Carbon Monoxide Poisoning


Every year there are at least 25 accidental deaths from Carbon Monoxide (CO) poisoning in England and Wales and over 200 non-fatal poisonings which require hospital admission.

Basic Science and Pathophysiology

Carbon monoxide has a high affinity to bind to haemoglobin. If there are significant amounts of carbon monoxide present, oxygen carriage to the tissues is seriously compromised, with the heart and the central nervous system being especially susceptible to the abnormally low levels of oxygen. Where carbon monoxide binds with haemoglobin it forms carboxyhaemoglobin (COHB), which does not carry oxygen to the body tissues.

Carbon Monoxide also causes damage to the mitochondria interfering with respiration by affecting production of reactive oxygen species.

Clinical Presentation

CO poisoning can cause sudden collapse and loss of consciousness within minutes but symptoms may also take time to develop over hours or even days. Sometimes a whole household may be affected.

According to the Department of Health, the commonest symptoms and signs and an indication of their approximate frequency in CO poisoning are shown below4:

  • Headache – 90%
  • Nausea and vomiting – 50%
  • Vertigo – 50%
  • Alteration in consciousness – 30%
  • Weakness – 20%


Levels of carboxyhaemoglobin in the body are detected by a blood gas which is taken as soon after CO exposure is suspected. The levels found in this blood test will reduce over time so it is important to note when a person with suspected Carbon Monoxide poisoning was removed from the CO source.

Management with Hyperbaric Oxygen Therapy

In the acute instance it may help increase oxygen delivery to areas in the body where insufficient oxygen is being delivered due to the effects of the CO poisoning.

Hyperbaric oxygen therapy speeds up elimination of the carbon monoxide from the body and helps reduce the damage that it causes within the cells.

Recommendation from the Royal College of Emergency Medicine amongst other sources of expert opinion is that HBO may be useful if a person has suffered any of the following –

  • new neurological deficit or mental status change
  • carboxyhaemoglobin of greater than 25% at any time
  • pregnancy
  • evidence of damage to the heart
  • loss of consciousness, even if subsequently recovered

Current recommendation is that three HBO sessions are undertaken in the first 24 hours after insult.