What Is Anoxic Brain Injury?

Medically Reviewed on 8/29/2022
Anoxic Brain Injury
Lack of oxygen supply to the brain, known as cerebral anoxia, results in a loss of consciousness within 15 seconds of oxygen deprivation.

Anoxic brain injury is damage to the brain due to a lack of oxygen supply (an: absence; oxia: oxygen).

  • The brain is a vital organ with a high oxygen requirement.
  • Its oxygen requirement is about 3.5 mL per 100 grams of brain tissue per minute
  • This translates to about 20 percent of total oxygen consumed by the body while at rest.

Such a high requirement can be further comprehended by considering that the weight of the human brain is about two percent of the body weight. Furthermore, this requirement almost stays constant while the person is awake or sleeping. 

The brain is a highly active organ controlling various body functions. Any disturbance with the oxygen supply to the brain can result in serious consequences due to interference with these functions. If the oxygen supply is cut off to the brain for about four minutes or more, the brain cells begin to die, leading to irreparable damage.

Is anoxic brain injury the same as hypoxic brain injury?

The terms anoxic and hypoxic brain injuries are often used interchangeably in clinical practice although they are not synonymous.

  • The term hypoxic brain injury or cerebral hypoxia means a decreased oxygen supply to the brain, which is not sufficient for proper brain functioning.
  • Anoxic brain injury or cerebral anoxia, on the other hand, means a complete cessation of oxygen supply to the brain for a certain period.

What causes anoxic brain injury?

Anoxic injury can result from various causes that affect the oxygen supply to the brain.

The exchange of oxygen and carbon dioxide between the body and the environment occurs through the lungs. Therefore, we breathe out carbon dioxide and breathe in oxygen, which is carried to the heart from the lungs through the pulmonary vein. This oxygenated blood is then distributed from the heart to various parts of the body, including the brain, through a network of blood vessels called arteries, arterioles, and capillaries. An impairment that affects any of these processes can result in cerebral anoxia or hypoxia.

Major causes of anoxic and hypoxic brain injuries can be divided into four major categories that include:

  1. Hypoxic-ischemic injury (stagnant anoxia): Occurs when the oxygenated blood cannot reach the brain. This may occur due to:
  2. Anemic anoxia: Occurs due to the reduced oxygen-carrying capacity of the blood. It can occur due to:
  3. Toxic anoxia: Caused by toxic substances that hamper the capacity of the brain to get oxygen from the blood. It may occur due to:
    • Carbon monoxide poisoning
    • Cyanide poisoning
    • Alcohol
    • Drug overdose
  4. Anoxic anoxia: Results when there is a lack of oxygen in the air, resulting in suffocation. Causes may include:
    • High altitude
    • Choking
    • Strangulation
    • Near drowning


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What are the signs of anoxic brain injury?

Lack of oxygen supply to the brain results in a loss of consciousness within 15 seconds of oxygen deprivation.

Other early signs of anoxic brain injury may include:

  • Slurring of speech
  • Facial drooping
  • Confusion
  • Disorientation
  • Shallow or rapid breathing
  • Bluish or grayish discoloration of the lips and skin
  • Abnormal body movements or seizures

How is anoxic brain injury diagnosed?

Anoxic brain injury can be diagnosed based on typical early signs. The patient’s caregivers may give a history of underlying health conditions such as heart disease or asthma, any medications the patient is on, or other relevant conditions such as an electric shock or congenital conditions such as thalassemia. 

The doctor may perform a physical examination and order certain investigations, such as:

How is anoxic brain injury treated?

The primary treatment goal for anoxic brain injury is the restoration of blood supply to the brain. This largely depends on the underlying cause of cerebral anoxia.

Treatment mainly includes supportive care to maintain the vitals, therapeutic hypothermia, and the use of drugs such as barbiturates. Patients may need rehabilitation and support in the form of speech, physical, occupational, and psychiatric therapy, and walking aids.

Can a person recover from anoxic brain injury?

The prognosis of a person with anoxic or hypoxic brain injury largely depends on the severity and duration of anoxia. Additionally, it depends on the general health of the patient and the presence of any underlying diseases. The earlier the treatment is initiated and the blood supply is restored to the brain, the better the prognosis.

The prognosis may be determined by other factors such as physical examination, length of coma, and age of the patient. Patients younger than 25 years tend to have better outcomes than older individuals. Electroencephalogram and imaging studies may suggest the extent of brain damage and the consequent prognosis for the patient.

Trials suggest that 27 percent of patients with posthypoxic coma regained consciousness within 28 days, whereas about 9 percent remained in a coma or vegetative state. Around 64 percent of the patients died due to cerebral damage.

Even those who survive may have persistent complications such as:

  • Headaches
  • Cognitive dysfunction including problems with memory, learning, and concentration
  • Abnormal body movements such as seizures and myoclonus
  • Weakness of the arms and legs
  • Speech abnormalities
  • Difficulty with balance and coordination
  • Vision problems
  • Loss of bowel and bladder control
  • Mood disturbances
  • Personality changes
  • Sleep disturbances
  • Sexual issues
Medically Reviewed on 8/29/2022
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