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Carbon monoxide poisoning - Management
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How do I manage suspected higher level carbon monoxide poisoning?

  • If features of higher level poisoning are present:
    • Remove the person (and all others) from the suspected source of poisoning.
    • Assess and manage the airway, breathing and circulation.
    • Give oxygen in the highest available concentration, preferably via a face mask with a reservoir.
    • Arrange an ambulance for immediate transport to hospital for urgent assessment, and check blood glucose to exclude hypoglycaemia while awaiting the ambulance.
    • Shut down all potential sources of carbon monoxide poisoning and ventilate the area, if it is possible to do so safely.
    • Contact the local Health Protection Unit who will coordinate Environmental Health and Safety, Social, and other services to protect your patient and others. For local contact details, see www.hpa.org.uk.
Basis for recommendation

These recommendations are based on expert opinion [Varon and Marik, 1997; HPA, 2007a; CMO, 2008; NPIS, 2008].

Admission

  • Admission is recommended by experts for:
    • Treatment with 100% oxygen.
    • Assessment and management of metabolic acidosis.
    • Assessment and management of hypoxic injury, especially to the heart and central nervous system.

Treatment with oxygen

  • Treatment with oxygen is recommended because breathing 100% oxygen is known to reduce the half-life of carboxyhaemoglobin, and is considered to be effective by experts [NPIS, 2008; Smollin and Olson, 2008].
    • CKS found no studies proving the benefit of 100% oxygen compared with air or lower concentrations of oxygen, but such studies are unlikely to be undertaken on ethical grounds.
  • Treatment with hyperbaric oxygen is not currently recommended, because there is insufficient evidence that hyperbaric oxygen therapy improves long-term outcomes of people with severe carbon monoxide poisoning, compared with standard oxygen therapy [NPIS, 2008].

How do I manage suspected lower level carbon monoxide poisoning?

If features of lower level poisoning are present:

  • Remove the person (and all others) from suspected sources of poisoning until all potential sources of carbon monoxide are shut down and the area has been ventilated.
  • If a woman is pregnant, arrange immediate hospital assessment by an obstetrician.
  • Establish a working diagnosis by simultaneously arranging assessment of:
    • The potential sources of carbon monoxide poisoning for raised environmental carbon monoxide levels. Contact the local Health Protection Unit (HPU) who will organize this. For local contact details see www.hpa.org.uk.
    • The person's carboxyhaemoglobin level for evidence of recent carbon monoxide exposure.
      • Take an anticoagulated venous sample as soon as possible after potential exposure and send to the biochemistry laboratory for measurement of carboxyhaemoglobin levels.
      • A rapid assessment of expired carbon monoxide can be made using a carbon monoxide breath monitor, as used in smoking cessation clinics. Some monitors are capable of converting carbon monoxide concentrations into carboxyhaemoglobin levels, but the clinical value of these devices has not been verified.
  • Necessary control measures and secondary prevention will be carried out by the HPU once the diagnosis has been established following investigations of the potential sources of poisoning and carboxyhaemoglobin level. The HPU will coordinate with the Local Authority Environment Services, and Health and Safety, Social, and other services to protect your patient and others.
  • If in doubt, seek specialist advice.
    • Advice is available 24 hours a day from the UK National Poisons Information Service (NPIS) by telephoning 0844 892 0111.
    • Advice about suspected poisoning of pregnant women is available during the day from the UK Teratology Information Service (UKTIS), formerly the National Teratology Information Service (NTIS), by telephoning 0844 892 0909, or out-of-hours from the NPIS.
Basis for recommendation

Removal from potential sources of poisoning and establishing a working diagnosis

Admit pregnant women

  • Some experts recommend admission for all pregnant women with suspected low level carbon monoxide poisoning for assessment of the fetus [Wolf et al, 2008].
    • The fetus is at a relatively greater risk of harm than the mother, because fetal haemoglobin has a higher affinity for carbon monoxide than maternal haemoglobin [HPA, 2007a].
    • Maternal symptoms cannot therefore be used to estimate the level of risk to the fetus.

Managing people with suspected lower level poisoning

  • CKS found no evidence or published expert opinion relating to the appropriateness of hospital admission or treatment for people with suspected low-level carbon monoxide poisoning.
  • CKS recommends managing people with suspected lower level poisoning in primary care based on the following considerations:
    • CKS considers it impractical to recommend hospital admission for all people with suspected lower levels of carbon monoxide poisoning, because many common conditions cause non-specific mild symptoms such as headache and nausea.
    • People with mild non-specific symptoms are unlikely to have high levels of poisoning from carbon monoxide. The correlation between symptoms and carboxyhaemoglobin levels has been examined by a number of studies of people immediately after exposure to carbon monoxide. A number of reviews of these trials found that people with carboxyhaemoglobin levels of [Varon and Marik, 1997; HPA, 2007a]:
      • Less than 10% are likely to be asymptomatic.
      • Less than 20% may be associated with equivocal non-specific symptoms such as headache.
      • Between 20–30% are likely to have more severe symptoms and signs such as confusion and loss of fine motor control.
      • Greater than 30% become breathlessness and may loose consciousness.
    • People with lower level carbon monoxide poisoning are likely to be at low risk of harm. This is based on limited evidence from people after lower level acute and long-term exposure sufficient to cause no more than mild non-specific symptoms [Micromedex, 2008; Smollin and Olson, 2008].
    • Logically, the benefit of hospital treatment with oxygen is likely to be very limited for people at low risk of harm.

