Brain injury occurs quickly from lack of oxygen, as the brain consumes 20% of our oxygen supply despite only being 2% of our body’s weight.
There are two types of brain injury caused by lack of oxygen:
- Hypoxic brain injury is caused by a reduction in oxygen supply
- Anoxic brain injury when there is a complete lack of oxygen to the brain.
Causes of anoxic & hypoxic injury
Causes include stroke, near drowning, heart attack, drug overdose, strangulation, severe asthma, accidents involving anesthesia, carbon monoxide inhalation and poisoning. Hypoxia can also occur as a secondary injury following a traumatic brain injury e.g. when there is serious blood loss resulting in low blood pressure, or as a result of brain swelling that restricts oxygen supply to areas of the brain.
Oxygen is crucial to the brain as it is used to metabolize glucose, which provides energy for all body cells. Brain cells are sensitive to the effects of restricted oxygen supply and can die within minutes of oxygen restriction. The immediate outcome of severe oxygen restriction is often coma and in very severe cases brain death. Long-term outcomes can be problems with cognition, emotions and movement.
Types of anoxic/hypoxic injury
- Anoxic anoxia is inadequate oxygen to be breathed in and absorbed by the body e.g. altitude sickness or suffocation
- Anemic anoxia is inadequate oxygen supply due to decrease in total hemoglobin or change in the hemoglobin’s ability to carry oxygen
- Stagnant hypoxia is inadequate oxygen supply to the brain due to reduction of cerebral blood flow or pressure e.g. stroke, heart attack
- Toxic anoxia is caused by toxins or substances that interfere with oxygen supply e.g. carbon monoxide, cyanide, narcotics, alcohol.
How long before a brain injury occurs?
Injury will usually set in after a lack of blood flow to the brain for around three to four minutes. This is why it is so important for emergency medical teams quickly re-establish normal oxygen supply to the brain. Later a ventilator may be used to maintain breathing and oxygen in the intensive care unit.
Effects of a hypoxic brain injury
The overall effects of a hypoxic/anoxic brain injury vary depending upon the severity of damage. Areas of the brain particularly vulnerable to lack of oxygen include those responsible for coordination, movement and memory.
A significant hypoxic brain injury can result in coma and possibly post-coma unresponsiveness. Symptoms following return to consciousness can include memory difficulties, abnormal movements, weakness in arms and legs, lack of coordination and visual problems. Movement disorders are quite common, including lack of coordination, spasticity (involuntary muscle tightness), tremors and impaired ability to adjust the body’s position.
As with other types of brain injury, challenging behaviors can result, as well as emotional problems including, depression, agitation and a reduced ability to tolerate stress and frustration.
Outcomes and recovery
Recovery is similar to that of other types of brain injury, but because a hypoxic injury usually results in diffuse widespread injury to the brain, the outcome may not be as positive.
A holistic level of support is important e.g. A physiotherapist and occupational therapist for movement disorders, speech pathologist for communication difficulties, and a neuropsychologist to assess for cognitive deficits. Support from a good team of specialists and family and friends will ensure the best recovery possible.