Peritoneal Small Solute Clearance is Nonlinearly Related to Patient Survival in the Australian and New Zealand Peritoneal Dialysis Patient Populations

Abstract

Background The contribution of peritoneal small solute clearance per se to peritoneal dialysis (PD) patient outcomes remains uncertain. The aim of the present study was to determine whether baseline peritoneal small solute clearance predicted subsequent survival in Australian and New Zealand PD patients. Methods The study included all adult patients in Australia and New Zealand that commenced PD between 1 April 2002 and 31 December 2005 and had a peritoneal Kt/V (pKt/V) measurement performed within 6 months of PD commencement. Time to death and death-censored technique failure were examined by Kaplan–Meier analyses and both univariate and multivariate Cox proportional hazards models. Results pKt/V measurements were available in 2434 (63%) of the 3841 individuals that began PD treatment in Australia and New Zealand during the study period. These patients were divided into 4 groups according to their baseline pKt/V values: <1.45 ( n = 599), 1.45 – 1.69 ( n = 550), 1.70 – 2.00 ( n = 607), and >2.00 ( n = 678). Compared with the reference group (pKt/V 1.70 – 2.00), patient mortality was significantly increased in individuals with pKt/V <1.45 [adjusted hazard ratio (HR) 1.87, 95% confidence interval (CI) 1.24 – 2.84; p = 0.003] and tended to be increased in those with pKt/V 1.45 – 1.69 (adjusted HR 1.46, 95% CI 0.96 – 2.21; p = 0.074). Importantly, higher pKt/V values (>2.00) also tended to be associated with higher mortality (adjusted HR 1.42, 95% CI 0.96 – 2.11; p = 0.079). The other independent predictors of death were lower residual renal function (RRF), older age, peripheral vascular disease, diabetes mellitus, late referral, higher peritoneal permeability, and untreated hypertension. No interaction was observed between pKt/V, RRF, and survival. Death-censored technique failure was demonstrated to be significantly worse in the pKt/V 1.45 – 1.69 group (adjusted HR 1.36, 95% CI 1.03 – 1.79; p = 0.028), older individuals, and individuals with Asian racial origin. Conclusions Initial peritoneal Kt/V significantly and independently influences patient survival in Australian and New Zealand PD patients. Overall survival appears to be optimal in the pKt/V range 1.70 – 2.00, with poorer outcomes observed above and below these values. In particular, survival is significantly worse when the achieved pKt/V is <1.45. In addition, RRF is an important independent predictor of patient survival in the Australian and New Zealand incident PD patient populations. The results of this study should therefore draw attention to the possible danger of not delivering adequate PD dose to patients with considerable RRF.