In Reply:-We appreciate the additional calculations of Drs. Woehlck and Dunning to our published data regarding calculated carboxyhemoglobin concentrations from CO exposure with desflurane and dry CO2absorbent. From our CO data, the calculated data by Woehlck and Dunning closely approximates our observed carboxyhemoglobin concentrations with 40% O2in pigs, which is encouraging. Their calculation involves several assumptions concerning ventilatory values, as shown in their table 1. Although these values for individual animals are not exact, the values closely approximate those of the mean for our study animals, and hence their calculated values parallel our experimental results. Their calculations for carboxyhemoglobin with 25% and 100% O2concentrations are useful additions-particularly the data regarding results in 100% O2, as this oxygen concentration would often be used by practitioners during the first few minutes of anesthesia when the greatest CO exposure is occurring. Several other variables will likely alter the CO exposure and resultant carboxyhemoglobin concentrations. These include the use of a higher fresh gas flow rate and lower anesthetic concentration, both of which might reduce the degree of CO exposure that occurs. These several factors, along with our inability to readily detect CO exposure, likely produce the low incidence of reports regarding this phenomenon.

Edward J. Frink, Jr., M.D.

Wallace M. Nogami, M.D.

Department of Anesthesiology; The University of Arizona Health Sciences Center; Tucson, Arizona 85724–5114

(Accepted for publication December 2, 1997.)