SIMPLE-MODELS FOR FLUID TRANSPORT DURING PERITONEAL-DIALYSIS

Peritoneal fluid transport can be predicted using different simplified formulas. To evaluate three such models, fluid transport was studied in 38 single six hour dwell studies using standard glucose 1.36% (n=9) , 2.27% (n=9) and 3.86% (n=20) dialysis fluids as well as amino acid 2 .70% fluid (n=8) in 33 patients on continuous ambulatory peritoneal di alysis (GAPD). Dialysate volume and the peritoneal absorption rate wer e measured using radioiodinated serum albumin (RISA) as a marker. The dialysate volume over dwell time curves were examined using three math ematical models of fluid transport for solutions with a crystalloid os motic agent: Model P based on phenomenologically derived exponential f unction of time (Pyle, 1981), Model OS based on linear relationship be tween the rate of net volume change, Qv, to the difference of osmolali ty in dialysate and blood, and Model G based on linear relationship be tween Qv and the difference of glucose concentration in dialysate and blood. All these models provided a good description of the measured di alysate volume over time curves, however the descriptions with Models OS and G for glucose 3.86% fluid were slightly but significantly less precise. The coefficients of Model:OS were stable in time, but the coe fficients of Model G and P dependend in general on the time period use d for their estimation, especially for glucose 3.86% dialysis fluid. T he evaluation of dwell studies with solutions containing amino acid 2. 70% (instead of glucose) as osmotic agent, using Model OS and P showed that the transport coefficients were stable in time and both models p rovided equally precise descriptions. These results suggested that all three models can be used but models P and OS can be preferred for pra ctical applications such as predictions of fluid transport with altern ative cristalloid osmotic agents. Furthermore, we found that the perit oneal barrier for fluid transport may change transiently during exchan ges with the standard glucose - based dialysis fluid, whereas such cha nges were not observed with the amino acid-based fluid. This discrepan cy may be due to a different composition of the dialysis fluids, inclu ding osmotic agent, buffer and pH.