Role of Drain and Fill Profile in automated Peritoneal Dialysis

What is the Optimal Frequency of Cycling in Automated Peritoneal Dialysis?

Objective

The recent increase in the use of automated peritoneal dialysis (APD) has led to concerns about the adequacy of clearances delivered by this modality. Few clinical studies looking at the effects of varying the individual components of the APD prescription on delivered clearance have been done, and most published data are derived from computer modeling. Most controversial is the optimal frequency of exchanges per APD session. Many centers prescribe 4 to 6 cycles per night but it is unclear if this is optimal. The purpose of this study was to address at what point the beneficial effect of more frequent cycles is outweighed by the concomitant increase in the proportion of the total cycling time spent draining and filling.

Methods

A comparison was made between the urea and creatinine clearances (CCrs) achieved by 4 different APD prescriptions, used for 7 days each, in 18 patients. The prescriptions were for 9 hours each and were all based on 2-L dwell volumes, but differed in the frequency of exchanges. They were 5 x 2 L, 7 x 2 L, and 9 x 2 L, as well as a 50% tidal peritoneal dialysis (TPD) prescription using 14 L. Ultrafiltration, dwell time, glucose absorption, sodium and potassium removal, protein excretion, and relative cost were also compared. Clearances due to day dwells and residual renal function were not included in the calculation.

Results

Mean urea clearances were 7.5, 8.6, 9.1, and 8.3 L/night for the four prescriptions respectively. Urea clearance with 9 x 2 L was significantly greater than with the other three prescriptions ( p < 0 0.05). Urea clearance with 7 x 2 L and TPD were superior to 5 x 2 L ( p < 0.05). Mean CCr was 5.1, 6.1, 6.4, and 5.6 L/night, respectively. Compared to 5 x 2-L, the 7 x 2-L, 9 x 2-L, and TPD prescriptions achieved greater CCr ( p < 0.05). Taking both urea and CCr into account, 9 x 2 L was the optimal prescription in 12 of the 18 patients. Ultrafiltration and sodium and potassium removals were all significantly greater with the higher frequency prescriptions.

Conclusion

The 5 x 2-L prescription significantly underutilizes the potential of APD to deliver high clearances, and 7 x 2 L is a consistently superior prescription if 2-L dwells are being used. Although more costly, 9 x 2 L should be considered if higher clearances are required.

Optimizing Automated Peritoneal Dialysis Using an Extended 3-Pore Model

Introduction

In the current study, an extended 3-pore model (TPM) is presented and applied to the problem of optimizing automated peritoneal dialysis (APD) with regard to osmotic water transport (UF), small/middle-molecule clearance, and glucose absorption.

Methods

Simulations were performed for either intermittent APD (IPD) or tidal APD (TPD). IPD was simulated for fill and drain volumes of 2 L, whereas TPD was simulated using a tidal volume of 0.5 L, 1 L, or 1.5 L with full drains and subsequent fills (2 L) occurring after every fifth dwell. A total of 25 cycles for a large number of different dialysate flow rates (DFR) were simulated using 3 different glucose concentrations (1.36%, 2.27%, and 3.86%) and 3 different peritoneal transport types: slow (peritoneal equilibrium test D/P_crea < 0.6), fast (peritoneal equilibrium test D/P_crea > 0.8), and average. Solute clearance and UF were simulated to occur during the entire dwell, including both fill and drain periods.

Results

It is demonstrated that DFRs exceeding ∼ 3 L/h are of little benefit both for UF and small-solute transport, whereas middle-molecule clearance is enhanced at higher DFRs. The simulations predict that large reductions (> 20%) in glucose absorption are possible by using moderately higher DFRs than a standard 6 × 2 L prescription and by using shorter optimized “bi-modal” APD regimens that alternate between a glucose-free solution and a glucose-containing solution.

Discussion

Reductions in glucose absorption appear to be significant with the proposed regimens for APD; however, further research is needed to assess the feasibility and safety of these regimens.

A modified peritoneal dialysis catheter with a new technique: Farewell to catheter migration

To evaluate the efficacy our new, three-cuff peritoneal dialysis (PD) catheter, with the low-entry technique and to study its impact on catheter survival and mechanical and infectious complications, we prospectively used it in 36 incident PD patients and compared the results with those of conventional double-cuff PD Tenckhoff catheters with the classic approach used in 37 patients. The study was carried out at our university hospital over a period of 18 months. At the end of the study, significantly higher survival rate was observed with the use of new catheter compared with the conventional two-cuff Tenckhoff catheter, 91.7% and 73%, respectively, (P <0.01); the difference in catheter survival was due to a lower incidence (P < 0.01) of catheter-tip migration and a lower incidence (P <0.01) of peritonitis. Dialysis fill and drain times were significantly shorter and Kt/V was better with our new catheter. In conclusion, the study suggests superiority of our new catheter and our new technique over the conventional one in terms of catheter survival. This is due to less incidences of catheter tip migration in addition to lower peritonitis rates. Dialysis adequacy was better because of shortened fill and drain time.

