Inclusion Criteria (Patient Cohort):  Subjects will be included if they are adults (>18 years of age) and have a neurological or neurosurgical diagnosis that place them at risk for cerebral edema. Subjects also have to be admitted to the enrolling site. Persons consenting for the study (whether patient or LAR) will need to be able to consent for the study in English.  Exclusion Criteria (Patient Cohort):  Patients that will be excluded from the study are those that are prisoners, under 18 years of age, or pregnant women.  Inclusion Criteria (Healthy Control Cohort):  Staff in the enrolling site  Exclusion Criteria (Healthy Control Cohort):  None