Evidence for the Benefit of Rrf in Dialysis Patients

Residual renal function not only provides small-solute clearance, but also plays an important role in maintaining fluid balance, phosphorus control, and removal of middle-molecular uremic toxins and shows strong inverse relationships with valvular calcification and cardiac hypertrophy in dialysis patients. The original CANUSA study, in which total (peritoneal and renal) small-solute clearance significantly predicted mortality, resulted in the assumption that peritoneal small-solute clearance must be important (1). However, a reanalysis of CANUSA by Bargman et al. (2), who compared renal small-solute clearance with volume of urine, found that peritoneal clearance lost statistical significance. Each increment of 5 L/1.73 m2 per week in residual kidney glomerular filtration rate (GFR) was associated with a 12% reduction in the relative risk (RR) of death, but no similar association with peritoneal creatinine clearance was found. Every 250 mL of urine output daily showed a 36% reduction in mortality. The ADEMEX study, a prospective randomized trial evaluating the effects of increased peritoneal small-solute clearances in 965 prevalent patients, showed no survival advantage for patients with an increase in peritoneal clearance, even when the data were adjusted for age, nutrition, and comorbidity. For each 10 L/ 1.73 m2 weekly increment in RRF, an 11% decrease in the RR of death was observed; no similar association with peritoneal creatinine clearance was found (3). The Netherlands Cooperative Study on the Adequacy of Dialysis (NECOSAD)—a prospective, multicenter, observational cohort study of incident dialysis patients— analyzed 740 HD patients and showed that RRF and delivered Kt/V were both positively associated with better survival (4). Each weekly increase of 1 unit in renal Kt/V was associated with a RR for death of 0.44, and each increase in delivered Kt/V was associated with a RR for death of 0.76. However, the effect of delivered Kt/V on mortality was strongly dependent on the presence of RRF. The effect of RRF appeared to be stronger than the effect of delivered Kt/V.