Skip to main content
  • Poster presentation
  • Open access
  • Published:

Strong ion gap can be accurately estimated with a simple bedside equation

Introduction

The anion gap (AG) is used routinely in the assessment of metabolic acidosis, but can be misleading in patients with hypoalbuminemia and other disorders commonly encountered in intensive care. This approach to acid-base analysis relies on assessment of pH, pCO2, sodium, bicarbonate and chloride, and can lead to underestimation or overestimation of the true electrochemical status of a patient, as it does not include important ions such as lactate, calcium, magnesium, and albumin. The strong ion gap (SIG) is an alternative to the AG and is based upon Stewart's physical chemistry approach. However, the SIG is cumbersome to calculate. As such, a number of shortcut equations have been developed in an effort to approximate the SIG. We sought to compare three such equations, the Kellum corrected anion gap (KellAGc), the Moviat equation, and EZSIG, in an effort to evaluate precision and accuracy [1–3].

Methods

We conducted a retrospective chart review of consecutive patients admitted to the ICU of George Washington University Medical Center from September 2010 to March 2011. Of the 1,516 patients screened, 200 met inclusion criteria, which included availability of all laboratory components to calculate the SIG, obtained within 1 hour of each other. Demographic data and serum values for pH, pCO2, albumin, lactate, sodium, potassium, chloride, bicarbonate, magnesium, phosphate, and calcium were collected. The AG, SIG, KellAGc, EZSIG, and Moviat equations were subsequently calculated and compared using Pearson correlation and Bland-Altman analysis.

Results

The mean SIG was 3.25 ± 3.5. Mean values for KellAGc, Moviat, and EZSIG were 4.5 ± 5.0, 1.77 ± 2.2, and 3.6 ± 3.7, respectively. Pearson correlation coefficients for KellAGc, Moviat, and EZSIG when compared with the SIG were r = 0.77, P = 0.0001; r = 0.88, P = 0.001; and r = 0.89, P = 0.001, respectively. In Bland-Altman analysis, the mean bias for the test equations versus the SIG were: KellAGc (1.25), Moviat (-1.48), and EZSIG (0.40).

Conclusion

While all three equations correlated highly with the SIG, the EZSIG and Moviat outperformed the KellAGc in Pearson and Bland-Altman analysis. The EZSIG had a smaller bias than the Moviat equation and a slightly better correlation (0.89 vs. 0.88). In the assessment of critically ill patients, EZSIG is a candidate scanning equation for the measurement of the SIG when all SIG components are not available.

References

  1. Kellum JA: Crit Care. 2005, 9: 500-507. 10.1186/cc3789

    Article  PubMed Central  PubMed  Google Scholar 

  2. Moviat M, et al.: Crit Care. 2003, 7: R41-R45.

    Article  PubMed Central  PubMed  Google Scholar 

  3. Busse L, et al.: Chest J. 2011, 140(4_MeetingAbstracts):1012A-1012A.

    Article  Google Scholar 

Download references

Author information

Authors and Affiliations

Authors

Rights and permissions

This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.

Reprints and permissions

About this article

Cite this article

Busse, L., Chawla, L., Panchamia, R. et al. Strong ion gap can be accurately estimated with a simple bedside equation. Crit Care 17 (Suppl 2), P444 (2013). https://doi.org/10.1186/cc12382

Download citation

  • Published:

  • DOI: https://doi.org/10.1186/cc12382

Keywords