Jang YE, Kim YC, Yoon HK, Jeon YT, Hwang JW, Kim E, Park HP. J Anesth. 2015 Jun;29(3):338-45
37 patients were randomly allocated to either a dexmedetomidine or control (saline) group. Authors conclude that preoperative dexmedetomidine reduced the EC50 of propofol.
Link to abstract