Adequacy of peritoneal dialysis.

The combined annual mortality and drop out rate for peritoneal dialysis (PD) patients is relatively uniform worldwide at approximately 35%. The level of PD therapy prescribed in clinical practice is largely empirical and typically consists of four 2-L exchanges daily. It might be speculated that the 35% annual attrition rate in PD may in part reflect under dialysis in some patients due to empirical rather than quantitative and individualized prescription of PD therapy. Urea kinetic modeling has been successfully used to quantitatively prescribe hemodialysis (HD) therapy and, in principle, it should be able to serve the same purpose in PD. Comparison of HD and PD is complicated, because peritoneal urea clearance is virtually continuous, while in HD clearance is provided only about 5% of the time and urea accumulates over 95% of each treatment cycle. The blood urea nitrogen (BUN) in PD (BUNpd) is essentially constant and reflects the steady state, while in HD a sawtooth BUN profile results that reflects the short intermittent dialyses. The HD BUN profile can be characterized by either the predialysis level (BUNo) or the time-averaged concentration (TAC) over each treatment cycle. TAC is substantially lower than BUNo due to the sharp obligatory decrease in BUN during each short high-clearance dialysis. The rate of clearance required in HD is approximately 30 times higher than in PD, and the total clearance (KT) required in HD is 50% higher than in PD to achieve BUNpd = BUNo (at identical normalized protein catabolic rate [NPCR]), which reflects the decreasing urea flux rate during HD due to the decreasing BUN.(ABSTRACT TRUNCATED AT 250 WORDS)