Quantification of free water transport in peritoneal dialysis

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

Dialysate copeptin and peritoneal transport in incident peritoneal dialysis patients

International Urology and Nephrology - Systemic and intraperitoneal inflammation are characteristic features of patients with end-stage renal disease undergoing chronic peritoneal dialysis (PD)....     

Buffer transport in peritoneal dialysis

Buffer transport in peritoneal dialysis. The success of peritoneal dialysis as a robust modality of renal replacement therapy has invited a quest for ameliorations in its underlying technology aimed at enhancing patient satisfaction and preserving the central instrument of the therapy, namely the peritoneal membrane. The health and longevity of the membrane have motivated and continue to drive a series of iterative innovations in the composition, methods of production, and delivery of dialysis solutions. It is the purpose of this article to review aspects of these innovations pertaining to buffer composition in dialysis solutions and the peritoneal mechanisms of buffer transport.     

Intraperitoneal heparin reduces peritoneal permeability and increases ultrafiltration in peritoneal dialysis patients.

BACKGROUND: Patients on long-term treatment with peritoneal dialysis (PD) suffer from increasing peritoneal permeability and loss of ultrafiltration as a result of persistent inflammation, which may be triggered by bioincompatible dialysis fluids. Heparins have anti-inflammatory and anticoagulant properties. We have examined the effect of intraperitoneal (IP) low-molecular weight heparin (tinzaparin) on peritoneal permeability and ultrafiltration in PD patients. METHODS: By means of a double-blinded cross-over design, 21 PD patients were randomized to receive either placebo or tinzaparin intraperitoneally once a day for two treatment periods of 3 months, separated by a wash-out period. The effect of heparin on peritoneal permeability and ultrafiltration was assessed using the 4 h standard peritoneal equilibration test. RESULTS: IP tinzaparin reduced significantly the dialysate-to-plasma ratios (D/P) of creatinine (P < 0.01), urea (P < 0.01) and albumin (P<0.05). In addition, the ratio of glucose concentration in dialysate at 4 h dwell to that of 0 h dwell (D(4)/D(0)) was increased (P<0.05) along with an increase in ultrafiltration volume (P<0.05). CONCLUSIONS: IP tinzaparin reduces peritoneal permeability to small solutes and increases ultrafiltration in PD patients.     

Long-term changes in transperitoneal water transport during continuous ambulatory peritoneal dialysis

9 patients were observed prospectively during 14-40 months 003 continuous ambulatory peritoneal dialysis (CAPD) treatment. From start of CAPD, each patient recorded dwell time, drained ultrafiltration volume (delta V), initial glucose concentration in dialysate, dialy fluid intake, body weight and blood pressure on a special form. These data, together with monthly values for albumin, urea, creatinin, phosphate, glucose and beta 2-microglobulin in plasma and in instilled dialysate, were later fed into a specially designed computer program to compare changes in the monthly mean (+/- SEM) values. During 5 episodes of peritonitis, daily changes in delta V were also computed. A long-term increase in delta V was found in 4 and a decrease in 5 patients. In all 9 patients delta V changed intermittently. All changes were most pronounced for long dwell times as compared to shorter dwell exchanges. The decrease in delta V started within the first 12 months of treatment. In the daily routine were aware of decreased ultrafiltration capacity in 3 patients only. Intermittent monthly changes in delta V could partly be correlated to changes in daily fluid intake. No correlations were found between long-term changes in delta V and fluid intake. All except 1 patient gained progressively in body weight, but without correlations to fluid balance, blood pressure and plasma albumin concentration. At the start of the observation period, most patients loosing delta V during this study appeared to have a more permeable membrane with a higher absorption rate of glucose and higher equilibration ratios for creatinine and beta 2-microglobulin in 5-hours drained dialysate as compared with the other patients. However, this was not statistically different between the two groups of patients. During the observation period, most patients with decreased delta V also increased transperitoneal solute transport, while the solute transport decreased in patients with increasing delta V, but these changes were only significant for some patients. During peritonitis, delta V decreased significantly 1 day before any other signs of peritonitis. All changes in delta V were most pronounced for long dwell times as compared with short dwell times. It is suggested that changes in ultrafiltration can be related to altered permeability of the peritoneal membrane, which appear earlier and more frequent than suggested by others, and any loss of delta V can be explained by a more permeable ('open') peritoneal membrane. It is also possible that different diseases act differently on the permeability of the peritoneal membrane.     

