A mixed-method feasibility study of a novel transitional regime of incremental haemodialysis: study design and protocol

Background

Incremental haemodialysis/haemodiafiltration (HD) may help reduce early mortality rates in patients starting HD. This mixed-method feasibility study aims to test the acceptability, tolerance and safety of a novel incremental HD regime, and to study its impact on parameters of patient wellbeing.

Method

We aim to enrol 20 patients who will commence HD twice-weekly with progressive increases in duration and frequency, achieving conventional treatment times over 15 weeks (incremental group). Participants will be followed-up for 6 months and will undergo regular tests including urine collections, bio-impedance analyses and quality-of-life questionnaires. Semi-structured interviews will be conducted to explore patients’ prior expectations from HD, their motivations for participation and experiences of receiving incremental HD. For comparison of safety and indicators of dialysis adequacy, a cohort of 40 matched patients who previously received conventional HD will be constructed from local dialysis records (historical controls).

Results

Data will be recorded on the numbers screened and proportions consented and completing the study (primary outcome). Incremental and conventional groups will be compared in terms of differences in blood pressure control, interdialytic weight changes, indicators of dialysis adequacy and differences in adverse and serious adverse events. In analyses restricted to incremental group, measurements of RRF, fluid load and quality-of-life during follow-up will be compared with baseline values. From patient interviews, a narrative description of key themes along with anonymised quotes will be presented.

Conclusion

Results from this study will address a significant knowledge gap in the prescription HD therapy and inform the development novel future therapy regimens.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10157-021-02072-1.

An update review of intradialytic hypotension: concept, risk factors, clinical implications and management

Intradialytic hypotension (IDH) is a frequent and serious complication of chronic haemodialysis, linked to adverse long-term outcomes including increased cardiovascular and all-cause mortality. IDH is the end result of the interaction between ultrafiltration rate (UFR), cardiac output and arteriolar tone. Thus excessive ultrafiltration may decrease the cardiac output, especially when compensatory mechanisms (heart rate, myocardial contractility, vascular tone and splanchnic flow shifts) fail to be optimally recruited. The repeated disruption of end-organ perfusion in IDH may lead to various adverse clinical outcomes affecting the heart, central nervous system, kidney and gastrointestinal system. Potential interventions to decrease the incidence or severity of IDH include optimization of the dialysis prescription (cool dialysate, UFR, sodium profiling and high-flux haemofiltration), interventions during the dialysis session (midodrine, mannitol, food intake, intradialytic exercise and intermittent pneumatic compression of the lower limbs) and interventions in the interdialysis period (lower interdialytic weight gain and blood pressure–lowering drugs). However, the evidence base for many of these interventions is thin and optimal prevention and management of IDH awaits further clinical investigation. Developing a consensus definition of IDH will facilitate clinical research. We review the most recent findings on risk factors, pathophysiology and management of IDH and, based on this, we call for a new consensus definition of IDH based on clinical outcomes and define a roadmap for IDH research.

Risk Factors Influencing the Decline of Residual Renal Function in Continuous Ambulatory Peritoneal Dialysis Patients

Objective

To assess the nature of the decline in residual renal function (RRF) after the initiation of peritoneal dialysis, and to identify risk factors influencing the preservation of RRF.

Design

A retrospective single-center study.

Setting

Tertiary medical center.

Patients

Eighty patients who were clinically stable and had been on continuous ambulatory peritoneal dialysis (CAPD) for a minimum of 6 months.

Main Outcome Measures

All subjects had at least three measurements of RRF, which was calculated as the average of creatinine clearance (Ccr) and urea clearance from a 24-hour urine collection. All measurements of RRF were plotted on a logarithmic scale and a linear scale against the duration of CAPD. Covariables used in the correlation analyses were age, sex, the presence of diabetes mellitus, mean blood pressure, mean diastolic blood pressure, hematocrit and Ccr at the start of peritoneal dialysis, peritoneal membrane transport characteristics by peritoneal equilibration test (PET), and the rate of peritonitis.

