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. 2013;8(2):e56635.
doi: 10.1371/journal.pone.0056635. Epub 2013 Feb 13.

Use of sodium-chloride difference and corrected anion gap as surrogates of Stewart variables in critically ill patients

Jihad Mallat  1 , Stéphanie Barrailler, Malcolm Lemyze, Florent Pepy, Gaëlle Gasan, Laurent Tronchon, Didier Thevenin
Affiliations

Use of sodium-chloride difference and corrected anion gap as surrogates of Stewart variables in critically ill patients

Jihad Mallat et al. PLoS One. 2013.

Abstract

Introduction: 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.

Methods: 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.

Results: 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).

Conclusions: SID(app) and SIG can be substituted by [Na(+)] - [Cl(-)] and by AG(corr) respectively in the diagnosis and management of acid-base disorders in critically ill patients.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Correlation and agreement between observed and predicted apparent strong ion difference (SIDapp) in the cross-validation group.
Panel A shows the agreement between observed and predicted SIDapp (bias = 0, limits of agreement 95% = −1.5 to 1.5 mEq/L). Panel B shows the correlation between observed and predicted SIDapp (R2 = 0.977, P<0.0001).
Figure 2
Figure 2. Correlation and agreement between observed and predicted strong ion gap (SIG) in the cross-validation group.
Panel A shows the agreement between observed and predicted SIG (bias = −0.2, limits of agreement 95% = −2.1 to 1.6 mEq/L). Panel B shows the correlation between observed and predicted SIG (R2 = 0.96, P<0.0001).
See this image and copyright information in PMC

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