The standard peritoneal permeability analysis: a tool for the assessment of peritoneal permeability characteristics in CAPD patients

Peritoneal equilibration testing: Your questions answered

The peritoneal equilibration test (PET), first described in 1987, is a semiquantitative assessment of peritoneal transfer characteristics in patients undergoing peritoneal dialysis. It is typically performed as a 4-h exchange using 2.27/2.5% dextrose dialysate with serial measurements of blood and dialysate creatinine, urea, and glucose concentrations. The percentage absorption of glucose and D/P creatinine ratio are used to determine peritoneal solute transfer rates. It is used to both help guide peritoneal dialysis prescriptions and to prognosticate. There are several derivative tests which have been described in the literature. In this review, we describe the original PET, the various iterations of the PET, the information gleaned, and the use in the setting of poor solute clearance and in the diagnosis of membrane dysfunction, and limitations of the PET.

Mass Spectrometry-Based Evaluation of the Bland-Altman Approach: Review, Discussion, and Proposal

Reliable quantification in biological systems of endogenous low- and high-molecular substances, drugs and their metabolites, is of particular importance in diagnosis and therapy, and in basic and clinical research. The analytical characteristics of analytical approaches have many differences, including in core features such as accuracy, precision, specificity, and limits of detection (LOD) and quantitation (LOQ). Several different mathematic approaches were developed and used for the comparison of two analytical methods applied to the same chemical compound in the same biological sample. Generally, comparisons of results obtained by two analytical methods yields different quantitative results. Yet, which mathematical approach gives the most reliable results? Which mathematical approach is best suited to demonstrate agreement between the methods, or the superiority of an analytical method A over analytical method B? The simplest and most frequently used method of comparison is the linear regression analysis of data observed by method A (y) and the data observed by method B (x): y = α + βx. In 1986, Bland and Altman indicated that linear regression analysis, notably the use of the correlation coefficient, is inappropriate for method-comparison. Instead, Bland and Altman have suggested an alternative approach, which is generally known as the Bland-Altman approach. Originally, this method of comparison was applied in medicine, for instance, to measure blood pressure by two devices. The Bland-Altman approach was rapidly adapted in analytical chemistry and in clinical chemistry. To date, the approach suggested by Bland-Altman approach is one of the most widely used mathematical approaches for method-comparison. With about 37,000 citations, the original paper published in the journal The Lancet in 1986 is among the most frequently cited scientific papers in this area to date. Nevertheless, the Bland-Altman approach has not been really set on a quantitative basis. No criteria have been proposed thus far, in which the Bland-Altman approach can form the basis on which analytical agreement or the better analytical method can be demonstrated. In this article, the Bland-Altman approach is re-valuated from a quantitative bioanalytical perspective, and an attempt is made to propose acceptance criteria. For this purpose, different analytical methods were compared with Gold Standard analytical methods based on mass spectrometry (MS) and tandem mass spectrometry (MS/MS), i.e., GC-MS, GC-MS/MS, LC-MS and LC-MS/MS. Other chromatographic and non-chromatographic methods were also considered. The results for several different endogenous substances, including nitrate, anandamide, homoarginine, creatinine and malondialdehyde in human plasma, serum and urine are discussed. In addition to the Bland-Altman approach, linear regression analysis and the Oldham-Eksborg method-comparison approaches were used and compared. Special emphasis was given to the relation of difference and mean in the Bland-Altman approach. Currently available guidelines for method validation were also considered. Acceptance criteria for method agreement were proposed, including the slope and correlation coefficient in linear regression, and the coefficient of variation for the percentage difference in the Bland-Altman and Oldham-Eksborg approaches.

Modelling of icodextrin hydrolysis and kinetics during peritoneal dialysis

In peritoneal dialysis, ultrafiltration is achieved by adding an osmotic agent into the dialysis fluid. During an exchange with icodextrin-based solution, polysaccharide chains are degraded by α-amylase activity in dialysate, influencing its osmotic properties. We modelled water and solute removal taking into account degradation by α-amylase and absorption of icodextrin from the peritoneal cavity. Data from 16 h dwells with icodextrin-based solution in 11 patients (3 icodextrin-exposed, 8 icodextrin-naïve at the start of the study) on dialysate volume, dialysate concentrations of glucose, urea, creatinine and α-amylase, and dialysate and blood concentrations of seven molecular weight fractions of icodextrin were analysed. The three-pore model was extended to describe hydrolysis of icodextrin by α-amylase. The extended model accurately predicted kinetics of ultrafiltration, small solutes and icodextrin fractions in dialysate, indicating differences in degradation kinetics between icodextrin-naïve and icodextrin-exposed patients. In addition, the model provided information on the patterns of icodextrin degradation caused by α-amylase. Modelling of icodextrin kinetics using an extended three-pore model that takes into account absorption of icodextrin and changes in α-amylase activity in the dialysate provided accurate description of peritoneal transport and information on patterns of icodextrin hydrolysis during long icodextrin dwells.

Factors related to ultrafiltration volume with icodextrin dialysate use in children

BACKGROUND

Icodextrin has a lower absorption rate, and icodextrin peritoneal dialysate contributes to more water removal than glucose dialysate in patients with high peritoneal permeability. There are limited data on icodextrin dialysate use in children.

METHODS

This study included all pediatric patients who received peritoneal equilibration tests and peritoneal dialysis with icodextrin dialysate at the study center. The factors related to ultrafiltration volume with icodextrin dialysate with long dwell time were statistically analyzed. Then the ultrafiltration volume with icodextrin and medium-concentration glucose dialysate was compared in individual cycles in the same patients.

RESULTS

Thirty-six samples were included in the icodextrin group, and nine samples were used to compare the ultrafiltration volume with icodextrin and glucose dialysate. Dwell time, D/P-creatinine, D/D₀-glucose, age, height, and weight correlated significantly with the ultrafiltration volume of icodextrin dialysate (p < 0.05). A dwell volume equal to or more than 550 mL/m² was associated with a significantly higher ultrafiltration volume than a lower dwell volume (p = 0.039). Multiple regression analysis revealed that dwell time (p = 0.038) and height (p < 0.01) correlated with ultrafiltration volume significantly. In addition, the ultrafiltration volume was superior (p < 0.01), and dwell time was longer (p = 0.02), with icodextrin dialysate than with medium-concentration glucose dialysate.

CONCLUSIONS

The ultrafiltration volume with icodextrin dialysate decreases in patients with small stature. Providing sufficient dwell time and volume is important for maximal water removal even in children. Ultrafiltration volume is superior with icodextrin than medium-concentration glucose dialysate for long dwell times. A higher resolution version of the Graphical abstract is available as Supplementary information.

A Uremic Pig Model for Peritoneal Dialysis

With increasing interest in home dialysis, there is a need for a translational uremic large animal model to evaluate technical innovations in peritoneal dialysis (PD). To this end, we developed a porcine model with kidney failure. Stable chronic kidney injury was induced by bilateral subtotal renal artery embolization. Before applying PD, temporary aggravation of uremia was induced by administration of gentamicin (10 mg/kg i.v. twice daily for 7 days), to obtain uremic solute levels within the range of those of dialysis patients. Peritoneal transport was assessed using a standard peritoneal permeability assessment (SPA). After embolization, urea and creatinine concentrations transiently increased from 1.6 ± 0.3 to 7.5 ± 1.2 mM and from 103 ± 14 to 338 ± 67 µM, respectively, followed by stabilization within 1–2 weeks to 2.5 ± 1.1 mM and 174 ± 28 µM, respectively. Gentamicin induced temporary acute-on-chronic kidney injury with peak urea and creatinine concentrations of 16.7 ± 5.3 mM and 932 ± 470 µM respectively. PD was successfully applied, although frequently complicated by peritonitis. SPA showed a low transport status (D/P creatinine at 4 h of 0.41 (0.36–0.53)) with a mass transfer area coefficient of 9.6 ± 3.1, 4.6 ± 2.6, 3.4 ± 2.3 mL/min for urea, creatinine, and phosphate respectively. In conclusion, this porcine model with on-demand aggravation of uremia is suitable for PD albeit with peritoneal transport characterized by a low transport status.

The Peritoneal Membrane—A Potential Mediator of Fibrosis and Inflammation among Heart Failure Patients on Peritoneal Dialysis

Peritoneal dialysis is a feasible, cost-effective, home-based treatment of renal replacement therapy, based on the dialytic properties of the peritoneal membrane. As compared with hemodialysis, peritoneal dialysis is cheaper, survival rate is similar, residual kidney function is better preserved, fluid and solutes are removed more gradually and continuously leading to minimal impact on hemodynamics, and risks related to a vascular access are avoided. Those features of peritoneal dialysis are useful to treat refractory congestive heart failure patients with fluid overload. It was shown that in such patients, peritoneal dialysis improves functional status and quality of life, reduces hospitalization rate, and may decrease mortality rate. High levels of serum proinflammatory cytokines and fibrosis markers, among other factors, play an important part in congestive heart failure pathogenesis and progression. We demonstrated that those levels decreased following peritoneal dialysis treatment in refractory congestive heart failure patients. The exact mechanism of beneficial effect of peritoneal dialysis in refractory congestive heart failure is currently unknown. Maintenance of fluid balance, leading to resetting of neurohumoral activation towards a more physiological condition, reduced remodeling due to the decrease in mechanical pressure on the heart, decreased inflammatory cytokine levels and oxidative stress, and a potential impact on uremic toxins could play a role in this regard. In this paper, we describe the unique characteristics of the peritoneal membrane, principals of peritoneal dialysis and its role in heart failure patients.

Baseline Peritoneal Membrane Transport Characteristics Are Associated with Peritonitis Risk in Incident Peritoneal Dialysis Patients

The peritoneal equilibration test (PET) is a semi-quantitative measurement that characterizes the rate of transfer of solutes and the water transfer rate across the peritoneum in patients treated with peritoneal dialysis (PD). The results of the PET are used to maximize daily peritoneal ultrafiltration and solute clearances. Previous studies have shown that high transport status is associated with ultrafiltration failure, malnutrition, and reduced survival; however, the way in which peritoneum transport characteristics affect peritonitis risk is unknown. In the current cohort study, we recruited 898 incident-PD patients and used intention-to-treat analysis to test if baseline PET affected the subsequent 3-year peritonitis rate. Among all recruited PD patients, 308 (34.2%) developed peritonitis within three years. Multivariate Cox regression analysis showed that the high-transport group has the greatest peritonitis risk (HR 1.98, 95% CI: 1.08-3.62) even after an adjustment for demographics, comorbid diseases, and biochemical measurements. We concluded that a baseline high peritoneal membrane transport rate is an independent risk factor for peritonitis in incident PD patients.

