Correctly identifying carbon monoxide exposure or poisoning is not as straightforward as it may seem. The majority of carbon monoxide poisonings are never diagnosed, and often misdiagnosed, which makes knowing the warning signs all the more critical.

Exposure Levels to Carbon Monoxide

Depending on how much a patient may have been exposed to carbon monoxide, the symptoms will vary.

  • Low CO concentrations: signs of influenza or food poisoning accident
  • High CO concentrations: a person can collapse and be dead within minutes

Minor symptoms may be associated with lasting neurological effects, such as difficulty concentrating. A patient should never hesitate to alert their doctor to the possibility of carbon monoxide poisoning. It could save their life.

Clinical Signs

Neurological examination is key in determining a chronic poisoning event. A doctor should conduct:

  • A neurological examination, including tests of fine movement and balance
  • A mini-mental state examination and testing of short-term memory testing the ability to calculate simple subtractions


Carbon monoxide can be measured in expired air. Breath analysers are commonly used; there are also analysers that convert carbon monoxide concentration into COHb concentration. These analysers must be used soon after the patient has been exposed to carbon monoxide gas. Smokers will also have high readings of carbon monoxide.

Managing Carbon Monoxide Poisoning

  • Remove the patient from the source of the carbon monoxide exposure
  • Ensure a mask with an inflated face-seal is correctly fitted for the administration of 100% oxygen
  • Consider referring for hyperbaric oxygen treatment
  • Advise the patient to have appliances and flues serviced before returning home

Clinical References

‘Think carbon monoxide’ – Author:  Dr Barbara Robertson (Director – Chase and Tyler Foundation) and Amanda J Cohn.