Arterial blood gas tensions - Effect of storage time and temperature

Abstract

Introduction: Arterial and venous blood gas analysis provide vital information on pH, oxygenation, ventilatory and acid-base status that guide clinician interventions. Factors such as syringe material, sampling technique, type of anticoagulant, storage time and temperature, and analysis may influence the accuracy of results. Aim: To determine the effect of storage time and temperature on blood gas analysis. Method: Nine 1-ml samples of arterial blood were collected by convenient sampling method involving 25 subjects in a single attempt from an in-dwelling arterial line. Four samples were stored in separate ice bags and four at room temperature. One sample was analysed immediately (‘reference’). One sample from each storage group was analysed at 15-min intervals for 60-min. The agreement of the ‘ureference’ value with values of samples taken at 15-, 30-, 45- and 60-min were determined using Lin’s concordance correlation and Bland and Altman’s 95% limits of agreement (LOA). Results: The rate of decay of pH and PaCO2 values over time were similar for samples stored at room temperature and ice. The average difference (95% LOA) in PaO2 on samples stored at room temperature at 15, 30, 45 and 60 min when compared with baseline were 1.80 (-18 to 21.7), 3.84 (-20.5 to 28.2), 3.40 (-18.8 to 25.6) and 4.36 (-17.5 to 26.2) respectively. The decay in PaO2 was less pronounced in samples stored in ice with differences of -2.04 (-18.3 to 14.2), -2.64 (-14.2 to 9.0), -3.08 (-20.0 to 13.5) and -2.40 (-12.2 to 7.4) at 15, 30, 45 and 60 min respectively. Conclusion: PaO2 values reduce with time. The changes are more pronounced when samples are stored in room temperature than in ice. The wide LOA would imply that blood gas samples should, as far as possible, be processed immediately.