Quantification of free water transport in peritoneal dialysis

Quantification of free water transport in peritoneal dialysis.BackgroundIn peritoneal dialysis (PD) total net ultrafiltration (NUF) is dependent on transport through small pores and through water channels in the peritoneum. These channels are impermeable to solutes, and therefore, crystalloid osmotic-induced free water transport occurs through them. Several indirect methods to assess free water transport have been suggested. The difference in NUF between a 3.86% and a 1.36% solution gives a rough indication, but is very time consuming. The magnitude of the dip in dialysate/plasma (D/P) sodium in the initial phase of a 3.86% exchange is another way to estimate free water transport. In the present study, a method was applied to calculate free water transport by calculating sodium-associated water transport in one single 3.86% glucose dwell.MethodsForty PD patients underwent one standard peritoneal permeability analysis (SPA) with a 1.36% glucose solution, and another with a 3.86% glucose solution. At different time points intraperitoneal volume and sodium concentration were assessed. This made it possible to calculate total sodium transport. By subtracting this transport (which must have occurred through the small pores) from the total fluid transport, free water transport remained. These results were compared with the other methods to estimate free water transport.ResultsFor the 1.36% glucose dwell, total transcapillary ultrafiltration in the first hour (TCUF0-60) was 164 mL, transport through the small pores was 129 mL, and free water transport was 35 mL (21%). For the 3.86% glucose solution, total TCUF0-60 was 404 mL, transport through the small pores was 269 mL, and free water transport was 135 mL (34%). The contribution of free water transport in the first minute (TCUF0-1) was 39% of the total fluid transport. From the 40 patients, 11 patients had ultrafiltration failure (NUF <400 mL after 4 hours). For these patients the contribution of free water to TCUF0-1 was significantly lower than for those with normal ultrafiltration (20% vs. 48%, P < 0.05). A strong correlation was present between free water transport as a percentage of total fluid transport and the maximum dip in D/P sodium (r = 0.84). The correlation was not significant with the difference in net ultrafiltration of 3.86% and 1.36% solutions (r = 0.24, P = 0.3).ConclusionThe method applied here is the first direct quantification of free water transport, calculated from a single standard peritoneal function test. It offers a quick possibility to evaluate patients suffering from ultrafiltration failure. In these patients free water transport was impaired, but the origin of this impairment is still to be determined

Augmenting solute clearance in peritoneal dialysis

Augmenting solute clearance in peritoneal dialysis.BackgroundThe removal of low molecular weight solutes by peritoneal dialysis is less than by hemodialysis. The targets for Kt/Vurea and creatinine clearance formulated in the Dialysis Outcome Quality Initiative are unlikely to be achieved in a substantial portion of peritoneal dialysis patients. Possibilities to increase small solute clearances have therefore been subject to many investigations.MethodsA review of the literature and of recent new data on determinants of solute removal, such as residual renal function, the role of drained dialysate volume and manipulation of the diffusive capacity of the peritoneum are presented.ResultsThe contribution of residual GFR is more important for the clearance of creatinine than for Kt/Vurea. It is even more important for the removal of organic acids that are removed from the body by tubular secretion. High dosages of furosemide increase the urinary volume and the fractional Na+ excretion, but have no effect on the magnitude of residual GFR, renal creatinine clearance, renal urea clearance, and peritoneal transport characteristics. The drained dialysate volume per day is the main determinant of the peritoneal removal of urea. Its effect decreases the higher the molecular weight of a solute. It can be augmented by using large instillation volumes, by the application of more exchanges, and by increasing peritoneal ultrafiltration. A large exchange volume is especially effective in patients with an average transport state, but in those with high solute transport rates, Kt/Vurea is especially influenced by the number of exchanges. Possibilities to increase ultrafiltration are discussed. The diffusive capacity of the peritoneum can be augmented by using low dosages of intraperitoneally administered nitroprusside. This increases solute transport most markedly when it is applied in combination with icodextrin as osmotic agent.ConclusionsSmall solutes clearances cannot be increased by furosemide. Increasing the instilled volume of dialysis fluid and the number of exchanges both affect solute clearance. Studies are necessary on long-term effects of manipulation of the peritoneal membrane with nitroprusside

Selection of modalities, prescription, and technical issues in children on peritoneal dialysis

Peritoneal dialysis (PD) is widely employed as a dialytic therapy for uraemic children, especially in its automated form (APD), that is associated with less burden of care on patient and family than continuous ambulatory PD. Since APD offers a wide range of treatment options, based on intermittent and continuous regimens, prescription can be individualized according to patient’s age, body size, residual renal function, nutritional intake, and growth-related metabolic needs. Transport capacity of the peritoneal membrane of each individual patient should be assessed, and regularly monitored, by means of standardized peritoneal function tests validated in pediatric patients. To ensure maximum recruitment of peritoneal exchange area, fill volume should be scaled to body surface area and adapted to each patient, according to clinical tolerance and intraperitoneal pressure. PD solutions should be employed according to their biocompatibility and potential ultrafiltration capacity; new pH-neutral, glucose-free solutions can be used in an integrated way in separate dwells, or by appropriately mixing during the same dialytic session. Kinetic modelling software programs may help in the tailoring of PD prescription to individual patients’ characteristics and needs. Owing to advances in the technology of new APD machines, greater programming flexibility, memorized delivery control, and tele-dialysis are currently possible

Analysis of ultrafiltration failure in peritoneal dialysis patients by means of standard peritoneal permeability analysis

