 Cleaved tau protein is a neuronal marker that has been detected in blood and CSF of stroke patients early in its time course. Since vasospasm can lead to stroke, the purpose of this project is to determine whether increase in cleaved tau protein in blood andor CSF can predict early stroke from vasospasm. Changes in brain oxygen tension measured by a brain tissue oxygen monitor and cerebral blood flow measured by CT perfusion will be correlated with cleaved tau protein levels and clinical status. Utilizing statistical analysis the levels of Cleaved tau protein, brain oxygen and blood flow during hospitalization will be correlated with patient outcome. Through this study we hope to identify increase in cleaved tau protein and decrease in cerebral blood flow and oxygenation as predictors of early vasospasm. Early detection and treatment of vasospasm could decrease the stroke rate in SAH patients and therefore be of great benefit to society. 