Evaluation of two methods to calculate p50 from a single blood sample

Acta Anaesthesiol Scand. 2001 May;45(5):550-2. doi: 10.1034/j.1399-6576.2001.045005550.x.


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.

MeSH terms

  • Algorithms
  • Carbon Dioxide / blood
  • Data Interpretation, Statistical
  • Hemoglobinometry / methods*
  • Humans
  • Models, Biological
  • Models, Theoretical
  • Oxygen / blood


  • Carbon Dioxide
  • Oxygen