The cellular contribution to effluent potassium and its relation to free water transport during peritoneal dialysis.

BACKGROUND: Aquaporin-1 (AQP-1) dysfunction is one of the valid theories for decreased free water transport (FWT) in long-term peritoneal dialysis (PD) ultrafiltration failure (UFF). We questioned whether apoptosis of peritoneal cells could be reflected in an increased release of cellular (CR) K(+) and explain AQP-1 dysfunction. If so, negative relationships between CR-K(+) and FWT would be expected. Therefore, we analysed CR-K(+) to total peritoneal K(+) removal, for possible relationships with FWT, the duration of PD, the presence of late UFF and effluent cancer antigen (CA) 125. METHODS: Standard peritoneal permeability analyses done with 3.86% glucose were investigated cross-sectionally in three extreme groups: group I: 19 patients <1 year on PD; group II: 20 patients >4 years on PD without UFF; group III: 19 patients >4 years on PD with UFF. RESULTS: Group III had the lowest values of FWT and CR-K(+) (P < 0.01). CR-K(+) had a positive correlation with FWT in groups I and II, but not in group III. These correlations were also present using much simpler methodologies: replacement of CR-K(+) by mass transfer area coefficient (MTAC)-K(+)/MTAC-creatinine ratio or dialysate over plasma (D/P)-K(+)/D/P-creatinine ratio and replacement of FWT by Na(+)-sieving. No relationship with CA125 was present. CONCLUSIONS: This study shows that other than diffusive and convectional, K(+) transport is not excluded in patients treated with conventional glucose-based PD solutions. We found evidence for release of K(+) from cells. In general, CR-K(+) was related to parameters of FWT, except for long-term patients with UFF. This suggests glucose-induced hypertonic cell shrinkage as a basic physiological phenomenon during PD. The absence of this relationship in long-term PD patients with UFF either suggests a reduction or inhibition of K(+)-channels and may be due to another mechanism than AQP-1 dysfunction. Most likely, CR-K(+) in UFF does not reflect apoptosis. However, the D/P-K(+)/D/P-creatinine ratio may be useful in detecting peritoneal changes.     

Phosphatidylcholine and peritoneal transport during peritoneal dialysis

Peritoneal effluent of patients on chronic ambulatory peritoneal dialysis (CAPD) contains a surface-active material (SAM) made up of phospholipids and showing phosphatidylcholine on thin-layer chromatography. This substance drastically lowers surface tension, helps to repel water and has a lubricating effect. The presence of stratified phosphatidylcholine on the peritoneum might narrow the stagnant dialysate fluid layer and situations which can alter the quantity or composition of SAM may affect peritoneal transport and also, perhaps, the formation of adherences. This led us to verify, experimentally, the presence of phospholipids in basal conditions, after CAPD and during peritonitis and to check if addition of phosphatidylcholine to dialysis liquid is able to modify water transport in patients with low ultrafiltration and peritonitis. Phospholipids in the dialysis effluent of patients who have been on CAPD for a long time are lower than observed in the first days of peritoneal dialysis. A more drastic, significant decrease in phospholipids was observed in patients with low ultrafiltration and in patients with peritonitis. Mean ultrafiltration significantly increases in patients with low ultrafiltration and in those with peritonitis during dialysis exchanges containing phosphatidylcholine (50 mg/l) indicating that the latter is able to restore normal physiological conditions.     

