Effects of different doses of dexmedetomidine on propofol-induced inhibition of responses to laryngeal mask airway insertion when combined with fentanyl in patients undergoing gynecological operation

Objective To evaluate the effects of different doses of dexmedetomidine on propofol-induced inhibition of responses to laryngeal mask airway （LMA） insertion when combined with fentanyl in patients undergo- ing gynecological operation. Methods One hundred and twenty-five ASA Ⅰ-Ⅱ female patients, aged 20-60 yr, scheduled for elective short-time surgery, were randomly divided into 5 groups （ n = 25 each） ： normal saline group （group NS） and different doses of dexmedetomidne groups （groups D1-4 ）. Normal saline 40 ml and dexmedeto- midne 0.4, 0.6, 0.8, 1.0 μg/kg （in 40 ml of normal saline） were infused over 10 min in groups NS and D1-4 re- spectively. 1% propofol was then given by target-controlled infusion. The concentration of propofol was determined by using modified Dixon＇s up-and-down method. The initial plasma concentration of propofol was 3.0 μg/ml and the ratio between the 2 successive concentrations was 1.1. Fentanyl 1. 5μg/kg was injected intravenously when the effect-site concentration of propofol reached the preset plasma concentration. LMA was inserted 4 min later. When LMA insertion was successful, the concentration of propofol was decreased in the next patient and when LMA inser- tion failed, the concentration of propofol was increased in the next patient. Failure of LMA insertion was defined asdifficulty in inserting LMA or body movement, corner of mouth movement, biting LMA, swallowing and/or lacrima- tion during insertion. The median effective target effect-site concentration and 95 % confidence interval of propofol blunting responses to LMA insertion when combined with fentanyl were calculated. Results The median effective target effect-site concentration （95% confidence interval） of propofol blunting responses to LMA insertion when combined with fentanyl were 3.09 （2.83-3.36）, 2.48 （2.26-2.73）, 2.29 （2.18-2.41）, 2.04 （1.95-2.12） and 1.67 （1.55-1.81 ）μg/ml in groups NS and D].4 , respectively. Conclusion Dexmedetomidine can enhance propo- fol-induced inhibition of responses to LMA insertion when combined with fentanyl in dose-dependent manner in pa- tients undergoing gynecological operation. Key words: Dexmedetomidine ;  Propofol ;  Piperidines ;  Dose-response relationship, drug ;  Laryngeal masks;  Gynecologic surgical procedures