In this study, the investigators explore anesthesia as a tool for providing further insight into the level of consciousness of individuals with a clinical diagnosis of unresponsive wakefulness syndrome (UWS), but who possess some neurophysiological signatures of conscious awareness. This group, who could potentially be conscious, will herein be referred to as the target population. Our goal is to assess whether or not neurological patterns of consciousness in the target population respond to anesthesia in a similar manner to neurologically compromised individuals with known consciousness (e.g. those in minimally conscious state (MCS). In healthy controls, propofol-induced unconsciousness results in an elimination of the mismatch negativity event-related brain potential (ERP) and a diminished directed connectivity. The investigators hypothesize that at doses well below those required for surgery, anesthesia will have similar effects on these neural patterns in neurologically compromised patients with the potential for conscious awareness, but will not affect these patterns in those who lack consciousness.

Inclusion Criteria:

• Patients admitted to the intensive care unit at Hamilton General Hospital who:

  • Clinical status consistent with UWS (no responsiveness to commands)
  • Clinical status consistent with MCS (minimal response to at least one command)
  • Presence of an endotracheal tube (ETT) or a tracheostomy tube
  • Between 18 and 50 years of age

Exclusion Criteria:

• • Elevated intracranial pressure (ICP)

  • Hepatic or renal failure
  • Hemodynamic instability
  • Active vasopressor therapy
  • Previous open-head injury
  • Previous intracranial pathology requiring neurosurgical interventions in the past 72 hours
  • Anticipated ICU stay < 24 hours
  • Documented allergy to propofol
  • Pregnancy
  • BMI > 35 kg/m2
  • Anyone who is deemed medically unsuitable for this study by the attending intensivist
  • Patients who are already in a medically-induced coma for intracranial hypertension or status epilepticus