Pharmacokinetics of Dexmedetomidine During Prolonged Infusion in ICU

Inclusion Criteria: * Written informed consent obtained from the patient's legal representative according to local regulations before starting any study procedures other than pre-screening * Patients sedated and ventilated in ICU for whom sedation is expected to be clinically required for at least 24 hours, as determined by the responsible physician * Prescribed light to moderate sedation (target RASS = 0 to -3) Exclusion Criteria: * Acute severe intracranial or spinal neurological disorder due to vascular causes, infection, intracranial expansion or injury * Uncompensated acute circulatory failure at screening (severe hypotension with mean arterial pressure(MAP) \< 55 mmHg despite vasopressor and inotrope therapy) * Heart rate (HR) \< 50 beats/min for longer than 5 min between screening and starting study treatment * Atrioventricular (AV)-conduction block II-III (unless pacemaker installed) * Severe hepatic impairment (e.g. bilirubin \> 101 μmol/L) * Need for continuous muscle relaxation * Any condition which would significantly interfere with the collection of study data * Burn injuries or other conditions requiring regular anesthesia or surgery * Use of centrally acting alpha-2 agonists or antagonists within 24 hours prior to starting the study (e.g. dexmedetomidine, clonidine, tizanidine, apraclonidine and brimonidine) * Known allergy to dexmedetomidine or any excipients of the study treatment * Patients who have or are expected to have treatment withdrawn or withheld due to poor prognosis * Patients receiving sedation for therapeutic indications rather than to tolerate the ventilator (e.g. epilepsy) * Patients unlikely to require continuous sedation during mechanical ventilation (e.g. Guillain-Barré syndrome) * Patients who are unlikely to be weaned from mechanical ventilation; e.g. diseases/injuries primarily affecting the neuromuscular function of the respiratory apparatus such as clearly irreversible disease requiring prolonged ventilatory support (e.g. high spinal cord injury or advanced amyotrophic lateral sclerosis)