Comparison and assessment of blood gas related quantities including base excess, the gas exchange indices, and temperature corrected pH/PO₂/PCO₂, as defined in approved NCCLS standard C12-A, using a computer simulation of input variables

Abstract

Blood gases and related quantities reported to clinicians have, since the earliest days, included both directly measured as well as calculated or estimated quantities. Some developed as substitutes for quantities that were or are difficult to measure routinely, others to explain relationships between older, difficult to measure quantities and newly measureable quantities, and still others attempt to better understand the physiology of the acid-base process. The net result is a plethora of acid-base and related quantities that may be reported by different blood gas systems. In an attempt to address the issue of which quantities have stood the test of usefulness over time, and further, to examine the optimum algorithm for use in quantification, the NCCLS has developed, through its consensus process, a recommended set of quantities and their quantlfying algorithms. We have studied these quantities and compared them with some other recognized approaches and present our analysis in this report. The major conclusion is that among those quantities recommended, the NCCLS algorithms present the most sensible overall approach and that we would recommend their use as described so that the quantities can be most effectively applied clinically, without differences in final values occurring due solely simple algorithm differences.

Key Words:

• A-aDO₂
• a/A ratio
• bicarbonate
• pCO₂
• pH
• physiologic shunt
• pO₂