Carbon monoxide is an odourless, colourless gas. Poisoning can cause hypoxia, cell damage, and death. Approximately one third of severe poisonings are fatal.
Poisoning can occur following exposure from fire or non-fire sources.
Early symptoms are non-specific and include headache, dizziness, and nausea.
Increasing exposure results in cardiovascular effects such as myocardial ischaemia, infarction, dysrhythmias, and cardiac arrest.
Neurological symptoms include acute stroke-like symptoms, altered mental status, confusion, coma, and syncope.
Make a clinical diagnosis based on the history and symptoms. Use a blood gas analysis to confirm the diagnosis based on the carboxyhaemoglobin level.
High-flow oxygen therapy and supportive therapy are the key treatments for carbon monoxide poisoning. Consult senior colleagues when deciding whether to refer a patient for hyperbaric oxygen treatment.
Complications of hyperbaric treatment include seizures related to oxygen toxicity, barotraumas, and pulmonary oedema.
Carbon monoxide poisoning can occur following exposure to a variety of sources. The increased affinity of carbon monoxide with haemoglobin results in tissue hypoxia and impairment of cellular respiration, and direct effects of carbon monoxide toxicity at the cellular level. The symptoms of carbon monoxide poisoning can be acute or chronic, depending on dose and duration of the exposure. They are mostly non-specific, and vary from headache, nausea, and dizziness to severe cardiovascular and neurological symptoms. People who are most at risk of having adverse outcomes after carbon monoxide poisoning are those with coronary heart disease, vascular disease, or anaemia; pregnant women and their fetuses; infants; and older people. About one third of severe poisonings are fatal.
History and exam
Key diagnostic factors
- risk of carbon monoxide exposure
- altered consciousness
- sleep changes
- emotional lability
Other diagnostic factors
- delayed neuropsychiatric features
- other severe neurological symptoms
- focal neurological abnormalities
- exposure to incomplete combustion of carbon-containing material
- exposure to methylene chloride
1st investigations to order
- blood gas analysis
- 12-lead ECG
- blood pressure
- cardiac monitoring
- full blood count
- urea and electrolytes
- creatine kinase
Investigations to consider
- mini-mental state examination
- CT head
- magnetic resonance spectroscopy
- chest x-ray
- liver function tests
Alexander Alexiou, MB, BS, BSc, DCH, FRCEM, Dip IMC RCSEd
Greater Sydney Area Helicopter Emergency Medical Service
AA declares that he has no competing interests.
BMJ Best Practice would like to gratefully acknowledge the previous team of expert contributors, whose work is retained in parts of the content:
Jason J Rose, MD, MBA
Assistant Professor of Medicine and Biomedical Engineering
University of Pittsburgh
Disclosures: JJR is a co-inventor on patent applications for the use of heme-based molecules as antidotes for CO poisoning. JJR is a shareholder, officer, and director of Globin Solutions, Inc. Globin Solutions, Inc. has an exclusive license to this technology. Globin Solutions, Inc. had an option agreement to technology directed at using hydroxycobalamin for CO poisoning from Virginia Commonwealth University in the last 12 months. JJR is an author of publications cited within this topic.
Robert Taylor, MBChB, MRCP(UK), MRCP(London), DipMedTox, DipTher PGDME, FHEA FRCEM
Acute Hospital Sub Dean (Cornwall)
Honorary Clinical Senior Lecturer
Consultant Emergency Physician
University of Exeter Medical School
Royal Cornwall Hospitals NHS trust
RT declares that he has no competing interests.
Section Editor, BMJ Best Practice
EQ declares that she has no competing interests.
Lead Section Editor, BMJ Best Practice
TAO declares that she has no competing interests.
Comorbidities Editor, BMJ Best Practice
JC declares that she has no competing interests.
Drug Editor, BMJ Best Practice
AM declares that he has no competing interests.
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