To the Editor:--I read with interest the case report in which Woehlck et al. proposed that the detection of mixed halogenated agents during isoflurance anesthesia is a clinically useful sign to suggest the presence of carbon monoxide. The authors correctly note that clinical mass spectrometry cannot directly measure carbon monoxide because its molecular weight is the same as nitrogen and its fragmentation products are similar to those of carbon dioxide.
Yet, mass spectrometry may be helpful in the direct detection of changing carbon monoxide fractions in respiratory gas. In canine studies in which carbon monoxide poisoning was induced by injection of a molar amount of the gas into the inspired limb during closed-circuit anesthesia, we monitored complete uptake of carbon monoxide from the circuit by mass spectrometry (model 6000, Ohmeda, Madison, WI). In that study, carbon monoxide in the circuit was qualitatively detected as spillover into and increase of the nitrogen channel (same molecular weight) and the carbon dioxide channel (conversion to C12fragment). As complete pulmonary uptake of carbon monoxide occurred, the nitrogen and carbon dioxide mass spectrometry signals decreased to baseline levels.
Peter H. Breen, M.D., F.R.C.P.C., Department of Anesthesiology, University of California, Irvine, Medical Center, 101 City Drive South, Orange, California 92613–1491.