**2. Material and methods**

A retrospective analysis of medical records of inpatient patients with acute COPD who were admitted to the therapeutic department of one of the multidisciplinary hospitals in Kazan from January 1, 2015 to December 31, 2018 was conducted.

Statistical data processing was performed using the SPSS Statistical programs. The data obtained are presented in the form of M ± σ and in the form of frequency (for absolute values). To assess the significance of differences, Pearson's *t*-test method was used. The differences were considered significant at *p* < 0.05. To assess the risk factors for frequent hospitalizations, we calculated absolute and relative risk (RR) with a 95% confidence interval (CI) at *p* < 0.05.
