Carbon monoxide (CO) is a common cause of non-medicinal poisoning. Most exposures happen secondary to suicidal intent but some may occur accidently at home or the workplace. An early carboxyhaemoglobin level may be of use in an occupational safety investigation.
There is a poor understanding of the neurotoxicity of CO. Severity of poisoning does not correlate with the admission carboxyhaemoglobin level which is therefore a poor guide to management but useful diagnostically. There is also no correlation between severity at presentation and development or severity of delayed sequelae.
There remains controversy over the role of hyperbaric oxygen treatment (HBOT) but a recent randomized double-blind clinical trial suggests that where it is readily available (as in Christchurch), it should be offered to some patients (see indications below).
Consider the diagnosis in all burns, smoke inhalation, coma or attempted suicide cases.
Treatment
100% oxygen for all patients via a breathing system with a tight-fitting mask, reservoir bag and high fresh gas flow for at least 6 hours. This hastens the elimination of CO.
Indications for HBOT include presence of at least one of these high risk criteria:
Loss of consciousness (clear history of LOC or unconscious on arrival in ED)
Any neurological symptoms or signs including cognitive, behavioural or psychological (but not headache and/or nausea alone), plus any one of:
Age >55 years
Metabolic acidosis
Pregnancy - fetal haemoglobin avidly binds CO making the fetus very susceptible to hypoxic injury.