of general anesthesia .Plasmalyte A was superior to stabilize physiological internal environment,while the effect of volume expansion and the time of maintainance of Voluven was superior to Plasmalyte A.