Association between the anion gap and mortality in critically ill patients with influenza: A cohort study

Introduction: Influenza is an important global health concern, particularly in critically ill patients. The anion gap, a marker of metabolic acidosis, is associated with mortality in various critical illnesses. However, its association with mortality in critically ill patients with influenza remains unclear. This study investigated the association between the anion gap on admission and 28-day mortality in critically ill patients with influenza. Methods: A retrospective cohort study was conducted using data from MIMIC-IV database. Patients admitted to the intensive care unit (ICU) with influenza were included. The anion gap was measured within the first 24 h of ICU admission. The primary outcome was the 28-day mortality. The secondary outcomes were 60-day mortality and in-hospital mortality. Multivariable Cox regression was used to assess the association between the anion gap and mortality. Results: A total of 276 critically ill patients with influenza were included in the study. The mean age was 65 years, and 60 % were male. The overall 28-day mortality was 15.5 %. A greater anion gap on admission was associated with significantly increased 28-day mortality in the unadjusted analysis (hazard ratio [HR], 1.11; 95 % confidence interval [CI], 1.03-1.2; p < 0.001). The association remained significant after adjusting for age, sex, race, and illness severity (adjusted HR, 1.09; 95 % CI, 1.02-1.17; p = 0.017). Subgroup analysis showed consistent results across the different groups. Conclusion: A greater anion gap on admission was independently associated with increased 28-day mortality in critically ill patients with influenza. These findings suggest that the anion gap can be used as a prognostic marker in patients with influenza, aiding in risk stratification and guiding clinical management.