This study evaluates pharmacokinetics and pharmacodynamics of dexmedetomidine for children under sedation at intensive care unit after surgery. Patients will receive dexmedetomidine intravenously for 50 minutes after surgery as as sedation drug.

Dexmedetomidine, an alpha-2 adrenergic agonist, is being effectively used for procedural sedation or sedation at intensive care unit. However, the safety and efficacy profile are not yet established for children. Although there have been some studies regrading it, still there is no public guideline, therefore making it difficult to use dexmedetomidine in children.

Inclusion Criteria:

• Pediatric patients planned to undergo mechanical ventilation at intensive care unit after surgery
• Pediatric patients planned to be extubated within 4 hours after surgery for neurological examination
• Patients whose parent of legal guardian agreed to enroll in the study after having enough time to review the complete explanation about the study.

Exclusion Criteria:

• History of hypersensitivity to any drugs including dexmedetomidine.
• Underlying cardiovascular/circulatory disease
• Underlying liver / kidney disease
• Patients under hemodialysis
• Obesity of BMI > 35
• Patients planned to receive patient-controlled analgesia including opioids
• Patients whose parent or legal guardian declined to enroll in the study
• Other conditions deemed unsuitable for the study