To investigate whether the difference between sodium and chloride ([Na +] – [Cl −]) and anion gap corrected for albumin and lactate (AG corr) could be used as apparent strong ion difference (SID app) and strong ion gap (SIG) surrogates (respectively) in critically ill patients.
A total of 341 patients were prospectively observed; 161 were allocated to the modeling group, and 180 to the validation group. Simple regression analysis was used to construct a mathematical model between SID app and [Na +] – [Cl −] and between SIG and AG corr in the modeling group. Area under the receiver operating characteristic (ROC) curve was also measured. The mathematical models were tested in the validation group.
in the modeling group, SID app and SIG were well predicted by [Na +] – [Cl −] and AG corr (R 2 = 0.973 and 0.96, respectively). Accuracy values of [Na +] – [Cl −] for the identification of SID app acidosis (<42.7 mEq/L) and alkalosis (>47.5 mEq/L) were 0.992 (95% confidence interval [CI], 0.963–1) and 0.998 (95%CI, 0.972–1), respectively. The accuracy of AG corr in revealing SIG acidosis (>8 mEq/L) was 0.974 (95%CI: 0.936–0.993). These results were validated by showing excellent correlations and good agreements between predicted and measured SID app and between predicted and measured SIG in the validation group (R 2 = 0.977; bias = 0±1.5 mEq/L and R 2 = 0.96; bias = −0.2±1.8 mEq/L, respectively).