The effect of ultra-low sodium dialysate in CAPD. A kinetic and clinical analysis

In peritoneal dialysis, sodium (Na) passes through the peritoneal membrane to a lesser extent than H2O and thus hypotonic fluid is removed indicating that Na removal is inefficient. Therefore we developed an ultra-low Na dialysate (ULNaD) [Na 98 mmol/liter, osmolality 340 mOsm/kg, glucose (G), 2.48%] to facilitate trans-peritoneal Na removal. The aim of the study was to examine (a) the fluid and Na kinetics of this solution, and (b) the clinical effect in the overhydrated patient. Regarding the former, in six cases, changes in the effluent Na levels during a 240-minute dwell of ULNaD were measured at 60-minute intervals. In eighteen cases, the transperitoneal net-Na removal (Na removal) and drained ultrafiltration (UF) volume after a 240-minute dwell of ULNaD were measured and compared to two types of standard Na dialysate (SNaD) [Na 132 mmol/liter, 1.36% G (348 mOsm/kg) and 2.27% G (396 mOsm/kg)]. The effluent Na levels increased gradually until the end of the dwelling. Drained UF volume of ULNaD (224 +/- 25 ml) was more than 1.36% G SNaD (77 +/- 33 ml, p < 0.01), but it was less than 2.27% G SNaD (341 +/- 32 ml, p < 0.01). However, a significant increase in Na removal by ULNaD (78.1 +/- 5.6 mmol) was found compared with both SNaD solutions (12.6 +/- 6.4 mmol in 1.36% G solution, p < 0.001; 27.8 +/- 5.1 mmol in 2.27% G solution, p < 0.001, respectively). Regarding the latter study aim, in six overhydrated patients with a Na excess, SNaD was replaced with ULNaD once a day for 7 consecutive days. At the end of the study as compared to the pre-values, a significant reduction in body weight (-2.5 +/- 1.0%, p < 0.05) and mean arterial pressure (-12.3 +/- 3.5%, p < 0.001) was observed. An increased drainage of daily UF volume (+86.5 +/- 31.1%, p < 0.05) and a markedly increased daily Na removal (+131.1 +/- 24.2%, p < 0.01) were also observed. The results of this study suggest that ULNaD actually facilitates trans-peritoneal Na removal mainly by diffusion force, and that ULNaD could benefit overhydrated patients with a Na excess.