Intensive care patients receiving artificial ventilation receive sedative medications for comfort. However, unintended deep sedation may occur which has been shown to be associated with prolonged ventilation and increased risk of death. Deep sedation is very common soon after initiating mechanical ventilation. In this randomised controlled trial, 4000 intensive care patients receiving mechanical ventilation in New Zealand, Australia and other countries will receive one of two sedation strategies: a standard approach based on clinician-determined sedatives and desired level of sedation (light sedation recommended) versus treatment based on targeting a light level of sedation using newer sedative, dexmedetomidine shown to promote wakefulness. Patients will receive sedation as clinically required while in ICU, and their outcomes compared, including adequacy of sedation, duration of intensive care (including ventilator and other organ support), and long-term outcomes including cognitive function, survival and quality of life. The costs of both approaches will also be compared.