Patterns of Dissimilarities Among Instrument Models in Measuring Po2, Pco2, and pH in Blood Gas Laboratories: Outcome

22 Apr

Patterns of Dissimilarities Among Instrument Models in Measuring Po2, Pco2, and pH in Blood Gas Laboratories: OutcomeTable 3 endeavors to illustrate representative variations that might be expected among models for each of three analytes. It can be noted that the range of values (ie, the difference between the model with the highest mean value and the model with the lowest mean value) obtained by these seven models at low, intermediate, and high intensities averaged 8.8 mm Hg for Po2, 4.4 mm Hg for Pco2, and 0.033 U for pH. buy yasmin online

Table 4 shows the number of model pairs out of the possible 190 model pairs that differed by arbitrary limits for each analyte at each level. For Po2, 168 of 570 model pairs differed by >4 mm Hg; 66 of 570 model pairs differed by >6 mm Hg; and 92 of 570 model pairs differed by >6.0%. For Pco2, 86 of 570 model pairs differed by >3 mm Hg, while 123 of 570 model pairs differed by >3.0%. For pH, 37 of 570 model pairs differed by >0.030 U.
Comparing the tonometered blood and FCE biases for Po2 measurements, the maximum range of model biases at 11 levels for blood was 9 mm Hg and for FCE was 9.5 mm Hg. The slope (bias) of the FCE deviations regressed against blood deviations was 0.81, indicating that, on average, each 0.81 mm Hg of difference in blood measures between models might be associated with a 1.0 mm Hg difference in FCE measures between models. The correlation coefficient was 0.629 with p<0.001. Therefore, it is likely that our detection of differences among models when measuring FCE indicates that the differences among models when measuring blood exists as well.
The clinician expects that laboratory analyses of clinical specimens will be accurate and reproducible. This study explores one source of analytic error in blood gas analysis: systematic differences among the results provided by commercially manufactured models of blood gas analyzers. In analyzing FCE proficiency testing material in a large number of instruments over a wide range of analyte values, we detected highly significant differences not only among manufacturers but also among models of a given manufacturer.
Our initial analyses were directed toward detecting differences among manufacturers (Figs 1-3). Having found appreciable and consistent differences among manufacturers, we expected to find only small differences among models of the same manufacturer. This often was not the case.
Table 3—Deviations From AIM Values for Seven Models for Three Lots of Proficiency Testing Materials

Po2, mm Hg43.4+4.3-4.1+ 1.0+0.4-2.4+ 1.6+2.78.4
Po2, mm Hg78.6+2.6-4.1+0.4+ 1.0-1.3+2.7+0.46.8
Po2, mm Hg Average range167.5+ 3.5-3.8+ 1.2-3.5-2.2+ 7.3+3.711.18.8
Pco2, mm Hg22.6+2.7-0.5-0.9+ 1.7-0.2-0.4-0.93.6
Pco2, mm Hg47.5+ 1.6+0.9-1.1-0.4+ 1.0-2.6-1.24.2
Pco2, mm Hg Average range67.9+2.0+2.0-1.1-2.2+2.4-2.9-
pH, U7.207-0.018+0.009+0.004-0.002-0.014+0.008+0.0020.026
pH, U7.377-0.019+0.010+0.005-0.005-0.015+0.009+0.0030.034
pH, UAverage range7.616-0.025+ 0.013+0.010-0.006-0.020+0.008+0.0080.0380.033

Table 4—Number of Pairs of Models Differing by Specific Amounts

MeasureMean Lot Value
Minimal difference: 6 mm Hg4 mm Hg6%
Po2, mm Hg43.4104162
Po2, mm Hg78.653118
Po2, mm Hg167.5519412
Minimal difference: 3 mm Hg6%
Pco2, mm Hg22.6965
Pco2, mm Hg47.5310
Pco2, mm Hg67.97448
Minimal difference: 0.030 U
pH, U7.2075
pH, U7.3775
pH, U7.61627