AbstractBackground Base excess (BE) partitioning is an established tool for bedside interpretation of metabolic acid–base disorders. However, this method assumes that changes in plasma strong ion difference, estimated as Na+−Cl−, directly relate to changes in standard BE. This assumption holds in isolated plasma but fails in vivo, where pH-dependent redistribution between body compartments alters plasma strong ion difference without producing an equivalent change in standard BE. We hypothesised that this introduces a clinically relevant pH-dependent bias into BE partitioning and that adjusting the Na+−Cl− reference value for pH would correct it. Methods Unmeasured ions were quantified using conventional BE partitioning and a novel pH-corrected version, in which the Na+−Cl− reference was adjusted by +1.5 mEq L−1 for every −0.1 change in pH. Agreement with strong ion gap was assessed in 5976 ICU patients from AmsterdamUMCdb using Bland–Altman analyses (including pH-stratified subgroups) and linear regression to quantify the independent effect of pH. Results The conventional method demonstrated wide limits of agreement (−5.6 to 2.9 mEq L−1) and a strong confounding effect of pH (1.45 mEq L−1 per 0.1 pH unit). The pH-corrected algorithm markedly improved agreement with the strong ion gap (limits of agreement −4.4 to 0.4 mEq L−1) and substantially reduced the confounding effect of pH (0.15 mEq L−1 per 0.1 pH unit). Conclusions Conventional base excess partitioning is subject to a clinically relevant pH-dependent error. A variable, pH-adjusted Na+−Cl− reference value eliminates this error and provides a more reliable assessment of metabolic acid–base disturbances, especially in patients with severe acidaemia or alkalaemia.
Krbec et al. (Sun,) studied this question.