title: Evaluation of two methods to calculate p50 from a single blood sample.
abstract: 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.
authors: Department of Anaesthesia, Holstebro County Hospital, Laegårdvej 12, DK-7500 Holstebro, Denmark. anpe@ringamt.dk
authors: N P
authors: NP
authors: Ekeloef
authors: J
authors: J
authors: Eriksen
authors: C B
authors: CB
authors: Kancir
mesh_terms: D000465:Algorithms; D002245:Carbon Dioxide / Q000097:blood; D003627:Data Interpretation, Statistical; D006452:Hemoglobinometry / Q000379:methods*; D006801:Humans; D008954:Models, Biological; D008962:Models, Theoretical; D010100:Oxygen / Q000097:blood
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen