Hemodialysis and peritoneal dialysis are two blood purification techniques that use similar operating systems. The hemodialysis system is based on three components (blood, membrane, and dialysate). The peritoneal dialysis system is based on the same components that can, however, be less manipulated and adjusted. In hemodialysis the blood flow is the main determinant of small solute removal thanks to a prevalently diffusive mechanism. Convection is also used to transport larger solutes across the membrane, but this mechanism relies on the high permeability coefficient of the membrane and high transmembrane pressure leading to high ultrafiltration rates. The membrane can therefore influence the performance of the techniques as far as solute removal and ultrafiltration are concerned. Finally, diffusion is facilitated by an improved distribution of dialysate flow in the dialysate compartment. This can be achieved with a special dialysate pathway configuration based on space yarns or micronodulation of the fibers. In peritoneal dialysis, blood flow and membrane characteristics can be less manipulated or almost not at all. The only variables are dialysate volume, flow, dwell time, and composition. Thanks to modification in these aspects of the dialysate, peritoneal dialysis techniques with different clearances and ultrafiltration rates can be accomplished.

Efficiency↗

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Reconciling differences in effective solute removal between intermittent and continuous therapies.

Solute removal by various forms of renal replacement therapy (RRT) differs from that occurring in the native kidney in several ways. Among the dialytic therapies, the relationship between clearance and mass removal rate may differ substantially. The purpose of this article is to review the various approaches that have been proposed to account for this differing relationship among the various types of RRT. Specific quantitative approaches along with clinical applications are provided.

Humans↗

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Continuous flow peritoneal dialysis: is there a need for it?

Automated peritoneal dialysis (APD) is the fastest growing technique of peritoneal dialysis. However, recently APD has displayed some limitations imposed by the characteristics of the technique and by the characteristics of the peritoneal membrane of some patients. In general, the advent of a new technique such as continuous flow peritoneal dialysis (CFPD) should be seen as a benefit for several patients based on different considerations: CFPD is a high-efficiency technique which could overcome some of the limitations imposed by other techniques in terms of adequacy targets and performance. CFPD may become a useful tool to keep patients on PD who would otherwise be transferred to hemodialysis. CFPD may present advantages in terms of biocompatibility and also in terms of the possible modulation of the peritoneal solution to patient needs. Recent developments in technology seem to have made CFPD easily feasible and well tolerated. A new era of PD is probably beginning and CFPD will definitely represent one of the key issues in the future of PD.

Catheterization↗

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Clinical experience with continuous flow and flow-through peritoneal dialysis.

Concern over the inherent inefficiency of solute removal by conventional peritoneal dialysis (PD) has led to renewed interest in continuous flow PD (CFPD). We present clinical data from two experiences with CFPD. In the first, two catheters were used to recirculate a fixed intraperitoneal volume through an external circuit comprised of a standard hemodialysis system. The second patient had a dual-lumen PD catheter and was studied during two sessions of flow-through PD (FTPD) using sterile PD solution. Urea clearances with both techniques were around 30 ml/min, which is consistent with data reported in the literature. Significant streaming of dialysate from port to port within the peritoneal cavity limited clearances. CFPD offers a potentially safe and effective alternative to daily or nightly home hemodialysis.

Catheterization↗

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Buffer balance in bicarbonate hemodiafiltration.

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Bicarbonates↗

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Brain density changes during renal replacement in critically ill patients with acute renal failure. Continuous hemofiltration versus intermittent hemodialysis.

