Creatinine generation from kinetic modeling with or without postdialysis serum creatinine measurement: results from the HEMO study.

BACKGROUND: A convenient method to estimate the creatinine generation rate and measures of creatinine clearance in hemodialysis patients using formal kinetic modeling and standard pre- and postdialysis blood samples has not been described. METHODS: We used data from 366 dialysis sessions characterized during follow-up month 4 of the HEMO study, during which cross-dialyzer clearances for both urea and creatinine were available. Blood samples taken at 1 h into dialysis and 30 min and 60 min after dialysis were used to determine how well a two-pool kinetic model could predict creatinine concentrations and other kinetic parameters, including the creatinine generation rate. An extrarenal creatinine clearance of 0.038 l/kg/24 h was included in the model. RESULTS: Diffusive cross-dialyzer clearances of urea [230 (SD 37 mL/min] correlated well (R2 = 0.78) with creatinine clearances [164 (SD 30) mL/min]. When the effective diffusion volume flow rate was set at 0.791 times the blood flow rate for the cross-dialyzer clearance measurements at 1 h into dialysis, the mean calculated volume of creatinine distribution averaged 29.6 (SD 7.2) L], compared with 31.6 (SD 7.0) L for urea (P < 0.01). The modeled creatinine generation rate [1183 (SD 463) mg/day] averaged 100.1 % (SD 29; median 99.3) of that predicted in nondialysis patients by an anthropometric equation. A simplified method for modeling the creatinine generation rate using the urea distribution volume and urea dialyzer clearance without use of the postdialysis serum creatinine measurement gave results for creatinine generation rate [1187 (SD 475) mg/day; that closely matched the value calculated using the formally modeled value, R2 = 0.971]. CONCLUSIONS: Our analysis confirms previous findings of similar distribution volumes for creatinine and urea. After taking extra-renal clearance into consideration, the creatinine generation rate in dialysis patients is similar to that in nondialysis patients. A simplified method based on urea clearance and urea distribution volume not requiring a postdialysis serum creatinine measurement can be used to yield creatinine generation rates that closely match those determined from standard modeling.

Assessing the Adequacy of Small Solute Clearance for Various Dialysis Modalities, with Inclusion of Residual Native Kidney Function.

Measurement of small molecule clearance remains important in the clinical care of patients requiring long-term dialysis. Many patients maintain a significant degree of residual native kidney function and may have nontraditional schedules with or without combined dialysis modalities. In this review, we examine and outline methods for comparing small molecule clearances among various dialysis prescriptions and modalities, with inclusion of residual kidney urea clearance.

Metabolic Profiling of Impaired Cognitive Function in Patients Receiving Dialysis.

Retention of uremic metabolites is a proposed cause of cognitive impairment in patients with ESRD. We used metabolic profiling to identify and validate uremic metabolites associated with impairment in executive function in two cohorts of patients receiving maintenance dialysis. We performed metabolic profiling using liquid chromatography/mass spectrometry applied to predialysis plasma samples from a discovery cohort of 141 patients and an independent replication cohort of 180 patients participating in a trial of frequent hemodialysis. We assessed executive function with the Trail Making Test Part B and the Digit Symbol Substitution test. Impaired executive function was defined as a score ≥2 SDs below normative values. Four metabolites-4-hydroxyphenylacetate, phenylacetylglutamine, hippurate, and prolyl-hydroxyproline-were associated with impaired executive function at the false-detection rate significance threshold. After adjustment for demographic and clinical characteristics, the associations remained statistically significant: relative risk 1.16 (95% confidence interval [95% CI], 1.03 to 1.32), 1.39 (95% CI, 1.13 to 1.71), 1.24 (95% CI, 1.03 to 1.50), and 1.20 (95% CI, 1.05 to 1.38) for each SD increase in 4-hydroxyphenylacetate, phenylacetylglutamine, hippurate, and prolyl-hydroxyproline, respectively. The association between 4-hydroxyphenylacetate and impaired executive function was replicated in the second cohort (relative risk 1.12; 95% CI, 1.02 to 1.23), whereas the associations for phenylacetylglutamine, hippurate, and prolyl-hydroxyproline did not reach statistical significance in this cohort. In summary, four metabolites related to phenylalanine, benzoate, and glutamate metabolism may be markers of cognitive impairment in patients receiving maintenance dialysis.

Dose Targeting Metrics in Conventional and Intensive Maintenance Dialysis.

Hemodialysis has come a long way since its early days and is a life sustaining therapy for millions of people with end-stage kidney disease throughout the world. Although thrice weekly hemodialysis remains the most common form of renal replacement therapy, other therapies such as more frequent, prolonged dialysis modalities have seen a rise recently. In this review, we compare and contrast methods for measuring the dialysis dose, with a focus on small molecule clearance (Kt/Vurea ) among various dialysis modalities. We also describe newer on-line methods to measure dialysis and limitations to current adequacy measurement. Distinguishing dialysis adequacy from adequate treatment of the patient is also emphasized.

