Accuracy of pleural fluid pH and PCO2 measurement in a blood gas analyser. Analysis of bias and precision

Pleural fluid pH measurements are used in the management of parapneumonic effusions. This study evaluated the accuracy of the pleural fluid pH and PCO2 measurement in a blood gas analyser (BGA) and the error induced by altering the aerobic environment and temperature of sample storage prior to analysis. The pH electrodes in a pH meter and a BGA were initially evaluated using aqueous reference solutions. The accuracy of pH and PCO2 electrodes was then assessed in pleural fluid tonometered to a known PCO2. The effects of aerobic compared to anaerobic storage and storage temperature, 0°C vs 37°C of pleural fluid were evaluated for errors in pH and PCO2