Abstract

The aim of this study was to determine the target-controlled concentration of propofol required for successful laryngeal mask airway (LMA) placement after dexmedetomidine pre-injection. Twenty ASA physical status I–II patients aged 20–60 years old, who were scheduled for general anesthesia, were studied. After receiving a loading dose of 1.0 μg/kg dexmedetomidine over 10 min, propofol was infused using a target-controlled infusion as determined by a modified Dixon's up-and-down method. The first patient received a target-controlled infusion of 3.0 μg/ml propofol. The response of each patient determined the propofol concentration given to the next patient. Cough, body movement, laryngospasm, intentional movement, mouth opening, and difficulty of LMA insertion indicated failure, and the propofol concentration was increased by a step of 0.2 μg/ml. If the insertion of the LMA was successful, then the target concentration was decreased by the same dose. The effect-site propofol concentration for successful LMA insertion was determined to be 2.351 μg/ml in 50% of the patients (EC50) with pre-injection of dexmedetomidine without muscle relaxant. Subsequent probit analysis showed an EC95 (95% CI) of 2.854 μg/ml (2.588–2.944 μg/ml).Thus, dexmedetomidine combined with target-controlled infusion of propofol can be used for LMA placement, with few adverse reactions. In addition, dexmedetomidine sedation can effectively reduce the target-controlled plasma concentration of propofol.

Key words: Dexmedetomidine, propofol, target-controlled infusion, laryngeal airway mask.