What Is Anoxic 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.

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:
   • Cardiac arrest
   • Stroke
   • Cardiac arrhythmia (abnormal heart rhythm)
   • Very low blood pressure
   • Respiratory failure
   • Severe asthma attack
   • Electric shock
2. Anemic anoxia: Occurs due to the reduced oxygen-carrying capacity of the blood. It can occur due to:
   • Severe blood loss
   • Iron deficiency anemia
   • Thalassemia
   • Sickle cell anemia
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

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

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:

• Electroencephalogram
• CT scan
• MRI
• Cerebral angiography
• Blood work (for conditions such as anemia, poisoning, and heart attack)

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.

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