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

Abstract

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

Abbreviations

AG, anion gap; bpm, beats per minute; AKI, acute kidney injury; BNU, blood urea nitrogen; COPD, chronic obstructive pulmonary disease; CHF, congestive heart failure; CCI, Charlson Comorbidity Index; CI, confidence interval; CRRT, continuous renal replacement therapy; HR, heart rate; HR, hazard ratio; ICU, Intensive Care Unit; MIMIC, Medical Information Mart for Intensive Care; MBP, mean blood pressure; Q, quartile; RR, respiratory rate; Ref, reference; SOFA, sequential organ failure assessment; WBC, white blood cells.

Acknowledgment

We thank Jie Liu, PhD (Department of Vascular and Endovascular Surgery, Chinese PLA General Hospital) for his helpful comments regarding the manuscript.

Author Contributions

All authors made a significant contribution to the work reported, whether that is in the conception, study design, execution, acquisition of data, analysis and interpretation, or in all these areas; took part in drafting, revising or critically reviewing the article; gave final approval of the version to be published; have agreed on the journal to which the article has been submitted; and agree to be accountable for all aspects of the work.

Disclosure

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Additional information

Funding

This work was supported by the Non-profit Central Research Institute Fund of Chinese Academy of Medical Sciences (2019PT350001), National Natural Science Foundation of China (81960013), Science and Technology Program of Inner Mongolia (NeiCaiKe [2022] No.662), The central government guided local science and technology development fund project (ZYZ20200486).