A Quantitative Approach to the CAPD Prescription

Abstract

The CAPD prescription, expressed as daily drainage volume, can be formulated as a function of the recommended dietary protein intake and the average BUN level. This process is greatly simplified because urea nitrogen reaches a state of equilibrium on CAPD. The ratio of the actual drainage volume to this prescribed drainage volume -a dialysis index (Dl), reflects the fraction of urea nitrogen clearance achieved. Used with the average BUN level, the dialysis index provides an estimate of the protein catabolic rate (PCR), in gm/kg/day. When integrated these three factors -BUN, Dl and PCR, can be applied to optimize diet and dialysis and may provide a basis for comparing treatment results between patients and between centers. As continuous ambulatory peritoneal dialysis (CAPD) approaches its ninth anniversary, it continues to grow and to enjoy wide acceptance. Only a small minority continue to question its role in the care of end-stage renal disease patients. However, they ask fundamental questions which deserve our attention. Why is rate of hospitalization higher -peritonitis and access-related difficulties are only partially responsible (I). Does this technique's low urea nitrogen clearance provide adequate dialysis? Why do nearly 30% of patients leave CAPD programs within one year (2)? Are some CAPD patients under-dialyzed or malnourished? After nearly a decade of experience we have not answered these nagging questions and perhaps they cannot be answered. However, it is clear that they cannot be avoided. As Huxley cautioned, “Facts do not cease to exist because they are ignored.” An objective analysis of these issues raises the fundamental question, namely, the adequacy of dialysis -and adequacy compared to what?