A critical analysis of the use of the CFK equation in predicting COHb formation

Fifteen healthy young males, nine at rest and six at exercise, were exposed to high transient levels of carbon monoxide (CO) to simulate the breathing environment measured in an armored vehicle during weapons firing. Depending on the dosage, the CO exposures raised the subjects' carboxyhemoglobin saturation (%COHb) from 1.7% to 17.3%. The measured %COHb levels compared favorably (regression coefficient, b = 1.04) to those predicted by the theoretical model of Coburn et al. When the application of this same model by a method proposed by NIOSH was used, however, a significant overprediction was found (b = 1.28). It appears that this overprediction results primarily from the omission of water vapor in the lungs when the inspired pressure of CO is considered, and to the use of incorrect values for alveolar ventilation. These results demonstrate the errors that may arise from the incorrect utilization of the equation by Coburn et al. and the effect that this may have upon the calculation of the limits for safe occupational exposure to CO.