Effects Of Dexmedetomidine On EC₅₀ Of Propofol For Endotracheal Intubation

Objective: To observe the effects of dexmedetomidine in different dosages on the median effective concentration(EC50)of propofol for endotracheal intubation.Methods: Patients undergoing elective general anesthesia were randomly divided into three groups: control group(C),low-dose dexmedetomidine group(D1),high-dose dexmdetomidine group(D2).Every patient received general anesthesia with Sufentanil target controlled infusion(TCI)(at an effect-site concentration of 0.4 ng/ml)after receiving different dosages of dexmedetomidine(0 μg/kg,group C;0.5 μg/kg,group D1;1 μg/kg,group D2)in 10 minutes.The target sequential effect-site concentration of propofol was TCI at the same time.Then 0.5 mg/kg atracurium was injected by intravenous.Preoxygenation for denitrogenation for 5 minutes,and endotracheal intubation was done while cerebral state index(CSI)was between 40 and 60 at least 30 seconds.The MAP,HR,CSI were recorded at the time of the patient into the operating room(T1),after receiving dexmedetomidine(T2),after induction(T3),before endotracheal intubation(T4),1 minute after intubation(T5),2 minute after intubation(T6),3 minute after intubation(T7),respectively.The modified Dixon’s up and down method was used to select target concentrations of propofol,the initial concentration was set at 2.0 μg/ml,the step size was 0.2 μg/ml.Each patient’s target concentration was determined by the results of sequential,if the case is positive,the next should be up a step size,if the case is negative,the next should be down a step size,conversely.The experiment ended when six crossovers appeared in each group,then calculate the EC50 of propofol.Positive standard was CSI>60 for 30 seconds from T3 to T7.Results: 64 cases were analyzed in the study.There were 23 cases in group C,18 in group D1,and 23 in group D2.There was no statistically significant difference of the general condition between the three groups(P>0.05).。1.The EC50 of propofol for endotracheal intubation was 2.07±0.32 μg/ml in group C,1.97±0.10 μ g/ml in group D1,1.63±0.10 μg/ml in group D2.The EC50 of group D2 was significantly lower than group C and group D1(P<0.05),with no significant difference between group C and group D1(P>0.05).2.Hemodynamic were compared in three groups: compared with T1,the MAP of group C were lower at T3,T4,T6,T7(P<0.01);the MAP of group D1 and D2 were lower at T2,T3,T4,T6,T7(P<0.01);compared with group C,the MAP of group D1 were lower at T5(P<0.05),the MAP of group D2 were higher at T3,T4(P<0.05).Compared with group D1,the MAP of group D2 were higher at T4,T5,T6(P<0.05).Compared with T1,the HR of group C were lower at T3,T4,T7(P<0.01);the HR of group D1 and D2 were lower at T2,T3,T4,T6,T7(P<0.01);compared with group C,the HR of group D1 and group D2 were lower at T2,T3(P<0.05).Compared with group D1,the MAP were no significant difference between group D1 and group D2.Conclusion: Dexmedetomidine can reduce the EC50 of propofol required for endotracheal intubation,the degree of reduction was associated with the dose of dexmedetomidine.