Longitudinal changes of solute transport in peritonitis-free peritoneal dialysis patients

BACKGROUND: The aim of this study was to evaluate the longitudinal changes in peritoneal transport in patients on long-term, peritonitis-free, continuous ambulatory peritoneal dialysis (CAPD) therapy. METHODS: Results were longitudinally recorded for the standard peritoneal equilibration test (PET) in 76 consecutive, nondiabetic, adult patients from the beginning of CAPD therapy until their first episodes of peritonitis, abdominal surgery, or any cause of drop out. The PET results were evaluated once annually using the dialysate-to-plasma ratio of creati-nine (D/PCr) and the dialysate-to-instilled dextrose ratio (D4/D0) at 4 hours after beginning dialysis. RESULTS: A total of 168 PET results were obtained. A statistically significant tendency toward decreased D/PCr and increased D4/D0 values over time for up to 3 years was found. CONCLUSIONS: This study shows a tendency toward progressive decline in small molecular transport over time in nondiabetic patients with uneventful CAPD therapy. Sequential PET follow-up cannot be overlooked in peritonitis-free CAPD patients.     

不同腹膜溶质转运特性腹膜透析患者营养状况的比较

目的 探讨腹膜转运特性对腹膜透析患者营养状态的影响。方法 按照腹膜平衡试验(PET)计算结果,将82例稳定的CAPD患者分为高转运组和低转运组。检测患者血浆和腹透透出液总蛋白、白蛋白及氨基酸量,同步计算蛋白质摄入量(DPI)和蛋白质分解率(nPCR)。比较两组营养状态及分析相关因素。结果两组的残余肾功能、腹透治疗时间、每日透析液剂量、超滤量、葡萄糖吸收量、血糖、BUN、Scr和Kt／V均无显著性差异。高转运组每日经腹透透出液丢失的总蛋白质和多种氨基酸量明显高于低转运组;各项营养指标均低于低转运组,且体重及血清白蛋白有显著性差异。血中及经腹透透出液丢失的白蛋白和氨基酸量均与转运类型相关。结论 腹膜透析高转运患者营养状态较低转运者差。单纯提高透析充分性并不能明显改善营养状态。要加强对高转运患者的营养管理和指导。     

腹膜透析患者腹膜转运功能与大动脉僵硬度的关系

腹膜透析作为终末期肾病替代治疗的一种方式,是通过腹膜对溶质和液体的转运实现的.因此,腹膜转运功能对溶质和液体的清除有十分重要的影响.     

重新评价腹膜平衡试验以确定腹膜透析患者的溶质转运类型

目的 确定由Twardowski提出的腹膜平衡试验（PET）的转运类型评判值是否适合本中心患者。方法 选取我院自1995年来首次进行PET测试的患者158例。首先依据Twardowski的评判标准（值）判断患者的转运类型,再根据本组患者实际4hD/Pcr的χ±s来确定患者的溶质转运类型,然后将患者重新分组:按两种数值均符合高转运为H1组,均符合平均转运为A组,均符合低转运为L1组,部分高转运患者经重新评价后符合平均转运为H2组,部分平均转运患者经重新评价后符合低转运为L2组。通过与临床情况（溶质和水的清除）进行对照,以进一步评价更适合本中心患者的评判标准。结果 按照Twardowski的标准,高转运、高平均转运、低平均转运及低转运患者的比例分别为21.5％、44.9％。27.8％及5.7％。本研究患者群中4hD/Pcr的均值和标准差为0.70和0.14,据此重新评判后,各组的比例分别为14.6％、33.5％、33.5％及18.4％。经与临床结果相对比,L2组对水份的清除能力明显高于A组（P<0.005）,与L1组差别无显著性意义。结论4hD/Pcr在不同的地区和人群中表现出不同的均数和标准差值,因而产生了不同的腹膜转运类型。根据本中心患者人群确定的值更适合本中心患者的临床情况。     

The treatment of anemia in peritoneal dialysis patients.

The management of anemia in patients with end-stage renal disease (ESRD) treated with peritoneal dialysis (PD) has gained increasing attention over the past decade, similar to patients on hemodialysis (HD). However, there are many differences between the 2 renal replacement therapies that pose unique challenges and solutions for monitoring, diagnosis and treatment of anemia in PD patients. These differences are not always evident and may be the result of different patient selection, physical, emotional and motivational factors, specific requirements of the modality or an indeterminate blend of infinite gradations of all these factors. This review will highlight current issues in anemia management in PD patients.     

