A comparison of intermittent sedation - keeping analgesia with fentanyl and midazolam or propofol as boluses if agitation (SAS 5 or more) after adequate analgesia - and daily interruption of sedation - analgesia with fentanyl and sedation wiht midazolam or propofol continuously with daily interruptions every morning until patients awake and can follow simple commands. Sedation is restarted in half previous dosage if agitation (SAS 5 or more) occur.