Small solute clearance target as an index of adequacy of dialysis in peritoneal dialysis

Abstract

Peritoneal dialysis (PD) is an important renal replacement therapy for survival of patients with end-stage renal failure. In the 1980s and early 1990s, the standard PD regime was four 2-liter daily exchanges in the western world but was only three 2-liter exchanges in Hong Kong. One important dimension of dialysis is small solute clearance. The formula Kt/V (K = urea clearance, t = time = 1 week, V = volume of distribution of urea = total body water) is a popular index used to represent adequacy of dialysis in terms of small solute clearance. The finding of better patient survival with higher Kt/V in an observational study in North America had led to the recommendation of a target Kt/V of 2.0 for PD by the National Kidney Foundation of the USA in 1997.In this thesis, a series of studies were conducted to better define the adequacy of dialysis in terms of small solute clearance in a stepwise manner. We started with analyzing and comparing the survival of 507 patients received PD in Tung Wah Hospital from 1983-1994 and the Kt/V of the existing 201 PD patients to the western world. The mean Kt/V (1.76+0.36) was substantially lower than the western world, and yet patient survival was not inferior. This casted doubt on the Kt/V target recommended. We then analyzed the Kt/V, nutritional status and subsequent survival of 937 prevalent PD patients in nine hospitals in Hong Kong and found no correlation between Kt/V and nutritional status. Nutritional status predicted patient survival but Kt/V did not. Peritoneal Kt/V in the anuric patients was also not predictive of survival. A randomized control study was conducted in six hospitals from 1996 to 2000. 320 incident PD patients with renal Kt/V less than 1.0 were randomized into three different Kt/V targets: 1.5-<1.7, 1.7-2.0, >2.0. There was no difference in the 2-year patient survival and outcome between groups except that more patients in the lowest Kt/V group were withdrawn for clinical problems and required erythropoietin treatment, suggesting that they had inadequate dialysis. We concluded that the total Kt/V(renal + peritoneal)target should be at least 1.7. To define the peritoneal Kt/V target for anuric patients whose survival is dependent on peritoneal clearance, we retrospectively analyzed the relationship between peritoneal Kt/V and anuric patients’ survival counting from the time of documentation of anuria. We found that baseline peritoneal Kt/V less than 1.67 was associated with worse survival, and patients with peritoneal Kt/V above 1.7 throughout had better survival than those with Kt/V less than 1.7, whether it was corrected to above 1.7 subsequently or not. This suggested that anuric patients should have peritoneal Kt/V maintained above 1.7 at all times. These findings led to the revision or formation of several international guidelines on adequacy of peritoneal dialysis in 2005-6. All recommended Kt/V 1.7 or above being the treatment target, and the peritoneal Kt/V target should also be above 1.7 for anuric patients. These recommendations were subsequently adopted into different national guidelines and quality assurance programs.