#3614 Is hyponatremia at the beginning of peritoneal dialysis relevant?

Abstract Background and Aims Hyponatremia is a common electrolyte disorder in patients undergoing peritoneal dialysis (PD). Hyponatremia has been identified as a poor prognostic factor and an independent mortality predictor, associated with fluid overload and weight gain. We aimed to analyze the impact of hyponatremia on mortality among PD patients. Methods A single-center retrospective study of incident PD patients treated at tertiary hospital between August 2015 to December 2024. We analyzed the demographic and epidemiologic data, along with baseline plasma sodium (Na) levels, adequacy and the results of the baseline peritoneal equilibration test (PET). Results We studied 154 incident PD patients (mean age 55.9 ± 14.7 years, 60.4% male, 93.5% with hypertension, and 26% with diabetes) mainly on automatized PD (79.2%) followed during a mean of 24.4 ± 18.5 months. Patients were divided according to plasma Na levels as normonatremic (Na >135 mEq/L) and hyponatremic (≤135 mEq/L). Hyponatremia was found in 20 patients (13%) with a mean plasma Na of 131 ± 4.5 mEq/L, while normonatremic patients presented a mean Na of 141.1 ± 2.6 mEq/L. Hyponatremic patients were older (63.2 ± 15.9 vs 54.86 ± 14.3 years, p 0.017), were also more frequently anuric at baseline (25% vs 8.2% p 0.022), and associated more comorbidities (Charlson index 6.8 ± 2.4 vs 5.6 ± 2.3, p 0.04) compared with normonatremic. Patients with hyponatremia underwent more frequently to continuous ambulatory (40% vs 17%, p 0.027) and assisted PD (25 vs 6%, p 0.004). Although total y renal KTV were similar in both groups, total baseline peritoneal KTV was significantly higher in hyponatremic patients (1.5 ± 1.8 vs 1.03 ± 0.4; p 0.01). Hyponatremic patients presented higher baseline peritoneal transport (41% vs 14, p 0.001), as well as higher sodium sieving (12.2 ± 7.7 vs 8.67 ± 6 mEq/L, p 0.04) and lower total ultrafiltration (428 ± 282 vs 667.3 ± 249 6 ml, <0.001) compared with normonatremic. The mortality rate in patients with hyponatremia was higher (n = 6, 30%) compared to normonatremic patients (n = 11, 8.2%) (p 0.004). No significant differences were found between those who discontinued the PD technique due to transfer to hemodialysis or kidney transplant, nor in the rate of peritonitis. Conclusions Baseline hyponatremia in patients undergoing peritoneal dialysis appear to be an early marker of poor prognosis. Patients with hyponatremia were older and more frail, which can explain its association with higher mortality. Hyponatremic patients presented higher baseline peritoneal transport, higher sodium sieving and lower total ultrafiltration compared with normonatremic patients. Further studies should explore the effectiveness of an early approach in PD patients with baseline hyponatremia.