Background Hyponatremia is known to be associated with a worse patient outcome in heart failure. In cardiorenal syndrome (CRS), the prognostic role of concomitant hyponatremia is unclear. We sought to evaluate potential risk factors for hyponatremia in patients with CRS presenting with or without hyponatremia on hospital admission. Methods In a retrospective study, we investigated 262 CRS patients without sepsis admitted to the University Hospital Halle over a course of 4 years. CRS diagnosis was derived from an electronic search of concomitant diagnoses of acute or chronic (NYHA 3–4) heart failure and acute kidney injury (AKIN 1–3) or chronic kidney disease (KDIGO G3-G5nonD). A verification of CRS diagnosis was done based on patient records. Depending on the presence (Na < 135 mmol/L) or absence (Na ≥ 135 mmol/L) of hyponatremia on admission, the CRS patients were analyzed for comorbidities such as diabetes, presence of hypovolemia on admission, need for renal replacement therapy and prognostic factors such as in-hospital and one-year mortality. Results Two hundred sixty-two CRS patients were included in this study, thereof, 90 CRS patients (34.4%) with hyponatremia (Na < 135 mmol/L). The diabetes prevalence among CRS patients was high (> 65%) and not related to the serum sodium concentration on admission. In comparison to non-hyponatremic CRS patients, the hyponatremic patients had a lower serum osmolality, hypovolemia was more prevalent (41.1% versus 16.3%, p < 0.001). As possible causes of hypovolemia, diarrhea, a higher number of diuretic drug classes and higher diuretic dosages were found. Hyponatremic and non-hyponatremic CRS patients had a comparable need for renal-replacement therapy (36.7% versus 31.4%) during the hospital stay. However, after discharge, relatively more hyponatremic CRS patients on renal replacement therapy switched to a non-dialysis therapy regimen (50.0% versus 22.2%). Hyponatremic CRS patients showed a trend for a higher in-hospital mortality (15.6% versus 7.6%, p = 0.054), but no difference in the one-year mortality (43.3% versus 40.1%, p = 0.692). Conclusions All CRS patients showed a high prevalence of diabetes mellitus and a high one-year mortality. In comparison to non-hyponatremic CRS patients, hyponatremic ones were more likely to have hypovolemia, and had a higher likelihood for temporary renal replacement therapy.

Background Cardiorenal syndrome (CRS) defined as concurrent acute or chronic heart failure and acute or chronic kidney injury or disease frequently coincides with hyponatremia. We sought to identify potential risk factors for and outcome of hyponatremia in CRS. Methods In this retrospective study, CRS patients being consecutively hospitalized over 4 years (Department of Internal Medicine II, Martin-Luther University Halle-Wittenberg, Germany) were included. Depending on the presence or absence of hyponatremia on admission, they were analyzed for diabetes comorbidity, signs of hypovolemia on admission, need for renal replacement therapy during and after the hospital stay, in-hospital and one-year mortality. Results 262 CRS patients were included in this study, thereof, 90 CRS patients (34.4%) with hyponatremia (Na <135 mmol/L). The diabetes prevalence among CRS patients was high (>65%) and not related to the serum sodium concentration on admission. In comparison to non-hyponatremic CRS patients, the hyponatremic ones had a lower serum osmolality (293 versus 303 mosm/kg, p<0.001), and hypovolemia was more prevalent (41.1% versus 16.3%, p<0.001). As possible causes of hypovolemia, diarrhea, a higher number of diuretic drug classes and higher diuretic dosages were found. Hyponatremic and non-hyponatremic CRS patients had a comparable need for renal-replacement therapy (36.7% versus 31.4%) during the hospital stay. However, after discharge, relatively more hyponatremic CRS patients on renal replacement therapy switched to a non-dialysis, medical therapy regimen (50.0% versus 22.2%). Hyponatremic CRS patients showed a trend for a higher in-hospital mortality (15.6% versus 7.6%, p=0.054), but no difference in the one-year mortality (43.3% versus 40.1%, p=0.692). Conclusions All CRS patients showed a high prevalence of diabetes mellitus and a high one-year mortality. In comparison to non-hyponatremic CRS patients, hyponatremic ones were more likely to have hypovolemia, and had a higher likelihood to initiate a temporary, rather than chronic new renal replacement therapy.