Henderson M, Apthorp GH. Rapid method for estimation of carbon monoxide in blood. Brit Med J 1960: 2: 1853
“Each subject washed the nitrogen from his lungs by breathing 100% oxygen from a simple open circuit (Fig. 1) for a period of three minutes. At the end of this time he was instructed to take a maximum inspiration and hold his breath. The three-way tap (T) was then turned and exhaled through a carbon dioxide absorber, previously washed out with oxygen into an empty and rebreathed from this bag for a further three minutes. The contents of the bag were then analysed for oxygen by the Haldane method and for carbon monoxide, using an infra-red meter.”