Nocturnal Respiratory Rate Predicts 3-Year Mortality in Hemodialysis

BACKGROUND: Vital parameters such as respiratory rate are well-established predictors of mortality in emergency medicine. In hemodialysis patients, respiratory rate is influenced by multiple factors, including cardiovascular stress and impaired renal acid-base regulation. We hypothesized that higher respiratory rates in hemodialysis patients are associated with increased mortality. METHODS: In 364 hemodialysis patients from the ISAR cohort, a large prospective multicenter dialysis cohort, the mean nocturnal respiratory rate between 0 and 5 a.m. was derived from 24-hour Holter ECG recordings. Associations with all-cause and cardiovascular mortality at 3 and 6 years were assessed using univariate and multivariable Cox proportional hazards models, including non-linear spline modeling. RESULTS: Hemodialysis patients had a mean nocturnal respiratory rate of 20.2 breaths/minute. Individuals with higher respiratory rates were younger, had higher nocturnal heart rates, net ultrafiltration, levels of C-reactive protein, and interleukin-6. After 3 years, nocturnal respiratory rate showed a significant, U-shaped association with mortality in both univariate and multivariable analyses. Patients in the highest and lowest quartiles of respiratory rate had a 2.7-fold increased cardiovascular and a 1.4-fold increased all-cause 3-year mortality, compared to patients in the inner quartiles. The association with cardiovascular mortality was confirmed after multivariate adjustment, but was no longer apparent after 6 years. CONCLUSIONS: Hemodialysis patients exhibit a mean nocturnal respiratory rate above the physiological range, with a U-shaped association with three-year mortality. These findings may reflect increased cardiopulmonary demand in the hemodialysis population, and that nocturnal respiratory rate may provide valuable additional information for risk stratification.