Association Between Serum Anion Gap and Mortality in Critically Ill Patients with COPD in ICU: Data from the MIMIC IV Database

Background: Serum anion gap (AG) has been proven to be associated with prognosis in critically ill patients. However, few studies have investigated the association between AG and all-cause mortality in critically ill patients with chronic obstructive pulmonary disease (COPD). Objective: We hypothesized that the initial AG level would predict the mortality risk in critically ill patients with COPD. Methods: This retrospective cohort study was based on the Medical Information Mart for Intensive Care (MIMIC) IV database. We extracted demographics, vital signs, laboratory tests, comorbidity, and scoring systems from the first 24 hours after patient ICU admission. Multivariable logistic regression analysis models were used to explore the association between serum AG levels and mortality. Interaction and stratified analyses were conducted including age, gender and comorbidity. Results: A total of 5531 critically ill patients with COPD were enrolled, composed of 53.6% male and 46.4% female with a median age of 73 years. The all-cause mortality of these patients during ICU hospitalization was 13.7%. The risk of all-cause mortality increased as the AG level increased in the univariate logistic regression analysis (OR=1.13, 95% CI: 1.11– 1.15, p< 0.01). After adjusting for all the covariates in multivariate logistic regression analysis, the odds ratio was 1.06 (95% CI: 1.04– 1.09, p< 0.01). Compared with the lowest AG group Q1 (≤ 11mmol/L), the adjusted OR value for AG and mortality in Q2 (12– 13mmol/L) was 0.89 (95% CI: 0.63– 1.25, p=0.502), Q3 (14– 15mmol/L) was 0.95 (95% CI: 0.68– 1.34, p=0.788), and Q4 (≥ 16mmol/L) was 1.49 (95% CI: 1.10– 2.02, p=0.009) respectively. In addition, the results of the subgroup and stratified analyses were robust. Conclusion: AG is positively related to all-cause mortality in critically ill patients with COPD. Keywords: AG, COPD, mortality, MIMIC IV