The objective is to map the pharmacokinetic / pharmacodynamic interaction between dexmedetomidine and remifentanil by observing changes in anesthetic depth, measured by hypnotic and analgesic endpoints such as modified observer's assessment of alertness and sedation scale (MOAA/S), response to electrical stimuli, response to laryngoscopy and electroencephalogram (EEG) derived indices. These effects will be related to drug concentrations using pharmacokinetic/pharmacodynamic (PKPD) modeling.