Lower dialysate sodium ‘independently associated’ with mortality in adults on hemodialysis
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Key takeaways:
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Dialysate sodium of 138 mmol/L or lower was associated with higher mortality.
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Mortality risk was lower among patients exposed to higher dialysate sodium concentrations.
Dialysate sodium of 138 mmol/L or lower was associated with higher mortality. Source: Adobe Stock.
Lower dialysate sodium concentrations may be “independently associated” with higher mortality in patients on hemodialysis, according to a multinational retrospective study.
Jule Pinter, MD, of the department of medicine and nephrology division at the University Hospital Würzburg, Germany, and colleagues examined 68,196 patients from 875 Fresenius Medical Care Nephrocare clinics across 25 countries on in-center hemodialysis from 2010 to 2019.
The aim of the study was to assess whether dialysate sodium affects survival in patients hemodialysis after adjusting for plasma sodium concentrations.
“Abnormal fluid status and plasma sodium concentrations, which are common in patients [with chronic hemodialysis], are believed to be major risk factors for poor cardiovascular outcomes,” Pinter and colleagues wrote. “An alternative approach is to modulate sodium, fluid volume balance and tonicity in hemodialysis patients by acting on diffusive sodium clearance.”
On average, 138 mmol/L of dialysate sodium was prescribed in 63.2% of patients, 139 mmol/L in 15.8%, 140 mmol/L in 20.7% and other concentrations in 0.4%. Visits occurred three times a week, and 78.6% of clinical centers used a standardized concentration.
During a median follow-up of 40 months, a third of the patients died (n = 21,644). Results indicated dialysate sodium of 138 mmol/L or lower was associated with higher mortality after adjusting for plasma sodium concentrations and other patient confounders. Researchers also highlighted that the risk for death was lower among patients exposed to higher dialysate sodium concentrations, regardless of plasma sodium levels.
“These results challenge the prevailing assumption that lower dialysate sodium concentrations improve outcomes in hemodialysis patients,” Pinter and colleagues wrote. Nephrologists should “remain cautious in reconsideration of dialysate sodium prescribing practices to optimize cardiovascular outcomes and reduce mortality in this population.”
Perspective
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This observational study by Pinter and colleagues challenges the view held by many that the use of high sodium dialysate or modeling of dialysate sodium concentration, which achieves positive sodium balance during hemodialysis, is associated with poorer patient outcomes.
On the one hand, use of high sodium dialysate (>138 mEq/L) attenuates the transcellular fluid shifts during hemodialysis that can contribute to hypotension, muscle cramps and organ stunning. On the other hand, use of high sodium dialysate leads to high post-dialysis serum sodium levels, which increases thirst and fluid intake and intradialytic weight gain, which increases ultrafiltration (UF) requirements.
High rates of UF are associated with increased morbidity and mortality, leading to the use of UF rate as a metric in the Medicare Quality Incentive Payment program for dialysis. Since many patients on hemodialysis have marked increases in extracellular fluid and tissue sodium accumulation, some practitioners have used low dialysate sodium concentrations (<138 mEq/L) to achieve diffusive gradient-driven sodium removal during hemodialysis.
Mean dialysate sodium concentration in the international Dialysis Outcome and Practice Patterns Study (DOPPS) database decreased from 140.06 mEq/L in 1996-2001 to 138.9 mEq/L in 2015-2018. In another study examining international DOPPS data between 1996 and 2008, dialysate sodium concentration was not associated with serum sodium level. Lower mortality risk was observed with dialysate sodium prescription greater than 140 mEq/L among patients in the serum sodium tertile with the highest mortality (<137 mEq/L).
Similarly in the study by Pinter and colleagues, mortality risk associated with dialysate sodium of no more than 138 mEq/L increased compared with dialysate sodium greater than 138 mEq/L and appeared to be additive to the increase in mortality risk associated with lower serum sodium level.
Although the study could not rule out confounding by indication in the prescription of dialysate sodium concentration, it appeared to be driven more by regional customs than patient-specific variables. As an observational study, the findings by Pinter and colleagues do not demonstrate cause and effect and are hypothesis-generating. The mechanism for the decreased mortality among patients with dialysate sodium of at least 138 mEq/L are unclear as there are no data regarding hypotensive episodes or other intradialytic events.
Future studies might compare “one-size-fits-all” dialysate sodium prescription vs. an individualized dialysate sodium approach vs. an automated electrolyte balance approach. It remains unclear whether increased total body sodium or intradialytic hypotension is the greater threat to survival. Answering that question may also require an individualized patient approach.
Jay B. Wish, MD
Professor of clinical medicine
Indiana University School of Medicine
Chief medical officer for dialysis
Indiana University Health in Indianapolis
Chair of the Editorial Advisory Board
Healio | Nephrology News & Issues
References:
Hecking M, et al. Am J Kidney Dis. doi:10.1053/j.ajkd.2011.07.013.
Marshall MR, et al. Semin Dial. 2020; doi:10.1111/sdi.12906.
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