Carbon monoxide poisoning

Overview 
Theory 
Diagnosis 
Management 
Follow up 
Resources 

Please note that formulations/routes and doses may differ between drug names and brands, drug formularies, or locations. Treatment recommendations are specific to patient groups: see disclaimer

ACUTE

all patients (acute or chronic carbon monoxide poisoning)

1st line – oxygen

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1st line –

oxygen

Start oxygen therapy.[1][2][21]

Give 100% oxygen.[17][18]
Use a reservoir mask at 15 L/minute.[17][32]
- The half-life of carboxyhaemoglobin in a patient breathing air is about 300 minutes.[32]
- The half-life of carboxyhaemoglobin in a patient breathing high-concentration oxygen via a reservoir mask is 90 minutes.[32]
Aim for an oxygen saturation of 100% irrespective of the initial oximeter reading and arterial oxygen tension (PaO ₂). An apparently ‘normal’ oximetry reading may be produced by carboxyhaemoglobin.[32]
- Call for senior help for a patient with chronic obstructive pulmonary disease, where aiming for an oxygen level of 100% is not appropriate.
Duration of treatment is dependent on the degree of poisoning, symptomatology, and the carboxyhaemoglobin levels identified on serial blood gases.

Seek senior support for comatose patients or patients with severe mental impairment. These patients should be intubated and ventilated with 100% oxygen.[32]

Plus – supportive care

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Plus –

supportive care

Treatment recommended for ALL patients in selected patient group

Ensure the patient and co-occupants have been removed from the source of carbon monoxide.[2][10]

Use the Airway, Breathing, Circulation, Disability, Exposure (ABCDE) approach. Resuscitate the patient according to standard guidelines, as needed.[40]

Consider calling the resuscitation team if the patient is unstable.

Start fluid resuscitation for hypotensive patients.[10] See our topic Shock for more information on this.

Consider escalation to a senior colleague, and the relevant public health bodies, such as your national poisons centre or social services, when more than one patient presents. This may indicate a public or major incident.

Obtain specialist advice for any patient:[22]

Presenting with a carboxyhaemoglobin level >25%
Who is pregnant
You suspect of self-harm/intentional poisoning
- A large proportion of deaths from carbon monoxide poisoning have been linked to suicide[29]
- See our topic Suicide risk mitigation
With substantial neurological or cardiovascular symptoms.

Discuss the management of a pregnant patient with specialist colleagues.

Consult your local trust protocol for the management of pregnant patients with carbon monoxide poisoning.
Fetal blood has a higher affinity for carbon monoxide than an adult’s, meaning carbon monoxide is more readily taken up by the fetus, and also more slowly released. This results in a prolonged exposure of the fetus. Exposure to carbon monoxide reduces the amount of oxygen available for the fetus.[18]
Fetal carbon monoxide exposure is linked to birth defects, and fetal and infant mortality.[18]
Maternal health status can be misleading. Fetal death can still occur even in the presence of apparent good health of the mother.[44]

Consider – hyperbaric oxygen therapy

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Consider –

hyperbaric oxygen therapy

Additional treatment recommended for SOME patients in selected patient group

Hyperbaric oxygen therapy is not a treatment routinely commissioned by NHS England, as there is not currently sufficient evidence to support it.[41] The UK National Poisons Information Service (NPIS) does not currently recommend hyperbaric oxygen therapy.[10]

Consult senior colleagues when deciding whether to refer a patient for hyperbaric oxygen treatment.

If so, the care of the patient will then transfer to the clinical team at the hyperbaric centre.
This treatment may not be available in all areas.
If hyperbaric oxygen is required, some centres recommend that it should be started within 6 hours and no later than 24 hours.[17]

Hyperbaric oxygen therapy is the administration of 100% oxygen at pressures higher than atmospheric pressure. This leads to carbon monoxide being eliminated faster.[41] There are potential risks and side effects, including:[41]

Reversible myopia, headache, and vomiting
Effects from oxygen toxicity, including convulsions, pulmonary oedema, or respiratory failure
Ear, lung, or sinus damage resulting from barotrauma.

Consider referring the patient for hyperbaric oxygen when there is a carboxyhaemoglobin concentration of >20%.[18]

Indications for hyperbaric oxygen include:[18]

Loss of consciousness at any stage
Neurological signs or symptoms other than headache
Myocardial ischaemia/arrhythmia diagnosed by ECG
Pregnancy.

