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.
Treatment:
- 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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