New directions in peritoneal dialysis concepts and applications.

A limited number of peritoneal capillaries involved in solute exchange during peritoneal dialysis and inaccessible stagnant fluid films within the peritoneal interstitium may account for most resistance to solute transport during peritoneal dialysis. The control of small solute concentrations in blood by intermittent peritoneal dialysis will probably always require 30 to 40 hr/week of treatment even with the most rapid cycling devices. Increased understanding of factors that effect the microcirculation of the peritoneum may allow manipulation of protein losses and optimization of the long-term health of the peritoneum but will probably have little impact on the efficiency of small solute transport. CAPD accepts peritoneal dialysis as a low-efficiency system in terms of small solute clearances and yet yields similar weekly clearances to hemodialysis for small solutes by utilizing continuous dialysis. Large solute clearances with CAPD markedly exceed weekly clearances with hemodialysis.