Dexmedetomidine, a central and peripheral α2-receptor agonist distinct from GABA receptor for benzodiazepines and propofol, has been approved by the US Food and Drug Administration only for use up to 24 h in mechanically ventilated patients. The investigators aim to compare dexmedetomidine with propofol for sedation >24h in poly traumatized mechanically ventilated patients.

The importance of optimizing the levels of sedation in critical care has been increasingly recognized. Many intensive care experts are focusing on maintaining a targeted ''ideal'' sedation level according to the individual patient's condition to avoid adverse events such as prolonged mechanical ventilation, respiratory depression, pneumonia, delirium, psychological problems, and increased treatment costs resulting from over sedation. Dexmedetomidine is a selective alpha-2-adrenoceptor agonist. It exerts both sedative and analgesic effects via mechanisms different from other sedatives such as midazolam and propofol, and provides sedation characterized by prompt response to stimuli with no respiratory depression. The investigators aim to compare dexmedetomidine with propofol for sedation >24h in poly traumatized mechanically ventilated patients. The investigators will perform a prospective, single center trial to investigate the safety and efficacy of dexmedetomidine for long-term sedation in poly traumatized mechanically ventilated ICU patients, in comparison with propofol.

Inclusion Criteria:

• Endotracheal Intubation
• Mechanical ventilation
• Poly traumatized
• ICU patients and estimated duration of sedation>24 h.

Exclusion Criteria:

• Patients with serious trauma in the central nervous system,
• with bleeding probably requiring surgical hemostasis,
• drug overdose within the last 30 days before study entry,
• pregnancy/lactation,
• contraindication to alpha-2-adrenoceptor agonists or antagonists,
• cardiovascular disease,
• conduction disturbances or difficulty in data collection or completing the study protocol