IMPROVED PCO2 MEASUREMENT IN 6 STANDARD BLOOD-GAS ANALYZERS USING A PHOSPHATE-BUFFERED SOLUTION FOR GASTRIC TONOMETRY

The measurement of gastric intramucosal pH serves as a non-invasive te chnique for early detection of gastrointestinal ischaemia in criticall y ill patients, The method is based on the determination of the partia l pressure of carbon dioxide in a 0.9% saline solution using a standar d blood gas analyser. However, the use of standard blood gas analysers leads to an underestimation of carbon dioxide partial pressure in sal ine. Instrumental biases of six blood gas analysers were investigated using either a saline or a phosphate-buffered solution. Both test solu tions were equilibrated with five defined carbon dioxide concentration s. Each blood gas analyser underestimated this defined partial pressur e of carbon dioxide with a bias between - 3.7% and - 57.5% if saline w as used. The phosphate-buffered solution considerably improved instrum ental precision, resulting in biases between +2.7% and - 17.6%. Thus, a phosphate-buffered solution increases the accuracy of gastric intram ucosal pH measurement.