Computerized tomography (CT) studies of the brain were made on 12 patients with acute renal failure from different origin. Patients were treated for two subsequent days in random sequence with intermittent hemodialysis (HD) (one 4-h session and Kt/V > or = 1) and continuous veno-venous hemofiltration (CVVH) (one 24-h session and Kt/V > or = 1). CT scans were done before and after the HD and CVVH session in each patient. In baseline conditions, the only macroscopic morphological alteration was a slight brain edema in some patients. Significant changes in the density of white and gray matter were observed after the HD session in all patients (gray matter from 52.3 +/- 5.2 to 38.9 +/- 5.3 and white matter from 36.7 +/- 3.5 to 24.8 +/- 3.2 Hounsfield units, average delta -26.7%). No changes were observed after CVVH. We conclude that intermittent HD involves a remarkable degree of "unphysiology", leading to increased water content in the brain after each session. In acute patients this may lead to a post-dialytic brain edematogenic state. The physiological stability provided by continuous therapies such as CVVH avoids this unwanted effect, and suggests that continuous renal replacement therapies should be a first choice in these patients.

Acute Kidney Injury↗

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The impact of residual renal function and total body water volume on achieving adequate dialysis in CAPD.

AIMS: The objective is to evaluate the impact of residual renal function (RRF) and total body water (TBW) on achieving adequate dialysis. METHODS: Sixty three CAPD patients performing four 2 liter exchanges daily were evaluated for RRF, total weekly Kt/V (TWKt/V), total weekly creatinine clearance (TWCC) and TBW. RESULTS: In patients with residual renal function (N = 41), TWKt/V and TWCC were 2.2 +/- 0.8 and 77.4 +/- 24.5 L, respectively. In patients without RRF (N = 22), TWKt/V was 1.6 +/- 0.4 and TWCC 42.6 +/- 9.2 L. TBW correlated negatively with TWKt/V in the group without RRF (r = -0.75, P<0.001). CONCLUSION: It is not possible for larger patients without RRF treated with CAPD (2L x 4 exchanges) to achieve the acceptable targets for TWKt/V and TWCC due to TBW.

Adult↗

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Cellulose triacetate: another membrane for continuous renal replacement therapy.

The evolution of technology and biomaterials has permitted a parallel development of renal replacement therapies in the acute, critically ill patient. From the original continuous artero-venous hemofiltration method new techniques such as continuous veno-venous hemofiltration, hemodiafiltration and high-flux dialysis have been developed and are clinically used. Similar progress has been made with artificial membranes. We investigated the possibility of using a modified cellulosic membrane for continuous therapies, assessing the hydraulic characteristics and clearance performances of high-flux cellulose triacetate hemodiafilter (0.7 m2) in vitro and in vivo. The flowdynamic characteristics of the filter suggest its optimal use in veno-venous pump-drive techniques. Efficiency was excellent, with urea daily clearances as high as 50 liters or more. The high permeability and porosity of the membrane also increased the clearances of larger solutes such as creatinine and inulin. No side effects occurred during treatment and we conclude that cellulose triacetate may be considered a good alternative to synthetic membranes in continuous renal replacement therapies.

Acute Kidney Injury↗

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The role of technology in hemodialysis.

The evolution of hemodialysis therapy has been characterized over the years by the search for reliable devices and supplies, for more efficient treatments and finally for a more tolerable therapy in long term dialysis patients. In this view, three steps can be identified: a) the first step was the creation of safe and reliable vascular access, dialyzers and machines. This step led to the birth of modern dialysis and treatment personalization was the logical consequence. Each patient is a single entity and he requires a specific therapy prescription and delivery. From this concept the search for adequacy and better outcomes has been generated, with the inevitable consequence that newer techniques were explored in the attempt to perform a more efficient and clinically tolerated dialysis therapy. b) The second step was the attempt to consider the intratreatment variations as possible source for dialytic morbidity. In this view, efforts were made to pre-set ultrafiltration and dialysate sodium profiles in the machine to counterbalance the negative effects of uncontrolled water and solute removal. However, this approach failed to provide significant results, because ultrafiltration and sodium profiles were predetermined and no adaptations could be made if the designed profile was inadequate. c) The third step in the evolution of dialysis was the understanding that on-line signals from the machine and from the patients were required in order to prepare and carry out the adequate response and variation of treatment parameters. For this reason a series of sensors have been developed including urea and blood volume sensors which are offering the most important signals from the patient. In this way, accurate responses could be made during treatment and from a simple manual feedback, we have today a completely automatic form of biofeedback. The question that now arises is where to find the financial resources to afford the upcoming technology. Another question is whether this new technology should be for everybody in routine dialysis or it should be designed for specific conditions. In other words, are these toys for nice experimental studies and speculations or are they tools to improve dialytic outcomes and morbidity? Probably, technology cannot be stopped in its evolution. What is exceptional today will probably be part of the routine of tomorrow. It seems that we are struggling more with the complex physiology of human body than with mechanical or electronic problems that certainly find their solution before or after. The increasing use of computers and the evolution of the applied software will certainly help in reducing the costs and improving the performances of our newer dialysis devices.

