Relative contribution of residual renal function and peritoneal clearance to adequacy of dialysis: A reanalysis of the CANUSA study

Studies of the adequacy of peritoneal dialysis and recommendations have ass umed that renal and peritoneal clearances are comparable and therefore addi tive. The CANUSA data were reanalyzed in an effort to address this assumpti on. Among the 680 patients in the original CANUSA study, 601 had all of the variables of interest for this report. Adequacy of dialysis was estimated from GFR (mean of renal urea and creatinine clearance) and from peritoneal creatinine clearance. The Cox proportional-hazards model was used to evalua te the time-dependent association of these independent variables with patie nt survival. For each 5 L/wk per 1.73 m(2) increment in GFR, there was a 12 % decrease in the relative risk (RR) of death (RR, 0.88: 95% confidence int erval [CI], 0.83 to 0.94) but no association with peritoneal creatinine cle arance (RR, 1.00; 95% CI. 0.90 to 1.10). Estimates of fluid removal (24-h u rine volume, net peritoneal ultrafiltration, and total fluid removal) then were added to the Cox model. For a 250-ml increment in urine volume, there was a 36% decrease in the RR of death (RR, 0.64; 95% CI, 0.51 to 0.80). The association of patient survival with GFR disappeared (RR. 0.99; 95% CI, 0. 94 to 1.04). However. neither net peritoneal ultrafiltration nor total flui d removal was associated with patient survival. Although these results may be explained partly, statistically, by less variability in peritoneal clear ance than in GFR, the latter seems to be physiologically more important tha n the former. The assumption of equivalence of peritoneal and renal clearan ces is not supported by these data. Recommendations for adequate peritoneal dialysis need to be reevaluated in light of these observations.