After genernal anesthesia using sevoflurane or desflurane, the investigators can observe many cases of agiation (over 80%) and despite of no report of long-term complication, agitation is a big issue in PACU for doctors and nurses. The investigators use dexmedetomidine for prevention of agiation of preschool aged children. The investigators expect single injection of dexmedetomidine lead to decrease postoperative agitation and pain without any complication like oculocardiac reflex requiring atopine for treatment.

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.

Inclusion Criteria:

• Physical status classification of American Society of Anesthesiologist 1-2,
• Healthy, normal
• 2-6 years old
• Elective operation

Exclusion Criteria:

• Lack of consent
• Known adverse effects to dexmedetomidine, mental retardation
• Developmental delay, or neurological or psychiatric illness that may associate with agitation (cerebral palsy, seizure, etc)
• No cardiac disease