Results

A significant correlation was found between CAPD duration and RRF decline represented on a logarithmic scale with a correlation coefficient ( r) of 0.355 ( p < 0.001). In contrast, on a linear scale, the correlation coefficient was only 0.273 ( p < 0.01). By linear multiple regression analysis, the only independent risk factor for the decline of RRF was the rate of peritonitis ( r = -0.446, p < 0.001).

Conclusion

These results suggest that RRF declines exponentially rather than linearly with time, and that the rate of peritonitis is an independent risk factor for the decline of RRF in CAPD patients.

The Role of Peritoneal Dialysis as the First-Line Renal Replacement Modality

Twenty years after its introduction, peritoneal dialysis (PD) is a well-established alternative to hemodialysis (HD) as a modality of renal replacement therapy. Much debate and research is apparent in the literature, comparing hemodialysis and PD as “opposite” modalities and trying to ascertain which modality should be more optimal.

In our opinion, HD and PD are two distinct modalities, each with its own advantages and disadvantages. In addition, it is clear that for both HD and PD, rates of technique failure are high, causing patients to transfer between modalities. The question is thus not which modality is best, but rather, which flow-chart of modalities makes best use of the advantages of each modality, while avoiding its disadvantages. In this respect, HD and PD appear to be complementary modalities.

The better preservation of residual renal function, lower risk of infection with hepatitis B and C, better outcome after transplantation, preservation of vascular access, and lower costs are arguments to promote PD as a good initial treatment. When PD-related problems arise (adequacy, ultrafiltration, peritonitis, patient burnout), a timely transfer to HD has to be planned.

This editorial tries to review arguments supporting the complementary nature of both modalities, and especially the role of PD as the first-line renal replacement therapy.

Rate of Decline of Residual Renal Function in Patients on Continuous Peritoneal Dialysis and Factors Affecting It

Objective

We analyzed residual renal function (RRF) in a large number of new peritoneal dialysis (PD) patients to prospectively define the time course of decline of RRF and to evaluate the risk factors assumed to be associated with faster decline.

Study Design

Single-center, prospective cohort study.

Setting

Home PD unit of a tertiary care University Hospital.

Patients

The study included 242 patients starting continuous PD between January 1994 and December 1997, with a minimum follow-up of 6 months and at least three measurements of RRF.

Measurement

All patients had data on demographic and laboratory variables, episodes of peritonitis and the use of aminoglycoside (AG) antibiotics, temporary hemodialysis, and number of radiocontrast studies. Adequacy of PD was measured from 24-hour urine and dialysate collection and peritoneal equilibration test using standard methodology. Further data on RRF was collected every 3 to 4 months until the patient became anuric (urine volume < 100 mL/day or creatinine clearance < 1.0 mL/min) or until the end of study in December 1998.

Outcome Measure

The slope of the decline of residual glomerular filtration rate (GFR) (an average of renal urea and creatinine clearance) was the main outcome measure. Risk factors associated with faster decline were evaluated by a comparative analysis between patients in the highest and the lowest quartiles of the slopes of GFR, and a multivariate analysis using a stepwise option within linear regression and general linear models.

Results

There was a gradual deterioration of residual GFR with time on PD, with 40% of patients developing anuria at a mean of 20 months after the initiation of PD. On multivariate analysis, use of a larger volume of dialysate ( p = 0.0001), higher rate of peritonitis ( p = 0.0005), higher use of AG ( p = 0.0006), presence of diabetes mellitus ( p = 0.005), larger body mass index (BMI) ( p = 0.01), and no use of antihypertensive medications ( p = 0.04) independently predicted the steep slope of residual GFR. Male gender, higher grades of left ventricular dysfunction, and higher 24-hour proteinuria were associated with faster decline on univariate analysis only.

