This document discusses anoxic brain injury caused by cardiac arrest. It defines anoxic brain injury as occurring when the brain does not receive enough oxygen, usually after the heart stops pumping. It outlines that the brain can become irreversibly damaged after only 4 minutes without blood supply. The document describes how clinicians use tests such as CT scans and those measuring brain electrical activity to determine the severity of brain damage following cardiac arrest. It also explains that the prognosis for most patients is poor, with predictors being older age, multiple pre-existing diseases, a long duration of cardiac arrest, and an unwitnessed cardiac arrest.