A written informed consent will be obtained from patients next-of-kin, before study enrollment according to inclusion and exclusion criterias. All consecutive brain-injured patients (traumatic brain injury, subarachnoid or intracerebral hemorrhage, postoperative neurosurgical procedure) admitted to our neurocritical care unit, older than 18 years and requiring sedation and analgesia for mechanical ventilation longer than 48 hours, will be eligible for the study. Depending on the absence or presence of lesion which may increase intracranial pressure, patients will be included in the "light to moderate" sedation subgroup (MLS) or in the "deep" sedation subgroup (DS).