Reduction in MACbar of Sevoflurane by Dexmedetomidine in Children

Inclusion Criteria: * aged 2 to 6 yr * American Society of anesthesiologists I or II * scheduled to have general anesthesia and to have skin incisions on the abdomen Exclusion Criteria: * anemia or abnormal preoperative electrolyte concentrations * a history of cardiovascular or central nervous system diseases * a history of pulmonary disease * known hepatic or renal disease * a body weight exceeding 50% of the upper limit of ideal body weight for height * taking drugs with cardiovascular or central nervous system effects * use of any experimental drug within the past 30 days * allergy to any drug that may be administered during the study * exposure to general anesthesia within the previous 7 days * second- or third-degree atrioventricular block * taking drugs preoperatively that would interfere with MAC determination(e.g.,opioids or sedatives)