ESTIMATION OF P 50 FROM A SINGLE VENOUS BLOOD SAMPLE

The oxygen tension at 50% saturation of haemoglobin, or P 50 was calculated from a single O 2 tension and saturation measurement on a venous blood sample by means of the proportional displacement assumption of Severinghaus and a parallel displacement assumption. These calculations were compared with a two‐point technique, based on Hill's formula, which was assumed to be accurate. The results obtained from the simpler, one‐point techniques correlated well with the more complex two‐point estimation. This correlation remained for subjects with normal, high, and low P 50 .