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Evaluation of two methods to calculate p50 from a single blood sample
N P Ekeloef1, J Eriksen, C B Kancir
1Department of Anaesthesia, Holstebro County Hospital, Laegårdvej 12, DK-7500 Holstebro, Denmark. anpe@ringamt.dk
Background:
The hemoglobin-oxygen affinity is conveniently described as the oxygen tension at which the hemoglobin is 50% saturated (p50). We compared two methods of single-point analysis for p50 calculation, using clinical data.
Methods:
From patients submitted to anesthesia for major surgery, 114 arterial or venous blood samples were analyzed by using the Sigaard-Andersen oxygen status algorithm (p50OSA) and Doyle's method (p50Doyle) based on Hill's equation.
Results:
The oxygen saturation and tension varied respectively between 0.64-0.96 and 3.8 kPa-11.0 kPa. A Bland-Altman analysis showed a mean difference of 0.04 kPa (SD 0.12 kPa). The limits of agreement were -0.20 kPa and +0.28 kPa.
Conclusions:
The Siggaard-Andersen oxygen status algorithm is presently the most clinically useful single-point method of p50 calculation.