Assessment of the size selectivity of peritoneal permeability by the restriction coefficient to protein transport

Transport of serum proteins from the circulation to peritoneal dialysate in peritoneal dialysis patients mainly focused on total protein. Individual proteins have hardly been studied. We determined serum and effluent concentrations of four individual proteins with a wide molecular weight range routinely in the standardised peritoneal permeability analysis performed yearly in all participating patients. These include β2-microglobulin, albumin, immunoglobulin G and α2-macroglobulin. The dependency of transport of these proteins on their molecular weight and diffusion coefficient led to the development of the peritoneal protein restriction coefficient (PPRC), which is the slope of the relation between the peritoneal clearances of these proteins and their free diffusion coefficients in water, when plotted on a double logarithmic scale. The higher the PPRC, the more size restriction to transport. In this review, we discuss the results obtained on the PPRC under various conditions, such as effects of various osmotic agents, vasoactive drugs, peritonitis and the hydrostatic pressure gradient. Long-term follow-up of patients shows an increase of the PPRC, the possible causes of which are discussed. Venous vasculopathy of the peritoneal microcirculation is the most likely explanation.

Peritoneal-Membrane Characteristics and Hypervolemia Management in Peritoneal Dialysis: A Randomized Control Trial

Excessive bodily-fluid retention is the major cause of hypertension and congestive heart failure in patients with end-stage renal disease. Compared to hemodialysis, peritoneal dialysis (PD) uses the abdominal peritoneum as a semipermeable dialysis membrane, providing continuous therapy as natural kidneys, and having fewer hemodynamic changes. One major challenge of PD treatment is to determine the dry weight, especially considering that the speed of small solutes and fluid across the peritoneal membrane varies among individuals; considerable between-patient variability is expected in both solute transportation and ultrafiltration capacity. This study explores the influence of peritoneal-membrane characteristics in the hydration status in patients on PD. A randomized control trial compares the bioimpedance-assessed dry weight with clinical judgment alone. A high peritoneal membrane D/P ratio was associated with the extracellular/total body water ratio, dialysate protein loss, and poor nutritional status in patients on PD. After a six-month intervention, patients with monthly bioimpedance analysis (BIA) assistance had better fluid (−1.2 ± 0.4 vs. 0.1 ± 0.4 kg, p = 0.014) and blood-pressure (124.7 ± 2.7 vs. 136.8 ± 2.8 mmHg, p < 0.001) control; however, hydration status and blood pressure returned to the baseline after we prolonged BIA assistance to a 3-month interval. The dry-weight reduction process had no negative effect on residual renal function or peritoneal-membrane function. We concluded that peritoneal-membrane characteristics affect fluid and nutritional status in patients on PD, and BIA is a helpful objective technique for fluid assessment for PD.

Traduction des Recommandations de l'ISPD pour l'évaluation du dysfonctionnement de la membrane péritonéale chez l'adulte

Informations concernant cette traductionDans le cadre d’un accord de partenariat entre l’ISPD et le RDPLF, le RDPLF est le traducteur français officiel des recommandations de l’ISPD. La traduction ne donne lieu à aucune compensation financière de la part de chaque société et le RDPLF s’est engagé à traduire fidèlement le texte original sous la responsabilité de deux néphrologues connus pour leur expertise dans le domaine. Avant publication le texte a été soumis à l’accord de l’ISPD. La traduction est disponible sur le site de l’ISPD et dans le Bulletin de la Dialyse à Domicile.Le texte est, comme l’original, libremement téléchargeable sous licence copyright CC By 4.0https://creativecommons.org/licenses/by/4.0/Cette traduction est destinée à aider les professionnels de la communauté francophone à prendre connaissance des recommandations de l’ISPD dans leur langue maternelle. Toute référence dans un article doit se faire au texte original en accès libre :Peritoneal Dialysis International https://doi.org/10.1177/0896860820982218 Dans les articles rédigés pour des revues françaises, conserver la référence à la version originale anglaise ci dessus, mais ajouter «version française  https://doi.org/10.25796/bdd.v4i3.62673"»TraducteursDr Christian Verger, néphrologue, président du RDPLFRDPLF, 30 rue Sere Depoin, 95300 Pontoise – FranceProfesseur Max Dratwa, néphrologueHôpital Universitaire Brugmann – Bruxelles – Belgique

A Uremic Goat Model Created by Subtotal Renal Artery Embolization and Gentamicin

A large animal model of (end-stage) kidney disease (ESKD) is needed for the preclinical testing of novel renal replacement therapies. This study aimed to create stable uremia via subtotal renal artery embolization in goats and induce a temporary further decline in kidney function by administration of gentamicin. Renal artery embolization was performed in five Dutch white goats by infusing polyvinyl alcohol particles in branches of the renal artery, aiming for the embolization of ~80% of one kidney and complete embolization of the contralateral kidney. Gentamicin was administered to temporarily further increase the plasma concentrations of uremic toxins. After initial acute kidney injury, urea and creatinine plasma concentrations stabilized 1.5 ± 0.7 months post-embolization and remained elevated (12 ± 1.4 vs. 5.6 ± 0.8 mmol/L and 174 ± 45 vs. 65 ± 5.6 µmol/L, resp.) during follow-up (16 ± 6 months). Gentamicin induced temporary acute-on-chronic kidney injury with a variable increase in plasma concentrations of small solutes (urea 29 ± 15 mmol/L, creatinine 841 ± 584 µmol/L, phosphate 2.2 ± 0.3 mmol/L and potassium 5.0 ± 0.6 mmol/L) and protein-bound uremic toxins representative of patients with ESKD. A uremic goat model characterized by stable moderate uremia was established via subtotal renal artery embolization with the induction of temporary severe acute-on-chronic kidney injury by the administration of gentamicin, allowing preclinical in vivo validation of novel renal replacement technologies.

ISPD recommendations for the evaluation of peritoneal membrane dysfunction in adults: Classification, measurement, interpretation and rationale for intervention

Lay summary

Peritoneal dialysis (PD) uses the peritoneal membrane for dialysis. The peritoneal membrane is a thin layer of tissue that lines the abdomen. The lining is used as a filter to help remove extra fluid and poisonous waste from the blood. Everybody is unique. What is normal for one person’s membrane may be very different from another person’s. The kidney care team wants to provide each person with the best dialysis prescription for them and to do this they must evaluate the person’s peritoneal lining. Sometimes dialysis treatment itself can cause the membrane to change after some years. This means more assessments (evaluations) will be needed to determine whether the person’s peritoneal membrane has changed. Changes in the membrane may require changes to the dialysis prescription. This is needed to achieve the best dialysis outcomes. A key tool for these assessments is the peritoneal equilibration test (PET). It is a simple, standardized and reproducible tool. This tool is used to measure the peritoneal function soon after the start of dialysis. The goal is to understand how well the peritoneal membrane works at the start of dialysis. Later on in treatment, the PET helps to monitor changes in peritoneal function. If there are changes between assessments causing problems, the PET data may explain the cause of the dysfunction. This may be used to change the dialysis prescription to achieve the best outcomes. The most common problem with the peritoneal membrane occurs when fluid is not removed as well as it should be. This happens when toxins (poisons) in the blood cross the membrane more quickly than they should. This is referred to as a fast peritoneal solute transfer rate (PSTR). Since more efficient fluid removal is associated with better outcomes, developing a personal PD prescription based on the person’s PSTR is critically important. A less common problem happens when the membrane fails to work properly (also called membrane dysfunction) because the peritoneal membrane is less efficient, either at the start of treatment or developing after some years. If membrane dysfunction gets worse over time, then this is associated with progressive damage, scarring and thickening of the membrane. This problem can be identified through another change of the PET. It is called reduced ‘sodium dip’. Membrane dysfunction of this type is more difficult to treat and has many implications for the individual. If the damage is major, the person may need to stop PD. They would need to begin haemodialysis treatment (also spelled hemodialysis). This is a very important and emotional decision for individuals with kidney failure. Any decision that involves stopping PD therapy or transitioning to haemodialysis therapy should be made jointly between the clinical team, the person on dialysis and a caregiver, if requested. Although evidence is lacking about how often tests should be performed to determine peritoneal function, it seems reasonable to repeat them whenever there is difficulty in removing the amount of fluid necessary for maintaining the health and well-being of the individual. Whether routine evaluation of membrane function is associated with better outcomes has not been studied. Further research is needed to answer this important question as national policies in many parts of the world and the COVID-19 has placed a greater emphasis and new incentives encouraging the greater adoption of home dialysis therapies, especially PD. For Chinese and Spanish Translation of the Lay Summary, see Online Supplement Appendix 1.

Key recommendations

Guideline 1:

A pathophysiological taxonomy: A pathophysiological classification of membrane dysfunction, which provides mechanistic links to functional characteristics, should be used when prescribing individualized dialysis or when planning modality transfer (e.g. to automated peritoneal dialysis (PD) or haemodialysis) in the context of shared and informed decision-making with the person on PD, taking individual circumstances and treatment goals into account. (practice point)

Guideline 2a:

Identification of fast peritoneal solute transfer rate (PSTR): It is recommended that the PSTR is determined from a 4-h peritoneal equilibration test (PET), using either 2.5%/2.27% or 4.25%/3.86% dextrose/glucose concentration and creatinine as the index solute. (practice point) This should be done early in the course dialysis treatment (between 6 weeks and 12 weeks) (GRADE 1A) and subsequently when clinically indicated. (practice point)

Guideline 2b:

Clinical implications and mitigation of fast solute transfer: A faster PSTR is associated with lower survival on PD. (GRADE 1A) This risk is in part due to the lower ultrafiltration (UF) and increased net fluid reabsorption that occurs when the PSTR is above the average value. The resulting lower net UF can be avoided by shortening glucose-based exchanges, using a polyglucose solution (icodextrin), and/or prescribing higher glucose concentrations. (GRADE 1A) Compared to glucose, use of icodextrin can translate into improved fluid status and fewer episodes of fluid overload. (GRADE 1A) Use of automated PD and icodextrin may mitigate the mortality risk associated with fast PSTR. (practice point)

Guideline 3:

Recognizing low UF capacity: This is easy to measure and a valuable screening test. Insufficient UF should be suspected when either (a) the net UF from a 4-h PET is <400 ml (3.86% glucose/4.25% dextrose) or <100 ml (2.27% glucose /2.5% dextrose), (GRADE 1B) and/or (b) the daily UF is insufficient to maintain adequate fluid status. (practice point) Besides membrane dysfunction, low UF capacity can also result from mechanical problems, leaks or increased fluid absorption across the peritoneal membrane not explained by fast PSTR.

