Carbon Monoxide: The Silent Killer

Carbon monoxide is a deadly gas, colloquially known as the silent killer because it is tasteless, odourless, colourless and non-irritating. It is still a problem here in the UK as every year around 50 people are killed from carbon monoxide poisoning due to faulty heating systems, which is almost one person every week. Carbon monoxide is a product of incomplete combustion. This means that when organic matter is burned in the presence of oxygen it produces carbon dioxide which in small quantities is harmless. However if the supply of oxygen is restricted then carbon monoxide is formed instead.

Carbon monoxide is significantly toxic to all forms of aerobic life as it easily absorbed through the lungs. When we breathe normally oxygen binds to a molecule in the blood called haemoglobin which transports it around the body to the tissues were it is deposited and used up. However haemoglobin has a affinity, or attraction, 230 times greater to carbon monoxide than oxygen. This means that if carbon monoxide is present then it will bind to the haemoglobin molecules instead of the oxygen, so the oxygen cannot be transported around the body. When carbon monoxide binds with haemoglobin it forms a product called carboxyhaemoglobin which affects the blood vessels and can cause them to leak and lead to swelling. The body is effectively starved of oxygen and the symptoms develop in the organs most dependent on oxygen: the heart and the central nervous system.

Carbon monoxide is particularly dangerous to unborn babies as foetal haemoglobin has a 10-15% higher affinity for carbon monoxide than adult haemoglobin. This is because the foetus depends on the mother for its oxygen supply and in order to get that supply its blood must have a higher affinity for oxygen than the mothers, however as you can see in the case of carbon monoxide this can be a fatal difference.

Mild symptoms can often be mistaken for a viral cold or flu infection. This can be a deadly mistake because the advice for treatment of a cold or flu is to stay at home and turn up the heating. If it turns out to be carbon monoxide poisoning this is the last thing you should do. However some of the warning signs that you may have carbon monoxide poisoning as opposed to flu are:

To put these symptoms into perspective the natural background level of carbon monoxide is 0.1ppm, while in homes the average level is 0.5-5ppm. In a chimney of a home wood fire the level would be around 500ppm while an undiluted, warm car exhaust without a catalytic converter it is around 7000ppm.

After acute poisoning severe neurological symptoms can occur in up to 50% of patients. These can present themselves anywhere between 2 and 40 days after the event. These include:

Usually once the victim has been removed from the source then the symptoms should clear unless they have been exposed to severe, acute poisoning.

The victim should be removed from the source of the poisoning and given basic life support if that is necessary. They should be treated with 100% of high-flow oxygen by a nonrebreather reservoir oxygen mask and transported to hospital. Oxygen hastens the dissociation of carbon monoxide from the haemoglobin so that the tissue can be oxygenated. Between 10-15% of cases suffer from long-term problems.

Carbon monoxide can be prevented from causing fatal injuries by having regular checks on gas appliances and heating systems. Chimneys and flues should also be maintained to prevent damages or blockages that might prevent carbon monoxide being released into the atmosphere. Cars, motorbikes and lawnmowers should never be used in closed garages otherwise carbon monoxide can build up in the enclosed space. Carbon monoxide alarms can be fitted, which are similar to smoke alarms, and detect high levels of carbon monoxide in the surroundings.