Spreading Depolarization and Ketamine Suppression

Ketamine will be used as a sedative alternative to other more conventional sedatives (such as propofol, versed, or dexmedetomidine) in 6 hour blocks of time. Ketamine will be titrated at the bedside based on clinically desired Riker Sedation-Agitation Scale target. Both groups will receive the drug in this multiple crossover design. The only difference between groups is which sedation regimen is started first to minimize any bias related to differences in physiology in the early post-operative phase.