ABSTRACT
Objective To evaluate the sedative interaction between dexmedetomidine and propofol.Methods Sixty-four American Society of Anesthesiologists physical status Ⅰ or Ⅱ patients,aged 20-60 yr,with body mass index of 19.0-25.0 kg/m2,scheduled for elective surgery under general anesthesia,were allocated into 4 groups (n =16 each) using a random number table:different target concentrations of dexmedetomidine groups (D1-4 groups).Dexmedetomidine was administered by target-controlled infusion (TCI) with the Markku model.The target plasma concentrations of dexmedetomidine were 0,0.4,0.6 and 0.8 ng/ml in D1-4 groups,respectively.At 15 min of dexmedetomidine TCI,propofol was given by TCI with Schnider model,and the initial target effect-site concentration was set at 1.0 μg/ml.After the target effect-site and plasma concentrations were balanced,the target effect-site concentration of propofol was gradually increased in increments of 0.2 μg/ml until loss of consciousness (Observer's Assessment of Alertness/Sedation Scale score was 1).The model of pharmacodynamic interaction was used to analyze the sedative interaction between the two drugs.Results There was no statistically significant difference in residual sums of squares fitted by using the model of pharmacodynamic interaction between the target effect-site concentration of propofol and target plasma concentration of dexmedetomidine at loss of consciousness (P＞0.05).The linear dimensionless parameter of pharmacodynamic interaction was 0.The median effective effect-site concentration of propofol was 2.38 μg/ml at loss of consciousness,and the median effective plasma concentration of dexmedetomidine was 2.03 ng/ml at loss of consciousness.Conclusion Dexmedetomidine and propofol interact additively in terms of sedation.
ABSTRACT
Objective To investigate the effects of target-controlled infusion (TCI)of dexme-detomidine on the median effective concentration of effect-site (Ce50 )of propofol at loss of conscious-ness (LOC)in patients.Methods Sixty-four patients,28 males and 36 females,aged 20-60 years, ASA physical status Ⅰ or Ⅱ,scheduled for elective surgery,were randomly allocated to receive dexmedetomidine of 0 ng/ml (group P),dexmedetomidine of 0.4 ng/ml (group D1),dexmedetomi-dine of 0.6 ng/ml (group D2)and dexmedetomidine of 0.8 ng/ml (group D3)for 1 5 min before TCI of propofol,n =1 6 in each group.The propofol infusion was started to provide an effect-site concen-tration of 1.0 μg/ml,and increased by 0.2 μg/ml when propofol effect-site concentration and target concentration were equilibrium until LOC.Results The Ce50 (95%CI )at loss of consciousness in groups P,D1,D2 and D3 were 2.30 (2.24-2.36)μg/ml,1.92 (1.87-1.96 )μg/ml,1.60 (1.55-1.65)μg/ml and 1.41 (1.35-1.45 )μg/ml,respectively.There was a negative correlation between the effect-site concentration of propofol-induced LOC and target concentration of dexmedetomidine (r=-0.84,P <0.01).Compared with groups P,D1 and D2,the incidence of bradycardia was higher in group D3 (P <0.05).Conclusion The Ce50 of propofol-induced LOC gradually decreases with in-creasing target concentration of dexmedetomidine.Combining propofol with dexmedetomidine of 0.4 or 0.6 ng/ml that can reduce the Ce50 of propofol-induced LOC,which is suitable for induction of an-esthesia with a lower incidence of bradycardia.