Dosages of these sedating medications will not be standardized, but rather titrated to clinical effect. The clinical effect will be determined by the attending intensivist based on the patient's clinical needs. This level of sedation will be communicated to nursing via the Riker Sedation-Agitation Score(20). A minimal dose of ketamine (0.1mg/min or 6mg/hr) will be infused during the ketamine periods, which is lower than required to induce sedation. No minimal sedation requirements will exist for the propofol or other regimen period. This will be done to test the effect of ketamine (which is hypothesized to affect frequency of SD) compared to other sedations regimens (which are not thought to affect SD.) Each period of adjustment of the sedation regimen will be treated as a "spontaneous breathing trial" which is a common standard of care procedure for nursing which involves holding sedation to determine a patient's neurologic exam and respiratory ability with subsequent titration back to appropriate clinical effect. These sedation breaks are very common in the ICU and titration to the desired clinical effect will be performed with the appropriate drug per the standard ICU nursing protocols. In the event that the patient no longer needs invasive positive pressure ventilation prior to discontinuation of ] neuromonitoring, propofol/other sedation intervals will not have mandatory sedative infusions, however, ketamine intervals will have a basal dose of 0.1mg/min (6mg/hr). 'The sedation protocol will end when the strip is removed. This is determined by the patients critical care needs. The strip is checked daily for function as well as any sign of problem such as leak of CSF. Once other critical care monitoring is discontinued (such as ventricular drains and invasive monitoring) the strip will be removed. Other endpoints will include any sign of CSF leak, adverse event reported, or treating intensivist does not think alternating sedation is safe.