Guideline 4a:

Diagnosing intrinsic membrane dysfunction (manifesting as low osmotic conductance to glucose) as a cause of UF insufficiency: When insufficient UF is suspected, the 4-h PET should be supplemented by measurement of the sodium dip at 1 h using a 3.86% glucose/4.25% dextrose exchange for diagnostic purposes. A sodium dip ≤5 mmol/L and/or a sodium sieving ratio ≤0.03 at 1 h indicates UF insufficiency. (GRADE 2B)

Guideline 4b:

Clinical implications of intrinsic membrane dysfunction (de novo or acquired): in the absence of residual kidney function, this is likely to necessitate the use of hypertonic glucose exchanges and possible transfer to haemodialysis. Acquired membrane injury, especially in the context of prolonged time on treatment, should prompt discussions about the risk of encapsulating peritoneal sclerosis. (practice point)

Guideline 5:

Additional membrane function tests: measures of peritoneal protein loss, intraperitoneal pressure and more complex tests that estimate osmotic conductance and ‘lymphatic’ reabsorption are not recommended for routine clinical practice but remain valuable research methods. (practice point)

Guideline 6:

Socioeconomic considerations: When resource constraints prevent the use of routine tests, consideration of membrane function should still be part of the clinical management and may be inferred from the daily UF in response to the prescription. (practice point)

Comparison of Longitudinal Membrane Function in Peritoneal Dialysis Patients According to Dialysis Fluid Biocompatibility

Introduction

Preservation of peritoneal function is essential in long-term peritoneal dialysis. Biocompatible dialysis solutions might prevent or postpone the membrane alteration resulting in ultrafiltration failure and consecutive morbidity and mortality.

Methods

We conducted an observational cohort study in which we made a longitudinal comparison between the course of peritoneal solute and fluid transport during treatment with conventional and biocompatible solutions. Therefore, prospectively collected peritoneal transport data from the yearly standard peritoneal permeability analysis were analyzed in 251 incident patients treated between 1994 and censoring in 2016. Fluid transport included small pore and free water transport. Solute transport was assessed by creatinine mass transfer area coefficient and glucose absorption. Linear mixed models including change point analyses were performed. Interaction with peritonitis was examined.

Results

One hundred thirty-five patients received conventional and 116 biocompatible solutions. Sixty-seven percent (conventional) and 64% (biocompatible) of these underwent minimally three transport measurements. Initially, biocompatible fluids showed higher small solute transport and lower ultrafiltration than conventional fluids up to 3 years. Thereafter, conventional fluids showed an increase in small solute transport (+2.7 ml/min per year; 95% confidence interval [CI]: 0.9 to 4.5) and a decrease of free water transport (−28.0 ml/min per year; 95% CI: −60.4 to 4.4). These were minor or absent in biocompatible treatment. Peritonitis induced a decrease of transcapillary ultrafiltration after 2 years on dialysis with conventional solutions (−291 ml/min per year; 95% CI: −550 to −32) while this was absent in biocompatible treatment.

Conclusion

Despite a higher initial solute transport with biocompatible solutions, these have less influence on functional long-term peritoneal alterations than conventional solutions.

Acute Effects of Peritoneal Dialysis on Hemodynamics

Objectives

To investigate the acute hemodynamic effects of peritoneal dialysis (PD) using the noninvasive Portapres technique [TNO Biomedical Instrumentation (TNO BMI); Amsterdam, The Netherlands].

Design and Methods

Blood pressure was measured in 21 consecutive patients on continuous ambulatory PD during a standard peritoneal permeability analysis (SPA). Blood pressure, stroke volume, cardiac output, and total peripheral resistance were recorded and calculated using continuous finger pressure recordings with Portapres and Modelflow software (TNO BMI). The SPA consists of four phases: ( 1 ) drainage of night dwell dialysate, ( 2 ) instillation of a rinsing solution (1.36% glucose), ( 3 ) drainage of rinsing solution, and ( 4 ) instillation of the test solution (3.86% glucose to which dextran 70 has been added).

Results

Both systolic blood pressure (SBP) (7 ± 9 mmHg, p < 0.005) and diastolic blood pressure (DBP) (5 ± 6 mmHg, p < 0.01) increased during phase 2. Systolic BP and DBP increased further during phase 4 (SBP 8 ± 14 mmHg, p < 0.05; DBP 6 ± 8 mmHg, p < 0.005). These BP increases were caused by a rise in total peripheral resistance of 10% ± 18% ( p < 0.05) during phase 1, and 15% ± 21% ( p < 0.005) during phase 2.

Conclusions

Instillation and dwell of a dialysis solution during PD causes a rise in blood pressure. This is caused by an increase in total peripheral resistance. Factors influencing total peripheral resistance could be a direct mechanical effect of dialysate on mesenteric resistance vessels or a temperature-related effect.

Monitoring of Long-Term Peritoneal Membrane Function

Objective

Peritoneal membrane function influences dialysis prescription and clinical outcome and may change with time on treatment. Increasingly sophisticated tools, ranging from the peritoneal equilibration test (PET) to the standard permeability analysis (SPA) and personal dialysis capacity (PDC) test, are available to the clinician and clinical researcher. These tests allow assessment of a number of aspects of membrane function, including solute transport rates, ultrafiltration capacity, effective reabsorption, transcellular water transport, and permeability to macromolecules. In considering which tests are of greatest value in monitoring long-term membrane function, two criteria were set: those that result in clinically relevant interpatient differences in achieved ultrafiltration or solute clearances, and those that change with time in treatment.

Study Selection

Clinical validation studies of the PET, SPA, and PDC tests. Studies reporting membrane function using these methods in either long-term (5 years) peritoneal dialysis patients or longitudinal observations (> 2 years).

Data Extraction

Directly from published data. Additional, previously unpublished analysis of data from the Stoke PD Study.

Results

Solute transport is the most important parameter. In addition to predicting patient and technique survival at baseline, there is strong evidence that it can increase with time on treatment. Whereas patients with initially high solute transport drop out early from treatment, those with low transport remain longer on treatment, although, over 5 years, a proportion develop increasing transport rates. Ultrafiltration capacity, while being a composite measure of membrane function, is a useful guide for the clinician. Using the PET (2.27% glucose), a net ultrafiltration capacity of < 200 mL is associated with a 50% chance of achieving less than 1 L daily ultrafiltration at the expense of 1.8 hypertonic (3.86%) exchanges in anuric patients. Using a SPA (3.86% glucose), a net ultrafiltration capacity of < 400 mL indicates ultrafiltration failure. While there is circumstantial evidence that, with time on peritoneal dialysis, loss of transcellular water transport might contribute to ultrafiltration failure, none of the current tests is able to demonstrate this unequivocally. Of the other membrane parameters, evidence that interpatient differences are clinically relevant (permeability to macro-molecules), or that they change significantly with time on treatment (effective reabsorption), is lacking.

Conclusion

A strong case can be made for the regular assessment by clinicians of solute transport and ultrafiltration capacity, a task made simple to achieve using any of the three tools available.

Mathematical Models for Peritoneal Transport Characteristics

Four mathematical models and for the description of peritoneal transport of fluid solutes are reviewed. The membrane model is usually applied for (1) separation of transport components, (2) formulation of the relationship between flow components and their driving forces, and (3) estimation of transport parameters. The three-pore model provides correct relationships between various transport parameters and demonstrates that the peritoneal membrane should be considered heteroporous. The extended threepore model discriminates between heteroporous capillary wall and tissue layer, which are assumed to be arranged in series; the model improves and modifies the results of the three-pore model. The distributed model includes all parameters involved in peritoneal transport and takes into account the real structure of the tissue with capillaries distributed at various distances from the surface of the tissue.

How the distributed model may be applied for the evaluation of the possible impact of perfusion rate on peritoneal transport, as recently discussed for clinical and experimental studies, is demonstrated. The distributed model should provide theoretical bases for the application of other models as approximate and simplified descriptions of peritoneal transport. However, an unsolved problem is the theoretical description of bi-directional fluid transport, which includes ultrafiltration to the peritoneal cavity owing to the osmotic pressure of dialysis fluid and absorption out of the peritoneal cavity owing to hydrostatic pressure.

The Standard Peritoneal Permeability Analysis in the Rabbit: A Longitudinal Model for Peritoneal Dialysis

Objective

The development of an experimental peritoneal dialysis (PD) model in rabbits to investigate peritoneal transport characteristics during a longitudinal follow-up and to assess normal values of these peritoneal transport parameters.

Design

Peritoneal transport parameters were determined in conscious, unrestrained rabbits by standard peritoneal permeability analysis adjusted for rabbits (SPAR). In this test a 1-hour dwell with 3.86% glucose dialysate is used. Dextran 70 (1 g/L) was added to the dialysate to allow calculation of fluid kinetics. Dialysate samples were taken before, 10, and 40 minutes after instillation and at the end of the dwell. Blood was drawn at the end of the dwell.

Experimental Animals

Eighteen female New Zealand White rabbits (2565 g) were included for catheter implantation. SPARs were performed in 15 animals; the other 3 were excluded due to complications.

Main Outcome

The mass transfer area coefficients (MTACs) of the low molecular weight solutes urea (MTACurea) and creatinine (MTACcr) were calculated. The clearances of albumin (Clalb) and IgG (ClIgG), glucose absorption, and fluid transport were computed. Coefficients of intraindividual variation (Vc) were calculated for these parameters.

