Patients enrolled in the study are recruited from the pool of neuro-critical care patients admitted to the surgical intensive care unit (SICU). When the patients are admitted in the surgical ICU, the study staff will determine eligibility based on the protocol inclusion criteria. Due to the nature of the disease, there is a high likelihood that patients are either unconscious, of limited mental capacity and/or have been intubated therefore when appropriate the legally authorized representative will be utilized to obtain research consent.~To meet study inclusion, transcranial Doppler (TCD) testing will be ordered as part of the standard of care for these patients. The test will not be ordered solely for research purposes. There are no known side effects from the non-invasive measurement of cerebral blood flow using ultrasound~Three different TCD technicians will do triplicate readings on 3 consecutive days on up to 12 patients already undergoing TCD as ordered by their treating team. Standard of care on specific neuro critical care patients (such as cerebral aneurysms) is to undergo daily TCD monitoring to assess for possible vasospasm. Patients will be in the supine position while measurements are obtained. The probe will be placed in the preauricular region of the temporal window
This study aims to determine the inter- and intra-variability of Transcranial Doppler (TCD) ultrasound in neuro-critical care patients who are planned for consecutive daily TCD evaluations.