INSTRUMENTAL VARIABILITY OF RESPIRATORY BLOOD-GASES AMONG DIFFERENT BLOOD-GAS ANALYZERS IN DIFFERENT LABORATORIES

The aim of this study was to test the hypothesis that differences in o xygen tension (Po-2) and carbon dioxide tension (Pco(2)) values from m easurements performed on different blood gas analysers in different la boratories are clinically insignificant, Samples of fresh whole human tonometered blood (Po-2 8.1 kPa (60.8 mmHg); Pco(2) 5.3 kPa (39.9 mmHg )) were placed in airtight glass syringes and transported in ice-water slush, Blood gas analysis was performed within 3.5 h by 17 analysers (10 different models) in 10 hospitals on one day, The mean of the diff erences between the measured and target values was -0.01+/- 0.19 and 0 .21+/-0.13 kPa (-0,06+/-1,45 and 1.55+/-1.01 mmHg) for Po-2 and Pco(2) , respectively, The mean of the differences between two samples on one analyser was 0.06+/-0.06 and 0.04+/-0.03 kPa (0.47+/-0.48 and 0,29+/- 0,24 mmHg), respectively, For Po-2 and Pco(2) the interinstrument stan dard deviations (s(b)) were 0.18 and 0.13 kPa (1.38 and 0.99 mmHg), re spectively, whereas the intra-instrument standard deviations (s) were 0.06 and 0.03 kPa (0.47 and 0.26 mmHg), respectively, Both for Po-2 an d Pco(2) the ratios of s(b)(2) and s(2) were statistically significant (analysis of variance tonometry (ANOVA) p<0,001), The standard deviat ions of a random measurement on a random variability dom analyser were 0.19 and 0.14 kPa (1.46 and 1.02 mmHg) for Po-2 and Pco(2), respectiv ely, We conclude that the variability in measurement of blood gas valu es among different blood gas analysers, although negligible, depends m uch more on inter- than intra-instrument variation, both for oxygen te nsion and carbon dioxide tension, Technical improvements and adequate quality control programmes, including tonometry, may explain why the v ariability in blood gas values depends mainly on errors in the pre-ana lytical phase.