Results

The main complications were catheter obstruction and/or dislocation. Five rabbits underwent uncomplicated PD during a 4-week period. Fifteen SPARs in 15 stable rabbits were performed and analyzed to obtain normal values. Means and standard deviations of the transport parameters were as follows: MTACurea 2.24 ± 0.57 mL/min, MTACcr 1.61 ± 0.30 mL/min, Clalb 52.9 ± 17.2 μL/min, ClIgG 44.5 ± 22.9 μL/min. The transcapillary ultrafiltration rate was 0.66 ± 0.13 mL/min and the lymphatic absorption rate 0.47 ± 0.26 mL/min. The parameters of solute transport were upscaled to those in humans using two different methods. MTACs of low molecular weight solutes in rabbits and patients were of the same order of magnitude, but the clearance of albumin was approximately four times higher in rabbits than in patients, and that of IgG eight times. In all rabbits sieving of sodium was observed. The dialysate/plasma (D/P) of sodium decreased to a minimum at 40 min ( p < 0.003 vs the initial value), followed by a rise to 60 min. The minimal value was 0.884 ± 0.002. The coefficients of variation calculated on 7 rabbits that underwent two or more SPARs were similar to those assessed from the patient data. This indicates stability of the model and reproducibility of the SPAR.

Conclusion

The conscious rabbit model for PD can be used for repeated studies on peritoneal transport.

Validation by Computer Simulation of Two Indirect Methods for Quantification of Free Water Transport in Peritoneal Dialysis

Background

In peritoneal dialysis, approximately 40% of the total osmotic ultrafiltration (UF) induced by glucose can be predicted to be due to “free” water transport across aquaporin-1 (APQ-1). Theoretically, it would be possible to assess the fraction of free water transport in the early phase of a hypertonic dwell, when UF rate is high and the relative contribution of Na+ diffusion is low. La Milia et al. [La Milia V. et al. Fast-fast peritoneal equilibration test (FAST-FAST-PET): a simple method for peritoneal hydraulic permeability study [Abstract]. Nephrol Dial Transplant 2002; 17 (Suppl 1):17–18] suggested a technique to assess sodium-associated water transport based on sodium removal (Na+R) divided by the plasma Na+ concentration during a “fast-fast” (60 minute) peritoneal equilibration test (PET) for 3.86% glucose, yielding an estimate of the UF passing through the small pores (UFSP). Free water transport (UF through ultrasmall pores; UFUSP) was obtained by subtracting UFSP from total UF. Although peritoneal Na+ transport is almost totally convective, this technique will slightly overestimate small-pore UF due to the presence of some small-pore Na+ diffusion from the circulation during the dwell. A way of dealing with this problem was presented recently by Smit (Smit W. et al. Quantification of free water transport in peritoneal dialysis. Kidney Int 2004; 66:849–854).

Methods

In the present study we used the three-pore model of peritoneal transport to predict the degree of overestimation of UFSP for the technique presented by La Milia et al., and any potential deviations from theory for the technique presented by Smit et al. Simulations were performed under ordinary conditions and during simulated UF failure for 3.86% glucose. The fractional UF coefficient accounted for by APQ-1 was set at 2%.

Results

Estimating the UFSP from the sodium-associated water transport according to the method by La Milia et al. consistently overestimated UFSP and underestimated UFUSP. These errors were, however, minimal for dwells lasting between 30 and 80 minutes. The technique by Smit et al. to calculate aquaporin-mediated water flow (UFUSP), using an elaborate correction for Na+ diffusion from the circulation during the dwell, seemed accurate in most situations but, in general, tended to moderately overestimate UFUSP at early dwell times (<30 minutes) and underestimate UFUSP at long dwell times (4 hours).

Conclusions

The technique presented by La Milia et al. to calculate free water transport during a fast-fast PET was found to be surprisingly accurate, although the procedure would further improve by the introduction of a correction algorithm. The technique by Smit is even more accurate for dwells up to 4 hours’ duration. However, since the Smit technique is elaborate, it is less practical for routine determinations of aquaporin-mediated water transport in peritoneal dialysis.

Assessment of the Effectiveness, Safety, and Biocompatibility of Icodextrin in Automated Peritoneal Dialysis

Objective

Our study assessed the efficacy, safety, and biocompatibility of icodextrin (I) solution compared to glucose (G) solution as the daytime dwell in continuous cycling peritoneal dialysis (CCPD).

Design

In a randomized, open, prospective, parallel group study of two years’ duration, either I or G was used for the long daytime dwell in CCPD patients.

Method

The study was carried out in a university hospital and teaching hospital. Established CCPD patients and patients new to the modality were both included. Clinic visits were made at three-month intervals. In all patients, clinical data were gathered; ultrafiltration (UF) was recorded; and serum, urine, and dialysate samples and effluents were collected. Peritoneal defense characteristics and mesothelial markers were determined. Every six months, peritoneal kinetics studies were performed, and serum samples for icodextrin metabolites were taken.

Results

Thirty-eight patients (19 G, 19 I) started the study. The median follow-up was 16 months and 17 months respectively (range: 0.5 – 26 months and 3 – 26 months, respectively). Daytime UF volumes increased significantly (p < 0.001), and 24-hour UF tended to increase from baseline in the I group. Dialysate creatinine clearance increased non significantly in both groups over time. In I patients, serum disaccharides (maltose) concentration increased from 0.05 ± 0.01 mg/mL [mean ± standard error of mean (SEM)] at baseline, to an average concentration in the follow-up visits of 1.15 ± 0.04 mg/mL (p < 0.001). At the same time, serum sodium levels decreased from 138.1 ± 0.7 mmol/L to an average concentration in the follow-up visits of 135.9 ± 0.8 mmol/L (p < 0.05). At 12 months, the serum sodium concentration increased to a non significant difference from baseline. Serum osmolality increased, but did not differ significantly from G users at any visit. During peritonitis (P), daytime dwell UF decreased significantly compared to non peritonitis (NP) episodes in G patients (p < 0.001), but remained stable in I patients. Total 24-hour UF also decreased in G patients (p < 0.001), but not in I patients. In these I patients, serum disaccharides increased from 0.05 ± 0.01 mg/mL to 1.26 ± 0.2 mg/mL during follow-up. During peritonitis, serum disaccharides concentration did not increase further (1.47 ± 0.2 mg/mL, p = 0.56). Thirty P episodes occurred during follow-up: 16 in G patients and 14 in I patients (1 per 17.6 months and 1 per 21.9 months, respectively). After one year, absolute number and percentage of effluent peritoneal macrophages (PMΦs) were significantly higher in I patients than in G patients. The difference in percentage persisted after two years. The phagocytic capacity of PMΦs decreased over time, resulting in a borderline significant difference for coagulase-negative staphylococci phagocytosis (p = 0.05) and a significant difference for E. coli phagocytosis (p < 0.05) in favor of I patients. PMΦ oxidative metabolism, PMΦ cytokine production, and effluent opsonic capacity remained stable over time with no difference between the groups. Mass transfer area coefficients (MTACs) and clearances were stable and appeared unaffected by G or I treatment. Effluent cancer antigen 125 (CA125) was stable in G users and tended to decrease in I users. Effluent interleukin-8 (IL-8), carboxy-terminal propeptide of type I procollagen (PICP), and amino-terminal propeptide of type III procollagen (PIIINP) did not change over time and did not differ between the groups.

Conclusions

The use of I for the long daytime dwell in CCPD led to an increase in total UF of at least 261 mL per day, which was maintained over at least 24 months. During I treatment, serum I metabolites increased significantly and serum sodium concentrations decreased initially. As a result, serum osmolality increased slightly. Clinical adverse effects did not accompany these findings. The UF gain in the I patients was even higher during P, without a further increase in serum I metabolites. CCPD patients using I did equally well as G-treated patients with regard to clinical infections and most peritoneal defense characteristics. However, in a few peritoneal defense tests, I-treated patients did better. Peritoneal transport variables did not change over time. Peritoneal membrane markers did not change throughout the study and did not differ between the groups.

Peritoneal Function and Assessment of Reference Values Using a 3.86% Glucose Solution

Background

The most widely used peritoneal function test, the peritoneal equilibration test (PET), is performed with a 2.27% glucose solution. Recently, the International Society for Peritoneal Dialysis committee on ultrafiltration failure (UFF) advised performing the test with 3.86% glucose solution because it is more sensitive for detecting clinically significant UFF. Because no reference values for this test were available, we analyzed the results of standard peritoneal permeability analyses (SPAs) using 3.86% glucose.

Methods

The tests were performed in our center on 154 clinically stable peritoneal dialysis (PD) patients that were free of peritonitis for at least 4 weeks. For the assessment of reference values, we used two approaches. In approach A, patients with UFF, defined as net ultrafiltration (UF)< 400 mL/4 hours, were excluded. In approach B, only patients within their first 2 years of PD treatment were included, regardless of net UF. Means and 95% confidence intervals (95% CI) were calculated for the transport parameters of the PET and SPA.

Results

Means of normal distribution with 95% CI in approach A were as follows: for 2.0-L exchanges, mass transfer area coefficient (MTAC) for creatinine 8.8 mL/minute (4.7 – 12.7 mL/min), dialysate/plasma ratio (D/P) creatinine 0.70 (0.52 – 0.88), glucose absorption 58% (44% – 72%), dialysate240/initial dialysate ratio of glucose (D t/D0) 0.28 (0.18 – 0.38), net UF 675 mL (375 – 975 mL), and maximal dip in D/P sodium after correction for diffusion from the circulation 0.110 (0.050 – 0.164); for 1.5-L exchanges, MTAC creatinine 7.4 mL/min (3.8 – 11.0 mL/min), D/P creatinine 0.69 (0.52 – 0.86), glucose absorption 62% (52% – 72%), D t/D0 glucose 0.25 (0.17 – 0.32), net UF 551 mL (430 – 670 mL), and maximal dip D/P sodium 0.120 (0.048 – 0.166). In approach B, most of the transport values were similar; however, values for lymphatic absorption were significantly higher [1.52 mL/min (2-L) and 1.40 mL/min (1.5-L), p < 0.01] and values for the maximum dip in D/P sodium were lower [0.101 (2-L) and 0.112 (1.5-L), p > 0.05]. This was probably the result of including patients with UFF in approach B, since these parameters can be causative factors of UFF.

Conclusions

A peritoneal transport function test using 3.86% glucose provides data on various aspects of transport. This study gives normal reference values that can be used for analysis of causes of UFF.

A Comparison between 1.36% and 3.86% Glucose Dialysis Solution for the Assessment of Peritoneal Membrane Function

Objective

To assess peritoneal membrane function with respect to fluid transport, parameters of low molecular weight solute transport, and estimations of the function of peritoneal water channels, comparing the results from a 1.36%/1.5% glucose solution with those from a 3.86%/4.25% solution in standardized peritoneal function tests.

