UC study: Fixing heart failure patients' blood sodium levels may be harmful

Researchers from the University of Cincinnati (UC) Division of Nephrology, Kidney CARE Program found that correcting hyponatremia—low levels of sodium in the blood—to near-normal sodium levels may be harmful in heart failure patients. The results come from a multi-center study of over 106,000 patients admitted to acute care facilities with a primary diagnosis of heart failure. Hyponatremia is a serious in-hospital complication and particularly common among heart failure patients.

"Hyponatremia is a part and parcel of pathophysiology of heart failure, and although we may be treating heart failure, we have to be cautious in how we titrate our therapies in optimally correcting serum sodium levels in these patients,” says Charuhas Thakar, MD, professor and director of the UC Division of Nephrology Kidney CARE Program at the UC College of Medicine.

Overall, five percent of heart failure patients were admitted with severe hyponatremia, which is defined as sodium levels lower than 130 milliequivalents per liter (mEq/L). An additional 13 percent had less severe hyponatremia (sodium levels 130 to 134 mEq/L), while 41 percent of patients had low-normal sodium levels (135 to 139 mEq/L), 36 percent were normal (140 to 144 mEq/L), and 5 percent were hypernatremic (sodium levels greater than or equal to 145 mEq/L).

The study found a relationship between sodium levels and in-hospital mortality in heart failure patients. The overall mortality was four percent, while in patients with severe hyponatremia, it was twice as high at eight percent.

"In addition to admission level of sodium in heart failure patients, admission level of renal function, measured as serum creatinine, also independently predicted risk of death,” says Thakar. "A similar qualitative relationship also existed in predicting the risk of 30-day readmissions in heart failure patients.”

The study was one of the first to also examine sodium levels when the patients were discharged from the hospital and compare the progression of patients for its predictive significance. Patients with severe hyponatremia upon admission (<130 mEq/L) experienced the lowest mortality rate at 7.8 percent when their discharge sodium levels were 135 to 139 mEq/L. Contrary to the prevalent notion, correcting sodium levels to the "normal” range (140 to 144 mEq/L) posed harm in severe hyponatremic patients who had a mortality rate of 15.7 percent.

"The study does not allow us to draw conclusions on a causal relationship,” says Thakar. "Several factors and treatment strategies could have determined the sodium levels, and the study is subject to unmeasured confounders. However, this is among the largest multi-center cohort examining the impact of sodium levels and renal function in heart failure patients admitted to acute care.”

Thakar and co-authors will present these findings at the American Society of Nephrology meetings in San Diego on Oct. 26, 2018. The study is co-authored by Masaaki Yamada, transplant fellow and Silvi Shah, MD, assistant professor in the Division of Nephrology, and Karthik Meganathan, and Annette Christianson both research associates in the Center for Health Informatics and Anthony Leonard, PhD, adjunct associate professor in the Department of Family and Community Medicine, all in the UC College of Medicine. The study was supported in part by an investigator-initiated grant by Otsuka Pharmaceuticals.