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Correspondence  |   April 1998
Predicting the Severity of Carbon Monoxide Poisoning at Varying FIO2
Author Notes
  • Associate Professor of Anesthesiology (Woehlck); Assistant Professor of Medicine (Dunning), Medical College of Wisconsin, Milwaukee, Wisconsin 53226.
  • .
Article Information
Correspondence
Correspondence   |   April 1998
Predicting the Severity of Carbon Monoxide Poisoning at Varying FIO2
Anesthesiology 4 1998, Vol.88, 1126-1127. doi:
Anesthesiology 4 1998, Vol.88, 1126-1127. doi:
To the Editor:-Frink et al. [1] showed that extremely high carboxyhemoglobin (COHb) concentrations can be produced in 25-kg pigs by the inhalation of desflurane through a breathing circuit with dried CO sub 2 absorbents, which produce carbon monoxide (CO) through anesthetic breakdown. These experiments were performed at 40% inspired oxygen, although in clinical practice, inspired oxygen concentrations can vary from less than 25% to nearly 100%, impacting the resultant severity of CO poisoning as measured by COHb concentrations.
We attempt to exemplify the clinical effect of various inspired oxygen concentrations during the rapidly changing CO concentrations produced by desflurane breakdown by using mathematical modeling to extrapolate the data of Frink et al. We interpolated parts per million CO from the graphic data presented in figures 3 and 4 of the study by Frink et al. and applied these data to the equation developed by Coburn et al., [2] (CFK equation) to determine the COHb concentration. Good experimental fit of this equation has been documented by Peterson et al. [3] We used this equation to calculate the accumulation of COHb as a function of the absorption and elimination of CO through respiration using Microsoft Excel (Microsoft Corporation) for the MacIntosh (Apple Computer, Inc., Cupertino, CA). The implementation of the CFK equation required that assumptions be made to complete the respiratory, profile, as shown in Table 1. We used the CFK equation to calculate the COHb concentration by an iterative method using CO concentrations interpolated from the graphic data of Frink et al. To validate the appropriateness of using the CFK equation, we graphically show the correlation of the calculated COHb data to the measured experimental data of Frink et al. in Figure 1. This results in an r2value of 0.997 for the descending data points and an overall r2value of 0.967. Several possible explanations exist for the slight deviation of the experimental and calculated data during the ascending phase of the curve. It is possible that physiologic parameters (e.g., cardiac output) were severely compromised during this phase of the experiment, and differences reflected changes in circulation in the experimental animals from those for which the CFK equation was developed. Despite these limitations, the CFK equation provides excellent predictions under these extreme conditions.
Table 1. Assumed Values for Experimental Data 
Image not available
Table 1. Assumed Values for Experimental Data 
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Figure 1. Shows the concentration of CO (open circles) in parts per million (ppm) interpolated from the graphic data of Frink et al. This figure also compares COHb % calculated at 40% inspired oxygen from these data (small triangles) using the CFK equation for comparison with the experimental COHb % taken from the graphic data of Frink et al. The experimental COHb data correlate well with those predicted by the CFK equation.
Figure 1. Shows the concentration of CO (open circles) in parts per million (ppm) interpolated from the graphic data of Frink et al. This figure also compares COHb % calculated at 40% inspired oxygen from these data (small triangles) using the CFK equation for comparison with the experimental COHb % taken from the graphic data of Frink et al. The experimental COHb data correlate well with those predicted by the CFK equation.
Figure 1. Shows the concentration of CO (open circles) in parts per million (ppm) interpolated from the graphic data of Frink et al. This figure also compares COHb % calculated at 40% inspired oxygen from these data (small triangles) using the CFK equation for comparison with the experimental COHb % taken from the graphic data of Frink et al. The experimental COHb data correlate well with those predicted by the CFK equation.
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In Figure 2, we show the results of mathematical modeling using the CFK equation to extrapolate the CO concentration data to different inspired oxygen concentrations (FIO2). These COHb concentrations would be predicted to result from exposure to the CO concentrations interpolated from the data of Frink et al. and also at 100% and 25% oxygen. Predicted results at 100% oxygen yielded smaller COHb concentrations, possibly accounting for the low incidence of CO poisoning detected by clinical signs. Conversely, the predicted results at 25% oxygen suggest that CO toxicity would be enhanced under these conditions. The routine use of an increased FIO2may reduce CO poisoning during anesthesia because of the competitive binding of CO and oxygen, but CO poisoning occurring with low FIO2may be more severe.
Figure 2. Shows the predicted concentration of COHb in % resulting from the use of the CFK equation as a function of time at different inspired oxygen concentrations. The data at 40% O2are identical to those in Figure 1.
Figure 2. Shows the predicted concentration of COHb in % resulting from the use of the CFK equation as a function of time at different inspired oxygen concentrations. The data at 40% O2are identical to those in Figure 1.
Figure 2. Shows the predicted concentration of COHb in % resulting from the use of the CFK equation as a function of time at different inspired oxygen concentrations. The data at 40% O2are identical to those in Figure 1.
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Harvey J. Woehlck, M.D.
Associate Professor of Anesthesiology
Marshall B. Dunning III, Ph.D.
Assistant Professor of Medicine; Medical College of Wisconsin; Milwaukee, Wisconsin 53226
(Accepted for publication December 2, 1997.)
REFERENCES
Frink EJ, Nogami WM, Morgan SE, Salmon RC: High carboxyhemoglobin concentrations occur in swine during desflurane anesthesia in the presence of partially dried carbon dioxide absorbents. Anesthesiology 1997; 87(2):308-16.
Coburn RF, Forster RE, Kane PB: Considerations of the physiological variables that determine the blood carboxyhemoglobin concentration in man. J Clin Invest 1965; 44(11):1899-910.
Peterson JE, Stewart RD: Absorption and elimination of carbon monoxide by inactive young men. Arch Environ Health 1970; 21(2):165-71.
Figure 1. Shows the concentration of CO (open circles) in parts per million (ppm) interpolated from the graphic data of Frink et al. This figure also compares COHb % calculated at 40% inspired oxygen from these data (small triangles) using the CFK equation for comparison with the experimental COHb % taken from the graphic data of Frink et al. The experimental COHb data correlate well with those predicted by the CFK equation.
Figure 1. Shows the concentration of CO (open circles) in parts per million (ppm) interpolated from the graphic data of Frink et al. This figure also compares COHb % calculated at 40% inspired oxygen from these data (small triangles) using the CFK equation for comparison with the experimental COHb % taken from the graphic data of Frink et al. The experimental COHb data correlate well with those predicted by the CFK equation.
Figure 1. Shows the concentration of CO (open circles) in parts per million (ppm) interpolated from the graphic data of Frink et al. This figure also compares COHb % calculated at 40% inspired oxygen from these data (small triangles) using the CFK equation for comparison with the experimental COHb % taken from the graphic data of Frink et al. The experimental COHb data correlate well with those predicted by the CFK equation.
×
Figure 2. Shows the predicted concentration of COHb in % resulting from the use of the CFK equation as a function of time at different inspired oxygen concentrations. The data at 40% O2are identical to those in Figure 1.
Figure 2. Shows the predicted concentration of COHb in % resulting from the use of the CFK equation as a function of time at different inspired oxygen concentrations. The data at 40% O2are identical to those in Figure 1.
Figure 2. Shows the predicted concentration of COHb in % resulting from the use of the CFK equation as a function of time at different inspired oxygen concentrations. The data at 40% O2are identical to those in Figure 1.
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Table 1. Assumed Values for Experimental Data 
Image not available
Table 1. Assumed Values for Experimental Data 
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