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BMC Anesthesiology
Published in: BMC Anesthesiology 1/2015

Open Access 01-12-2015 | Research article

Anion gap as a prognostic tool for risk stratification in critically ill patients – a systematic review and meta-analysis

Authors: Stella Andrea Glasmacher, William Stones

Published in: BMC Anesthesiology | Issue 1/2015

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Abstract

Background

Lactate concentration is a robust predictor of mortality but in many low resource settings facilities for its analysis are not available. Anion gap (AG), calculated from clinical chemistry results, is a marker of metabolic acidosis and may be more easily obtained in such settings. In this systematic review and meta-analysis we investigated whether the AG predicts mortality in adult patients admitted to critical care settings.

Methods

We searched Medline, Embase, Web of Science, Scopus, The Cochrane Library and regional electronic databases from inception until May 2016. Studies conducted in any clinical setting that related AG to in-hospital mortality, in-intensive care unit mortality, 31-day mortality or comparable outcome measures were eligible for inclusion. Methodological quality of included studies was assessed using the Quality in Prognostic Studies tool. Descriptive meta-analysis was performed and the I2 test was used to quantify heterogeneity. Subgroup analysis was undertaken to identify potential sources of heterogeneity between studies.

Results

Nineteen studies reporting findings in 12,497 patients were included. Overall, quality of studies was poor and most studies were rated as being at moderate or high risk of attrition bias and confounding. There was substantial diversity between studies with regards to clinical setting, age and mortality rates of patient cohorts. High statistical heterogeneity was found in the meta-analyses of area under the ROC curve (I2 = 99 %) and mean difference (I2 = 97 %) for the observed AG. Three studies reported good discriminatory power of the AG to predict mortality and were responsible for a large proportion of statistical heterogeneity. The remaining 16 studies reported poor to moderate ability of the AG to predict mortality. Subgroup analysis suggested that intravenous fluids affect the ability of the AG to predict mortality.

Conclusion

Based on the limited quality of available evidence, a single AG measurement cannot be recommended for risk stratification in critically ill patients. The probable influence of intravenous fluids on AG levels renders the AG an impractical tool in clinical practice. Future research should focus on increasing the availability of lactate monitoring in low resource settings.

PROSPERO registration number

CRD42015015249. Registered on 4th February 2015.
Appendix
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Metadata
Title
Anion gap as a prognostic tool for risk stratification in critically ill patients – a systematic review and meta-analysis
Authors
Stella Andrea Glasmacher
William Stones
Publication date
01-12-2015
Publisher
BioMed Central
Published in
BMC Anesthesiology / Issue 1/2015
Electronic ISSN: 1471-2253
DOI
https://doi.org/10.1186/s12871-016-0241-y

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