Effect of dexmedetomidine on median effective target effect-sire concentration of remifentanil required for preventing body movement in response to skin incision

Objective To investigate the effect of dexmedetomidine on the median effectivetarget effectsite concentration (EC50) of remifentanil required for preventing body movement in response to skin incision made under propofol sedation.Methods Forty ASA Ⅰ or Ⅱ patients aged 20-50 yr weighing 45-58 kg scheduled for elective breast tumor excision were randomly allocated into 2 groups ( n =20 each):group remifentanil (group R) and group remifentanil + demedetomidine ( group RD).Sedation was induced with propofol TCI at target plasma concentration of 3.0 mg/L in both groups.In group RD dexmedetomidine 1.0 μg/kg was infused iv over 10 min before start of propofol TCI,while in group R equal volume of normal saline was infused instead of dexmedetomidine.Remifentanil TCI was started with target effect-site concentration set at 3.0 and 2.5 μg/L in groups R and RD respective at 13 min after beginning of propofol TCI.Skin incision (3 cm in length) was made when the target concentrations of propofol and remifentanil TCI were reached.Body movement was assessed by a nurse not involved in this study.EC50 and 95％ confidence interval (CI) of remifentanil were determined by up-and-down technique.The target effect-site concentration was increased or decreased by 20％ depending on the response of the previous patient to skin-incision.Results The EC50 of remifentanil for preventing body movement in response to skin incision performed under propofol sedation was 1.7 μg/L (95％ CI 1.5-1.9 μg/L) and 2.5 μg/L (95％ CI 2.2-2.7μg/L) in groups RD and R respectively.The EC50 of remifentanil was significantly lower in group RD than in group R.Conclusion Dexmedetomidine 1.0 μg/kg can decrease EC50 of remifentanil for preventing body movement in response to skin incision made under propofol sedation. Key words: Dexmedetomidine;  Piperidines;  Dose-response relationship, drug;  Drug delivery systems;  Stress