Opinion: How Much Peritoneal Dialysis is Needed for Optimal Outcomes?

The results of the Adequacy of Peritoneal Dialysis in Mexico (ADEMEX) trial bring into question the current U.S. guidelines for adequacy, which state that the minimum target weeklyKt/V for continuous ambulatory peritoneal dialysis (CAPD) patients should be 2.0 (1). In this trial, CAPD patients with a mean total weekly Kt/V of 2.27 had patient and technique survival equivalent to that of patients with a mean totalKt/Vof 1.80; peritoneal small molecule clearances bore no relationship to survival. This very well done study must be contrasted with the observational study from Hong Kong of anuric CAPD patients—which did show a relationship of peritoneal clearance with patient and technique survival (2). A comparison of the two studies is shown in Table 1. The patients in the Hong Kong and Mexican studies were quite similar in respect to size, initial albumin, and follow-up. Both studies excluded patients at high risk for death. The Mexican study had more patients with diabetes, but excluded patients with preexisting congestive heart failure (CHF)—patients who were not excluded in the Hong Kong study. An examination of the prescription and average small molecule clearances of the two studies gives us some important clues for the different results. The usual CAPD prescription for the anuric Chinese patients was 2 L three times a day, with an increase only for volume overload, resulting in an average daily dialysate volume of 7.4, and a meanKt/Vof 1.72 per week at time zero and 1.73 after 2 years follow-up (Table 1). Therefore it appears likely that approximately half of the patients were below 1.72 and half above. This then is a study of considerably lower clearances than are seen in either the Canada-USA (CANUSA) trial or in ADEMEX, where the standard prescription was 8 L/day. Peritoneal clearance was significant in the Hong Kong study because the range of clearances of these patients was much lower than seen in the other studies. Using a Cox proportional hazards model that included age at enrollment, gender, previous dialysis duration, presence or absence of diabetes, hepatitis B status, cardiovascular disease, and nutritional markers, an increase of 0.2 Kt/V per week resulted in a 6% decreased risk of death (confidence interval [CI] 1⁄4 0.92, 0.99). This study is important because it examined patients without the confounding effects of residual renal function, lower levels of peritoneal clearance than is generally accepted in the United States and Canada, and very limited indications for either an increase in the prescription or transfer to hemodialysis (HD) for cost reasons. The results indicate that peritoneal dialysis (PD) dose does have an effect on outcome. Optimal dialysis includes not only survival, but sufficient dialysis for the patient to feel well, without nausea, anorexia, fatigue, sleeplessness, or difficulty concentrating. The well-dialyzed patient should be functional, have a good quality of life, with few or no hospitalizations. In the Hong Kong study, nine (6.4%) of the anuric patients were transferred to HD for symptomatic inadequate dialysis (Table 1). In the ADEMEX trial, 5% of patients (n 1⁄4 24) in the control arm (2 L four times a day) dropped out due to uremia, compared to zero in the treated higher-dose group whose total Kt/V was 2.27 (p < 0.01). A 5% dropout rate due to uremia indicates that for some patients a prescription of 2 L four times a day is not enough, which in this study represented a total Kt/V (including residual renal function) of 1.8.