How do I interpret investigations into carbon monoxide poisoning?

  • In people with suspected carbon monoxide poisoning the diagnosis is based on identifying a source of carbon monoxide emissions and measuring carboxyhaemoglobin levels.
  • A definite diagnosis is not always possible because:
    • Identifying a source of carbon monoxide exposure supports the diagnosis, but not finding a source does not exclude it. Sources of carbon monoxide poisoning may be intermittent making them difficult to detect.
    • Identifying an abnormally raised carboxyhaemoglobin level confirms the diagnosis, but finding a normal level does not exclude it. Even a relatively short delay between exposure and taking the test can result in a normal carboxyhaemoglobin level because levels fall by half every 2 to 5 hours after exposure. Normal carboxyhaemoglobin levels are:
      • Less than 1–2% for people who live away from urban areas and who do not smoke.
      • Up to 5% for people who smoke up to 20 cigarettes a day, people living in urban areas who do not smoke, and pregnant women.
      • Up to 13% for heavy smokers has been recorded.
  • Diagnose:
    • Possible carbon monoxide poisoning if:
      • The person has symptoms of carbon monoxide poisoning, but
      • A source of carbon monoxide emissions cannot be identified, and
      • Carboxyhaemoglobin levels are normal.
    • Probable carbon monoxide poisoning if:
      • The person has symptoms of carbon monoxide poisoning, and
      • A source of carbon monoxide emissions was identified, but
      • Carboxyhaemoglobin levels are within normal range.
    • Confirmed carbon monoxide poisoning if:
      • The person has symptoms of carbon monoxide poisoning, and
      • A source of carbon monoxide emissions was identified, and
      • Carboxyhaemoglobin levels are abnormally raised.
Basis for recommendation

Normal carboxyhaemoglobin levels

  • Normal carboxyhaemoglobin levels are based upon studies summarized in the Compendium of Chemical Hazards issued by the Health Protection Agency [HPA, 2007a].

Classification of people with suspected carbon monoxide

  • Recommendations for the classification of people with suspected carbon monoxide poisoning into possible, probable, or confirmed carbon monoxide poisoning are taken from a toolkit produced for Health Protection Unit staff [HPA Chemical Hazards and Poisons Division, 2008].
    • It is based on evidence of the probability of correctly predicting carbon monoxide poisoning from symptoms, carboxyhaemoglobin levels, and identification of a source of carbon monoxide emission, when considered together.

What advice can I give about preventing carbon monoxide poisoning?

  • Advise people to:
    • Fit an audible carbon monoxide alarm that meets European Standard EN 50291 showing a British Standards Kitemark or Loss Prevention Certification Board logo. These are inexpensive and widely available in hardware stores.
    • Keep rooms well ventilated while using an appliance.
    • Have all appliances, flues, and chimneys correctly installed and serviced regularly by a registered engineer.
      • By law, engineers fitting or servicing gas appliances must be CORGI registered. This is due to be replaced in 2009 by a new registration scheme approved by the Health and Safety Executive called the Gas Safe Register.
      • It is recommended that engineers working on solid-fuel appliances are registered with the Heating Equipment Testing and Approval Scheme (HETAS).
      • It is recommended that engineers working on oil appliances are registered with the Oil Firing Technical Association (OFTEC).
    • Have chimneys swept at least once a year and preferably twice a year if burning coal or wood. It is recommended that a qualified sweep is used, such as a member of the National Association of Chimney Sweeps, the Guild of Master Sweeps, or the Association of Professional and Independent Chimney sweeps.
    • Do not used unflued appliances, that are designed for outdoor use, indoors (such as paraffin heaters, camping stoves, barbecues, or similar devices).
    • Do not burn charcoal indoors to cook or heat the home. Charcoal always produces carbon monoxide when burnt.
  • Advise people that it is the legal duty of a landlord to have any gas appliances provided checked annually and to provide a copy of the safety check record to their tenants.
  • The Department of Health leaflet Carbon monoxide. Are you at risk? (pdf) may be a useful resource for patients.
Basis for recommendation

These recommendations are based on legal requirements and expert opinion [HSE, 2007; DH, 2008; HPA, 2008].

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