Strong ion gap and anion gap corrected for albumin and lactate in patients with sepsis in the intensive care unit.

Abstract

Introduction: Metabolic acidosis is very common amongst critically ill sepsis patients partly due to the presence of unmeasured ions in serum. These ions can be detected by anion gap (AG) or strong ion gap (SIG) concentration values. The purpose of this study is to assess the correlation and potential agreement of the two methods in critically ill patients with sepsis.

Materials and methods: The present is a retrospective study including septic patients admitted to the Intensive Care Unit from December 2014 to July 2016. The [SIG] and the [AG] corrected for albumin and lactate ([AG_cl]) were calculated on admission and on sepsis remission or deterioration. The correlation of the two parameters was assessed in all patient groups using the Pearson correlation coefficient and linear regression analysis and the agreement with Bland-Altman plots. ROC survival curves were also generated for the patients in relation to the values of [AG_cl], [SIG] and inorganic [SIG] ([SIG_i]) on admission.

Results: There was a strong correlation linking [AG_cl] and [SIG] values (r>0.9, P<0.05) in all patient groups. The results from all three linear regression equations were statistically significant as the models predicted the [AG_cl] value from the [SIG] value with high accuracy. The mean difference of the two methods (i.e. [AG_cl] - [SIG] in every patient separately) in septic patients on admission was 11.75 mEq/l with 95% limits of agreement [9.7-13.8]; in patients with sepsis deterioration, it was 11.8 mEq/l with 95% limits of agreement [9.8-13.7] and in patients with sepsis remission, it was 11.5 mEq/l with 95% limits of agreement [10.4-12.7]. ROC survival curves demonstrated a small area under the curve (AUC): [SIG] AUC: 0.479, 95% CI [0.351, 0.606], [SIG_i] AUC: 0.581, 95% CI [0.457, 0.705], [AG_cl] AUC: 0.529, 95% CI [0.401, 0.656].

Conclusion: [AG_cl] and [SIG] demonstrate excellent correlation in septic patients, with a mean difference of about 12 mEq/l. Both parameters failed to demonstrate any predictive ability regarding patient mortality.