Practical tip

The use of hyperbaric oxygen is likely to depend on how close and accessible a hyperbaric chamber is.

Evidence: Hyperbaric oxygen therapy

Hyperbaric oxygen therapy may be beneficial in selected patients with carbon monoxide poisoning; however, the evidence is weak and inconsistent.

A Cochrane systematic review on hyperbaric oxygen for carbon monoxide poisoning in non-pregnant adults (search date June 2010) included six trials (n=1361).[42]

The population, duration, timing, and dose of both hyperbaric and normobaric oxygen, and outcomes assessment, varied among the trials.
- All of the included studies were at appreciable risk of bias and only two had a sham control.
For the primary outcome, which was the presence of symptoms or signs possibly indicative of neurological injury at 4 to 6 weeks post randomisation, there was no benefit from hyperbaric oxygen therapy compared with normobaric oxygen (OR 0.78 [95%CI 0.54 to 1.12]).
- However, this should be interpreted with caution as there were important differences in the included studies (outlined above) and moderate statistical heterogeneity in the meta-analysis.
Only two trials found hyperbaric oxygen reduced neurological sequelae at one month.
- Both had issues with how the results were analysed.
- One included small numbers, was unblinded, and made no adjustment for testing multiple hypotheses, while the other applied numerous assumptions (all of which favoured hyperbaric oxygen) and included a change in the primary outcome from delayed neurological sequelae to all neurological sequelae.
- Both were also stopped early 'for benefit', which is likely to overestimate the treatment effect.
Two of the ‘negative’ trials were underpowered to show any benefit of hyperbaric oxygen as the trials excluded people with severe carbon monoxide poisoning.
- The other was an abstract of an interim analysis only; it was never published in full.
The authors concluded that:
- There was insufficient evidence to routinely recommend hyperbaric oxygen therapy for carbon monoxide poisoning
- From the current evidence it was not possible to distinguish if particular subgroups, especially people with severe poisoning, would benefit.

A more recent systematic review (search date December 2017) included six studies.[43]

Five were also included in the 2010 Cochrane review. The authors excluded the interim analysis as they only included publications in full, however they included one study which had been excluded by the Cochrane review as it only reported on surrogate outcomes.
There was no significant difference between groups in headache (RR 0.83 [95% CI 0.38 to 1.80]), memory impairment (RR 0.80 [95% CI 0.43 to 1.49]), difficulty concentrating (RR 0.86 [95% CI 0.55 to 1.34]), or disturbed sleep (RR 0.91 [95% CI 0.59 to 1.39]).

Plus – monitoring

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Plus –

monitoring

Treatment recommended for ALL patients in selected patient group

Observe patients who require assessment for at least 4 hours after exposure.[10]

Assess the patient’s recovery in terms of resolution of their symptoms.[22]

Continue treatment until the carboxyhaemoglobin level has fallen to a normal value, and the patient is asymptomatic.[17]

Contact your national poisons centre (the National Poisons Information Service [NPIS] in the UK) for any patient that does not improve.[21]

Consider the possibility of cyanide poisoning in a patient exposed to carbon monoxide due to smoke inhalation, for example from a house fire.[10][17][32]

Patients with severe carbon monoxide poisoning require admission.[22]

Patients with multiple or complex comorbidities, or frailty, are at higher risk of complications. Discuss these patients with senior colleagues and consider longer periods of monitoring or admission.

If your patient is aged ≥65 years, use the Clinical Frailty Scale to assess their level of frailty as part of a holistic assessment where appropriate. NHS Specialised Clinical Frailty Network: Clinical Frailty Scale Opens in new window

Consider discharge for patients who are no longer symptomatic. Most patients with acute presentations can be treated and discharged to a safe place (where there is no further risk of carbon monoxide exposure).[22]

Advise the patient to return if symptoms develop.[10]

Arrange the appropriate follow-up for any long-term effects.[17][19][22]

Advise all patients about the possibility of delayed neurological complications, including specific instructions on what to do if these occur.[19]

Contact social services, if necessary.[18]

Provide further guidance for the patient on other services that can help them.

Recommend that all appliances and flues are checked.[10] Do not allow the patient to go home without warning them not to use any suspect appliances.[21]

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Carbon monoxide poisoning

Treatment algorithm

all patients (acute or chronic carbon monoxide poisoning)

oxygen

supportive care

hyperbaric oxygen therapy

Practical tip

Evidence: Hyperbaric oxygen therapy

monitoring