Symptoms and treatment of carbon monoxide poisoning

What are the symptoms of carbon monoxide poisoning?

In acute carbon monoxide (CO) poisoning (rapid onset, with short-term exposure), the symptoms will depend on the degree of exposure:


Headache, nausea and vomiting are the features of mild CO exposure, often along with a general feeling of malaise. These non-specific symptoms may be misdiagnosed as more common illnesses, such as flu, gastroenteritis or food poisoning. This may lead to CO poisoning being overlooked initially, unless there is a clear history of exposure.


As the degree of CO poisoning becomes more marked, there may be a generalised feeling of weakness, with dizziness, unsteadiness and problems with concentration and thinking. More obvious changes in behaviour, confusion and drowsiness develop and there may be shortness of breath and chest pains.


In severe CO exposure, serious deterioration can occur quite quickly, with seizures, coma and death. MRI scans may show changes in the basal ganglia and the white matter.

What are the long-term effects of Carbon Monoxide poisoning?

Like other types of anoxic brain injury, acute CO poisoning may lead to quite severe long-term neurological problems, with disturbances in memory, language, cognition, mood and behaviour. The damage to the basal ganglia, which is a particular feature of CO poisoning, may lead to a movement disorder resembling Parkinson's disease.

An unusual feature of acute CO poisoning is the delayed deterioration in neurological condition which may be seen in some cases, occurring anything from a few days to as long as five to six weeks after the initial exposure. The reason for this is not entirely clear, but changes in the white matter seem to be involved. It has been suggested that these may result from demyelination, in which there is loss of the fatty, insulating myelin sheath of the nerve axons, therefore impairing their ability to conduct electrical nerve impulses.

Chronic Carbon Monoxide (CO) exposure

Chronic (persistent and long-term) exposure to lower levels of CO, as can occur with faulty domestic boilers, may go unrecognised. The symptoms include milder versions of those seen in acute CO poisoning, with headache, nausea, dizziness, light-headedness, fatigue and sleepiness, difficulty concentrating and memory problems, as well as changes in mood.

People may be aware that something is wrong, but be unable to identify exactly what is the matter, or may attribute the problems to overwork, stress or depression. If symptoms disappear while away at work, reappearing on returning home, or if other people in the same premises develop similar symptoms, it may become more obvious that there is an environmental cause.

Although most people seem to recover following chronic low level CO exposure when the source is removed, it can lead to anoxic brain injury. There have been some documented cases of subtle Magnetic Resonance Imaging (MRI) abnormalities and long-term neuropsychological effects.

How is Carbon Monoxide (CO) poisoning treated?

Treatment of acute exposure to CO involves immediate removal from the source of the poisoning and administration of 100% oxygen, together with general supportive medical care.

Hyperbaric oxygen therapy is sometimes advocated for severe cases of CO poisoning and involves giving pure oxygen at increased pressures in a hyperbaric chamber. It has been suggested that this may improve the long-term neurological outcome, although it remains controversial. Hyperbaric oxygen therapy is a specialised technique, which is only available in a few centres. It may also be associated with complications of its own and it is not used routinely.