Quantitative relationships among plasma [Lactate], [Pi], [Albumin], unmeasured anions ([UA]) and the anion gap (AGK) in lactic acidosis (LA) are not well defined.Methods:
A mathematical model featuring compensatory potassium and chloride shifts and respiratory changes in LA demonstrated: (1) AGK = [Lactate] + Zp × [Pi] + 2.4 × [Albumin] + constant1 + e, where Zp is a function of pH, and e reflects unmeasured anions and cations plus pH-related variations. Eq. (1) can be algebraically rearranged to incorporate the albumin-corrected anion gap, cAGK: (2) cAGK = [Lactate] + Zp × [Pi] + constant2 + e. Eq. (1) was tested against 948 data sets from critically ill patients with [Lactate] 4.0 mEq/L or greater. AGK and cAGK were evaluated against 12,341 data sets for their ability to detect [Lactate] > 4.0 mEq/L.Results:
Analysis of Eq. (1) revealed r2 = 0.5950, p < 0.001. cAGk > 15 mEq/L exhibited a sensitivity of 93.0% [95% CI: 91.3–94.5] in detecting [Lactate] > 4.0 mEq/L, whereas AGK > 15 mEq/L exhibited a sensitivity of only 70.4% [67.5–73.2]. Additionally, [Lactate] > 4.0 mEq/L and cAGK > 20 mEq/L were each strongly associated with intensive care unit mortality (χ2 > 200, p < 0.0001 for each).Conclusions:
In LA, cAGK is more sensitive than AGK in predicting [Lactate] > 4.0 mEq/L.