Severity of acidosis affects long-term survival in COPD patients with hypoxemia after intensive care unit discharge

Abstract

Background

Patients admitted to the intensive care unit (ICU) with acute respiratory failure (ARF) due to COPD have high mortality and morbidity. Acidosis has several harmful effects on hemodynamics and metabolism, and the current knowledge regarding the relationship between respiratory acidosis severity on the short- and long-term survival of COPD patients is limited. We hypothesized that COPD patients with severe acidosis would have a poorer short- and long-term prognosis compared with COPD patients with mild-to-moderate acidosis.

Patients and methods

This retrospective observational cohort study was conducted in a level III respiratory ICU of a tertiary teaching hospital for chest diseases between December 1, 2013, and December 30, 2014. Subject characteristics, comorbidities, ICU parameters, duration of mechanical ventilation, length of ICU stay, ICU mortality, use of domiciliary noninvasive mechanical ventilation (NIMV) and long-term oxygen therapy (LTOT), and short- and long-term mortality were recorded. Patients were grouped according to their arterial blood gas (ABG) values during ICU admission: severe acidotic (pH≤7.20) and mild-to-moderate acidotic (pH 7.21–7.35). These groups were compared with the recorded data. The mortality predictors were analyzed by logistic regression test in the ICU and the Cox regression test for long-term mortality predictors.

Results

During the study period, a total of 312 COPD patients admitted to the ICU with ARF, 69 (72.5% male) in the severe acidosis group and 243 (79% male) in the mild-to-moderate acidosis group, were enrolled. Group demographics, comorbidities, duration of mechanical ventilation, and length of ICU stay were similar in the two groups. The severe acidosis group had a significantly higher rate of NIMV failure (60.7% vs 40%) in the ICU. Mild-to-moderate acidotic COPD patients using LTOT had longer survival after ICU discharge than those without LTOT. On the other hand, severely acidotic COPD patients without LTOT showed shorter survival than those with LTOT. Kaplan–Meier cumulative survival analysis showed that the 28-day and 1-, 2-, and 3-year mortality rates were 12.2%, 36.2%, 52.6%, 63.3%, respectively (p=0.09). The Cox regression analyses showed that older age, PaO₂/FiO₂ <300 mmHg, and body mass index ≤20 kg/m² was associated with mortality of all patients after 3 years.

Conclusion

Severely acidotic COPD patients had a poorer short- and long-term prognosis compared with mild-to-moderate acidotic COPD patients if acute and chronic hypoxemia was predominant.

Keywords:

• COPD
• long term oxygen therapy
• non-invasive mechanical ventilation
• mortality
• acute respiratory failure

Acknowledgments

The authors thank Gokay Gungor, Ozlem Yazicioglu Mocin, Huriye Berk Takir, Cuneyt Salturk, and Nezihe Ciftaslan Goksenoglu for providing support for this study and Sharon Forsyth for editing the manuscript. The English in this document has been checked by at least two professional editors; both are native speakers of English (http://www.biomedicalediting.com). The manuscript has been read and approved by all the authors, and each author believes that the manuscript represents honest work.

Author contributions

All the authors have made substantial contributions to conception and design, or acquisition of data, or analysis and interpretation of data; they have been involved in drafting the manuscript or revising it critically for important intellectual content; and they approved the final version of the manuscript. SG contributed to conception and design, acquisition, analysis, interpretation of data, and drafting the submitted article and provided final approval of the version to be published. FK contributed to conception, interpretation of data, and critical revision of the submitted article for important intellectual content and provided final approval of the version to be published. II contributed to analysis, interpretation of data and provided final approval of the version to be published. FC contributed to conception, interpretation of data and provided final approval of the version to be published. ET contributed to conception, design, and critical revision of the submitted article for important intellectual content and provided final approval of the version to be published. PAG contributed to conception and interpretation of data and provided final approval of the version to be published. EA contributed to conception, design, analysis, and critical revision of the submitted article for important intellectual content and provided final approval of the version to be published. BO contributed to conception, design, interpretation of data, and critical revision of the submitted article for important intellectual content and provided final approval of the version to be published. NA contributed to conception, design, interpretation of data, and critical revision of the submitted article for important intellectual content and provided final approval of the version to be published. ZK contributed to analysis, interpretation of data, and critical revision of the submitted article for important intellectual content and provided final approval of the version to be published.

Disclosure

All the authors who contributed to the study do not have any industry relationships for the past 2 years. The authors report no other conflicts of interest in this work.