Sources of error in oxygen tension measurement.

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Abstract
Several potential sources of error were explored in measurement of blood oxygen tension (PBO2) by a polarographic system incorporating a micro-electrode. Values of tonometered blood and tonometer gas were compared when the electrode was covered first by a polyethylene, then by a polypropylene membrane. It was found that PBO2 was consistently below gas oxygen tension (PGO2). The PGO2/PBO2 relationship with polyethylene was nonlinear over the 10-700 mm Hg range and characterized by the equation PGO2 = (1. 24 X PBO2) below 62. 5 mm Hg and the equation PGO2 = (1. 08 X PBO2) + 10 above 62. 5 mm Hg. With the polypropylene membrane, the PGO2/PBO2 relationship was linear and such that PGO2 = 1.05 X PBO2. The reasons for these PGO2/PBO9 differentials are discussed. The pH and hematocrit of blood were found to have no effect on measured blood oxygen tension, nor did the presence of heparin in samples. Premeasurement handling of blood samples was also explored. It was found that maintenance of samples at 25 C and 37 C was accompanied by significant declines in PBO2, while P-BO2 was stable in samples held at o C. Introduction of samples into the system at o C was not found to introduce a measurement error.