Impact of Hyponatraemia at Clinical Stable-State on Survival in Patients with Chronic Obstructive Pulmonary Disease.

Introduction: Hyponatraemia has been suggested to be associated with morbidity and mortality among various medical disorders. Evidence on the association between stable-state hyponatraemia and prognosis in patients with chronic obstructive pulmonary disease (COPD) is lacking. Methods: All COPD patients followed up in a regional hospital in year 2015 were included, with their clinical outcomes reviewed in the subsequent eight years. Association between stable-state hyponatraemia and mortality was evaluated. Stable-state hyponatraemia is defined as baseline serum sodium levels, at least 90 days away from the last AECOPD <135 mmol/L. Results: There were 271 COPD patients included. Hyponatraemia was associated with shorter overall survival with adjusted hazard ratio (aHR) 1.74 (95% CI = 1.07-2.65, p = 0.026). The median overall survival was 3.05 years (95% CI = 2.65-3.46) for patients in the hyponatraemia group, in contrast to 3.35 years (95% CI = 2.86-3.83) for those without hyponatraemia. The highest baseline serum sodium levels were significantly negatively associated with annual acute exacerbation of COPD (AECOPD) and annual hospitalized AECOPD frequency in the follow-up period, with Pearson correlation coefficient of -0.16 (p = 0.011) and - 0.14 (p = 0.027), respectively. Conclusion: Stable-state hyponatraemia was associated with increased mortality and probably AECOPD frequency among patients with COPD.