Dexmedetomidine may improve outcomes in older critically ill patients, as seen in the SPICE -III trial. The observed benefit to outcomes was a secondary endpoint in a trial using two targets of sedation, in which separation was not achieved and light sedation was successfully applied in all patients. This trial aims to confirm the exploratory finding of SPICE-IV and elucidate with minimal bias whether there is truly a benefit to dexmedetomidine, by using a placebo controlled, double blinded design.