Hypoxic Brain Injury (HBI) occurs when the brain supply of oxygen is dramatically reduced; it is similar to Anoxic Brain injury and both are acquired, not traumatic, brain injuries. Hypoxic Brain Injury can be caused by a number of circumstances, including drowning, strangulation, choking, suffocation, carbon monoxide poisoning, cardiac arrest (heart attack), complications arising from surgery, and head trauma. Brain cells require oxygen to survive and function; they begin to die within minutes of oxygen depravation.

During more mild cases of Hypoxic Brain Injury, there may be memory loss, limited and temporary symptoms of amnesia, difficulty concentrating, and impairment of motor skills. However, more severe instances may be marked by unconsciousness and total unresponsiveness to any stimuli; brain death is likely to follow.