Hemodiafiltration↗

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Continuous urea monitoring in hemodialysis: a model approach to forecast dialytic performance. Results of a multicenter study.

BACKGROUND: A urea biosensor, inserted into the ultrafiltrate collection-line of paired filtration dialysis (PFD), not only allows on-line dialysis quantification, but also forecasts final (Cend) and 30 min equilibrated urea concentration (Ceq), the most reliable value for calculating dialysis efficiency. The urea biosensor processes plasma ultrafiltrate continuously, delivering a large amount of data to the computer, which estimates the parameters by a mathematical model, thus predicting the whole urea profile with rebound. METHODS: A multicenter randomized trial on 41 patients was conducted to ascertain the ability of a two-pool variable-volume urea model to forecast Cend and Ceq at 60 and 90 min after the start of dialysis. Two alternative dialytic treatments, A or B, were chosen, the latter being more efficient. Each treatment included six serial PFD. The accuracy of forecasting was evaluated through four indices based on forecast errors, calculated as the difference between observed and forecasted urea values: mean percent error (MPE) (%), mean absolute deviation (MAD) (mg/dl), mean absolute percent error (MAPE) (%) and root mean squared error (RMSE) (mg/dl). RESULTS: Forecasted urea concentrations were lower than those measured by the biosensor. MPE for Cend was negligible in A (+1.2%) and much higher in B (+7.2%); both values improved at 90 min, +1.0% and +5.8%, respectively. MAD for Cend was similar in both treatments and improved slightly at 90 min, ranging from 4.9 to 5.9 mg/dl. MPE for Ceq was +4% in A and and more than doubled in B (+11.5%); both values improved at 90 min, +3.7% and +9.7%, respectively. MAD for Ceq was 7.5 mg/dl in A and 8.5 mg/dl in B; both improved at 90 min, 6.7 and 7.4 m g/dl, respectively. The other indices, MAPE and RMSE, showed similar results. Comparison between the errors of the two treatments with analysis of variance (ANOVA) for repeated measures gave no significant results. CONCLUSIONS: Our model forecasts of urea concentrations were overall lower than the measured ones: the bias was negligible for A-Cend, greater for the A-Ceq and when the more efficient treatment B was used. The 60 min predictions improved at 90 min. The comparison between the prediction errors in the two treatments were not statistically significant. The recirculation measurement would probably reduce the bias if it were properly incorporated into the model.

Filtration↗

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Oxalate removal by differing dialysis techniques.

Secondary hyperoxalemia is a common feature in patients with chronic renal failure, but oxalate removal is not adequately accomplished by regular dialysis treatment. Oxalate removal in two groups of patients, 11 on continuous ambulatory peritoneal dialysis (CAPD) and 12 on hemodialysis (HD), was investigated. HD patients were studied during a regular bicarbonate dialysis and during hemodiafiltration (HDF) with a high convective component (UF = 66 mL/min) and AN69 filter (Hospal Filtral 12, 1.2 m2, Hospal Industrie, Meyzieu, France). All HD and HDF spent dialysate and all 24 hr CAPD effluents were collected; oxalate concentration was measured by high performance liquid chromatography (HPLC) using an ion exchange column. Both oxalate flux and total extraction were statistically higher during HDF treatments (HDF = 1.87 +/- 0.77 mg/min and 335.9 +/- 131.5 mg/session, respectively; HD = 0.99 +/- 0.74 mg/min, 226 +/- 153 mg/session, respectively; p < 0.02). The positive interaction of convective and diffusive fluxes probably played a major role in oxalate removal during treatment with a high convective component; solute-membrane interactions can occur by using either cellulosic or synthetic fibers. In CAPD patients, oxalate removal (76.42 +/- 50.85 mg/day) was lower than in patients on either HD or HDF, although weekly oxalate extraction was statistically no different between CAPD (535.46 +/- 356 mg/week) and HD (677.72 +/- 460.82 mg/week). It was concluded that HDF is more effective than HD or CAPD in oxalate removal. Long-term studies are needed to demonstrate whether these kinetic findings have clinical relevance.