Conclusion

Faster decline of residual GFR corresponds with male gender, large BMI, presence of diabetes mellitus, higher grades of congestive heart failure, and higher 24-hour proteinuria. Higher rate of peritonitis and use of AG for the treatment of peritonitis is also associated independently with faster decline of residual GFR. Whether the type of PD (CAPD vs CCPD/NIPD) is associated with faster decline of residual GFR remains speculative.

Mechanisms, Clinical Implications, and Treatment of Intradialytic Hypotension

Individuals with ESKD requiring maintenance hemodialysis face a unique hemodynamic challenge, typically on a thrice-weekly basis. In an effort to achieve some degree of euvolemia, ultrafiltration goals often involve removal of the equivalent of an entire plasma volume. Maintenance of adequate end-organ perfusion in this setting is dependent on the institution of a variety of complex compensatory mechanisms. Unfortunately, secondary to a myriad of patient- and dialysis-related factors, this compensation often falls short and results in intradialytic hypotension. Physicians and patients have developed a greater appreciation for the breadth of adverse outcomes associated with intradialytic hypotension, including higher cardiovascular and all-cause mortality. In this review, we summarize the evidence for adverse outcomes associated with intradialytic hypotension, explore the underlying pathophysiology, and use this as a basis to introduce potential strategies for its prevention and treatment.

Preserving residual renal function in dialysis patients: an update on evidence to assist clinical decision making

It has been documented that preservation of residual renal function in dialysis patients improves quality of life as well as survival. Clinical trials on strategies to preserve residual renal function are clearly lacking. While waiting for more results from clinical trials, patients will benefit from clinicians being aware of available knowledge. The aim of this review was to offer an update on current evidence assisting doctors in clinical practice.

Considerations in the statistical analysis of hemodialysis patient survival

The association of hemodialysis dosage with patient survival is controversial. Here, we tested the hypothesis that methods for survival analysis may influence conclusions regarding dialysis dosage and mortality. We analyzed all-cause mortality by proportional hazards and accelerated failure time regression models in a cohort of incident hemodialysis patients who were followed for 9 yr. Both models identified age, race, heart failure, physical functioning, and comorbidity scores as important predictors of patient survival. Using proportional hazards, there was no statistically significant association between mortality and Kt/V (hazard ratio 0.72; 95% confidence interval 0.45 to 1.14). In contrast, using accelerated failure time models, each 0.1-U increment of Kt/V improved adjusted median patient survival by 3.50% (95% confidence interval 0.20 to 7.08%). Proportional hazard models also yielded less accurate estimates for median survival. These findings are consistent with an additive damage model for the survival of patients who are on hemodialysis. In this conceptual model, the assumptions of the proportional hazard model are violated, leading to underestimation of the importance of dialysis dosage. These results suggest that future studies of dialysis adequacy should consider this additive damage model when selecting methods for survival analysis. Accelerated failure time models may be useful adjuncts to the Cox model when studying outcomes of dialysis patients.

Is it time to revisit residual renal function in haemodialysis? (Review Article)

Residual renal function (RRF) is not currently emphasized for patients undergoing haemodialysis (HD). The role of RRF is well recognized in the peritoneal dialysis population as studies have clearly demonstrated a survival benefit with preservation of RRF. There is however, data to suggest that RRF is important in HD patients as well. Contemporary HD therapies using high flux biocompatible synthetic dialysers, bicarbonate buffered ultrapure dialysis fluids with ultrafiltration control appear to allow better preservation of RRF. The long held belief that peritoneal dialysis is better at preserving RRF than HD may no longer be true. More robust studies are required to determine the relative importance of RRF in HD and strategies to best preserve this vital asset.

