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.

Treatment:

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

References:

Blumenthal, I. Carbon monoxide poisoning. J R Soc Med. 2001; 94(6): 270-272.

Harper, A. and Croft-Baker, J. Carbon monoxide poisoning: undetected by both patients and their doctors. Age Ageing. 2004; 33(2): 105-109.