A comparison of prognostic significance of strong ion gap (SIG) with other acid-base markers in the critically ill: a cohort study

Abstract

BackgroundThis cohort study compared the prognostic significance of strong ion gap (SIG) with other acid-base markers in the critically ill.MethodsThe relationships between SIG, lactate, anion gap (AG), anion gap albumin-corrected (AG-corrected), base excess or strong ion difference-effective (SIDe), all obtained within the first hour of intensive care unit (ICU) admission, and the hospital mortality of 6878 patients were analysed. The prognostic significance of each acid-base marker, both alone and in combination with the Admission Mortality Prediction Model (MPM0 III) predicted mortality, were assessed by the area under the receiver operating characteristic curve (AUROC).ResultsOf the 6878 patients included in the study, 924 patients (13.4 %) died after ICU admission. Except for plasma chloride concentrations, all acid-base markers were significantly different between the survivors and non-survivors. SIG (with lactate: AUROC 0.631, confidence interval [CI] 0.611–0.652; without lactate: AUROC 0.521, 95 % CI 0.500–0.542) only had a modest ability to predict hospital mortality, and this was no better than using lactate concentration alone (AUROC 0.701, 95 % 0.682–0.721). Adding AG-corrected or SIG to a combination of lactate and MPM0 III predicted risks also did not substantially improve the latter’s ability to differentiate between survivors and non-survivors. Arterial lactate concentrations explained about 11 % of the variability in the observed mortality, and it was more important than SIG (0.6 %) and SIDe (0.9 %) in predicting hospital mortality after adjusting for MPM0 III predicted risks. Lactate remained as the strongest predictor for mortality in a sensitivity multivariate analysis, allowing for non-linearity of all acid-base markers.ConclusionsThe prognostic significance of SIG was modest and inferior to arterial lactate concentration for the critically ill. Lactate concentration should always be considered regardless whether physiological, base excess or physical-chemical approach is used to interpret acid-base disturbances in critically ill patients.

Combining quick Sequential Organ Failure Assessment with plasma lactate concentration is comparable to standard Sequential Organ Failure Assessment score in predicting mortality of patients with and without suspected infection

“…ICU readmissions during same hospitalization were excluded from this study [3]. [3][4][5][6], and were described in our previous publications [13,14].…”

Traditional approach versus Stewart approach for acid–base disorders: Inconsistent evidence

“…Several studies showed that patients with renal failure, 54 liver diseases, 55 sepsis and trauma 56 often have accumulations of unmeasured anions. However, Dubin et al 33 and Ho et al 47 reported patient demographics in their studies; the percentage of patients with shock, acute renal failure, and hepatic failure was only 13%, 13%, and 4%, respectively, in one study, and liver diseases were only 2% in the other. A study by Cusack et al 41 included a high proportion of post-elective surgery patients, who generally have low severity of illness and low mortality.…”

“…While 10 studies have shown the potential superiority of the Stewart approach, 6 , 27 – 29 , 40 , 44 , 46 , 48 – 50 four articles failed to show the superiority of the physicochemical approach over the traditional one, 33 , 41 – 43 and three articles even showed greater strength of the traditional method than the modern one. 24 , 45 , 47 …”

Can base excess and anion gap predict lactate level in diagnosis of septic shock?

“…Zampieri et al 25 reported on the associations between acid–base variables, specifically strong ion gap (SIG) with immunological activation. On the contrary, Ho et al 26 showed in more than 6,800 patients that SIG was of modest prognostic significance in the critically ill, whereas lactate concentration was most important when comparing SIG with other acid–base markers. However, SIG is composed of many cations and anions that are not routinely checked in the initial blood sample, especially in rural areas.…”