Effect of frequent hemodialysis on residual kidney function.

Frequent hemodialysis can alter volume status, blood pressure, and the concentration of osmotically active solutes, each of which might affect residual kidney function (RKF). In the Frequent Hemodialysis Network Daily and Nocturnal Trials, we examined the effects of assignment to six compared with three-times-per-week hemodialysis on follow-up RKF. In both trials, baseline RKF was inversely correlated with number of years since onset of ESRD. In the Nocturnal Trial, 63 participants had non-zero RKF at baseline (mean urine volume 0.76 liter/day, urea clearance 2.3 ml/min, and creatinine clearance 4.7 ml/min). In those assigned to frequent nocturnal dialysis, these indices were all significantly lower at month 4 and were mostly so at month 12 compared with controls. In the frequent dialysis group, urine volume had declined to zero in 52% and 67% of patients at months 4 and 12, respectively, compared with 18% and 36% in controls. In the Daily Trial, 83 patients had non-zero RKF at baseline (mean urine volume 0.43 liter/day, urea clearance 1.2 ml/min, and creatinine clearance 2.7 ml/min). Here, treatment assignment did not significantly influence follow-up levels of the measured indices, although the range in baseline RKF was narrower, potentially limiting power to detect differences. Thus, frequent nocturnal hemodialysis appears to promote a more rapid loss of RKF, the mechanism of which remains to be determined. Whether RKF also declines with frequent daily treatment could not be determined.

In-center hemodialysis six times per week versus three times per week.

BACKGROUND: In this randomized clinical trial, we aimed to determine whether increasing the frequency of in-center hemodialysis would result in beneficial changes in left ventricular mass, self-reported physical health, and other intermediate outcomes among patients undergoing maintenance hemodialysis. METHODS: Patients were randomly assigned to undergo hemodialysis six times per week (frequent hemodialysis, 125 patients) or three times per week (conventional hemodialysis, 120 patients) for 12 months. The two coprimary composite outcomes were death or change (from baseline to 12 months) in left ventricular mass, as assessed by cardiac magnetic resonance imaging, and death or change in the physical-health composite score of the RAND 36-item health survey. Secondary outcomes included cognitive performance; self-reported depression; laboratory markers of nutrition, mineral metabolism, and anemia; blood pressure; and rates of hospitalization and of interventions related to vascular access. RESULTS: Patients in the frequent-hemodialysis group averaged 5.2 sessions per week; the weekly standard Kt/V(urea) (the product of the urea clearance and the duration of the dialysis session normalized to the volume of distribution of urea) was significantly higher in the frequent-hemodialysis group than in the conventional-hemodialysis group (3.54±0.56 vs. 2.49±0.27). Frequent hemodialysis was associated with significant benefits with respect to both coprimary composite outcomes (hazard ratio for death or increase in left ventricular mass, 0.61; 95% confidence interval [CI], 0.46 to 0.82; hazard ratio for death or a decrease in the physical-health composite score, 0.70; 95% CI, 0.53 to 0.92). Patients randomly assigned to frequent hemodialysis were more likely to undergo interventions related to vascular access than were patients assigned to conventional hemodialysis (hazard ratio, 1.71; 95% CI, 1.08 to 2.73). Frequent hemodialysis was associated with improved control of hypertension and hyperphosphatemia. There were no significant effects of frequent hemodialysis on cognitive performance, self-reported depression, serum albumin concentration, or use of erythropoiesis-stimulating agents. CONCLUSIONS: Frequent hemodialysis, as compared with conventional hemodialysis, was associated with favorable results with respect to the composite outcomes of death or change in left ventricular mass and death or change in a physical-health composite score but prompted more frequent interventions related to vascular access. (Funded by the National Institute of Diabetes and Digestive and Kidney Diseases and others; ClinicalTrials.gov number, NCT00264758.).

Improved equation for estimating single-pool Kt/V at higher dialysis frequencies.

RATIONALE: To measure adequacy in patients dialyzed other than three times per week, guidelines recommend the use of 'standard' Kt/V, which commonly is estimated from treatment Kt/V, time and frequency; however, the accuracy of equations that predict treatment Kt/V in patients being dialyzed other than three times per week has not been evaluated. METHODS: In patients enrolled in the Frequent Hemodialysis Network (FHN) Daily and Nocturnal Trials who were being dialyzed three, four or six times per week, we tested the accuracy of the following Kt/V prediction equation: Kt/V = -ln(R - GFAC × T_hours) + (4-3.5 × R) × 0.55 × weight loss/V, where R = post-dialysis/pre-dialysis blood urea nitrogen and GFAC, originally set to 0.008 for a 3/week schedule (Daugirdas, J Am Soc Nephrol 1993), is a factor that adjusts for urea generation. RESULTS: With the above equation, there was <0.1% mean error in predicted treatment Kt/V for 3/week patients, but mean errors were -5, -9 and -13% for the 6/week daily, 4/week nocturnal and 6/week nocturnal patients. Modeling simulations were performed to optimize the GFAC term for dialysis schedule and length of the preceding interdialysis interval (PIDI). After substituting schedule- and interval-optimized GFAC terms, the treatment Kt/V prediction errors were reduced to -0.81, +0.1 and -1.3% for the three frequent dialysis schedules tested. CONCLUSION: For frequent dialysis schedules, the urea generation factor (GFAC) of one commonly used Kt/V prediction equation should be adjusted based on length in days of the PIDI and number of treatments per week.

