• achieving target sedation level [ Time Frame: Patients will receive study drug for a maximum of 120 hours (5 days) ] [ Designated as safety issue: No ]
  The patients' managing team will set the "goal" or "target" as medically indicated using the RASS 37. A trained research nurse or physician blinded to patients' group assignment and medical management will perform measurement of the "actual" RASS level every 12 hours. Comparisons will be made between the actual and target RASS levels to determine the primary outcome measure, which is the accuracy of achieving the target sedation level.
  
  

• duration and severity of delirium [ Time Frame: Patients will receive study drug for a maximum of 120 hours (5 days) ] [ Designated as safety issue: No ]
  Delirium will be measured using the CAM-ICU, every 12 hours, by the same research personnel performing the assessment of the patients' sedation level. Together, these instruments take on average only 1 to 2 minutes to perform. Delirium is said to be present if the patients are responsive to verbal stimulation with eye opening (i.e., RASS -3 or better) and are found to have an acute change or fluctuation in the course of their mental status, inattention, and either disorganized thinking or an altered level of consciousness.
  
  

Delirium occurs in 60-80% of ventilated Intensive Care Unit (ICU) patients and is independently associated with prolonged hospital stay, higher cost, a 3-fold increased risk of dying by six months and ongoing neuropsychological dysfunction. Hypothesis: Based on our preliminary work, we hypothesize that standard use of GABA agonist sedatives such as lorazepam and propofol may contribute to ICU delirium and its attendant untoward clinical outcomes. An alternative sedation strategy targeting alpha2 receptors and sparing GABA receptors (dexmedetomidine) might reduce delirium, provide adequate sedation, reduce analgesic requirement, and concurrently improve cognitive performance.

Long-term objective: To standardize and compare different strategies of sedation and analgesia for ventilated ICU patients in order to optimize their clinical outcomes focusing on delirium and the long-term neuropsychological dysfunction of ICU survivors.

Specific Aims:

• to study prevalence and duration of delirium in critically ill patients using differential exposure to alpha2 vs. GABA receptor agonists while evaluating efficacy of sedation and analgesia;
• to compare clinical outcomes including duration of mechanical ventilation, ICU length of stay and severity of neuropsychological dysfunction at hospital discharge; and
• to develop pharmacokinetic and pharmacodynamic models for dexmedetomidine and lorazepam when used for up to 5 days in ICU patients.

Relationship to anesthesiology: We will study whether the adverse clinical outcomes associated with ICU delirium including long-term neuropsychological dysfunction can be modified by the choice of psychoactive agents frequently used by anesthesiologists and intensivists.

Design: A blinded, randomized controlled trial of adult mechanically ventilated patients using a sedation strategy of dexmedetomidine ± fentanyl versus lorazepam ± fentanyl, with relevant outcomes and safety monitoring.