Design

The study was performed in 40 stable continuous ambulatory peritoneal dialysis (CAPD) patients [median age 50 years (range: 22 – 74 years); duration of CAPD 9 months (range: 2 – 45 months)] who underwent two standard peritoneal permeability analyses (SPAs) within 1 month. One SPA used 1.36% glucose; the other, 3.86% glucose. Mass transfer area coefficients (MTACs) and dialysate-to-plasma (D/P) ratios were compared for the two solutions. Also, two different methods of estimating aquaporin-mediated water transport were compared: the sieving of sodium (3.86% glucose) and the difference in net ultrafiltration (ΔNUF), calculated as NUF 3.86% SPA – NUF 1.36% SPA.

Results

Median NUF in the 1.36% glucose SPA was –46 mL (range: –582 mL to 238 mL); in the 3.86% SPA, it was 554 mL (range: –274 mL to 1126 mL). The median difference in NUF for the two SPAs was 597 mL (range: 90 – 1320 mL). No difference between the two solutions was seen for the MTAC of creatinine (11.4 mL/min for 1.36% vs 12.0 mL/min for 3.86%) and absorption of glucose (64% vs 65%, respectively). Also, D/P creatinine was not different: 0.77 (1.36%) and 0.78 (3.86%). However, the ratio of dialysate glucose at 240 minutes and at 0 minutes (Dt/D0) was 0.34 (1.36%) and 0.24 (3.86%), p < 0.01. Values of D/P creatinine from the two glucose solutions were strongly correlated. The intra-individual differences were small and showed a random distribution. Patient transport category was minimally influenced by the tonicity of the dialysate. The minimum D/P Na+(3.86%) was 0.884, and it was reached after 60 minutes. After correction for Na+diffusion, D/P Na+decreased to 0.849 after 120 minutes. The correlation coefficient between the diffusion-corrected D/P Na+and the ΔNUF was 0.49, p < 0.01. An inverse relationship was present between MTAC creatinine and D/P Na+( p < 0.01) This correlation can be explained by the rapid disappearance of the osmotic gradient owing to a large vascular surface area. Such a correlation was not present between MTAC creatinine and ΔNUF.

Conclusions

We conclude that a standardized 4-hour peritoneal permeability test using 3.86%/4.25% glucose is the preferred method to assess peritoneal membrane function, including aquaporin-mediated water transport. The D/P Na+after correction for Na+diffusion is probably more useful for the assessment of aquaporin-mediated water transport than is ΔNUF obtained with 3.86%/ 4.25% and 1.36%/1.5% glucose-based dialysis solutions.

Icodextrin'S Effects on Peritoneal Transport

Objective

To give a survey of the principles of peritoneal fluid transport in general, followed by an analysis of the effects of icodextrin on the transport of fluid and solutes.

Design

A review of the literature and of data on the effects of icodextrin in continuous ambulatory peritoneal dialysis (CAPD) patients at the Academic Medical Center, Amsterdam.

Results

Icodextrin had no effect on the mass transfer area coefficients of low molecular weight solutes. Also no effect was found on the clearances of albumin and larger serum proteins. Due to convective transport, the clearance of β2-microglobulin was greater with icodextrin than with glucose solutions. Icodextrin was especially superior to glucose in the induction of net ultrafiltration during long dwells, during peritonitis, and in patients with ultrafiltration failure caused by a large effective peritoneal surface area.

Conclusion

Icodextrin has no effect on the permeability characteristics of the peritoneal membrane, but increases convective flow through the small-pore system. As a result, the peritoneal clearance of β2-microglobulin is higher than with glucose-based solutions.lcodextrin is especially indicated for long dwells and in patients with impaired ultrafiltration caused by a large peritoneal surface area, leading to high transport rates of low molecular weight solutes.

Solute Clearance Approach to Adequacy of Peritoneal Dialysis

To investigate the effect of dialysis prescription on patient outcome for peritoneal dialysis patients, the relationship between total solute clearance and the relative risk of death has been investigated. Preliminary studies have suggested that more clearance is better and that patient outcome is predicted by total solute clearance. The recently published Canada-U.S.A. (CANUSA) multicenter study, evaluating adequacy of dialysis and nutrition in peritoneal dialysis patients, has further defined this relationship. Although these publications allow us to establish guidelines for the treatment of peritoneal dialysis patients, they also define the limitations of our knowledge and raise new questions.

In this article we review our current knowledge regarding the predicted value of total solute clearance with patient outcome and nutritional status. Furthermore, we attempt to outline a practical approach for optimizing total solute clearance in peritoneal dialysis patients.

Based on a review of the published literature and clinical recommendations, we feel that the minimal target total solute clearance for continuous forms of peritoneal dialysis is a weekly total KTN > 2.0 and/or a weekly total creatinine clearance >60 L/week/1.73 m2. For intermittent therapies, a weekly total KTN > 2.2 and/or a weekly total creatinine clearance >70 L/week/1.73 m2 is recommended.

Peritoneal Kinetics and Mesothelial Markers in CCPD Using Icodextrin for Daytime Dwell for Two Years

Objective

To evaluate the safety, efficacy, and biocompatibility of icodextrin (Ico), continuous cycling peritoneal dialysis (CCPD) patients were treated for 2 years with either Ico- or glucose (Glu)-containing dialysis fluid for their daytime dwell (14 – 15 hours). Prior to entry into the study, all patients used standard Glu solutions (Dianeal, Baxter BV, Utrecht, The Netherlands).

Design

Open, randomized, prospective two-center study.

Setting

University hospital and teaching hospital.

Patients

Both established patients and patients new to CCPD were included. A life expectancy of more than 2 years, a stable clinical condition, and written informed consent were necessary before entry. Patients aged under 18 years or with peritonitis in the previous month, and women of childbearing potential unless taking adequate contraceptive precautions, were excluded. Thirty-eight patients entered the study (19 Glu, 19 Ico).

Main Outcome Measures

Daytime dwell peritoneal effluents were collected every 3 months in combination with other study variables (clinical data, laboratory measurements, dialysis-related data, and urine collection). Peritoneal transport studies were carried out every 6 months.

Results

In Glu- and Ico-treated patients, peritoneal transport of low molecular weight solutes and protein clearances neither changed during follow-up nor differed between the two groups. Peritoneal membrane markers (CA125, interleukin-8, carboxyterminal propeptide of type I procollagen, and aminoterminal propeptide of type III procollagen) measured in effluents did not differ between the groups and did not change over time. All these markers showed a dialysate/plasma ratio of more than 1, suggesting local production. Residual renal function remained stable during follow-up and adverse clinical effects were not observed.

Conclusions

Peritoneal membrane transport kinetics and markers remained stable in both groups over a 2-year follow-up period. Membrane markers were higher in effluents than in serum, suggesting local production. No clinical side effects were demonstrated. Icodextrin was a well-tolerated effective treatment.

Peritoneal Transport Characteristics with Glycerol-Based Dialysate in Peritoneal Dialysis

Background

Glycerol is a low molecular weight solute (MW 92 D) that can be used as an osmotic agent in continuous ambulatory peritoneal dialysis (CAPD). Due to its low molecular weight, the osmotic gradient disappears rapidly. Despite the higher osmolality at the beginning of a dwell, ultrafiltration has been found to be lower for glycerol compared to glucose (MW 180 D) when equimolar concentrations are used. Previous studies have shown glycerol to be safe for long-term use, but some discrepancies have been reported in small solute transport and protein loss.

Objective

To assess permeability characteristics for a 1.4% glycerol dialysis solution compared to 1.36% glucose.

Design

Two standardized peritoneal permeability analyses (SPA), one using 1.4% glycerol and the other using 1.36% glucose, in random order, were performed within a span of 2 weeks in 10 stable CAPD patients. The length of the study dwell was 4 hours. Fluid kinetics and solute transport were calculated and signs of cell damage were compared for the two solutions.

Setting

Peritoneal dialysis unit in the Academic Medical Center, Amsterdam.

Results

Median values for the 1.4% glycerol SPA were as follows: net ultrafiltration 251 mL, which was higher than that for 1.36% glucose (12 mL, p < 0.01); transcapillary ultrafiltration rate 2.12 mL/min, which was higher than that for glucose (1.52 mL/min, p = 0.01); and effective lymphatic absorption rate 1.01 mL/min, which was not different from the glucose-based solution. Calculation of peritoneal reflection coefficients for glycerol and glucose showed lower values for glycerol compared to glucose (0.03 vs 0.04, calculated with both the convection and the diffusion models). A marked dip in dialysate-to-plasma ratio for sodium was seen in the 1.4% glycerol exchange, suggesting uncoupled water transport through water channels. Mass transfer area coefficients for urea, creatinine, and urate were similar for both solutions. Also, clearances of the macromolecules P2-microglobulin, albumin, IgG, and α2-macroglobulin were not different for the two osmotic agents. The median absorption was higher for glycerol, 71% compared to 49% for glucose ( p < 0.01), as could be expected from the lower molecular weight. The use of a 1.4% glycerol solution during a 4-hour dwell caused a small but significant median rise in plasma glycerol, from 0.22 mmol/L to 0.45 mmol/L ( p = 0.02). Dialysate cancer antigen 125 and lactate dehydrogenase (LDH) concentrations during the dwell were not different for both solutions.

Conclusions

These findings show that glycerol is an effective osmotic agent that can replace glucose in short dwells and show no acute mesothelial damage. The higher net ultrafiltration obtained with 1.4% glycerol can be explained by the higher initial net osmotic pressure gradient. This was seen especially in the first hour of the dwell. Thereafter, the osmotic gradient diminished as a result of absorption. The dip in dialysate-to-plasma ratio for sodium seen in the glycerol dwell can also be explained by this high initial osmotic pressure gradient, implying that the effect of glycerol as an osmotic agent is more dependent on intact water channels than is glucose.

