What is hypoxia? A first aid guide
Hypoxia is important as the brain require a constant supply of oxygen to function normally. If a lack of oxygen exists for longer than 3 – 4 minutes irreversible brain damage may occur.
Hypoxia may be caused by:
- A lack of atmospheric oxygen
- Obstruction of the airway
- Chest or lung trauma
- Conditions affecting the respiratory system
- An inability to use oxygen
Lack of atmospheric oxygen
There may be no oxygen available in the air. It may have been replaced by a poisonous gas (eg carbon monoxide). Alternatively oxygen may be present but at the wrong pressure (eg high altitudes).
Obstruction of the airway
This can be due to:
External pressures: for example strangling, hanging and smothering
The tongue: This may fall back and block the airway in a casualty who is unconscious as they have no control over their airway.
Foreign body: Choking on a foreign body such as food can quickly cause hypoxia
Blood: Bleeding from a facial injury can obstruct the airway
Chest or lung damage
This can be due to:
Penetrating wounds of the chest wall: In this situation air may enter the pleural cavity, resulting in collapse of the lung (a pneumothorax). Air may be drawn into the pleural cavity on inspiration, but not released on expiration. The longer this wound persists the more air is drawn into the pleural cavity and the larger the pneumothorax.
Blast injury: An explosion can cause many small bleeds (hemorrhages) in the lungs.
Conditions affecting the respiratory system
Electrocution: Electricity passing through the body may cause breathing to stop suddenly.
Head and spinal injuries: If the spinal cord is damaged in the neck, the nerves supplying the diaphragm and intercostal muscles may be affected.
Poisons and drugs: These can have a depressant effect on the respiratory centre in the brain and slow down the respiratory rate
Inability to use oxygen
Even if the respiratory system is working adequately and oxygen is available for use by the body, it may be unable to use the oxygen. For example in cyanide poisoning the cyanide prevents the tissues from taking up the oxygen supplied by the blood stream.