Traumatic brain injury (TBI) accounts for approximately 2.5 million visits to emergency departments in the United States each year. After decades of research, management strategies for severe TBI (sTBI) patients are still evolving. Optimizing intracranial pressure (ICP) and cerebral perfusion pressure (CPP) are paramount in the management of these patients and placement of these monitors is the current standard-of-care. However, monitoring brain oxygenation (PbtO2) with invasive intraparenchymal monitors is currently under investigation in the management of severe TBI and placement of these monitors is gaining widespread use. This has opened the door for the use of tiered therapy to optimize ICP and PbtO2 simultaneously. Current evidence indicates that correction of ICP, CPP and PbtO2 in sTBI requires optimized analgesia and sedation. Ketamine is one of the few drugs available that has both sedative and analgesic properties and does not commonly compromise respiratory drive like opioids and sedative-hypnotics. However, traditionally, ketamine has been viewed as contraindicated in the setting of TBI due to concerns for elevation in ICP. Yet, new data has cast this long-held assumption into significant doubt. Hence the present pilot study will characterize the neurophysiological response to a single dose of ketamine in critically-ill TBI patient with ICP and PbtO2 monitoring.