Inclusion Criteria:  Pediatric patients who need procedural sedation (Age < 7 years) ASA (American Society of Anesthesiologists) physical status 1-3 Failed to induce sedation with oral chloral hydrate 50mg/kg  Exclusion Criteria:  ASA (American Society of Anesthesiologists) physical status 4-5 History of hypersensitivity to Dexmedetomidine, Ketamine, or Chloral hydrate Recent administration of Alpha 2 adrenergic receptor agonist or antagonist Cannot administrate oral medication (e.g. Swallowing difficulty) Cannot administrate intranasal medication(e.g. Excessive rhinorrhea) Unstable vital signs, Unstable arrhythmia