Effects of Dexmedetomidine Sedation on Delirium and Haemodynamic in Mechanical Ventilated Elderly Patients

Inclusion Criteria: * Written informed consent * Intensive care unit patients who need mechanical ventilation * Anticipate duration of mechanical ventilation longer than 24 hours,and shorter than 96 hours prior to giving investigational products * Acute physiology and chronic health evaluation II score more than 10 * Aged between 60 to 80 years old * Weight between plus or minus 20% of the standard weight. Male: (height cm - 80) × 70% = standard weight Female: (height cm - 70) × 60% = standard weight Exclusion Criteria: * Trauma and burn patients * Any kind of dialysis * Suspected or confirmed difficult airway * Use of neuromuscular blocking drugs(Except using for intubation ) * Neuromuscular disease * Epidural or subarachnoid anesthesia * Plan to give general anesthesia before 24 hours drugs intervention or after giving investigational drugs * Serious central nervous system disease * Mental disability or mental disease * Acute hepatitis and serious liver disease(Child-Pugh C) * Unstable angina and acute myocardium infarction * Left ventricular ejection volume less than 30%,heart rate less than 50 beats per minute * II and III degree atrioventricular block * Systolic pressure less than 90 mmHg after giving vasopressors twice before beginning of this study * Consciousness disturbance patients whose blood pressure less than 70mmHg and blood lactate more than 4.0mmol/L * Suspected or confirmed long term use of narcotic analgesics * Subjects who are breastfeeding or pregnant * Allergic to investigational products or with other contraindication * Participated in other study within 30 days