Adult↗

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[Pregnancy after kidney transplantation. Case load of the Transplantation Center of Vicenza].

BACKGROUND: Pregnancy after kidney transplant has become possible thanks to recent surgical and pharmacological breakthroughs. MATERIALS AND METHODS: We performed a retrospective study including all pregnant women transplanted in our center after 1997. The following variables were analyzed. The type of nephropathy, patient age when dialysis began, patient age at trans-plantation, the time between dialysis and transplantation and the time between transplantation and childbirth. Immunosuppressive therapy, type of delivery, baby's weight and Apgar score were also considered. RESULTS: We followed four pregnancies in three patients who were, respectively, diagnosed with chronic pyelonephritis, post-partum cortical necrosis and immunoglobulin A (IgA) glomerulonephritis (GN). We observed complications in three cases and two pre-term births. In one case, the baby's weight at birth was lower when compared to the gestation age. We did not observe any significant disease in the baby's follow-up. CONCLUSIONS: We concluded that our data were in agreement with those in the literature confirming that pregnancy after kidney transplant, although possible, carries an elevated risk; and therefore, patients have to be referred to highly specialized centers.

Adult↗

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[Long-term intermittent renal replacement therapy at an intensive care unit].

Standard intermittent hemodialysis (IHD) used for the treatment of acute renal failure (ARF) at an intensive care unit has significant biochemical and physiological drawbacks. In the past 20 years, these drawbacks have stimulated the development of continuous renal replacement therapy (CRRT) and its ever-increasing use. However, CRRT is technically complicated and requires 24-hour monitoring. In some clinics, the use of CRRT leads to that each patient is under his/her nurse's surveillance, instead 1 nurse per 2 patients as before; this change has economic consequences and may limit nursing accessibility to other patients. The procedures prolonging intermittent therapy do not require 24-hour monitoring may benefit the treatment of ARF at the intensive care therapy. In this paper the authors call such procedures for continuous intermittent renal replacement therapy. They are characterized by a number of basic principles: (1) the use of modified or standard dialysis apparatuses; (2) the application of diffuse, convection, or both; (3) a certain reduction in the rate of elimination of dissolved substances as compared with IHD; (4) more prolonged treatment: above usual 3 or 4 hours of IHD, but not more than 8-12 hours (hence the term "intermittent"); (5) the use of on-line generation dialysate or substituting fluid. Information on the effectiveness and safety of this procedure is being now compiled.

Acute Kidney Injury↗

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[Rationale for the use of extracorporeal treatments for sepsis].

Sepsis is the leading cause of disability and mortality among critical patients; moreover, it causes high economic expenditures. Although very much is known about the pathophysiology of this condition and its mediators despite great investments directed to its control, mortality rates remain high. Recent treatment manuals emphasize the value of early goal-oriented therapy and also point to the high efficacy of activated protein C. Extracorporeal blood clearance may potentially become a new approach to treating this condition. There are reports on its positive clinical results that are likely associated with the effective removal of septic mediators. Human and animal studies, few and rather alike as they are, have yielded promising results. It is evident that the use of these procedures is justified; however, their efficiency in sepsis requires large-scale, correctly conducted studies.

Extracorporeal Circulation↗