Carbon monoxide poisoning

Carbon monoxide has 210x more affinity for Hb than oxygen. This results in a left shift of the oxygen dissociation curve.

Normal levels of carboxyhaemoglobin are <2% in non-smokers and <13% in heavy smokers. Pregnancy and haemolytic anaemia can raise levels to 5%. Severe poisoning is generally taken to be a level >30%.

The classical appearance is of cherry red skin but this is not always present even in severe poisoning.

Features of carbon monoxide poisoning are vague:
  • 90% have a headache
  • 50% nausea/vomiting
  • 50% lethargy
  • 30% confused/altered conscious level

Severe poisoning can cause
  • Cardiac arrthymias/infarction
  • Coma
  • Muscle necrosis
  • seizures

Diagnosis is by blood carboxyhaemoglobin level. Pulse oximetry is not helpful.

  • 100% oxygen
  • hyperbaric oxygen if LOC/pregnant/neuro signs/MI - decreases half life of COHb from over 5 hrs to 22 minutes

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