The frequency of acid-base disorders on admission to the intensive care and its association with in-hospital outcome, Cape Town, South Africa: a retrospective cohort study

Introduction acid-base disorders are very common in critically ill patients and contribute significantly to morbidity and mortality. The aim of this study was to identify the types of acid-base disorders at the time of admission to the intensive care unit (ICU) and its associated ICU and in-hospital mortality. Methods we conducted a retrospective cohort study of all adult patients that were admitted to the ICU and had an arterial blood gas sample at the time of admission from 1st January 2019 to 31 December 2019. Using the traditional approach, acid-base disorders were categorised into six disorders. Variables predicting in-hospital death were identified using logistic regression. Results a total of 375 patients were included. The median age for the entire cohort was 39 (IQR 30–52) years and 48.3% (n=181) were female. Mixed acid-base disorders were the most common at 48.8% (n=183), followed by no disorder at 24.8% (n=93), metabolic acidosis at 9.3% (n=35), metabolic alkalosis at 6.7% (n=25), respiratory acidosis 6.1% (n=23) and respiratory alkalosis at 4.3% (n=16). A total of 94 (25.0%) patients died. There were no differences in ICU (p = 0.35) or in-hospital death (p = 0.32) by acid-base disorder. Male sex (aOR: 5.8, 95% CI 1.55-21.42; p < 0.01), APACHE II score (aOR: 1.17, 95% CI 1.06-1.30; p < 0.01) and the corrected anion gap (aOR: 1.14, 95% CI 1.02-1.27; p = 0.02) were identified as predictors of in-hospital death using multivariable logistic regression. Conclusion there was no association between acid-base disorders at the time of ICU admission and ICU or in-hospital death. Therefore, in our setting, acid-base disorders at the time of ICU admission should not be used to predict the outcome of patients requiring intensive care.