Hyponatremia is an independent predictor of emergency department revisits in acute exacerbation of COPD

INTRODUCTION: Hyponatremia is shown to prolong hospitalization and increase mortality. The role of hyponatremia in chronic obstructive pulmonary disease is widely studied with a focus on hospitalized patients. OBJECTIVES: To investigate whether hyponatremia increases the probability of re-exacerbations in non-hospitalized patients with acute exacerbations of chronic obstructive pulmonary disease (AECOPD). METHODS: Patients with AECOPD who required an emergency department (ED) visit and who were discharged home were included in this single-center, retrospective study. Demographics and laboratory values were compared between patients with hyponatremia (<135 mmol/L) and normonatremia (135-145 mmol/L). The predictors of the patients' ED revisit in the course of one year were analyzed. RESULTS: Of all the 3274 patients, baseline sodium values were classified as hyponatremia in 720 (22%). Hyponatremia was most frequently present as mild (85%). Patients with hyponatremia had higher Charlson comorbidity scores, higher leucocytes, lower hemoglobin, lower platelet, higher neutrophil to lymphocyte ratios, lower eosinophilia, higher aspartate aminotransferase and C-reactive protein values (P < 0.001, for all), and higher frequency of 1-month revisit (36.7% vs. 31.5%, P = 0.009). Independent predictors of revisits within 1 year after the index visit were detected as long-term oxygen treatment requirement (HR: 0.768 CI: 0.695-0.848, P < 0.0001), higher urea levels (HR: 0.997 CI: 0.995-0.999, P = 0.003), and baseline hyponatremia (HR: 0.786 CI: 0.707-0.873, P < 0.001). Revisit interval was median 78 ± 3.4 days in patients with normonatremia and 51 ± 4.8 days in hyponatremia. CONCLUSION: In non-hospitalized AECOPD, hyponatremia is relatively frequent and correlates with inflammatory markers. The presence of hyponatremia is an independent predictor of an earlier ED return visit within 1 year. For patients with AECOPD, sodium values may present guidance on discharge versus longer observation decisions.