Development of a computer-aided diagnosis system for a new modality of renal replacement therapy: an integrated approach combining both peritoneal dialysis and hemodialysis

The authors developed a computer-aided diagnosis system that includes a simple clinical test for the chronic renal disease patient who needs an integrated approach that combines both peritoneal dialysis and hemodialysis (PD-HD therapy). In this case study, the system simulated and estimated the dialysis outcome, the ultrafiltration volume and nutritional analysis by employing a pharmacokinetic model, and assessed the peritoneal permeable enhancement that can be a grave complication with peritoneal dialysis. This system requires only a minimum amount of nursing time and may be able to predict the optimal treatment schedule for PD-HD therapy and provide therapeutic monitoring in long-term peritoneal dialysis.

Residual renal function: considerations on its importance and preservation in dialysis patients

Residual renal function (RRF) remains important even after commencement of dialysis. Its role in the adequacy of peritoneal dialysis (PD) is well recognized and is increasingly utilized in incremental PD regimes, but it is also vitally important in hemodialysis (HD) patients, in whom it, as in PD patients, may improve survival. It may allow for a reduction in the duration of HD sessions. It reduces the need for dietary and fluid restrictions in both PD and HD patients. Other contributions include improved middle molecule clearance, better hemoglobin, phosphate, potassium, and urate levels, enhanced nutritional status and quality of life scores, and better outcomes in pregnancy. On the negative side, hypoalbuminemia may be prolonged in patients with persistent nephrotic-range proteinuria. Contrary to popular belief, RRF does not necessarily decline rapidly with the initiation of HD. PD may be better than HD in preserving RRF, although this difference may not persist if biocompatible membranes, bicarbonate buffer, and ultrapure water are used. Nocturnal ambulatory peritoneal dialysis (APD) patients may fare worse than continuous ambulatory peritoneal dialysis (CAPD) patients. RRF can be adversely affected by angiotensin-converting enzyme (ACE) inhibitors, nonsteroidal anti-inflammatory drugs (NSAIDs), aminoglycosides, and radiocontrast agents. Diuretics can help maintain fluid balance but not RRF.

Predictors of the rate of decline of residual renal function in incident dialysis patients

BACKGROUND

Residual renal function (RRF) influences morbidity, mortality and quality of life in chronic dialysis patients. Few studies have been published on risk factors for loss of RRF in dialysis patients. These studies were either retrospective, performed in a small number of patients, or estimated GFR without a urine collection.

METHODS

We analyzed the decline rates of residual GFR (rGFR) prospectively in 522 incident HD and PD patients who had structured follow-up assessments. GFR was measured as the mean of urea and creatinine clearance, calculated from urine collections. The initial value was obtained 0 to 4 weeks before the start of dialysis. The measurements were repeated 3, 6, and 12 months after the start of dialysis treatment. After logarithmic transformation, differences in rGFR changes over time were analyzed using repeated measurement analysis of variance.

RESULTS

Baseline factors that were negatively associated with rGFR at 12 months were a higher diastolic blood pressure (P < 0.001) and a higher urinary protein loss (P < 0.001). Primary kidney disease did not affect rGFR. Averaged over time, PD patients had a higher rGFR (P < 0.001) than HD patients. This relative difference increased over time (P = 0.04). Investigation of possible effects of the dialysis procedure on the decline rate between 0 and three months showed that dialysis hypotension (P = 0.02) contributed to the decline in HD and the presence of episodes with dehydration contributed in PD (P = 0.004).

CONCLUSIONS

rGFR is better maintained in PD patients than in HD patients. The associated factors such as a higher diastolic blood pressure, proteinuria, dialysis hypotension and dehydration can either be treated or avoided.

