Effects of different sample volumes on arterial blood gas and electrolytes testing

ABSTRACT

BACKGROUND: Insufficient sample volume can cause unnecessary blood loss and inaccurate arterial blood gas and electrolytes testing. The aim of this study was to determine the adequate sample volume, that is required for accurate arterial blood gas and electrolyte testing from arterial catheters. METHODS: Patients had four different arterial blood samples (0.2 ml, 0.4 ml, 0.6 ml and 1 ml [control], respectively) taken sequentially in random order. Samples were analyzed for pH, PaCO2, PaO2, hematocrit, Na+, K+, Ca2+ and Mg2+ using NOVA blood gas analyzer. RESULTS: A total of 27 patients were recruited for the study. All sample volumes tested provided the results of pH, PaCO2, PaO2 and hematocrit that were statistically similar to control values. However, the results of electrolytes (K+, Ca2+ and Mg2+) in all sample volumes tested were significantly lower than the control values and an increasing sample volume equated to blood results trending closer to those obtained with the control sample. CONCLUSIONS: This study showed that there is not one sample volume that will provide accurate results for all blood components. The study tested a variety of sample volumes and found that although even small sample volume of 0.2 ml provided accurate results for pH, PaCO2, PaO2 and hematocrit. No sample volume that was tested provided accurate results for K+, Ca2+ and Mg2+.