ULTRAFILTRATION AND SOLUTE KINETICS USING LOW-SODIUM PERITONEAL DIALYSATE

Low sodium peritoneal dialysate has been reported to enhance sodium lo ss and alleviate signs of fluid overload in continuous ambulatory peri toneal dialysis patients. To elucidate the mechanisms involved, we com pared ultrafiltration and solute kinetics using low sodium dialysate ( LNaD; 105 mEq/liter sodium, 2.5% glucose, 348 mOsm/liter), conventiona l dialysate with equal osmolality (CD1.5; 132 mEq/liter sodium, 1.5% g lucose, 348 mOsm/liter) and conventional dialysate with equal glucose concentration (CD2.5; 132 mEq/liter sodium, 2.5% glucose, 403 mOsm/lit er). A 2 liter, six hour exchange of each dialysate was performed on s eparate days in 10 chronic peritoneal dialysis patients. Transperitone al solute diffusion was assessed by calculating the permeability-area product (PA) of the peritoneal membrane from the dependence of plasma and dialysate solute concentrations on time. Net fluid removed using L NaD of 190 +/- 90 (SEM) ml was similar to that using CD2.5 (250 +/- 90 mi) but higher (P < 0.01) than that using CD1.5 (-200 +/- 60 ml). Sod ium loss was higher using LNaD (72 +/- 11 mEq, P < 0.01) and CD2.5 (41 +/- 12 mEq, P < 0.05) than using CD1.5 (-18 +/- 8 mEq). Changes in pl asma sodium concentration were small during each dwell and were not di fferent among the study dialysates. PA values for urea (123.4 +/- 1.6 ml/min), creatinine (10.0 +/- 1.0 ml/min), and glucose (10.3 +/- 1.3 m l/min) were similar when determined in each dialysate. The PA value fo r sodium (7.6 +/- 1.5 ml/min) could only be accurately determined in L NaD. We conclude that: (1) net fluid removed is greater using LNaD tha n CD1.5 despite similar osmolalities because LNaD has a higher glucose concentration and glucose is a more effective osmotic solute than sod ium; (2) sodium loss when using LNaD is enhanced by both diffusion and convection; and (3) sodium diffuses across the peritoneum slower than urea, creatinine: and glucose. These data suggest that LNaD alleviate s signs of fluid overload by increasing net fluid removal and enhancin g sodium loss.