Transcutaneous Pulse Oximetry Brain Monitoring Study (US)

Inclusion Criteria: * 1\. Adult brain-injured patients who have undergone external ventricular drain insertion for cerebrospinal fluid drainage and invasive intracranial pressure monitoring as part of standard medical care * 2\. Adult brain-injured patients who have undergone external ventricular drain insertion for cerebrospinal fluid drainage and invasive intracranial pressure monitoring that have concomitant continuous electroencephalography (EEG) monitoring as part of standard medical care Exclusion Criteria: * 1\. Inability to obtain the brain pulse oximeter signal from at least one brain hemisphere due to interface issue such as severe agitation, head dressing, severe skin or bone trauma, or skull removal preventing brain pulse detection for the initial monitoring session. a. Note: If unable to obtain brain pulse oximeter signal for subsequent monitoring sessions, the only the recordings that were obtained will be used for analysis * 2\. Hemodynamically unstable patients (defined as increasing vasopressors requirements) * 3\. Patients with unstable mechanical ventilation support defined as increasing fractional inspired oxygen (FiO2) requirements