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.

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.

Peritoneal Equilibration Test and Patient Outcomes

BACKGROUND AND OBJECTIVES

Although a peritoneal equilibration test yields data on three parameters (4-hour dialysate/plasma creatinine, 4- to 0-hour dialysate glucose, and 4-hour ultrafiltration volume), all studies have focused on the prognostic value of dialysate/plasma creatinine for patients undergoing peritoneal dialysis. Because dialysate 4- to 0-hour glucose and ultrafiltration volume may be superior in predicting daily ultrafiltration, the likely mechanism for the association of peritoneal equilibration test results with outcomes, we hypothesized that they are superior to dialysate/plasma creatinine for risk prediction.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We examined unadjusted and adjusted associations of three peritoneal equilibration test parameters with all-cause mortality, technique failure, and hospitalization rate in 10,142 patients on peritoneal dialysis treated between January 1, 2007 and December 31, 2011 in 764 dialysis facilities operated by a single large dialysis organization in the United States, with a median follow-up period of 15.8 months; 87% were treated with automated peritoneal dialysis.

RESULTS

Demographic and clinical parameters explained only 8% of the variability in dialysate/plasma creatinine. There was a linear association between dialysate/plasma creatinine and mortality (adjusted hazards ratio per 0.1 unit higher, 1.07; 95% confidence interval, 1.02 to 1.13) and hospitalization rate (adjusted incidence rate ratio per 0.1 unit higher, 1.05; 95% confidence interval, 1.03 to 1.06). Dialysate/plasma creatinine and dialysate glucose were highly correlated (r=-0.84) and yielded similar risk prediction. Ultrafiltration volume was inversely related with hospitalization rate but not with all-cause mortality. None of the parameters were associated with technique failure. Adding 4- to 0-hour dialysate glucose, ultrafiltration volume, or both did not result in any improvement in risk prediction with dialysate/plasma creatinine alone.

CONCLUSIONS

This analysis from a large contemporary cohort treated primarily with automated peritoneal dialysis validates dialysate/plasma creatinine as a robust predictor of outcomes in patients treated with peritoneal dialysis.

Dialysate cancer antigen 125 in long-term peritoneal dialysis patients

Structural and functional peritoneal membrane changes are associated with long-term peritoneal dialysis. These changes can lead to ultrafiltration failure and peritoneal fibrosis, reducing the efficacy of the peritoneal membrane to remove waste and balance fluid and electrolytes. The loss of mesothelial cells from the basement membrane is one of the major characteristics in peritoneal membrane structural change. Thus, if the reduction of peritoneal mesothelial cell mass in peritoneal dialysis patients is monitored, signs of ultrafiltration failure and peritoneal fibrosis can be detected early. One of biomarkers that can be used to indicate the change in peritoneal mesothelial cell mass is CA125, which is produced by mesothelial cells. In this article, we review the measurement and clinical use of CA125 in peritoneal dialysate effluent. Additionally, we address the data and studies on the association between dialysate CA125 levels and factors related to ultrafiltration failure and peritoneal fibrosis, including the parameters used to monitor the functional status of the peritoneal membrane. Our review shows that dialysate CA125 can be used to evaluate the peritoneal membrane in noninfected patients to predict peritoneal fibrosis, and it can also be used as a biomarker of biocompatible dialysis solutions.

The Stoke contribution to peritoneal dialysis research

The Stoke Renal Unit has been at the forefront of peritoneal dialysis (PD) research for much of the past two decades. Central to this work is the PD cohort study, which was started in 1990 and is based on regular outpatient measurements of peritoneal and clinical function, correlating these with long-term outcomes. It has provided a wealth of information on risk factors for morbidity and mortality in patients on PD, the most significant being demonstration of the effects of time and dialysate glucose exposure on changes to the peritoneal membrane, as evidenced by increases in small solute transport. Early on, the study confirmed the adverse relationship between high small-solute transport status and outcome but more recently suggested that this relationship no longer held with modern techniques for managing patients on PD. Central themes of the PD research in Stoke have included evaluation of euvolemia, the importance of ultrafiltration and how best to achieve it, and detailed assessments of transmembrane water movement. The work has included the study of sodium removal and the use of novel low sodium dialysates. More recently, attention has turned to the significance of impaired ultrafiltration capacity in patients on PD as a sign of structural membrane damage. It is hoped that further work in this area will identify preventive strategies.

