There are four groups accoding to dosage of dexmedetomidine. Dexmedetomidine 0.25 microg.kg(-1),(group D0.25), dexmedetomidine 0.5 microg.kg(-1),(Group D0.5), dexmedetomidine 1 microg.kg(-1) (Group D 1) and normal saline(group P) is administered ivs. for 10mins when we are inducing each patient.