Effect of dexmedetomidine on bispectral index value at loss of consciousness caused by propofol given by target-controlled infusion

Abstract

Objective To investigate the effect of dexmedetomidine on bispectral index (BIS) value at loss of consciousness (LOC) caused by propofol given by target-controlled infusion (TCI).Methods One hundred and twenty ASA Ⅰ or Ⅱ patients,aged 20-50 yr,weighing 41-68 kg,scheduled for general surgery were randomly divided into 3 groups (n =40 each):propofol group (group P),dexmedetomidine 0.5 μg/kg + propofol group (group D1P) and dexmedetomidine 1.0 μg/kg + propofol group (group D2P).The patients in each group were randomly assigned into 5 subgroups ( n =8 each):groups P0-4 receiving TCI of propofol with the target effect-site concentration (Ce) set at0,1,2,3 and 4 mg/L respectively.Groups D1P0-4 received iv infusion of dexmedetomidine 0.5 μg/kg at a rate of0.05μg·kg-1 ·min-1 and TCI of propofol with the target Ce set at 0,1,2,3 and 4 mg/L respectively at 5 min after the end of dexmedetomidine infusion.Groups D2 P0-4 received iv infusion of dexmedetomidine 1.0 μg/kg at a rate of 0.1μg· kg- 1· min- 1 and TCI of propofol with the target Ce set at 0,1,2,3 and 4 mg/L respectively at 5 min after the end of dexmedetomidine infusion.Three minutes after TCI of propofol was started,OAA/S score and BIS value were recorded.The OAMS score ≤ 2 was defined as LOC.The EC50 and 95％ confidence interval of propofol for LOC and BIS50 and 95％ confidence interval at LOC were calculated by Probit analysis.Prediction probability (Pk) of BIS value at LOC was calculated using Smith method.Results Compared with group P,EC50 was significantly decreased,BIS50 was significantly increased ( P ＜ 0.05 or 0.01 ),and no significant change was found in Pk in groups D2 P and D1 P ( P ＞ 0.05).There were no significant differences in EC50,BIS50 and Pk between groups D2 P and D1P ( P ＞ 0.05).Conclusion BIS value can accurately predict the level of consciousness during anesthesia with dexmedetomidine and TCI of propofol,but BIS value is increased at LOC. Key words: Dexmedetomidine; Propofol; Drug delivery systems; Electroencephalography; Unconsciousness