Adequate oxygen is vital for the brain. Many factors can cause the brain to receive inadequate oxygen. Anoxia definition: when oxygen levels are significantly low for four minutes or longer, brain cells begin to die and after five minutes permanent anoxic brain injury can occur. Anoxic encephalopathy, a brain injury related to cerebral hypoxia and cerebral anoxia, types of hypoxic-anoxic injuries (HAIs) is a serious, life-threatening injury; it can cause cognitive problems and disabilities. Some HAI injuries are due to a partial lack of oxygen; the term hypoxic means partial lack. Other HAI injuries are due to a complete lack of oxygen; the term anoxic means total lack. The greater the loss of oxygen, the more wide-spread and serious the injury will be.