A technique for estimating the position of the oxygen-hemoglobin dissociation curve.

A nomogram was constructed which allows estimation of the P(50) value from the Po(2) and per cent O(2) saturation of a single venous blood sample. There was excellent correlation between 50 estimated P(50) values obtained in 27 severely ill patients when compared with P(50) values determined from constructed OH-DC's (correlation coefficient 0.92). The mean of the differences between the estimated and determined P(50) values was 1.5 mm Hg with a standard deviation of +/-1.1, and the maximum difference was 4 mm Hg.