THE TANH-EQUATION MODIFIED FOR THE HEMOGLOBIN, OXYGEN, AND CARBON-MONOXIDE EQUILIBRIUM

The model of the hemoglobin-oxygen equilibrium represented by the TANH -equation is incorporated in the Oxygen Status Algorithm, a computer p rogram for calculating and displaying the oxygen status and the acid-b ase status of the blood. In the presence of carbon monoxide it is nece ssary to take the Haldane equation into account. We here describe the necessary equations and methods for iterative solutions. The validity of the Haldane equation has previously been demonstrated by Zwart et a l. (J Appl Physiol 1984; 57: 14-20). We have performed a few experimen ts to confirm this. Like Zwart et al. we find a small deviation from t he theory, but in the opposite direction, i.e. the measured p50 values are slightly higher than predicted. We conclude that the Haldane equa tion adequately accounts for the carbon monoxide effect up to 30 % car boxy-hemoglobin, but further studies are needed to confirm or exclude any minor deviation from the Haldane relationship which may be signifi cant at higher carboxy-hemoglobin fractions.