Carbon monoxide (CO) is an odourless, colourless, non-irritant gas. It is the most common cause of fatal poisoning in Britain today. It causes the accidental deaths of up to 500 people each year in the USA and a much larger number of sub-lethal poisonings.
These figures could be just the tip of the iceberg as poisoning by carbon monoxide is almost certainly underdetected. There are two main reasons for this.
Firstly, there is generally little awareness of carbon monoxide poisoning among the general public and the medical profession.
Secondly, the signs and symptoms associated with carbon monoxide poisoning are not easy to diagnose as they often mimic many other conditions.
To overcome this deadly killer requires improved awareness among the public of the risks and dangers of carbon monoxide poisoning and increased vigilance on the part of healthcare professionals in its detection.
Children, pregnant women, babies, and individuals with a heart condition are those at most risk but CO poisoning can affect anyone.
Where does carbon monoxide come from?
Carbon monoxide is produced by the incomplete combustion of carbon-containing fuels, such as gas (domestic or bottled), coal, oil, coke and wood. Gas stoves, fires, heating boilers, gas-powered water heaters, paraffin heaters, and solid fuel-powered water heaters are all potential sources of carbon monoxide. The problem arises when such appliances are poorly maintained, not serviced and housed in poorly ventilated areas.
When the waste products of combustion are not effectively removed, for example because of blocked flues and chimneys, then poisonous gas mixtures may re-enter the room. This problem is not just associated with older or poorer homes; it can also affect the occupants of newer homes with gas central heating. Exhaust fumes from cars is another obvious source.
Domestic sources of carbon monoxide include:
- domestic heating systems
- blocked flues/chimneys
- inadequate ventilation in living areas
- inadequate ventilation in adjoining car garages
- leakage from faulty appliances and chimneys/flues.
How is carbon monoxide formed?
When any fire burns, in an enclosed room, the amount of oxygen available gradually decreases. At the same time the amount of carbon dioxide increases. As the amounts of these two gases change, this increasingly causes the combustion process to alter from one of complete combustion to one of incomplete combustion. This results in the release of increasing amounts of CO.
This highlights an important issue. Even with perfectly designed and maintained heating appliances (or any kind of combustion device), they too will eventually begin producing dangerous amounts of CO if used in confined and poorly ventilated areas. Having poorly operating appliances, only makes the problem worse more quickly. Maintaining appliances and ensuring sufficient fresh air is available are two easy ways of avoiding potentially lethal scenarios.
How does carbon monoxide cause poisoning?
To explain this aspect, we need to explain how the body uses oxygen from the air. Oxygen is transported around the body via the red blood cells. Specifically, oxygen binds to a substance within the red blood cells called haemoglobin, which is also responsible for their red colour.
Haemoglobin takes up oxygen as blood passes through the lungs, and at the same time carbon dioxide, produced by the body’s metabolism, is released from the blood into the exhaled breath. The combination of oxygen with haemoglobin is called oxyhaemoglobin and this ‘oxygenated’ blood is carried away from the lungs through the bloodstream to all the tissues of the body.
Carbon monoxide can also bind to haemoglobin but does so about 240 times more tightly than oxygen, forming a compound called carboxyhaemoglobin. This means that if both carbon monoxide and oxygen are inhaled, carbon monoxide will preferentially bind to haemoglobin. This reduces the amount of haemoglobin available to bind to oxygen, so the body and tissues become starved of oxygen.
Carboxyhaemoglobin also has direct effects on the blood vessels of the body – causing them to become ‘leaky’. This is seen especially in the brain, causing the brain to swell, leading to unconsciousness and neurological damage.
What are the symptoms of carbon monoxide poisoning?
One of the difficulties with diagnosing carbon monoxide poisoning is that many of its symptoms are similar to those of other conditions. Often the onset of symptoms is gradual, occurring without the individual or doctor being fully aware of what is happening. Coupled with this is the fact that the severity of the poisoning depends on:
- how much carbon monoxide is actually present in the environment.
- the duration you are exposed to carbon monoxide.
- the age of the individual concerned – elderly, children and the foetus are all at greater risk.
- the general state of health.
- the extent of physical activity – effects are increased with higher activity levels.
The commonest symptoms (with frequency of occurrence in brackets) include:
- headache (90 per cent)
- nausea and vomiting (50 per cent)
- vertigo (50 per cent)
- altering states of consciousness (30 per cent)
- weakness (20 per cent).
The likely symptoms in adults, children and infants are shown below:
|General||Dizziness, fatigue, weakness||Not feeling well|
|Neurological||Headache, drowsiness, disorientation, fits||Headache, drowsiness, fits, uncoordinated movement|
|Stomach/intestine||Nausea, vomiting, stomach pains||Vomiting, stomach pains, anorexia, diarrhoea||Loss of appetite|
|Heart||Chest pain, wheeziness, palpitations, hyperventilation||Hyperventilation|