What is hypoxic/anoxic brain injury?
The brain needs a continuous supply of oxygen to survive. If the oxygen supply is interrupted, the functioning of the brain is disturbed immediately and irreversible damage can quickly follow. This is known as hypoxic or anoxic brain injury. Hypoxic and anoxic brain injury need to be treated urgently as they can be life-threatening.
A complete interruption of the supply of oxygen to the brain is referred to as anoxia. If there is still a partial supply of oxygen, but at a level which is inadequate to maintain normal brain function, this is known as hypoxia. In practice, these two terms tend to be used interchangeably.
How is hypoxic/anoxic brain injury caused?
There are many potential causes of hypoxia/anoxia, including:
Cardiac or respiratory arrest;
Irregular heart rhythm or poor function of the heart muscle after a heart attack, resulting in inefficient supply of blood to the brain;
Very low blood pressure (shock), resulting from blood loss (haemorrhage) or disturbed heart function;
Suffocation;
Choking;
Strangulation;
Very severe asthma attack;
Complication of general anaesthesia (where there has been inadequate oxygen supply or cardiac arrest);
Near drowning;
Exposure to high altitudes;
Smoke inhalation;
Carbon monoxide inhalation;
Poisoning;
Drug overdose;
Electric shock.
What happens in hypoxic/anoxic brain injury?
The brain relies on a constant supply of oxygen to survive. In fact, it uses around 20% of the body’s total oxygen supply despite only making up 2% of body weight. Oxygen is needed by the brain to sustain chemical processes that ultimately create energy. If the oxygen supply is interrupted, the functioning of the brain can be disturbed.
Oxygen is delivered to the brain by binding tightly to molecules in the blood called haemoglobin. If the oxygen supply that the brain so heavily relies on gets disrupted, this can cause poisoning, and subsequently a type of brain injury called an anoxic or hypoxic brain injury.
Max's story
“Having celebrated my birthday a few days before, I collapsed and suffered a cardiac arrest, resulting in a hypoxic brain injury.
"After spending four weeks in the intensive care unit, I gradually recovered enough to go to the main ward to further my rehabilitation.
"I had to relearn pretty much everything again; walking, talking, holding cutlery, tying my shoelaces etc. The simplest everyday tasks suddenly became impossible for me to try and do. It’s not what your average person has to go through in their mid 20s, and it doesn’t come quickly.”
Learn more about Max’s journey of recovering from an anoxic brain injury.
How is hypoxic/anoxic brain injury treated?
The diagnosis of a hypoxic/anoxic brain injury is usually quite clear at an early stage from the details of what has happened and the patient's condition on arrival at hospital.
Due to the wide variety of causes, immediate treatment will depend on the particular circumstances. In all cases, efforts will be directed at restoring a normal heartbeat, blood pressure and a good supply of oxygen to the brain.
Patients who have suffered a serious hypoxic/anoxic episode will usually be admitted to an intensive care unit and put on a ventilator, preferably in a specialist neurosciences centre. The patient may need drugs to maintain adequate blood pressure and normal heartbeat.
Seizures are quite common after a hypoxic/anoxic brain injury and they can be prolonged and sometimes difficult to bring under control.
This is a stage of critical illness, and the full range of intensive care support is needed to give the best chances of survival and the best possible outcome.
In some centres, patients may undergo medically induced cooling, referred to as therapeutic hypothermia. There is some evidence that this may have a protective effect on the brain and aid recovery by decreasing the oxygen and energy requirements of brain cells. However, although therapeutic hypothermia has been known about for many years, it is still an area of controversy and can produce problems of its own, such as increased risk of infection or interference with blood clotting.
What happens after hypoxic/anoxic brain injury is treated?
Following treatment for a hypoxic/anoxic brain injury, a person will usually need to stay in hospital for several weeks to recover from their treatment. They will continue to be monitored by the medical team.
The person may need to undergo a period of rehabilitation to cope with the physical, cognitive or emotional impact of the injury. This can either take place within the hospital or at a specialist brain injury rehabilitation unit.
The person may be able to return directly home from hospital, but they will need to continue resting and may not be ready to return to their usual activity for several weeks.
For more information on these next stages, see Treatment and rehabilitation.