Bidirectional peritoneal transport of albumin in continuous ambulatory peritoneal dialysis

The present study was undertaken in order to assess bidirectionalperitoneal kinetics of albumin after simultaneous i.v. and i.p.injection of radioiodinated albumin tracers (¹²⁵I-RISA and ¹³¹I-RISA)in eight clinically stable uraemic patients undergoing continuousambulatory peritoneal dialysis (CAPD). The plasma volume, intravascularalbumin mass (IVM), and overall extravasation rate of albuminwere not significantly different from that found in healthycontrols. Albumin flux from the plasma into the peritoneal cavitywas 3.71 ± 0.82 (SD) µmol/h, which was only 3%of the overall extravasation rate (137 ± 52 µmol/h).Albumin flux from the peritoneal cavity into the plasma wassubstantially lower (0.22 ± 0.07 µmol/h, P<0.01).The net peritoneal accumulation of the albumin from plasma over4 h was 14 ± 3.2 µmol, which was significantlylower than the intraperitoneal albumin mass at the end of thedialysis (54 ± 19 µmol, P<0.01). This indicatesthat only about 25% of the albumin loss during CAPD occurs directlyfrom the plasma. The initial osmotic net filtration was 508± 302 ml. The volume flow equivalent to the albumin fluxwas 6.3 ± 1.5ml/h into the peritoneal cavity and 7.8± 1.9ml/h back into the plasma. Although minor, as comparedto the osmotic net filtration (508 ml), the albumin flux equivalentvolume (31.2 ml) exceeded the steady state filtration (25.2ml) significantly (P<0.01) during the 4 h investigation. In conclusion, albumin flux into the peritoneal cavity is smallcompared to the overall extravasation rate, but our resultssuggest that CAPD loss of albumin predominantly occurs fromthe subperitoneal interstitial space and only to a minor degreedirectly from the plasma. Albumin flux equivalent volume flowis relatively small and most probably represents peritoneallymph drainage.     

腹膜通透性与腹透患者长期生存的关系

目的：探讨腹膜通透性类型与腹透长期存活的关系。方法：测定71例腹透病例透析初期（3个月内）,以及其中18例持续腹透超过4年的病例透析初期和远期（4年以上）的腹膜平衡试验（PET）,计算并分析各种腹膜通透类型长期生存概率,及长期存活病人腹膜通透性的变化情况。结果：71例病人透析初期各种腹膜通透类型的比例辚高转运23．94％,高平均转运39．44％,低平均转运26．76％和低转运9．86％,18例持续腹透超过4年的病例中,高或高平均转运各2例,低或低平均转运分别为4例和10例,生存概率分别为11．76％,7．14％,57．14％和52．63％,其中7例透析初期和远期腹膜通透性未发生变化,9例通透性较前降低,另2例高血压肾病患腹膜通透性则较前增高,结论：各种腹膜通透类型均可能长期存活,但以低通透性腹膜长期生存概率较高,提示更适宜进行长期腹膜透析治疗,长期透析腹膜通透 可保持不变或不同程度降低,并观察到高血压肾病长期腹透后通透性较前增加的现象。     

Longitudinal relationship between solute transport and ultrafiltration capacity in peritoneal dialysis patients

