What is an Anoxic Brain Injury? - Definition & Causes

Instructor: Courtney Dohse
In this lesson, we will learn the definition of anoxic brain injury, what may cause it, and how to minimize the risk of lifelong effects from oxygen depletion to the brain.

Case Study

It is 3 o'clock in the morning after a bustling Friday night, and a local bar is just closing its doors. As you walk to your car, you encounter two men, alone in a back alley, getting into an altercation. The larger man picks up the other man by the throat and forces him to the ground while he continues to hold pressure around his neck. The man begins to turn blue, loses consciousness, and the perpetrator jumps into the passenger seat of a nearby car that quickly drives away. You immediately begin CPR and yell to a bystander to call 911.

When EMS arrives at the scene, after assessing the unconscious man and listening to your story, they state he has probably suffered either a hypoxic or anoxic brain injury

Definition of Anoxic Brain Injury

An anoxic brain injury is an injury that occurs to brain tissue due to oxygen deprivation. Whereas a hypoxic brain injury occurs due to insufficient oxygen to the brain, an anoxic brain injury occurs during complete and total loss of oxygen to the brain. When this happens, the body does its best to recover by increasing the amount of blood being pumped to the brain, but it can only compensate by so much. The body will double its efforts by increasing blood flow to the cerebral tissue of the brain by two times the normal amount, but it is unable to compensate more than this. If this compensation is sufficient, no symptoms will occur. However, if the extra blood volume is not enough to fix the oxygen deprivation, injury and death of the cerebral tissue will occur, and the person will suffer an anoxic brain injury. In the event that someone becomes oxygen deprived, it is important to act quickly. Brain cells are very sensitive to a lack of oxygen and begin to die off within 5 minutes from the start of oxygen deprivation.

So, when does this occur? Let's take a look at some various events that may cause an anoxic brain injury.


There are many events that may lead to an anoxic brain injury. Let's take a look at a few.

When a person is not able to breathe effectively, carbon dioxide builds up in the blood, and oxygen supply is cut off. This may occur as a result of strangulation (like the man in our case study), drowning, choking, or suffocation. All of these impede the body's ability to obtain oxygen, and therefore the circulatory system is not able to pump healthy, oxygenated blood to the brain.

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