A randomized controlled trial of the effect of preoperative dexmedetomidine on the half maximal effective concentration of propofol for successful i-gel insertion without muscle relaxants. 
Dexmedetomidine is a useful anesthetic adjuvant for general anesthesia.  We determined whether preoperative dexmedetomidine administration could reduce the half maximal effective concentration (EC50) of propofol for successful i-gel insertion without muscle relaxants.  Thirty-seven patients were randomly allocated to one of two groups.  In the dexmedetomidine group (n = 19), dexmedetomidine (1 µg/kg) was loaded for 10 min preoperatively.  In the control group (n = 20), the same volume of 0.9% normal saline was administered in the same manner.  The EC50 of propofol for successful i-gel insertion was determined using Dixon's up-and-down method.  The EC50 of propofol was calculated as the midpoint concentration after at least six crossover points had been obtained.  For successful i-gel insertion, all of the following four factors were required—(1) no major movement of the body within 1 min of insertion, (2) no significant resistance to mouth opening, (3) cough ≤2, and (4) visible square wave capnogram without air leakage at a peak airway pressure of <10 cmH2O. Mean blood pressure (MBP) and heart rate (HR) were monitored during the peri-insertion period of i-gel.  The EC50 of propofol for successful i-gel insertion was 3.18 μg/mL in the dexmedetomidine group and 6.75 μg/mL in the control group (p < 0.001).  The incidence of hypotension (MBP <80% of the baseline) during the peri-insertion period of i-gel was higher in the control group (p = 0.001), whereas the incidence of bradycardia (HR <80% of the baseline) was higher in the dexmedetomidine group (p = 0.001).  Preoperative dexmedetomidine reduced the EC50 of propofol for successful i-gel insertion without muscle relaxants.