The effect of intravenous dexmedetomidine premedication on the dose requirement of propofol to induce loss of consciousness in patients receiving alfentanil

Dexmedetomidine reduces the dose requirements for opioids and anaesthetic a gents. We conducted a single-centre, open-label, noncomparative phase II st udy of the effect of intravenous dexmedetomidine on the dose requirement of propofol to induce loss of consciousness in 49 ASA I and II patients. The initial dexmedetomidine infusion scheme was reduced twice because of advers e events. Forty patients who received the final infusion scheme were random ly allocated to receive one of five stepped propofol infusions; loss of con sciousness was assessed after 21 min. The ED50 for the final infusion rate of propofol to suppress consciousness was 3.45 mg.kg(-1).h(-1) (95% CL 2.7- 4.2): ED95 was 6.68 mg.kg(-1).h(-1) (95% CL 5.1-19.1), EC50 was 1.69 mug.ml (-1) (95% CL. 0.95-2.5) and EC95 was 5.7 mug.ml(-1) (95% CL 3.2 to > 10). O ur final dose of dexmedetomidine of 0.63 mug.kg(-1) caused a reduction in t he overall concentration and dose of propofol required to produce loss of c onsciousness, but no significant shift in the dose-response curve compared with other studies.