The main outcome determinant following cardiac arrest is hypoxic ischemic brain injury. Management has involved increasing the delivery of oxygen to the brain. This logic assumes that oxygen transport from blood into the brain is normal. We have demonstrated that this assumption is not true. A large proportion of post-cardiac arrest patients demonstrate an inability to unload oxygen into the brain. The mechanisms explaining this observation are unclear. This project involves using a series of evaluations to differentiate post-cardiac arrest patients who exhibit normal and abnormal oxygen transport dynamics and also investigate the underlying mechanisms for abnormal oxygen transport.