• Incidence rate of adverse drug reactions of hypotension, hypertension and bradycardia, which correspond to the protocol definitions [ Time Frame: >24hours and ≤28days ]
  

• 1) Percentage of time spent Richmond Agitation-Sedation Sedation Score ≤0 during the study drug infusion 2) Percentage of time spent Richmond Agitation-Sedation Sedation Score =0, -1,-2 during the study drug infusion 3) Adverse events [ Time Frame: >24hours and ≤28days ]
  

According to the current dexmedetomidine indication, the duration of dexmedetomidine administration is limited within 24 hours. However, there is a strong demand from the medical specialists for continued administration of dexmedetomidine in excess of 24 hours in the medical practice because a large number of patients require sedation for more than 24 hours in ICU. To meet such clinical demand, it was planned to conduct a phase III long-term administration study of dexmedetomidine to obtain the approval on the infusion of dexmedetomidine for more than 24 hours.

Inclusion Criteria:

1. Patient or legally acceptable representative (if acceptable by Institutional Review Board/Ethics Committee) has signed and dated the Informed Consent after the study had been fully explained.
2. Patient is male or female, at least 20 years of age.
3. In case of surgical ICU patient, who is in condition of ASA I to III Class preoperatively.
4. Patient is on mechanical ventilation and anticipated to require sedation more than 24 hours following a surgery.
5. If patient is female with child bearing potential, she is to be non-pregnant, and not lactating.

Exclusion Criteria:

1. Patient has serious CNS trauma.
2. Patient requires the use of neuromuscular blocking agents after admission to ICU, except for the insertion of the endotracheal tube.
3. Patient is hospitalized for drug overdose within the last 30 days.
4. Patient in whom alpha-2 antagonists or alpha-2 agonists are contraindicated.
5. Patient is currently being treated or has been treated within the last 30 days with alpha-2 agonist or antagonist.
6. Patient has participated in a trial with any experimental drug within 30 days prior to admission to the ICU.
7. Terminally ill patient, whose life duration expectancy is no more or around 30 days.
8. Patient is considered unable to undergo any procedure required by the protocol.
9. Patient with excessive bleeding which will likely require surgery.
10. In the Investigator's opinion, patient has any symptom or factor, which might increase risk to the patient or preclude obtaining satisfactory study data.