This study will be a multicentre randomized, open-label, phase IIIb study. This study will evaluate two different techniques of sedation: an analgesia based regimen with remifentanil versus a conventional sedation based regimen using propofol in subjects that require mechanical ventilation for at least 2 days in the ICU. The conventional sedation based regimen will consist of propofol combined with an opioid according to routine clinical practice (morphine, fentanyl, sufentanil or other as required) . The analgesia based regimen will consist of remifentanil, with propofol added on if required.