[The measurement of pH and gases in the blood using microanalysis: the effect of storage at 4 degrees C for an hour. A study in the rat].

The effects of one hour storage at 4 degrees C on micro blood gas samples (150 microliters) were studied for a wide range of values (pH: 7.11-7.58; PCO2: 26-97 mmHg; PO2: 31-503 mmHg) in 20 rats with indwelling carotid artery catheters. Blood gas values were modified by varying the composition of inspired gases: normoxia, hypocapnic hypoxia, hyperoxia, hypercapnia (in this case eight animals were anaesthetized with halothane 1.1%). One hundred and eight double micro-samples were taken. For each double sample, one was analysed immediately (H0) and compared with the second sample after one hr storage at 4 degrees C (H1). The Bland and Altman method was used for the statistical analysis of results. After one hr storage at 4 degrees C, the PCO2 was slightly higher than at H0 (mean difference +/- SD: +1.08 +/- 1.7 mmHg) and arterial pH was slightly lower (mean difference +/- SD: -0.016 upH +/- 0.011 upH). These results show that for these two variables, in the range studied, one hour storage at 4 degrees C had little effect. In contrast, for arterial PO2 the mean difference between all measurements between H1 and H0 was -17 +/- 25 mmHg. If results lower than 200 mmHg (56 double samples) are considered separately, the mean difference between values at H1 and H0 was only -0.98 +/- 5.3 mmHg. For PaO2 greater than 200 mmHg (52 double samples), the mean difference was -34 +/- 26.3 mmHg; this may be due to low reproducibility of measurements of elevated PO2 levels and to the effects of cellular metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)