1. Adequate sedation with classical sedative agents, propofol
2. Sedation with propofol may induce paradoxical excitement response in heavy alcohol drinkers
3. Dexmedetomidine, α2 receptor agonist, may provide adequate sedation in heavy alcohol drinkers

1. Adequate sedation during surgery provide anxiolysis and comfort to patient. Insufficient sedation can't provide comfort to patient during surgery, otherwise excessive sedation can cause variable complications like respiratory depression or delayed awakening.
2. Dexmedetomidine is a centrally acting α2 receptor agonist that is increasingly being used as a sedative for MAC and intensive care with mechanical ventilated patients because of its analgesic properties, "cooperative sedation," and lack of respiratory depression.
3. Because of the different site of action between dexmedetomidine and propofol, we assumed that paradoxical excitement responses which appeared in heavy alcohol drinkers in midazolam or propofol-induced sedation might be less observed in dexmedetomidine-induced sedation.

Inclusion Criteria:

• 19~65 yr-old patients who is scheduled to undergo knee surgery with regional anesthesia

Exclusion Criteria:

• History of taking anxiolytics, hypnotics, antiepileptic drugs
• Abnormal liver function test (eg: Liver cirrhosis, elevated liver enzymes)
• History of allergic reaction with dexmedetomidine or propofol
• Contraindication with regional anesthesia
• American society of anesthesiologist Physical status III or IV