What is “anoxia” and “hypoxia”?

When blood flow to the brain is depleted of oxygen, then irreversible brain injury can occur from anoxia or hypoxia.  Anoxia is when the brain receives no oxygen.  Hypoxia is when the brain receives reduced oxygen.  This can occur within a short period of time, like minutes.  It can be caused by medical emergencies like heart attacks or respiratory failure.  If this type of brain injury happens, the consequences can be severe.