Carbon Monoxide Poisoning: The Silent Emergency
Why flu-like symptoms in winter may not be flu, and how to recognise when a patient presenting at the pharmacy counter could be suffering from carbon monoxide poisoning.
Why this matters
Carbon monoxide is produced by the incomplete combustion of gas, oil, coal, wood, and other fuels: a colourless, odourless gas that gives patients no warning of exposure. Carbon monoxide poisoning continues to cause preventable deaths and hospital admissions in the UK each year. Community pharmacists are well placed to identify the condition because patients with mild to moderate poisoning commonly seek advice for what they believe to be a viral illness.
While early poisoning presents as a flu-like illness, symptoms can progress rapidly. More severe exposure causes visual disturbance, unsteadiness, confusion, syncope, and loss of consciousness. Cardiac complications including myocardial ischaemia and arrhythmias can occur, particularly in patients with pre-existing heart disease. Pharmacists should recognise that patients presenting after significant exposure may have symptoms well beyond a simple headache or nausea.
Exposure occurs not only in domestic settings. Garages, workshops, boats, caravans, and workplaces with generators or fuel-burning equipment are all potential sources. Occupational exposure may be overlooked if the consultation focuses only on home heating.
The critical question in any consultation involving headache, nausea, and dizziness is whether there are features that distinguish carbon monoxide poisoning from a common cold or flu. The most useful clues are that symptoms affect multiple people in the same household simultaneously, that pets may also be unwell, and that symptoms improve when the patient leaves the building. Missing this presentation can be fatal, particularly in winter when heating appliances are in frequent use and properties are less well ventilated.
Red flags vs more likely benign
| Feature | More likely benign | Red flag ⚠ |
|---|---|---|
| Headache pattern | Gradual onset; constant | Worsening on exertion; improves when away from the building |
| Who is affected | Individual; spreads person to person over days | Multiple people in the same building affected simultaneously |
| Pets | Unaffected | Pets also appear unwell, lethargic, or have collapsed |
| Nausea and vomiting | Often with sore throat, cough, or runny nose | Present without other typical viral features |
| Consciousness | Alert and orientated | Any loss of consciousness, even briefly, is a red flag. Drowsiness, confusion, or difficulty rousing also require emergency assessment |
| Neurological features | None | Unsteadiness, ataxia, visual disturbance, or personality change: these suggest significant exposure and require emergency medical assessment |
| Symptoms by location | Present regardless of location | Symptoms improve when away from home or workplace |
| Season and context | Any time of year | Winter; use of fuel-burning appliances; poorly ventilated property or workplace; garages, workshops, boats, caravans, or generators; faulty or poorly maintained heating system |
| Pregnancy | Not pregnant | Pregnant patient with suspected exposure |
| Carbon monoxide alarm | Not activated | Activated carbon monoxide alarm |
A Note on Pulse Oximetry
Pulse oximetry has a critical limitation in the context of carbon monoxide poisoning that pharmacists and clinicians should be aware of.
- Normal oxygen saturation readings do not exclude carbon monoxide poisoning. Pulse oximeters cannot reliably distinguish oxyhaemoglobin from carboxyhaemoglobin, and a normal reading should not reassure clinicians when exposure is suspected.
Diagnosis of carbon monoxide poisoning requires blood gas testing and carboxyhaemoglobin measurement in hospital. Do not delay referral on the basis of a normal pulse oximetry reading.
🛑 CARBON: A Quick Assessment Framework
Use this prompt list whenever carbon monoxide poisoning is a possibility.
Has any alarm in the building triggered? This is a red flag regardless of how mild symptoms appear.
Are multiple people in the same building experiencing similar symptoms at the same time?
Do symptoms improve when the patient leaves the property? This is the most useful distinguishing feature.
Gas boiler, wood burner, open fire, portable heater, generator, or any fuel-burning equipment in use?
Pets are highly sensitive to carbon monoxide. Any animal appearing unwell or collapsed is a significant warning sign.
Confusion, unsteadiness, visual disturbance, or personality change require emergency medical assessment.
What to do in pharmacy
Pregnant patients require particularly urgent assessment because carbon monoxide crosses the placenta and fetal exposure may be significant even when maternal symptoms appear mild.
Key takeaways
- Ask the key question in every winter headache and nausea consultation: do the symptoms improve when the patient is away from home, and is anyone else in the household affected?
- Carbon monoxide is odourless and colourless. Patients will not know they are being exposed. The classic cherry-red skin sign is rarely seen in living patients and should not be relied upon.
- If carbon monoxide poisoning is suspected, tell the patient to leave the building immediately, call 999 if they feel unwell, and contact the National Gas Emergency Service on 0800 111 999 before re-entering.
📚 References
- National Institute for Health and Care Excellence. Carbon monoxide poisoning. NICE Clinical Knowledge Summary. London: NICE; 2022. Available from: https://cks.nice.org.uk/topics/carbon-monoxide-poisoning/
- Health and Safety Executive. Carbon monoxide: causes and symptoms. London: HSE; 2023. Available from: https://www.hse.gov.uk/gas/domestic/co-poisoning.htm
- Weaver LK. Carbon monoxide poisoning. N Engl J Med. 2009;360(12):1217-1225.
- Chief Medical Officers. Carbon monoxide: properties, incident management and toxicology. London: Public Health England; 2011 [updated 2020]. Available from: https://www.gov.uk/government/publications/carbon-monoxide-properties-incident-management-and-toxicology