Salt and Fluid Intake in the Development of Hypertension in Peritoneal Dialysis Patients

BACKGROUND

Although fluid overload contributes to hypertension in CAPD patients, less attention has been paid to the role of excess salt and fluid intake. Therefore, we investigated the role of salt and fluid intake in the development of hypertension in CAPD patients.

METHODS

A total of 165 stable CAPD patients were included into this study. Based on the blood pressure in three consecutive months, they were divided into three groups: persistent hypertensive (PH; n = 33), intercurrent hypertensive (IH; n = 58) and persistent normotensive (PN; n = 74). The IH group was further divided into two phases: normotensive and hypertensive. Fluid status was evaluated by clinical assessment and bioimpedance analysis (BIA).

RESULTS

There were no differences in age, gender, and duration of dialysis among groups. Patients were more fluid overloaded in the PH group. Extracellular water (ECW), total body water (TBW), and normalized extracellular water by height (NECW) were higher in the PH group than the PN group (16.77 +/- 3.62 L vs. 14.61 +/- 2.92 L for ECW, p < 0.01; 32.22 +/- 8.23 L vs. 28.98 +/- 6.00 L for TBW, p < 0.05; and 10.28 +/- 1.86 L/m vs. 9.08 +/- 1.63 L/m for NECW, p < 0.01). However, patients in the PH group also had more total fluid removal (TFR) and total sodium removal (TSR) compared with the PN group (1346.82 +/- 431.27 mL/d vs. 1139.28 +/- 412.65 mL/d for TFR, p < 0.05; and 141.52 +/- 61.57 mmol/d vs. 102.42 +/- 62.51 mmol/d for TSR, p < 0.01). The same trend was demonstrated when compared values of hypertensive and normotensive phase in IH group; patients had higher ECW, TBW, NECW, TSR, and PNa when they were in hypertensive phase than in the normotensive phase.

CONCLUSIONS

This study confirmed that fluid overload was closely associated with the development of hypertension in CAPD patients. It also showed that hypertensive patients were in general more fluid overloaded despite a higher fluid and sodium removal as compared with normotensive patients.

Contrasting clinical outcomes between different modes of peritoneal dialysis regimens: two center experiences in China

In the present study, we compared the clinical outcomes between two different modes of peritoneal dialysis (PD) and explored the possible role of volume overload in continuous ambulatory peritoneal dialysis (CAPD) patients. A longitudinal and a cross-sectional study were included. Patients received either an 'adaptative ultrafiltration (UF)' PD regimen, which focused on gradually increasing peritoneal ultrafiltration (PDi group), or traditional PD treatment (PDt group). Patients' demographic characteristics, nutritional status, fluid removal as well as fluid status were recorded. In the cross-sectional study, all clinically stable patients who were treated with CAPD for at least three months were enrolled and grouped according to their time on dialysis: short term, medium term, and long term. Both studies showed that PDi and PDt patients had distinct fluid removal patterns. PDt patients had decreased total fluid removal with worsening fluid status and deteriorating nutritional status, whereas PDi patients remained rather stable in relation to fluid removal, fluid status, and improving nutritional status. Cox regression analysis confirmed that the PDi group had better patient survival than the PDt group. Our data suggest that traditional and 'adaptative UF' PD therapy may have distinct fluid removal patterns over time on dialysis, and this unique pattern might partly explain the still unacceptable high mortality of long-term CAPD patients.

Aquaporin-1 plays an essential role in water permeability and ultrafiltration during peritoneal dialysis

The water channel aquaporin-1 (AQP1) is considered as the molecular counterpart of the ultrasmall pore predicted by the three-pore model of fluid transport across the peritoneal membrane. However, the definitive proof of the implication of AQP1 in solute-free water transport, sodium sieving, and ultrafiltration (UF) during peritoneal dialysis (PD) is lacking, and the effects of its deletion on the structure of the membrane are unknown. Using real-time reverse transcriptase-polymerase chain reaction and immunogold electron microscopy, we showed that AQP1 is the most abundant member of the AQP gene family expressed in the mouse peritoneum, and the only one located in the capillary endothelium. Transport studies during a 2-h dwell demonstrated that, in comparison with Aqp1(+/+) littermates, Aqp1(-/-) mice had no sodium sieving; an approximately 70% decrease in the initial, solute-free UF; and an approximately 50% decrease in cumulative UF. These modifications occurred despite unchanged osmotic gradient and transport of small solutes in the Aqp1(-/-) mice. Heterozygous Aqp1(+/-) mice showed intermediate values in sodium sieving and initial UF, whereas cumulative UF was similar to Aqp1(+/+) mice. The deletion of AQP1 had no effect on the expression of other AQPs and on the density, structure, or diameter of peritoneal capillaries. These data provide direct evidence for the role of AQP1 during PD. They validate essential predictions of the three-pore model: (i) the ultrasmall pores account for the sodium sieving, and (ii) they mediate 50% of UF during a hypertonic dwell.