Fluid and Electrolyte Transport across the Peritoneal Membrane during CAPD According to the Three-pore Model

In the present review, we summarize the principles governing the transport of fluid and electrolytes across the peritoneum during continuous ambulatory peritoneal dialysis (CAPD) in “average” patients and during ultrafiltration failure (UFF), according to the three-pore model of peritoneal transport. The UF volume curves as a function of dwell time [V( t)] are determined in their early phase by the glucose osmotic conductance [product of the UF coefficient (LpS) and the glucose reflection coefficient (σg)] of the peritoneum; in their middle portion by intraperitoneal volume and glucose diffusivity; and in their late portion by the LpS, Starling forces, and lymph flow. The most common cause of UFF is increased transport of small solutes (glucose) across the peritoneum, whereas the LpS is only moderately affected. Concerning peritoneal ion transport, ions that are already more or less fully equilibrated across the membrane at the start of the dwell, such as Na+(Cl–), Ca2+, and Mg2+, have a convection-dominated transport. The removal of these ions is proportional to UF volume (approximately 10 mmol/L Na+and 0.12 mmol/L Ca2+removed per deciliter UF in 4 hours).

The present article examines the impact on fluid and solute transport of varying concentrations of Ca2+and Na+in peritoneal dialysis solutions. Particularly, the effect of “ultralow” sodium solutions on transport and UF is simulated and discussed. Ions with high initial concentration gradients across the peritoneum, such as K+, phosphate, and bicarbonate, display a diffusion-dominated transport. The transport of these ions can be adequately described by non-electrolyte equations. However, for ions that are in (or near) their diffusion equilibrium over the peritoneum (Na+, Ca2+, Mg2+), more complex ion transport equations need to be used. Due to the complexity of these equations, however, non-electrolyte transport formalism is commonly employed, which leads to a marked underestimation of mass transfer area coefficients (PS). This can be avoided by determining the PS when transperitoneal ion concentration gradients are steep.

Does Lymphatic Absorption Change with the Duration of Peritoneal Dialysis?

Background

Ultrafiltration failure is an important complication of long-term peritoneal dialysis (PD). A high effective lymphatic absorption rate (ELAR) can contribute to impaired ultrafiltration. It is unknown whether the ELAR increases with time on PD.

Objective

The relationship between the ELAR and duration of PD was analyzed, as well as the correlation between the ELAR and other transport parameters. We also studied the relation between the ELAR and cancer antigen 125 (CA125) a marker for mesothelial cell mass.

Setting

Peritoneal dialysis unit in the Academic Medical Center, Amsterdam.

Design

Cross-sectional and longitudinal studies of standard peritoneal permeability analyses (SPAs; 4-hour dwells, dextran 70 as a volume marker) with glucose 3.86% in 130 PD patients.

Methods

SPAs were analyzed in 130 stable PD patients (77 males). Median duration of PD was 25 months (range 1 – 214) in a cross-sectional study. The last SPA from each patient was analyzed. The longitudinal analysis included 24 patients (12 males) from whom at least 3 SPAs were available with a minimum interval of 8 months. Dextran 70, 1 g/L, was administered intraperitoneally at the initiation of the test. Lymphatic absorption was calculated from the disappearance rate of dextran 70 during the 4-hour dwell. Therefore, the ELAR included both transmesothelial and subdiaphragmatic uptake of dextran 70.

Results

Median ELAR was 1.43 mL/minute (range 0.17 – 6.59 mL/minute). No relationship was found between the ELAR and duration of PD in the cross-sectional analysis, nor was there a trend in time for 20 of the 24 patients studied longitudinally. In 4 patients, a negative trend was found. None of these had ultrafiltration failure and all 4 patients had a different cause for end-stage renal failure. The ELAR was correlated with parameters of peritoneal solute transport, but not with CA125 when investigated in a cross-sectional analysis. Only after 48 months of PD treatment was a significant relationship between the ELAR and CA125 seen ( r = 0.46, p < 0.05).

Conclusions

No time trend is present for the effective peritoneal lymphatic absorption rate, and it is not associated with patient or technique survival. Although increased lymphatic absorption is one of the causes of ultrafiltration failure, it is unlikely to contribute to the development of ultrafiltration failure in long-term PD patients with well-maintained transcapillary ultrafiltration.

Amadori Albumin and Advanced Glycation End-Product Formation in Peritoneal Dialysis using Icodextrin

Objective

To study the influence of peritoneal dialysis (PD) solutions on the formation of early glycated products and advanced glycation end-products (AGEs).

Design and Patients

The formation of both Amadori albumin and AGEs in glucose- and icodextrin-based PD fluids was analyzed in vitro and in peritoneal effluents of continuous cyclic peritoneal dialysis (CCPD) patients.

Results

Albumin incubated with glucose-based PD fluids showed a time- and glucose concentration-dependent formation of Amadori albumin and AGEs. Aminoguanidine completely inhibited AGE but not Amadori albumin formation. Albumin incubated in icodextrin resulted in the lowest levels of Amadori albumin and AGE. Amadori albumin levels in effluents of 24 CCPD patients (12 glucose and 12 icodextrin for their daytime dwells) were similar. Dialysate samples collected during a mass transfer area coefficient test in 16 CCPD patients (8 glucose, 8 icodextrin) showed an increase in Amadori albumin formation from baseline ( p < 0.0001), without a difference between the groups. In the total group, there was a positive relationship between duration on PD and dialysate Amadori albumin concentration at 240 minutes ( p = 0.03). The Amadori albumin dialysate-to-plasma (D/P) ratio at 240 minutes was 0.82 ± 0.11, and its clearance amounted to 7.71 ± 1.14 mL/min, while the albumin D/P ratio was 0.010 ± 0.003 and its clearance was 0.089 ± 0.017 mL/min. In a peritoneal biopsy of a CCPD patient, Amadori albumin was observed in the mesothelial layer and the endothelium of the peritoneum.

Conclusions

Using icodextrin-based instead of glucose-based PD fluids can largely reduce the formation of Amadori albumin and AGEs. However, CCPD patients using icodextrin during daytime dwells do not have lower effluent levels of Amadori albumin and AGEs, probably due to the exposure to glucose during their nighttime exchanges. Kinetic studies suggest washout of locally produced Amadori albumin.

Neoangiogenesis in the Peritoneal Membrane

Objective

This study reviews relevant publications on the peritoneal vasculature and tries to establish morphological–functional relationships.

Design

The design is a review article.

Results

Recent morphological studies in peritoneal dialysis (PD) patients have shown the presence of diabetiform neoangiogenesis in long-term peritoneal dialysis. The same abnormalities could be induced in rats administered a high glucose dialysis solution daily for 20 weeks. The animals showed functional abnormalities in peritoneal transport similar to those found in long-term PD patients. Evidence was obtained in patients that vascular endothelial growth factor could be involved in glucose-induced peritoneal neoangiogenesis.

Conclusions

Diabetiform peritoneal neoangiogenesis is an important pathogenetic factor in ultrafiltration failure in long-term peritoneal dialysis patients.

Association between an Increased Surface Area of Peritoneal Microvessels and a High Peritoneal Solute Transport Rate

Objective

The peritoneal solute transport rate (PSTR) often increases, especially for small solutes, during long-term peritoneal dialysis (PD) treatment. Although the mechanism by which PSTR increases in PD patients is not known, it is likely that an increased PSTR reflects an increased surface area of the peritoneal capillary and postcapillary venules (microvessels), but this has not previously been investigated. The aim of this study was to clarify the relationship between PSTR and peritoneal microvessel alterations in biopsy specimens of peritoneum obtained from PD patients after various times on PD, and the possible contribution of the duration of PD in relation to these alterations.

Design

Tissue from the parietal peritoneum was obtained from 22 PD patients (age 48.5± 9.0 years, duration of PD 66.3 ± 46.6 months, incidence of peritonitis 0.3/patient-year). The patients were subdivided into three groups according to duration of PD: zero months (group 0, n = 4), less than 60 months (group I, n = 7), and more than 60 months (group II, n = 11).

Methods

For each specimen, the relative microvessel area (RVA) calculated as total area of microvessels/total area of peritoneal field, and the relative microvessel number (RVN), calculated as number of microvessels/total area of peritoneal field, were determined. The ratio RVA/RVN was used to assess the average area of microvessels. The PSTR was evaluated for creatinine, glucose, β2-microglobulin, and albumin using the peritoneal equilibration test.

Results

The dialysate-to-plasma concentration ratio (D/P) for creatinine showed a significant positive correlation with both RVA (rho = 0.77, p < 0.001) and RVA/RVN (rho = 0.51, p = 0.01), but not with RVN. The D/P for β2-microglobulin correlated with RVA (rho = 0.51 p = 0.015) but not with RVN or RVA/RVN. No differences were found between the three groups in the values for RVN, whereas there was an apparent significant increase in RVA with time on PD ( p < 0.001 for group 0 vs both groups I and Furthermore, in high transporters, RVA tended to be higher in group II than in group I.

Conclusions

The present study demonstrates for the first time that an increased peritoneal solute transport rate (for both creatinine and β2-microglobulin) is associated with an increased surface area of peritoneal microvessels, especially in patients on long-term PD treatment. This indicates that increased vascularization and/or dilatation of peritoneal microvessels may play a key role in the development of a high PSTR.

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, dlPV < 0 mL) were analyzed further using 3.86% glucose, whenever possible.

Results

Among 68 patients (duration of PD 0.3 -178 months), 39 had negative net UF with 1.36% glucose. These patients had greater MTAC creatinine and glucose absorption, and higher ELAR (p < 10–4) than the patients with positive UF. dIPV and transcapillary UF rate (TCUFR) were lower (p < 10–5). Twenty of these patients could be studied using 3.86% glucose. dlPV was greater than 400 mL/4 hr in this test in 12 patients, implying that no clinically important UFF was present. Ultrafiltration failure (dIPV < 400 mL) was found in 8 patients, giving a prevalence of 23%. This last group had been treated with PD for a longer period (p = 0.03), had higher ELAR (p = 0.07), but lower residual volume (p = 0.03), and lower TCUFR (p = 0.01). Ultrafiltration failure was associated with a high MTAC creatinine in 3 patients, a high ELAR in 4 patients, and a combination of factors in one. As an additional possible cause, TCWT was studied, using the sodium gradient in the first hour of the dwell, corrected for diffus ion (dNA). Five patients had dNA > 5 mmol/L, indicating normal TCWT. The 3 patients with dNA < 5 mmol/L tended to be treated longer (p = 0.19) and had lower TCUFR (p = 0.04). A smaller difference was found between dlPV 3.86% and 1.36% (p = 0.04) compared to the dNA > 5 mmol/L group, but no differences were present for MTAC creatinine, ELAR, residual volume, or glucose absorption.

Conclusions

ln 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 exchange.

