Evaluating Hyponatremia in Non-Diabetic Uremic Patients on Peritoneal Dialysis

Abstract

Background An approach to hyponatremia in uremic patients on peritoneal dialysis (PD) necessitates the assessment of intra-cellular fluid volume (ICV) and extracellular volume (ECV). The aim of the study was to evaluate the association of plasma sodium (Na+) concentration and body fluid composition and identify the causes of hyponatremia in non-diabetic PD patients. Methods Sixty non-diabetic uremic patients on PD were enrolled. Baseline body fluid composition, biochemistry, hand-grip test, peritoneal membrane characteristics, dialysis adequacy, Na+ and water balance, and residual renal function (RRF) were measured. These parameters were reevaluated for those who developed hyponatremia, defined as serum Na+ concentration < 132 mmol/L and a decline in serum Na+ > 7 mmol/L, during monthly visits for 1 year. Body fluid composition was determined by multi-frequency bioelectrical impedance (BIA). Results There was no significant correlation between serum Na+ concentrations and any other parameters except a negative correction with overnight ultrafiltration (UF) amount ( p = 0.02). The ICV/ECV ratio was positively correlated with serum albumin ( p < 0.005) and hand grip strength ( p < 0.05). Over 1 year, 9 patients (M:F = 3:6, aged 35 – 77) with 4 different etiologies of hyponatremia were identified. Hyponatremic patients with a body weight (BW) loss had either an increased ICV/ECV ratio associated with primarily a negative Na+ balance ( n = 2) or a reduced ratio of ICV/ECV associated with malnutrition ( n = 2). In contrast, hyponatremic patients with a BW gain had either a reduced ICV/ECV ratio associated with a rapid loss of RRF and a higher peritoneal permeability ( n = 2) or a normal to increased ICV/ECV ratio associated with high water intake ( n = 3). Conclusion Besides BW change and ultrafiltration rate, the assessment of ICV/ECV ratio is valuable in identifying the etiologies of hyponatremia in PD and provides a guide for optimal therapy.