RESUMO
Objective To investigate the effect-site concentration for 50% of maximal effect (EC50 )of propofol required for loss of consciousness and onset of burst suppression and to assess the effect of target-control infusion(TCI)of remifentanil on these EC50 of propofol.Methods Sixty patients undergoning general anesthesia for scheduled surgery were randomly divided into 2 groups (n=30):group R received TCI of remifentanil with a target concentraton of 4 ng/ml 10 minutes before TCI of propofol,which started at a target plasma concentration of 1μg/ml and then increased by 1μg/ml step every 1 minute until the burst suppression ratio reach to 15%.Group N received a mock TCI of saline instead of remifentanil and the other procedures were as same as group R.During this,all patients were assessed by modified Observ-er’s Assessment of Alertness/Sedation (OAA/S)scale,the loss of consciousness was definited by modified OAA/S values less than 2,the onset of burst suppression was definited by 15% of burst suppression ratio. Results The EC50 of effect-site concentration of propofol required for loss of consciousness and onset of burst suppression were 2.35 (95%CI 2.29-2.41)and 6.31 (95%CI 6.13-6.47)μg/ml respectively.The EC50 of propofol required for loss of consciousness was decreased to 1.73μg/ml by TCI of remifentanil,but the EC50 of propofol required for onset of burst suppression did not changed by TCI of remifentanil. Conclusion TCI of remifentanil could decrease the EC50 of propofol effect-site concentration required for loss of consciousness but has no effect on the EC50 of propofol required for onset of burst suppression.