Calculation of O2 saturation and of the oxyhemoglobin dissociation curve for different species, using a new...

The degree of O2 saturation and different data of acid-base status are determined from pO2, pH, and pCO2 values bya programmable pocket calculator. Since the operating program should be usable for different species and also in the range of very low O2 saturations, obviously the usual Hill equation for calculating the oxygen dissociation curve of hemoglobin is not applicable; the same is true is some cases for the Adair equation. Thus a 3-fold subdivision of the dissociation curve was undertaken and programmed. Suitable programs for several species could be established despite the limited number of program steps in the new calculator, giving systematic deviations in calculated O2 saturations of less than or equal to +/- 0.9 saturation precent over the full range of dissociation curves. A reverse procedure for calculation of pO2 from saturation is added. In situations where pCO2 or base excess are not known or only estimated, limits of the arising error are stated. In the acid-base program 7 parameters are evaluated partially using empirical formulae derived from nomograms. The programmable pocket calculator offers advantages of small size, economy, and independence of line voltage compared to much more spacious units and a precision equal or superior to nomograms.