The study aims to demonstrate that dexmedetomidine is non-inferior to current best practice sedation with propofol/midazolam and daily sedation stops, in maintaining a target depth of sedation in long-stay intensive care unit (ICU) patients, and that dexmedetomidine, compared with current best practice, reduces the length of ICU stay.

Inclusion Criteria:

• Clinical need for sedation and mechanical ventilation
• Receiving full intensive care life support
• Expected stay in ICU of at least 48 hours (h) from time of admission
• Expected requirement for sedation of at least 24h from time of randomisation
• Written informed consent within 36h of ICU admission

Exclusion Criteria:

• Acute severe neurological disorder
• Acute uncompensated circulatory failure at time of randomisation
• Severe bradycardia
• Atrioventricular (AV) conduction block (II-III) unless pacemaker fitted
• Severe hepatic impairment
• Need for muscle relaxation at time of randomisation
• Loss of hearing or vision or any condition interfering significantly with RASS assessment
• Positive pregnancy test or currently lactating