Nocturnal ultrafiltration profiles in patients on APD: impact on fluid and solute transport

In order to prevent morbidity and mortality in peritoneal dialysis (PD), sodium and water balance as well as a minimal level of small-solute clearances are needed. The impact of three nocturnal peritoneal ultrafiltration (UF) profiles on UF and small solute clearance in patients on automated PD (APD) was studied: constant glucose concentration of 1.36% (flat) or modifying the glucose concentration of the heater bag (descendant: 3.86-1.36%; ascendant: 1.36-3.86%). Sixty-two patients were enrolled in the study and received each profile within a four-month period, thus serving as their own controls. UF was lower with the flat profile (367+/-420ml; P<0.01), but no difference was seen between the two higher glucose concentration profiles. Peritoneal Kt/V (pKt/V) and peritoneal creatinine clearance (CrpC) showed statistically higher values from the descendant vs ascendant vs flat profiles (pKt/V: 1.54+/-0.30 vs 1.45+/-0.30 vs 1.38+/-0.27, and CrpC: 36.9+/-7.9 vs 33.5+/-7.48 vs 29.92+/-7.5 mlmin(-1)). Multivariate analysis showed statistical significance for the following: in the intrasubject comparisons, the profile for pKt/V (F=9.109, P<0.001) and CrpC (F=11.697, P<0.001), and in the intersubjects comparisons, the effects of both gender (F=14.334, P<0.01) for pKt/V and peritoneal permeability for both parameters (pKt/V: F=4.37, P<0.05; CrpC: F=11.697, P<0.001). In conclusion, the application of ascendant and descendant UF profiles in automated PD is feasible and results in better UF and small solute clearances, thus preventing inadequate dialysis and volume overload..

Improving cycler prescriptions in peritoneal dialysis through informatic profiling

Cycler-based dialysis is the most common form of peritoneal dialysis in the United States of America, accounting for more than two thirds of patients on the modality. The advent of modern cyclers has enhanced the accessibility of therapy-delivery data. Cyclers have transformed peritoneal dialysis from an unobserved home therapy into an observable home therapy on many levels. We will discuss 3 of these levels herein. The ability to profile prescription behavior at a population level with attention to fill volume, number of cycles used per night, and total time on the cycler will be analyzed. Insights into the dynamics of flow during cycler therapy and the concept of transition point will then be explored. Finally, we will review the impact on patient care of making the delivery of the dialysis prescription easily observable to the medical team. It is our contention that these 3 levels of profiling offer practical lessons to enhance delivery of care for patients on cycler-based peritoneal dialysis.

Tidal PD: its role in the current practice of peritoneal dialysis

The role of tidal peritoneal dialysis (TPD) has been the subject of several studies over the past 30 years. The use of the newest generation of cyclers combined with the increasing number of chronic peritoneal dialysis (CPD) patients being maintained on cycler therapy has stimulated a reexamination of the role of TPD in the care of CPD patients. Several studies over the past decade have examined solute clearances with TPD in patients. These studies suggest that TPD does not result in an increase in clearances when compared to conventional intermittent peritoneal dialysis (IPD). TPD is now primarily used for comfort in patients who experience pain at the start of inflow and/or at the end of outflow. In TPD, the presence of at least some fluid in the abdomen during the exchanges generally eliminates these episodes of pain. It has recently been suggested that accurate assessment of drain and fill phases during automated PD may be helpful in redefining a role for TPD in CPD patients. If the 'slow' drainage time can be kept to a minimum, then it is possible that the efficiency of PD could be enhanced. Defining the critical volume and then optimizing the TPD regimen could perhaps increase the clearances noted with TPD.

Multidisciplinary modelling of biomedical systems

This paper describes general principles and example results of a new software tool being developed for physiologically-based modelling of biomedical systems within a multidisciplinary framework. The aim is to overcome some limitations of currently available software designed either for general purpose or for highly specialised modelling applications. In fact, general purpose tools usually impose explicit coding of mathematical model equations or non-intuitive system representations, whereas specialised software use domain-specific notations that allow efficient and convenient model building only for special classes of systems. The aim of the present study is to pursue intuitive representation of various, possibly interacting, types of biological systems described as interconnected physical components, such as mass and energy storage elements, active and passive transport or biochemical transformations. The presented software generates automatically the mathematical model equations that can be coded in different formats. This allows interoperability with other existing software, e.g. for numerical simulation, symbolic analysis or text processing. A multi-domain structural language has been defined for an intuitive, hierarchical and self-explanatory specification of physiological models. The proposed strategies may become useful for dissemination and integration of multidisciplinary modelling knowledge.