Carbon monoxide poisoning

Editor—In their editorial about carbon monoxide poisoning, Walker and Hay note that it is tissue poisoning rather than merely the effects of carboxyhaemoglobin that contributes to its toxicity.¹ We recently reported that metabolic acidosis was a better indicator of the severity of poisoning than carboxyhaemoglobin,² as the acidosis reflects tissue poisoning.

Walker and Hay concentrate on cerebral toxicity. The heart, however, as the next most vulnerable organ may help to give a clue to the diagnosis. We reviewed 139 electrocardiograms from patients with acute severe carbon monoxide poisoning who had been referred for treatment with hyperbaric oxygen, and we found that 41% were abnormal (unpublished data). Previously, 3% of patients presenting with unstable angina were found to have significant carbon monoxide intoxication.³ Thus the possibility of carbon monoxide poisoning should be considered when patients present with non-specific symptoms and have abnormalities on their electrocardiograms. Patients with known coronary disease who present with unstable angina and carbon monoxide intoxication should be given high flow oxygen via a tight fitting mask and reservoir bag (aiming to give 100%) in addition to standard treatment.

Arterial blood gases need not be used to measure carboxyhaemoglobin, as venous and arterial concentrations are not significantly different.⁴ Thus carboxyhaemoglobin can be measured simultaneously with other standard blood tests, without the need for an additional arterial puncture.