BIDIRECTIONAL SOLUTE TRANSPORT IN PERITONEAL-DIALYSIS

Objective: Three transport components are involved in solute transport in peritoneal dialysis: diffusion, convective transport, and peritone al reabsorption of dialysate (fluid and solutes). The relative impact of these components on measurable transport characteristics (dialysate -to-plasma concentration ratio, diffusive mass transport coefficient, unidirectional clearances) may depend on the direction of sol ute tran sport, that is, from blood to dialysate or vice versa. The application of the bidirectional characteristics for the assessment of fluid and solute transport in peritoneal dialysis is reviewed and evaluated. Dat a Sources: Theoretical analysis as well as computer simulations were a pplied to discuss available data from our own studies on peritoneal tr ansport as well as from published clinical, experimental, and theoreti cal studies in the same field. Study Selection: Thirty-three relevant clinical and experimental studies as well as theoretical analyses deri ved from the literature were reviewed. Data Extraction: Data were extr acted to highlight current controversies in the literature concerning the assessment of peritoneal reabsorption rate based on transport of m acromolecules, middle molecules, and small solutes. Results: Peritonea l reabsorption is the main component of the transport of macromolecule s infused into the peritoneal cavity, and these solutes are currently being used for the assessment of the rate of reabsorption. in contrast , diffusive transport and peritoneal reabsorption cannot be experiment ally discriminated for small solutes which exhibit negligible sieving through the membrane in convective transport (i.e., solutes with sievi ng coefficient equal to 1). For middle molecules each transport compon ent may be of importance and may have an independent impact on bidirec tional transport characteristics. Conclusions: Middle molecules, with sieving coefficients substantially less than 1, may be applied for est imation of peritoneal reabsorption rate using bidirectional transport characteristics, as apparent diffusive mass transport coefficients or unidirectional clearances. However, an independent measurement of siev ing coefficient is necessary for this method.