Physiological variables of the “metabolic component” of acid-base balance and mortality in intensive care patients

Abstract

Introduction: Metabolic acidosis is a frequent pathophysiological condition in critically ill patients. It can be assessed using different physiological variables, but their prognostic value has not yet been well established. Objective: To evaluate the association between the variables that allow assessing the metabolic component of acid-base balance (ABB) and 28-day mortality in patients admitted to an intensive care unit (ICU) in Bogotá, D.C., Colombia. Materials and methods: Prospective cohort study conducted in 122 patients admitted to an ICU between January and June 2013 and with a stay >24 hours. On admission to the ICU, blood samples were taken, and an arterial blood gas test was performed in order to calculate the following variables: anion gap (AG), corrected anion gap (AGc), standard base excess (BEst), metabolic H+, base excess-unmeasurable anions (BEua), arterial pH, arterial lactate, standard HCO3-st, and strong ion difference (SID). APACHE II and SOFA scores were also calculated. A bivariate analysis was performed in which ORs and their respective 95%CI were calculated, and then a multivariate analysis was conducted using a logistic regression model to identify the variables associated with 28-day mortality; a significance level of p<0.05 was considered. Results: Out of the 122 patients, 33 (27.05%) died at 28 days and 51 (48.80%) were women. Participants’ mean age was 46.5 years (±15.7). The following variables were significantly associated with 28-day mortality in the bivariate analysis: SID (OR=1.150; p=0.008), BEua (OR=0.897; p=0.023), AG (OR=1.231; p=0.002), AGc (OR=1.232; p=0.003), blood pH (OR=0.001; p=0.023), APACHE II (OR=1.180; p=0.001), HCO3-st (OR=0.841; p=0.015). In the multivariate analysis, only the APACHE II score variable was significantly associated with 28-day mortality (OR=1.188; p=0.008). Conclusion: The physiological variables that allow assessing the metabolic component of ABB, both from the Henderson model and the Stewart model, were not significantly associated with 28-day mortality.