Washout kinetics of inhaled hydrogen cyanide in breath

Hydrogen cyanide (HCN) intoxication causes or contributes significantly to many of the fatalities among fire victims. To enable fast treatment of HCN poisoning, a more rapid diagnostic method than currently available is required. One possibility would be measurement in exhaled air. However, as HCN is highly water soluble, it may be absorbed during inhalation and reabsorbed during exhalation. If this, so-called, washin-washout effect is substantial it may interfere with the diagnosis, as a major part of breath HCN may originate from the respiratory tract, due to recent exposure, and not from systemic exposure. The aim of this study was to estimate the importance of the washin-washout effect of HCN. The time-course of cyanide in exhaled air was measured with an electrochemical detector in 10 volunteers during and after a 1 min x 10 ppm exposure to HCN. The experiment revealed an average half-life of 16s (range 10-24s) in breath. Extrapolating the results to higher exposures suggests that the contribution from washin-washout from the airways will be negligible even at fatal exposures. The results support the use of breath HCN as a potential indicator of systemic intoxication.