Carbon monoxide poisoning

Carbon monoxide poisoning

Carbon monoxide has a high affinity for haemoglobin and myoglobin resulting in a left-shift of the oxygen dissociation curve and tissue hypoxia. There are approximately 50 per year deaths from accidental carbon monoxide poisoning in the UK.

Pathophysiology

• carbon monoxide binds readily to haemoglobin, forming carboxyhaemoglobin → reduced oxygen-carrying capacity
  carbon monoxide binds readily to haemoglobin, forming carboxyhaemoglobin → reduced oxygen-carrying capacity
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• in carbon monoxide poisoning the oxygen saturation of haemoglobin decreases leading to an early plateau in the oxygen dissociation curve
  In carbon monoxide poisoning the oxygen saturation of haemoglobin decreases leading to an early plateau in the oxygen dissociation curve
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  Importance: 93

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Features of carbon monoxide toxicity

• headache: 90% of cases
  Carbon monoxide poisoning - most common feature = headache
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  Importance: 88
• nausea and vomiting: 50%
• vertigo: 50%
• confusion: 30%
• subjective weakness: 20%
• severe toxicity: 'pink' skin and mucosae, hyperpyrexia, arrhythmias, extrapyramidal features, coma, death

Investigations

• pulse oximetry may be falsely high due to similarities between oxyhaemoglobin and carboxyhaemoglobin
  pulse oximetry may be falsely high due to similarities between oxyhaemoglobin and carboxyhaemoglobin
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• therefore a venous or arterial blood gas should be taken
• typical carboxyhaemoglobin
  carboxyhaemoglobin
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  levels
  • < 3% non-smokers
  • < 10% smokers
    < 10% smokers
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  • 10 - 30% symptomatic: headache, vomiting
  • > 30% severe toxicity
• an ECG is a useful supplementary investgation to look for cardiac ischaemia

Management

• patients with suspected carbon monoxide poisoning should be assessed in the emergency department
• 100% high-flow oxygen
  Carbon monoxide poisoning: 100% high-flow oxygen is the first-line treatment
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  Importance: 92
  via a non-rebreather mask
  • from a physiological perspective, this decreases the half-life of carboxyhemoglobin (COHb)
  • should be administered as soon as possible, with treatment continuing for a minimum of six hours
  • target oxygen saturations are 100%
    target oxygen saturations are 100%
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  • treatment is generally continued until all symptoms have resolved, rather than monitoring CO levels
• hyperbaric oxygen
  • due to the small number of cases the evidence base is limited, but there is some evidence that long-term outcomes may be better than standard oxygen therapy for more severe cases
  • therefore, discussion with a specialist should be considered for more severe cases (e.g. levels > 25%)
  • in 2008, the Department of Health publication 'Recognising Carbon Monoxide Poisoning' also listed loss of consciousness at any point, neurological signs other than headache, myocardial ischaemia or arrhythmia and pregnancy as indications for hyperbaric oxygen

+PassMedicine Notes

Carbon monoxide has a high affinity for haemoglobin and myoglobin resulting in a left-shift of the oxygen dissociation curve and tissue hypoxia. There are approximately 50 per year deaths from accidental carbon monoxide poisoning in the UK.

Pathophysiology

• carbon monoxide binds readily to haemoglobin, forming carboxyhaemoglobin --> reduced oxygen-carrying capacity
• in carbon monoxide poisoning the oxygen saturation of haemoglobin decreases leading to an early plateau in the oxygen dissociation curve

Questions may hint at badly maintained housing e.g. student houses.

Features of carbon monoxide toxicity

• headache: 90% of cases
• nausea and vomiting: 50%
• vertigo: 50%
• confusion: 30%
• subjective weakness: 20%
• severe toxicity: 'pink' skin and mucosae, hyperpyrexia, arrhythmias, extrapyramidal features, coma, death

Investigations

• pulse oximetry may be falsely high due to similarities between oxyhaemoglobin and carboxyhaemoglobin
• therefore a venous or arterial blood gas should be taken
• typical carboxyhaemoglobin levels
• < 3% non-smokers
• < 10% smokers
• 10 - 30% symptomatic: headache, vomiting
• > 30% severe toxicity
• an ECG is a useful supplementary investgation to look for cardiac ischaemia

Management

• patients with suspected carbon monoxide poisoning should be assessed in the emergency department
• 100% high-flow oxygen via a non-rebreather mask
• from a physiological perspective, this decreases the half-life of carboxyhemoglobin (COHb)
• should be administered as soon as possible, with treatment continuing for a minimum of six hours
• target oxygen saturations are 100%
• treatment is generally continued until all symptoms have resolved, rather than monitoring CO levels
• hyperbaric oxygen
• due to the small number of cases the evidence base is limited, but there is some evidence that long-term outcomes may be better than standard oxygen therapy for more severe cases
• therefore, discussion with a specialist should be considered for more severe cases (e.g. levels > 25%)
• in 2008, the Department of Health publication 'Recognising Carbon Monoxide Poisoning' also listed loss of consciousness at any point, neurological signs other than headache, myocardial ischaemia or arrhythmia and pregnancy as indications for hyperbaric oxygen