Dexmedetomidine Neuroprotection in Pediatric Cardiac Surgery

Inclusion Criteria: * Neonates undergoing cardiac surgery * Infants undergoing cardiac surgery with cardiopulmonary bypass (atrial septal defect repair, ventricular septal defect repair, or tetralogy of fallot repair) Exclusion Criteria: * History of hypersensitivity of any drug * Presence of hypotension or bradycardia considering age Bradycardia (heart rate \< 80 beats/min) or hypotension (systolic blood pressure \< 70mmHg for infants, \< 60mmHg for neonates) * Elevated liver enzyme levels (aspartate transaminase \>100unit/L, alanine aminostrasferase \> 50 unit/L) * surgery with deep hypothermic circulatory arrest * Presence of complex cardiac defect * single ventricular physiology * plan of additional operation within a year * preoperative use of beta-agonists * presence of history of any neurological disorder