Adjustment of hemodialysis dose for residual renal urea clearance: a two year study of impact on dialysis time

Urea kinetic modeling suggests that significant time reductions may be realized in hemodialysis patients with residual renal urea clearance (K(r)t/V urea). However, the actual impact of a strategy that integrates such function into the dialysis prescription is not clear, because of both uncertainty regarding the rate of decay of K(r)t/V urea, as well as potential clinical constraints upon dose reduction. To examine this issue, we retrospectively reviewed data from 51 patients with K(r)t/N urea after initiation of maintenance hemodialysis. In 31 cases, there were no clinical barriers to adjustment of the dialysis prescriptions. Regression analysis revealed that each 0.10 increment in K(r)t/V urea yielded an actual dialysis time reduction of 12 minutes per week with average cumulative reduction of 80 minutes per week per patient. At approximately 1 year after initiation of dialysis, there were still 10 patients whose dialysis prescriptions were being adjusted on the basis of K(r)t/V urea. In conclusion, our results suggest that the incorporation of K(r)t/V urea in the hemodialysis prescription allows for substantial and enduring reductions in dialysis time in a significant minority of patients. Larger prospective studies are needed to evaluate the long-term safety of this strategy in modifying the dose of hemodialysis.

Utility of the inferior vena cava diameter as a marker of dry weight in nonoliguric hemodialyzed patients

We have previously reported that the maximal inferior vena cava (IVC) diameter during quiet expiration (IVCe) measured by ultrasonography correlates well with the amount of body fluid, especially the circulating blood volume(2) and proposed using the criteria of IVC diameter to determine dry weight (DW) in anuric hemodialyzed (HD) patients: standard IVCe of pre- and post-HD are 14.9 +/- 0.4 and 8.2 +/- 0.3 mm, respectively (1). However, the same post-HD IVC criterion should not be applied to nonoliguric HD patients because it could result in rapid deterioration of residual renal function due to forced dehydration. Although the biochemical DW marker plasma atrial natriuretic peptide (ANP) is useful to evaluate hypervolemia but not hypovolemia, both hyper- and hypovolemia can be detected by IVC measurement. In the present study, we investigated whether the IVC diameter serves as an optimal evaluation of DW in nonoliguric HD (NO-HD) patients, avoiding not only overhydration but also dehydration. The IVCe and plasma ANP levels were measured in 14 euvolemic patients with chronic renal failure at conservative period (CP-CRF) and 11 NO-HD patients, in whom the average daily urine volume was more than 500 ml/day. In NO-HD patients, DW was adjusted to attain the euvolemic state with normotensive blood pressure, lack of edema, and lack of temporal oliguria after HD. The ANP in CP-CRF patients was 109.3 +/- 15.3 pg/ml, and pre- and post-HD ANP levels in NO-HD patients were 145.3 +/- 23.5 and 97.5 +/- 13.5 pg/ml, respectively. IVCe in CP-CRF was 13.4 +/- 0.9 mm, and pre- and post-HD IVCe in NO-HD patients were 14.2 +/- 1.0 mm and 11.9 +/- 0.9 mm, respectively. Although the post-HD IVCe was greater (i.e., less hypovolemic) than that in anuric HD patients, and close to the IVCe in CP-CRF, pre-HD IVCe was comparable with that in anuric HD patients. In addition, the pre-HD ANP level was no higher than that in CP-CRF. Thus, in NO-HD patients, the post-IVCe of 11.9 +/- 0.9 mm would be a marker for an appropriate DW setting avoiding severe post-HD dehydration as well as excessive hypervolemia during the interdialytic period.

Effect of cause and time of dropout on the residual GFR: a comparative analysis of the decline of GFR on dialysis

BACKGROUND

The decline of residual renal function (RRF) on dialysis has been reported to be slower in peritoneal dialysis (PD) then hemodialysis (HD). However, some clinicians have questioned whether this reported difference might not be caused by selection bias. In particular, if continuous ambulatory PD (CAPD) delivers only marginally adequate therapy as some clinicians speculate, then perhaps those patients on CAPD with low glomerular filtration rate (GFR) are purposefully switched to HD. If true, transferring CAPD patients with low GFR to HD could create a selection bias that very well may account for the differences in GFR between PD and HD. This is particularly problematic if one then censors patients at the time of transfer from PD to HD from analysis (that is, patients are no longer followed in the study once they have switched treatment modalities). When this occurs, the data are said to be informatively censored, a term used by statisticians to describe any kind of systematic bias associated with censored or incomplete data. In particular, informative censoring occurs when patients who die or transfer to another modality very early have an associated lower starting GFR or higher rate of decline of GFR than patients who either complete the study or who die or transfer much later. If patient dropout is indeed related to the rate of decline in GFR and if this relationship differs between PD and HD but is ignored in the analysis, then the results of such analysis may be biased.

