With on-going emphasis on early extubation, as well as further recognition of morbidity and mortality associated with delirium, the specific sedatives and analgesics used in the ICU is an issue of interest. Recent studies have focused on comparing sedatives, but interpretations are often confounded by the fact that in most studies, different analgesics were used when comparing two sedative medications. The role of remifentanil as the main analgesic in the ICU is being recognized. Pharmacodynamic and pharmacokinetic profiles of remifentanil makes it an ideal analgesic in the ICU setting. The investigators therefore designed this randomized study to compare sedation with propofol and midazolam in a remifentanil-based sedation and analgesia.