Post-Marketing Clinical Study to Assess Efficacy and Safety of Dexmedetomidine in Post-Operative Patients

Inclusion Criteria: * Patient or legally acceptable representative (if acceptable by Institutional Review Board/Ethics Committee) has signed and dated the Informed Consent after the study has been fully explained. * Patient is male or female; at least 20 years of age. * Patient who is in condition of American Society of Anesthesiology (ASA) I to III Class preoperatively * Patient is orally intubated and anticipated to require sedation for mechanical ventilation for a minimum period of 4 hours following open-heart surgery, coronary artery bypass grafting (CABG), or major vascular surgery * If patient is female with child bearing potential, she is to be non-pregnant, and not lactating Exclusion Criteria: * Patient with serious disturbance of the central nervous system (disturbance of consciousness). * Patient has undergone or requires intracranial surgery during current hospitalization * Patient requires muscle relaxant drugs after admission to the ICU (except when an endotracheal tube is reinserted). * Patient requires epidural or intrathecal administration of analgesia/anesthesia after surgery and during their ICU stay. * Patients for whom propofol or opioids are contraindicated. * Patient has known or suspected allergies to any medication that might be administered during the course of the study. * Patient is obese (body mass index \>35) * Patient was recently hospitalized for drug overdose * Patient for whom alpha-2 antagonists or alpha-2 agonists are contraindicated * Patient is currently or previously treated, within 30 days before the start of the study, with an alpha-2 antagonist or alpha-2 receptor agonist. * Patient has participated in another clinical study within 30 days prior to admission to the ICU and patient is currently participating in another clinical study. * Patient was diagnosed with severe symptoms and judged likely to die within 24 hours. * Patient is considered unable to undergo all procedures required by the protocol. * Patient with excessive bleeding that is likely require reoperation. * Patient with an ejection fraction of \< 30%. * Patient, in the opinion of the investigator or subinvestigator in the post-marketing clinical study, that has symptoms or factors that may increase his/her risk as a result of the clinical study, or that may not provide sufficient study data.