METHODS

This article analyzes the decline in GFR among 141 incident dialysis patients (39 HD and 102 PD) undergoing either HD or PD at the University of Missouri-Columbia. The decline in GFR was modeled as a nonlinear function of time, taking into account the possibility that missing values of GFR may be associated with patient dropout (death, transfer to another modality, or transplantation). To safeguard against this possibility, we utilized a conditional nonlinear mixed-effects model. The model was used to fit and compare each patient's GFR data to time adjusting for the patient's treatment modality (HD vs. PD), cause of dropout (death, transfer, transplant, lost to follow-up/study ended), and time to dropout. The model allowed a comparison of the starting GFR and the rate of decline in GFR between PD and HD adjusting for these three factors.

RESULTS AND CONCLUSIONS

The results of our analysis suggest that such informative censoring is independent of treatment modality and that even after correcting for dropout caused by death or transfer to another modality, patients starting on PD have a lower rate of decline in GFR (that is, better preservation of GFR) than patients starting on HD.

Biocompatible membranes preserve residual renal function in patients undergoing regular hemodialysis

Initiation of hemodialysis causes a further decrease of residual renal function (RRF). To assess the impact of the biocompatibility of the dialysis membrane, we performed a prospective randomized investigation in 20 normotensive patients with tubulointerstitial nephritis. The patients were randomly allocated to treatment with either a high-flux polysulfone or cellulose membrane over a period of 12 months. RRF, defined by creatinine clearance and daily urine volume, was found to decrease in both groups of patients after the initiation of hemodialysis. Of the two membranes used, however, the cellulose membrane caused an accelerated decrease of RRF (P < 0.05). The better maintenance of RRF in patients treated with polysulfone membranes was associated with higher Kt/V values and increased hematocrit values (P < 0.05). The pathophysiologic mechanism underlying the more rapid decline of RRF could not be explained by intradialytic hypotension, but may be related to the nephrotoxic effects of inflammatory mediators due to bioincompatibility. Therefore, the use of polysulfone membranes might be preferable in patients with relevant RRF.

Improved preservation of residual renal function in chronic hemodialysis patients using polysulfone dialyzers