Alterations in Water and Solute Transport with Time on Peritoneal Dialysis

Peritoneal ultrafiltration capacity and small -solute transport characteristics seem to be relatively stable in most patients treated with PD for up to 3 years. However, in patients treated with PD for 4 years or more, there is a tendency towards increasing diffusive transport for small solutes as well as a tendency towards decreasing net UF, whereas the peritoneal protein clearances seem to be reduced or stable.

Loss of UFC is a well-known complication during long-term PD treatment, and the risk for loss of UFC may be as high as 50% after 6 years on PD. Several different mechanisms of UFC loss have been reported. In particular, the most common mechanism for loss of UFC is increased diffusive transport resulting in rapid glucose absorption and thus rapid loss of the osmotic driving force. Also reported as causes of UFC loss have been: reduced efficiency of the osmotic agent (perhaps owing to decreased transcellular water transport); loss of peritoneal surface area with slow solute transport owing to fibrosis and the formation of adhesions (during the late stage of sclerosing peritonitis); and increased peritoneal fluid absorption. In individual patients, a combination of several mechanisms may be involved in the apparent UFC failure.

Effect of Fluid Supplementation and Modality on Peritoneal Permeability Characteristics in a Rat Peritoneal Dialysis Model

Objective

Hemoconcentration may influence peritoneal permeability parameters in anesthetized animals without fluid supplementation. Therefore, the aim of this study was to investigate the effects of fluid supplementation on peritoneal permeability in an acute peritoneal dialysis model in anesthetized rats.

Design

To study the effect of fluid supplementation on peritoneal permeability characteristics, 24 anesthetized male Wistar rats were investigated in 3 groups during a 4-hour standardized peritoneal permeability analysis with a 3.86% glucose dialysis solution (SPARa). The groups included a control group with no fluid supplementation (None, n = 8), a group with continuous subcutaneous infusion of 0.9% NaCl 3 mL/hr (SC, n = 9), and a group with continuous intravenous infusion of 0.9% NaCl 3 mL/hr (IV, n = 7). Inflow, sampling, and outflow of the dialysate during the SPARa occurred via a cannula inserted intraperitoneally in the lower left quadrant of the abdomen. Blood was drawn at the end of the dwell. Baseline blood samples were obtained from six separate untreated rats.

Results

Plasma osmolality was significantly lower in the IV group (334 ± 1.4 mOsm/kg) compared to the None group (348 ± 0.7 mOsm/kg, p < 0.01), and not different from the SC group (335 ± 6.4 mOsm/kg), but higher than baseline (314 ± 5.3 mOsm/kg, p < 0.001). Urine production during the dwell was not different among the groups: None 10.6 ± 5.3 mL; SC 8.0 ± 6.0 mL; and IV 10.5 ± 5.6 mL. Transcapillary ultrafiltration after 4 hours was significantly higher in the IV group ( p < 0.05) compared to the other two groups. Net ultrafiltration and effective lymphatic absorption were similar in all groups. Mass transfer area coefficient of urea (MTACurea) was significantly greater in the IV group (155 ± 23.2 μL/minute, p < 0.003), but not different between the None (118 ± 16.2 μL/min) and SC (123 ± 25.9 μL/min) groups. Correcting these for the baseline plasma concentration resulted in higher values, but the IV data remained greater than the SC and None groups ( p < 0.01). The glucose absorption, albumin, and IgG clearances and the sieving of sodium were alike in all groups.

Conclusion

It can be concluded that IV fluid supplementation is more effective in preventing dehydration than SC supplementation, and it enhanced some peritoneal permeability characteristics in anesthetized rats during a 4-hour investigation. It is therefore important to standardize fluid supplementation in experiments with anesthetized animals.

The Difference in Causes of Early and Late Ultrafiltration Failure in Peritoneal Dialysis

♦ Objective

Ultrafiltration failure (UFF) is a major complication of peritoneal dialysis. Although it seems associated with long-term treatment, it can also occur in recently started patients. To identify the causes of this complication in patients with early and late UFF we studied a group of 48 patients. Patients were classified as early if they had been treated for less than 2 years and as late if they had been treated for more than 4 years.

♦ Method

The patients were studied using a standard peritoneal permeability analysis. They all had a net ultrafiltration of less than 400 mL after a 4-hour dwell with 3.86% glucose. As possible causes for UFF, the solute transport parameters dialysate-to-plasma ratio (D/P) and mass transfer area coefficient of creatinine were compared, as well as the effective lymphatic absorption rate (ELAR) and the maximum dip in D/P sodium as an assessment of osmotic conductance to glucose.

♦ Results

25 short-term patients were compared with 23 long-term patients. Both groups showed an equal distribution of high small solute transport rates as a cause of UFF. The chi-square test showed that a high ELAR was a more frequent cause in early UFF compared to late UFF. However, a decreased osmotic conductance to glucose was significantly more often observed in late UFF. Some patients showed more than one cause of the complication.

♦ Conclusion

This study has shown that UFF in long-term patients is often caused by a decreased osmotic conductance to glucose, most likely caused by a dysfunction of peritoneal water channels in combination with increased peritoneal surface area. In short-term patients, aquaporin dysfunction is rare, but a high ELAR was a very important factor in the occurrence of UFF.

Comparison of a 2.5% and a 4.25% Dextrose Peritoneal Equilibration Test

Background

Ultrafiltration (UF) failure develops over time in some patients on peritoneal dialysis. The workup of UF failure can be difficult and the 4.25% peritoneal equilibration test (PET) has been suggested to be more useful than the 2.5% PET for the workup of UF failure. It is unknown how a 4.25% PET compares to a 2.5% PET in individual patients.

Objectives

To assess the differences in drain volumes and sodium sieving using a 4.25% PET compared to a 2.5% PET, and to determine whether peritoneal transport rates, in terms of dialysate-to-plasma (D/P) ratios, are comparable between the two.

Design

Pilot study with each patient serving as his or her own control.

Setting

Outpatient dialysis facility of Wake Forest University Baptist Medical Center.

Patients

47 patients, all of whom had a 2.5% PET and a 4.25% PET performed within 1 week of each other.

Outcome Measures

Dialysate-to-plasma ratios of urea and creatinine, dialysate total protein, and dialysate glucose compared to time zero (D/D0) at 0, 2, and 4 hours. Four-hour drain volumes and sodium sieving at 2 hours were also measured.

Results

There was reproducibility between the 2.5% and 4.25% PET for D/P ratios of urea and creatinine and for dialysate total protein. There were expected differences in drain volume, sodium sieving, and D/D0 glucose between the two methods.

Conclusions

The use of a 4.25% PET may be more useful for the workup of UF failure because of the accentuation of drain volume and sodium sieving, while remaining useful for prescription management.

Correlation between Peritoneal Equilibration Test and Dialysis Adequacy and Transport Test, for Peritoneal Transport Type Characterization

Objective

The aim of this study was to analyze the correlation between the peritoneal equilibration test (PET) and the dialysis adequacy and transport test (DATT) for peritoneal transport type characterization, and the degree of patients’ acceptance for each test.

Design

Cross-sectional, observational multicenter study.

Setting

Five referral (tertiary) dialysis centers of institutional practice.

Patients

The study included 107 adult continuous ambulatory peritoneal dialysis (CAPD) patients with a prescription of four exchanges of 2 L per day, irrespective of age, gender, cause of end-stage renal disease, time on dialysis, nutritional status, or residual renal function. Patients on immunosuppressive therapy and those with cancer, hepatitis B, or HIV, and those having a peritonitis episode within the previous 30 days, or three or more episodes during the previous 12 months, were excluded.

Main Measures

Peritoneal transport type as classified by creatinine and urea dialysis-to-plasma (D/P) ratios by PET and DATT.

Results

Correlation coefficients between D/P ratios for creatinine and urea, obtained for the PET and the DATT, were 0.73 for D/P creatinine and 0.96 for D/P urea. Patients were classified into high, high-average, low-average, and low transport categories according to the mean and standard deviation of D/P creatinine values obtained from the PET at 4 hours. These values showed excellent concordance with those generated from the DATT data (κ = 0.82, 95% confidence interval 0.67 – 0.93). Nineteen percent of patients showed discordance in their category when classified according to the PET versus the DATT. Patients’ acceptance was better for the DATT than for the PET, as evaluated with a questionnaire.

Conclusion

The DATT is an easy, inexpensive, and reliable test to assess peritoneal transport type, and it also provides information about peritoneal clearance of solutes and ultrafiltration. The DATT has better patient acceptance than the PET. Since the DATT has only been validated for patients on a fixed CAPD daily schedule of 4 x 2 L, the results should be confined only to patients receiving such a prescription.

Determinants of Peritoneal Solute Transport Rates in Newly Started Nondiabetic Peritoneal Dialysis Patients

Objective

An overrepresentation of a fast peritoneal transport status in new peritoneal dialysis (PD) patients with extensive comorbidity has been reported in some studies. High mass transfer area coefficients (MTACs) of low MW solutes suggest the presence of a large effective peritoneal surface area. The mechanism is unknown. It might include comorbidity, chronic inflammation, or an effect of mesothelial cell mass on peritoneal transport by the production of vasoactive substances. To investigate their relative importance in early PD, peritoneal permeability characteristics in incident PD patients were analyzed for relationships with comorbidity, serum concentrations of inflammatory markers, and products of the mesothelial cells that can be detected in dialysate.

Design

A cross-sectional study.

Setting

A university hospital.

Methods

46 patients who fulfilled the following inclusion criteria were analyzed: a standard peritoneal permeability analysis (SPA) within 6 months after the start of PD, no peritonitis prior to the SPA, older than 18 years, and without diabetes mellitus as a primary renal disease. The patients were divided into tertiles based on the MTAC creatinine: slow, medium, and fast transport groups. The Davies comorbidity score was used to assess comorbidity. Serum and dialysate samples obtained during the SPA were used to determine hyaluronan, interleukin (IL)-6, vascular endothelial growth factor (VEGF), and cancer antigen 125 (CA125). The dialysate concentrations of these substances were expressed as their dialysate appearance rates.