Free-water transport in fast transport status: A comparison between CAPD peritonitis and long-term PD

BACKGROUND

Ultrafiltration failure (UFF) in continuous ambulatory peritoneal dialysis (CAPD) is a transient phenomenon during acute peritonitis and a permanent complication in long-term peritoneal dialysis (PD). The high solute transport rates during acute peritonitis are probably caused by an increased number of perfused peritoneal capillaries. Long-term PD is associated with an increased number of peritoneal microvessels, leading to an enlargement of the anatomic vascular surface area. This leads to high mass transfer area coefficients (MTAC) and to UFF. Impaired conductance to glucose, leading to a reduction in free-water transport, may be a contributing factor to UFF in long-term PD. We hypothesized that UFF during acute peritonitis is, in the absence of permanent structural changes, only caused by an increased vascular surface area, while in long-term patients it is often the result of an increased surface area in combination with an impaired conductance to glucose. Therefore, the peritoneal transport parameters of patients with acute peritonitis were compared to those in long-term PD patients.

METHODS

A standard peritoneal permeability analysis (SPA) was done in 10 PD patients during the first 48 hours after the diagnosis of peritonitis. The results were compared to those obtained in 10 long-term PD patients matched for the MTAC creatinine. In addition, the results of 8 peritonitis patients were compared with SPA results of 8 recently started PD patients, matched for MTAC creatinine.

RESULTS

Peritonitis patients had a deeper maximal dip in D/P sodium, corrected for diffusion, than long-term patients (0.058 vs. 0.039, P < 0.05). Most parameters of peritoneal fluid transport were not different, except that t50 (i.e., the time to reach 50% of the maximum transcapillary ultrafiltration) was reached earlier during the dwell in peritonitis than in long-term PD-128 versus 175 minutes, P < 0.05. This confirmed the difference in the shape of the intraperitoneal volume versus time curve, which was blunted in the long-term patients. No differences were found for the parameters of solute transport between peritonitis patients and recently started patients.

CONCLUSION

In contrast to patients with long-term PD, the osmotic conductance to glucose is unaffected in peritonitis, despite the lower net ultrafiltration caused by high solute transport. This implies that impaired free- water transport in chronic PD must be regarded as a contributing factor to UFF.

Icodextrin as salvage therapy in peritoneal dialysis patients with refractory fluid overload

BACKGROUND

Icodextrin is a high molecular weight, starch-derived glucose polymer, which is capable of inducing sustained ultrafiltration over prolonged (12-16 hour) peritoneal dialysis (PD) dwells. The aim of this study was to evaluate the ability of icodextrin to alleviate refractory, symptomatic fluid overload and prolong technique survival in PD patients.

METHODS

A prospective, open-label, pre-test/post-test study was conducted in 17 PD patients (8 females/9 males, mean age 56.8 +/- 2.9 years) who were on the verge of being transferred to haemodialysis because of symptomatic fluid retention that was refractory to fluid restriction, loop diuretic therapy, hypertonic glucose exchanges and dwell time optimisation. One icodextrin exchange (2.5 L 7.5%, 12-hour dwell) was substituted for a long-dwell glucose exchange each day.

RESULTS

Icodextrin significantly increased peritoneal ultrafiltration (885 +/- 210 ml to 1454 +/- 215 ml, p < 0.05) and reduced mean arterial pressure (106 +/- 4 to 96 +/- 4 mmHg, p < 0.05), but did not affect weight, plasma albumin concentration, haemoglobin levels or dialysate:plasma creatinine ratio. Diabetic patients (n = 12) also experienced improved glycaemic control (haemoglobin Alc decreased from 8.9 +/- 0.7% to 7.9 +/- 0.7%, p < 0.05). Overall PD technique survival was prolonged by a mean of 11.6 months (95% CI 6.0-17.3 months). On multivariate Cox proportional hazards analysis, extension of technique survival by icodextrin was only significantly predicted by baseline net daily peritoneal ultrafiltration (adjusted HR 2.52, 95% CI 1.13-5.62, p < 0.05).

CONCLUSIONS

Icodextrin significantly improved peritoneal ultrafiltration and extended technique survival in PD patients with symptomatic fluid overload, especially those who had substantially impaired peritoneal ultrafiltration.