BACKGROUND: Ultrafiltration failure (UFF) is a complication of peritoneal dialysis (PD) treatment that occurs especially in long-term patients. Etiological factors include a large effective peritoneal surface area [measured as high mass transfer area coefficient (MTAC) of creatinine], a high effective lymphatic absorption rate (ELAR), a large residual volume, or combinations. OBJECTIVE: The prevalence and etiology of UFF were studied and the contribution of transcellular water transport (TCWT) was analyzed. A new definition of UFF and guidelines for the analysis of its etiology were derived from the results. SETTING: Peritoneal dialysis unit in the Academic Medical Center in Amsterdam. DESIGN: Cross-sectional study of standard peritoneal permeability analyses (4-hr dwells, dextran 70 as volume marker) with 1.36% glucose in 68 PD patients. Patients with negative net UF (change in intraperitoneal volume, dIPV 5 mmol/L, indicating normal TCWT. The 3 patients with dNA 5 mmol/L group, but no differences were present for MTAC creatinine, ELAR, residual volume, or glucose absorption. CONCLUSIONS: In addition to known factors, impairment of TCWT can be a cause of UFF. A standardized dwell with 1.36% glucose overestimates UFF. Therefore, 3.86% glucose should be used for identification of patients with UFF, especially because it provides additional information on TCWT. Ultrafiltration failure can be defined as net UF < 400 mL/4 hr with 3.86% glucose during a 4-hour exchang

Restriction coefficients of low molecular weight solutes and macromolecules during peritoneal dialysis

The intrinsic permeability of the peritoneal membrane can be functionally represented by the restriction coefficient (RC). The RC can be calculated as the exponent of the power relation between the mass transfer area coefficients (MTACs) of various solutes and their free diffusion coefficients in water. When the RC = 1.0, transport is determined by free diffusion only, as is expected for low molecular weight (LMW) solutes. A RC > 1.0 suggests that transport is restricted by the peritoneal membrane in a size-selective way, as has been found previously for macromolecules (MM). RCLMW can be calculated using the MTACs of urea, creatinine, urate, and beta 2-microglobulin, whereas RCMM can be calculated from clearances of beta 2-microglobulin, albumin, IgG, and alpha 2-macroglobulin. RCLMW and RCMM were determined in 108 peritoneal dialysis (PD) patients. In 36 patients, 3 or more (range 3-13) observations for RCLMW during a period of at least 2 years were available. RCMM were analyzed when present in the same patients. The median cross sectional values (n = 108) were: RCLMW: 1.22 (range 0.75-2.18) and RCMM: 2.30 (range 1.86-3.27). RCLMW was not correlated with time on PD, neither cross sectionally (r = -0.07, NS) nor after analysis of trend (mean regression coefficient t = 0.26, SD = 0.07). For RCMM a positive correlation with duration of PD was demonstrated (cross sectionally r = -0.18, p = 0.02, analysis of trend: t = 2.27, SD = 0.11, n = 27). Both RCs were not interrelated (r = -0.18, NS). The absence of a relation between both RCs suggests that LMW solutes and MM are transported by different pathways. The mean value of 1.22 for the RCLMW illustrates that the transport of LMW solutes is mainly by free diffusion, through the small-pore system. MM, which have to pass through the large-pore system, are restricted by the peritoneal membrane in a size-selective way, as shown by the high value of the RCMM. The lack of a correlation between the RCLMW and duration of PD indicates that no systematic changes occur in the small pores of the peritoneal vessels. In contrast, the increase of RCMM with duration of PD suggests restrictive changes at the level of the large-pore syste

Quantification of free water transport in peritoneal dialysis

BACKGROUND: In peritoneal dialysis (PD) total net ultrafiltration (NUF) is dependent on transport through small pores and through water channels in the peritoneum. These channels are impermeable to solutes, and therefore, crystalloid osmotic-induced free water transport occurs through them. Several indirect methods to assess free water transport have been suggested. The difference in NUF between a 3.86% and a 1.36% solution gives a rough indication, but is very time consuming. The magnitude of the dip in dialysate/plasma (D/P) sodium in the initial phase of a 3.86% exchange is another way to estimate free water transport. In the present study, a method was applied to calculate free water transport by calculating sodium-associated water transport in one single 3.86% glucose dwell. METHODS: Forty PD patients underwent one standard peritoneal permeability analysis (SPA) with a 1.36% glucose solution, and another with a 3.86% glucose solution. At different time points intraperitoneal volume and sodium concentration were assessed. This made it possible to calculate total sodium transport. By subtracting this transport (which must have occurred through the small pores) from the total fluid transport, free water transport remained. These results were compared with the other methods to estimate free water transport. RESULTS: For the 1.36% glucose dwell, total transcapillary ultrafiltration in the first hour (TCUF(0-60)) was 164 mL, transport through the small pores was 129 mL, and free water transport was 35 mL (21%). For the 3.86% glucose solution, total TCUF(0-60) was 404 mL, transport through the small pores was 269 mL, and free water transport was 135 mL (34%). The contribution of free water transport in the first minute (TCUF(0-1)) was 39% of the total fluid transport. From the 40 patients, 11 patients had ultrafiltration failure (NUF <400 mL after 4 hours). For these patients the contribution of free water to TCUF(0-1) was significantly lower than for those with normal ultrafiltration (20% vs. 48%, P < 0.05). A strong correlation was present between free water transport as a percentage of total fluid transport and the maximum dip in D/P sodium (r= 0.84). The correlation was not significant with the difference in net ultrafiltration of 3.86% and 1.36% solutions (r= 0.24, P= 0.3). CONCLUSION: The method applied here is the first direct quantification of free water transport, calculated from a single standard peritoneal function test. It offers a quick possibility to evaluate patients suffering from ultrafiltration failure. In these patients free water transport was impaired, but the origin of this impairment is still to be determine