Peritoneal Mass Transfer

relates to solute transport, is the overall mass transfer coefficient (MTC) .To some clinicians this term may sound as if it is not connected to clinical reality. In fact, it is of fundamental importance because it is the maximum achievable clearance, without the effect of ultrafiltration. Clearly, the latter can enhance clearance by solute-solvent coupling due to convection. However, to determine the capacity of a given peritoneum to remove solutes, be they drugs, waste metabolites or whatever, one would need to know the peritoneal MTC. Furthermore, serial measurements of the MTC provide the most accurate indicator of variations in the permeability of the peritoneum. Even a rapid clearance measurement ( 45 minutes ) would only provide a rough indication of changes in peritoneal permeability because even if adhesions were causing peritoneal area loss, or if fibrosis of the peritoneum was leading to peritoneal thickening, the reduction in diffusive capacity of the peritoneum is likely to be balanced by an improved convective removal of solute. The explanation is simple. A reduction in peritoneal MTC affects both outgoing (e.g. urea, creatinine) and ingoing (e.g. glucose) solutes in the same way. A reduction in the diffusive capacity for, say, urea means that the diffusion of glucose into the blood must also be compromised. As a consequence, for any given dialysate, there will be greater ultrafiltration due to the retention of glucose within the peritoneal cavity. The net result is improved convective solute removal overcoming, to a greater or lesser degree, the reduction in the peritoneum's diffusive mass transfer. In brief , the only way to be sure about subtle (as opposed to gross) changes in the peritoneum is to determine the mass transfer coefficient. Various models of peritoneal mass transfer have been proposed ( 1-4) none of which are perfect but all of which, if correctly applied under appropriate exper