Our objective was to determine whether patients with chronic renal failure requiring maintenance hemodialysis retain intrinsic renal function longer when using reprocessed polysulfone (PS) membrane hemodialyzers or single-use cellulose acetate (CA) membrane hemodialyzers. Fifty consecutive patients with residual renal function (urea clearance > 2.0 mL/min) using PS dialyzers were compared with a retrospective, disease- and time-matched population of patients using CA dialyzers. Endogenous urea clearance was measured every 3 months in all patients with remaining residual function. Other data collected included age, sex, cause of chronic renal failure, use of angiotensin-converting enzyme inhibitors or calcium channel blockers, and hemodynamic stability during hemodialysis. All patients were observed for at least 6 months while using a single type of dialyzer. Study end points included loss of residual renal function (urea clearance < 1.0 mL/min), death, transplant, transfer to peritoneal dialysis, or change of dialyzer. The PS and CA groups of patients were well matched for sex, age, initial renal clearance, predialysis blood pressure, and hemodynamic stability during hemodialysis. The PS patients had a higher delivered Kt/V (1.34 +/- 0.30 [mean +/- SD]) than the CA patients (1.06 +/- 0.20). The PS group had a higher average urea clearance than the CA group after 4 to 9 months of dialysis (2.8 +/- 2.6 mL/min v 1.7 +/- 1.6 mL/min, respectively), after 10 to 15 months of chronic dialysis (2.0 +/- 2.4 mL/min v 1.1 +/- 1.5 mL/min, respectively), and after 16 to 21 months of dialysis (1.3 +/- 1.9 mL/min v 0.5 +/- 1.1 mL/min, respectively; all P < 0.03, t-test). After 22 to 24 months of dialysis, the difference between the two groups was not significant. When comparing patients with identical causes of chronic renal failure, there were no differences between the PS and CA groups for those with diabetes mellitus, tubulointerstitial disease, or polycystic disease. Patients with parenchymal renal disease (glomerulonephritis or nephrosclerosis) had markedly better retention of intrinsic renal function with PS than with CA dialyzers (all P < 0.01). Kaplan-Meier analysis for retention of intrinsic renal function showed that PS patients with parenchymal renal disease had a mean of 23 months before loss of intrinsic renal function, whereas for CA patients the mean was 11 months before loss of intrinsic renal function (P = 0.0005). Cellulose acetate patients lost renal function at an average rate of 0.27 +/- 0.22 mL/min/mo, whereas for PS patients the rate was 0.14 +/- 0.56 mL/min/mo (P = 0.06, rank sum). CA patients with parenchymal renal disease lost renal function at a rate of 0.29 +/- 0.22 mL/min/mo, whereas for PS patients the rate was 0.0 +/- 0.8 mL/min/mo (P = 0.004, rank sum). Age, sex, and the use of either angiotensin-converting enzyme inhibitors or calcium channel blockers did not have an effect on the loss of intrinsic renal function. Patients with nondiabetic parenchymal renal disease receiving chronic hemodialysis with hydrogen peroxide/peroxyacetic acid-reprocessed PS dialyzers and a higher Kt/V lose residual renal function at a slower rate than disease-matched patients using single-use CA dialyzers. Our findings provide further evidence that the choice of dialyzer membrane may have an effect on intrinsic renal function.

Residual renal function in children on haemodialysis and peritoneal dialysis therapy

Residual renal function was studied in 28 haemodialysis (HD) and 31 peritoneal dialysis (PD) patients aged 1-20 years observed over 6-43 (median 19) months. After the start of dialysis urine volume (UV) decreased to 57%, 46% and 26% of initial mean values in HD patients after 6, 12 and 24 months, respectively. In PD patients the corresponding figures were 57%, 69% and 62%. Mean UV calculated from all individual mean UV measurements observed was higher in PD than HD patients (954 vs. 537 ml/m2 per 24 h, P < 0.01). A better conservation of diuresis in PD patients was also suggested by a significantly longer persistence of a UV greater than 500 ml/m2 per 24 h compared with HD patients. Cox proportional hazard analysis identified dialysis modality and pre-dialysis UV of less than 1,000 ml/m2 per 24 h as the only significant risk factors for UV survival. However, the decline of UV per time was similar in both modes of treatment. No significant changes of glomerular filtration rate were observed during both HD and PD treatment.

Biocompatibility issues in hemodialysis

Hemodialysis, as a life-saving treatment modality for uremic patients, implies a repeated and compulsory contact of blood with foreign materials. As a consequence, biocompatibility problems are unavoidable. The same applies for the material used for the creation of vascular access, and for the alternative dialysis method, CAPD (continuous ambulatory peritoneal dialysis), although each system might cause its own and specific problems. Although in early dialysis the focus has been on maintenance of life and elimination of toxins, later on the important morbid implications of this lack of biocompatibility have been recognized. Eight major problems will be discussed, especially in the perspective of recent new findings in this field: (1) coagulation and clotting; (2) complement and leukocyte activation; (3) susceptibility to infection; (4) leaching or spallation; (5) surface alterations of solid materials; (6) allergic reactions; (7) shear; (8) transfer of compounds from contaminated dialysate. After description of the major biochemical and clinical implications of these problems, ways to prevent morbid events and future perspectives will be described.