Low serum sodium levels are associated with a higher risk of death among adult patients on peritoneal dialysis (PD), independent of sociodemographic factors and comorbidities, according to a new study.

In this study, incrementally lower baseline and time-dependent serum sodium categories below 140 mEq/L were increasingly associated with higher death risk compared to a reference category of 140 to less than 142 mEq/L independent of case-mix covariates, lead investigator Connie M. Rhee, MD, MSc, of the University of California Irvine School of Medicine and colleagues reported in Nephrology Dialysis Transplantation. For example, in time-dependent analyses, sodium categories of 138-<140, 136-<138, 134-<136, and <134 mEq/L were associated with a 1.5-, 2.0-, 2.8-, and 4.1-fold higher death risk compared to the reference category.

The study included 4687 adult incident PD patients who underwent at least 1 serum sodium measurement within the first 3 months of dialysis.

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Dr Rhee’s team suggested a number of potential mechanisms by which low serum sodium may lead to greater mortality among PD patients. For example, they noted that severe hyponatremia may be directly toxic to the brain, resulting in cerebral edema and herniation, encephalopathy, seizure, and coma. In addition, emerging data suggest that hyponatremia leads to derangements in cardiac conduction and function as a result of inhibition of calcium channel circuits. The investigators also cited research showing that hyponatremia is a risk factor for worse outcomes in patients with PD-related peritonitis and infection-related mortality risk in PD patients.

The researchers acknowledged the study’s limitations. Patients were required to have at least 1 serum sodium value, “and while the indications for which sodium measurement within the study population cannot be ascertained, this was likely at the discretion of medical providers.” The investigators also pointed out that although they adjusted for a large number of confounders, they were unable to account for certain dietary factors (such as sodium, potassium, and fluid intake) and PD treatment characteristics (such as use of icodextrin vs glucose-based PD solutions).

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