Results

No significant differences were present in the three transport groups for comorbidity, serum concentrations of inflammatory markers, or serum VEGF. Interleukin-6 and VEGF concentration attributed to local VEGF production were not different between the tertiles. Levels of VEGF were higher in the medium transport group compared to the slow transport group ( p = 0.02); CA125 was higher in the fast transport group compared to the medium transport group ( p = 0.01). When analyzed as continuous variables, MTAC creatinine was related to VEGF ( r = 0.33, p < 0.05) and CA125 ( r = 0.41, p = 0.03). In linear regression analysis, VEGF influenced the association between CA125 and MTAC creatinine; IL-6 weakened this association only marginally.

Conclusion

A fast peritoneal transport status in incident nondiabetic PD patients was not related to comorbidity. The relationships found between VEGF, CA125, and MTAC creatinine may suggest a role of VEGF in the regulation of the vascular peritoneal surface area, possibly already before structural abnormalities have developed. Our analyses are consistent with the hypothesis that mesothelial cell mass is an important determinant of the peritoneal transport status in incident nondiabetic PD patients without previous peritonitis. Of the many potential mediators produced by mesothelial cells, VEGF was more important than the inflammation marker IL-6.

A Pyruvate-Buffered Dialysis Fluid Induces Less Peritoneal Angiogenesis and Fibrosis than a Conventional Solution

Background

Conventional lactate-buffered peritoneal dialysis (PD) fluids containing glucose and glucose degradation products are believed to contribute to the development of fibrosis and angiogenesis in the dialyzed peritoneum. To reduce potential negative effects of lactate, pyruvate was substituted as a buffer and its effects on peritoneal pathological alterations were studied in a chronic peritoneal exposure model in the rat.

Methods

20 Wistar rats were infused intraperitoneally with pyruvate-buffered ( n = 9) or lactate-buffered PD fluid. After 20 weeks of daily infusion, peritoneal function was assessed. In omental peritoneal tissue, the number of blood vessels was analyzed following alpha-smooth muscle actin staining. The degree of fibrosis was quantitated in Picro Sirius Red-stained sections and by assessment of the hydroxyproline content. Plasma lactate/pyruvate and beta-hydroxybutyrate/acetoacetate (BBA/AA) ratios were determined. Plasma and dialysate vascular endothelial growth factor (VEGF) levels were quantitated by ELISA.

Results

The mass transfer area coefficient of creatinine was higher and the dialysate-to-plasma ratio of sodium was lower in pyruvate-treated animals compared to the lactatetreated group (0.11 vs 0.05 mL/min, p < 0.05, and 78% vs 89%, p < 0.05). The BBA/AA ratio tended to be lower in the pyruvate animals ( p = 0.07). The number of blood vessels was lower in pyruvate-treated animals (16 vs 37 per field, p < 0.001). Total surface area, luminal area, and wall/total area of the vessels were larger in the pyruvate group. The degree of fibrosis was lower in intersegmental and perivascular areas of pyruvate-exposed animals. Effluent VEGF was higher in the pyruvate group.

Conclusions

Replacement of lactate by pyruvate resulted in changes in peritoneal solute transport, accompanied by a reduction in both peritoneal membrane angiogenesis and fibrosis, suggesting potentially novel mechanisms to reduce glucose-driven alterations to the peritoneal membrane in PD patients.

Does the Biocompatibility of the Peritoneal Dialysis Solution Matter in Assessment of Peritoneal Function?

Background

Peritoneal function tests are performed in peritoneal dialysis (PD) patients to characterize peritoneal membrane status. A low pH/high glucose degradation product (GDP) dialysis solution is used as the test solution. The objective of the present study was to compare a 3.86% glucose, low pH/high GDP dialysis solution (pH 5.5) with a 3.86% glucose, normal pH/low GDP dialysis solution (pH 7.4) in assessments of peritoneal membrane function.

Methods

Two standard peritoneal permeability analyses (SPA) were performed in 10 stable PD patients within 2 weeks. One SPA was done with the 3.86% low pH/high GDP solution, and the other with the 3.86% normal pH/low GDP solution. The sequence of the two tests was randomized.

Results

Fluid transport parameters and glucose absorption were not different between the two groups. No differences were found for the mass transfer area coefficients (MTACs) of low molecular weight solutes calculated over the whole dwell. However, MTAC urea in the first hour of the dwell was higher in the test done with low pH/high GDP dialysate, suggesting more peritoneal vasodilation. No difference was found in protein clearances. Sodium sieving at multiple time points during the dwell was similar with the two solutions.

Conclusion

The results obtained with the glucose-containing normal pH/low GDP dialysis solution were similar to those obtained with the glucose-containing low pH/high GDP dialysate in assessments of peritoneal membrane function.

Physiological Properties of the Peritoneum in an Adult Peritoneal Dialysis Population over a Three-Year Period

Objectives

To describe the physiological properties of the peritoneal membrane in adult patients treated with peritoneal dialysis (PD) and to analyze the effects of patient characteristics and time.

Design

Observational study.

Setting

Department of Nephrology at the Sahlgrenska University Hospital.

Method

Peritoneal function was analyzed by the Personal Dialysis Capacity (PDC) test, based on the three-pore theory of capillary transport. The functional PDC variables are absorption, large-pore flow, and the area parameter (A0/Δx), which determines the diffusion of small solutes. The ultra-filtration (UF) coefficient is determined mainly by A0/Δx.

Patients

All patients ( n = 280) who had at least one PDC test done between September 1990 and August 1999.

Results

In 249 patients examined soon after start of PD, area was 19000 (SD 7100) cm2/cm/1.73 m2, large-pore flow 0.112 (SD 0.052) mL/min/1.73 m2, and the UF coefficient 0.071 (SD 0.032) mL/minute/mmHg/1.73 m2. Absorption was 1.54 (SD +2.64, –0.97) mL/min/1.73 m2. Large-pore flow was greater in patients with severe comorbidity than in patients with fewer comorbid conditions. Elderly patients had a lower UF coefficient than did younger patients ( p < 0.05). Repeated PDC tests were performed in 208 patients during a mean observation time of 18.4 months. There was a slight increase in the slope of the area-versus-time curve of 54 cm2/cm/1.73 m2 per month (approximately 10% after 3 years, p < 0.01); all other parameters remained constant.

Conclusion

Patient characteristics have an impact on peritoneal performance already at the start of dialysis. Peritoneal function can remain essentially stable during medium long-term PD.

Analysis of the Prevalence and Causes of Ultrafiltration Failure during Long-Term Peritoneal Dialysis: A Cross-Sectional Study

Background

Ultrafiltration failure (UFF) is a major complication of peritoneal dialysis (PD). It can occur at any stage of PD, but develops in time and is, therefore, especially important in long-term treatment. To investigate its prevalence and to identify possible causes, we performed a multicenter study in The Netherlands, where patients treated with PD for more than 4 years were studied using a peritoneal function test (standard peritoneal permeability analysis) with 3.86% glucose. UFF was defined as net UF < 400 mL after a 4-hour dwell.

Results

55 patients unselected for the presence or absence of UFF were analyzed. Mean age was 48 years (range 18 – 74 years); duration of PD ranged from 48 to 144 months (median 61 months); UFF was present in 20 patients (36%). Patients with and without UFF did not differ in age or duration of PD. Median values for patients with normal UF compared to patients with UFF were, for net UF 659 mL versus 120 mL ( p < 0.01), transcapillary UF rate 3.8 versus 2.1 mL/minute ( p < 0.01), effective lymphatic absorption 1.0 versus 1.6 mL/min ( p < 0.05), mass transfer area coefficient (MTAC) for creatinine 9.0 versus 12.9 mL/min ( p < 0.01), dialysate-to-plasma ratio (D/P) for creatinine 0.71 versus 0.86 ( p < 0.01), glucose absorption 60% versus 73% ( p < 0.01), maximum dip in D/P sodium (as a measure of free water transport) 0.109 versus 0.032 ( p < 0.01), and osmotic conductance to glucose 3.0 versus 2.1 μL/min/mmHg ( p < 0.05). As causes for UFF, high MTAC creatinine, defined as > 12.5 mL/min, or a glucose absorption > 72%, both reflecting a large vascular surface, a lymphatic absorption rate (LAR) of > 2.14 mL/min, and a decreased dip in D/P sodium of < 0.046 were identified. Most patients had a combination of causes (12 patients), whereas there was only a decreased dip in D/P sodium in 3 patients, only high MTAC creatinine in 1 patient, and only high LAR in 2 patients. We could not identify a cause in 2 patients. Both groups had similar clearances of serum proteins and peritoneal restriction coefficients. However, dialysate cancer antigen 125 concentrations, reflecting mesothelial cell mass, were lower in the UFF patients (2.79 vs 5.38 U/L).

Conclusion

The prevalence of UFF is high in long-term PD. It is caused mainly by a large vascular surface area and by impaired channel-mediated water transport. In addition, these patients also had signs of a reduced mesothelial cell mass, indicating damage of the peritoneum on both vascular and mesothelial sites.

Impact of ACE Inhibitors and AII Receptor Blockers on Peritoneal Membrane Transport Characteristics in Long-Term Peritoneal Dialysis Patients

Background

Long-term peritoneal dialysis (PD) may lead to peritoneal fibrosis and ultrafiltration failure. The latter occurs due to high solute transport rates and diabetiform peritoneal sclerosis. Angiotensin-II (AII) is known to be a growth factor in the development of fibrosis and a number of animal studies have shown it likely that inhibiting the effects of AII by angiotensin-converting enzyme (ACE) or angiotensin receptor blocker (ARB) will attenuate these complications.

Objective

To investigate the effects of ACE/AII inhibitors in long-term PD patients.

Patients and Setting

We analyzed data from 66 patients treated with PD therapy at our center for at least 2 years, during which time at least 2 standard peritoneal permeability analyses (SPAs) were performed. 36 patients were treated with ACE/AII inhibitors (ACE/ARB group); the other 30 received none of the above drugs during the entire follow-up (control group). The two groups were compared with respect to changes in peritoneal transport over the follow-up time.

Results

A significant difference in time course of peritoneal transport was found between the 2 groups: in the ACE/ARB group, small solute transport had decreased, while it had increased in the control group. This finding was confirmed by analysis using mixed model for repeated measures. The value of mass transfer area coefficient of creatinine was influenced by the duration of PD therapy ( p = 0.017) and this interaction was different with respect to use of ACE/AII inhibitors ( p = 0.037). The trend was not found in protein clearances or fluid kinetics.

Conclusion

Our findings suggest that ACE/AII inhibition is likely to prevent the increase in mass transfer area coefficients that occurs in long-term PD, which is in line with results of experimental animal studies.