Carbon Monoxide & Cyanide Poisoning

Meet the patient

A 32-year-old woman, 28 weeks pregnant, and her four-year-old son arrive in mid-winter with headache, nausea and confusion from a faulty gas heater. Both are drowsy but talking; the pulse oximeter reads 99 per cent on room air, yet a venous gas shows a lactate of 4.2 mmol/L and CO-oximetry returns a carboxyhaemoglobin of 32 per cent in the mother and 28 per cent in the child. The reassuring pulse-oximeter reading is expected rather than reassuring: in the presence of carboxyhaemoglobin the SpO2 approximates the sum of carboxyhaemoglobin and oxyhaemoglobin and so seriously overestimates the true oxyhaemoglobin.^[10]

The question that reassuring number hides is the one that decides her hour: how hypoxic is she really, and does the smoke or the heater point to a second asphyxiant? Carbon monoxide stops oxygen reaching the tissues; cyanide stops the tissues using it; a fire victim can carry both. Hold that single fork and every step below follows from it.^[3]

References16ShowHide

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