BACKGROUND: Time on treatment is associated with a greater risk of impaired ultrafiltration (UF) in peritoneal dialysis (PD) patients. In addition to increasing solute transport, a potentially treatable cause of impaired ultrafiltration, cross-sectional studies suggest that there is also reduced osmotic conductance of the membrane. If this were the case then it would be expected that the UF capacity for a given rate of solute transport would change with time. The purpose of this analysis was to establish how solute transport and UF capacity change relative to one another with time on therapy. METHODS: Membrane function, using a standard peritoneal equilibration test, was measured at least annually in a well-characterized, single-center observational cohort of PD patients between 1990 and 2003. Demography included age, gender, original cause of renal failure, body surface area (BSA), validated comorbidity score, residual urine volume and urea clearances, peritoneal urea clearances, and plasma albumin. RESULTS: Data from 574 new PD patients were available for analysis. Independent demographic factors associated with higher solute transport at baseline were male gender and higher residual urine volume. Throughout time on therapy there was a negative relationship between solute transport and UF capacity and a significant increase and decrease in these parameters, respectively. During the first 12 months of treatment, the increase in solute transport was not associated with the expected fall in UF capacity, a phenomenon that was not explained by informative censoring, but was associated with an increased, albeit weak, correlation with BSA. In contrast, later in treatment there was a disproportionate fall in UF capacity, more accelerated in patients developing UF failure. Early exposure to higher intraperitoneal glucose concentrations, in the context of more comorbidity and relative lack of residual renal function, was associated with more rapid deterioration in membrane function. CONCLUSION: Despite a causal link between solute transport and UF capacity of the membrane, due to the effect of the former on the osmotic gradient, there is evidence of their longitudinal dissociation. This implies a change in the structure-function relationship with time on treatment that can, to some extent, be predicted from clinical factors present within the first year of treatment. Dialysis-induced membrane injury must involve at least two processes, for example, increased vascular surface area contact with dialysate combined with changes in hydraulic conductance due to scarring of the vessels and interstitium.     

Hyponatremia in peritoneal dialysis patients

BACKGROUND: Low serum sodium is uncommon in peritoneal dialysis (PD), which is surprising in view of the important role of normal kidney function to regulate water and sodium balance. METHODS: We report 2 cases of persistent hyponatremia with balance studies in Case 1. We performed measurements of dialysate sodium and volume output over 24 hours in a group of chronic PD patients. RESULTS: The low serum sodium concentration did not vary too much with overall fluid removal via dialysis in patient 1, mainly because large quantities of sodium were removed in the dialysate. In the 24-hour studies, a significant relationship was found between net daily PD sodium removal and net daily dialysate volume removed (r = 0.65). There was no relationship between net daily PD sodium removal and serum sodium concentration. There was a linear direct correlation between serum and dialysate sodium concentration (r = 0.8) as shown by others previously. CONCLUSIONS: These results suggest that the main determinant of PD sodium loss is net dialysate ultrafiltration volume. Water loss via dialysis is necessarily associated with sodium loss. In order to maintain a normal serum sodium concentration salt intake must be proportional to the water loss induced by dialysis. The stimuli that allow dialysis patients to maintain this delicate balance between water and salt intake are of considerable interest but remain undetermined.     

Dioctyl sodium sulphosuccinate increases net ultrafiltration in peritoneal dialysis

Background. The surface-active substance dioctyl sodium sulphosuccinate (DSS) has been reported to increase the peritoneal clearances of urea and creatinine. This study investigated the effects of DSS on the fluid and solute transport characteristics of the peritoneum. Design. A 4-h single-dwell experiment session of peritoneal dialysis using 25 ml of 3.86% glucose dialysis solution with an intraperitoneal volume maker was performed in 16 male Sprague-Dawley rats. In eight rats, 0.005% (50 p.p.m.) DSS was added to the dialysis fluid. No DSS was given to the other eight rats (control group). The transport of fluid, glucose, potassium, sodium, urea, phosphate and urate were analysed. Results. There was a significant increase in the intraperitoneal volume in the DSS group (33.0±2.9 ml) was significantly higher compared to the control group (28.8±2.1 ml. P<0.01). This increase in the drain volume was mainly due to a decrease in peritoneal fluid absorption rate in the DSS group (0.040±0.013 ml/min) as compared to the control group (0.054±0.010 ml/min, P0.05). There was no significant difference in the diffusive permeability and sieving coefficient for the small solutes between these two group. However, the clearances for urea and sodium were higher in the DSS group, mainly due to the increase in the dialysate volume. Conclusion. Our results suggest that DSS significantly increases the net ultrafiltration of peritoneal dialysis. This effect, which was mainly due to a decrease in the fluid absorption rate, contributed to the increased clearances for urea and sodium. DSS did not alter the diffusive permeability and sieving coefficient for the small solutes.