Standard Kt/Vurea: a method of calculation that includes effects of fluid removal and residual kidney clearance.

Standard Kt/V(urea) (stdKt/V) is a hypothetical continuous clearance in patients treated with intermittent hemodialysis based on the generation rate of urea nitrogen and the average predialysis urea nitrogen. Previous equations to estimate stdKt/V were derived using a fixed-volume model. To determine the impact of fluid removal as well as residual urea clearance on stdKt/V, we modeled 245 hemodialysis sessions (including conventional 3/week, in-center 6/week, and at-home nocturnal 6/week) in 210 patients enrolled in the Frequent Hemodialysis Network Daily and Nocturnal clinical trials. To examine the role of fluid removal, modeled stdKt/V was compared to stdKt/V estimated from a previously published simplified equation. In a subgroup of 45 sessions with residual urea clearance over 1.5 ml/min, the contribution of residual urea clearance to stdKt/V was measured. For all dialysis schedules, the fixed-volume equation predicted stdKt/V well when both fluid removal and residual urea clearance were set to zero. When fluid removal was included, modeled stdKt/V was slightly underestimated for all three modes of hemodialysis. The shortfall correlated directly with weekly fluid removal and inversely with modeled urea volume. Modeled stdKt/V compressed residual urea clearance to about 70% of its measured value and the fractional downsizing significantly correlated inversely with treatment Kt/V. Our new equation predicted modeled stdKt/V with a high level of accuracy, even when substantial fluid removal and residual urea clearance were present.

Effects of reduced intradialytic urea generation rate and residual renal clearance on modeled urea distribution volume and Kt/V in conventional, daily, and nocturnal dialysis.

Classic urea modeling assumes that both urea generation rate (G) and residual renal urea clearance (Kru) are constant throughout the week, but this may not be true. Reductions in intradialysis G could be caused by lower plasma amino acid levels due to predialysis/intradialysis fasting and also to losses of amino acids into the dialysate. Intradialytic reductions in Kru could be due to lower intravascular volume, blood pressure, or osmotic load. To determine the possible effects of reduced G or Kru during dialysis on the calculation of the volume of distribution (V) and Kt/Vurea, we modeled 3 and 6/week nocturnal, 6/week short daily, and 3/week conventional hemodialysis. A modified 2-pool mathematical model of urea mass balance with a constant time-averaged G was used, but the model was altered to allow adjustment of the ratio of dialytic/interdialytic G (Gd/Gid) and dialytic/total Kru (Krud/Kru) to vary from 1.0 down to near zero. In patients dialyzed six times per week for 400 minutes per session, when Gd/Gid was decreased from 1.0 to 0.05, the predicted urea reduction ratio (URR) increased from 68.9% to 80.2%. To achieve an increased URR of this magnitude under conditions of constant G (Gd/Gid=1.0) required a decrease in modeled urea volume (V) of 36%. At Gd/Gid ratios of 0.8 or 0.6 (corresponding to 20% or 40% reductions in intradialysis G), the modeled URR was increased to 71.0% or 73.3%, causing a 7% or 15% factitious decrease in V. The error was intermediate for the 3/week nocturnal schedule, and was much less pronounced for the 6/week daily and 3/week conventional treatments. Reductions in intradialytic Kru had the opposite effect, lowering the predicted URR and increasing the apparent V, but here the errors were of much lesser amplitude. The results suggest that, particularly for nocturnal dialysis, the standard "constant G" urea kinetic model may need to be modified.

Solute-solver: a web-based tool for modeling urea kinetics for a broad range of hemodialysis schedules in multiple patients.

Practical application of urea kinetic modeling to measure the delivered dose of hemodialysis is hampered by lack of a reference or gold-standard program that would be widely available and freely distributed. We developed and here describe an open-source JavaScript tool, "Solute-Solver," capable of batch processing of urea kinetics calculations. The Solute-Solver online interface is available at (www.ureakinetics.org); in addition, the tool can be used as a standalone HTML file that is designed to be run using a web browser. Solute-Solver is written in uncompiled JavaScript for transparency and easy modification, and the source code is available for download and modification. The program uses fourth-order Runge-Kutta numerical integration applied to a variable-extracellular-volume 2-pool model to compute a variety of clearance measures, including 1-pool and 2-pool Kt/V, "standard" weekly Kt/V, and other equivalent clearance measures. The program accepts comma- or semicolon-delimited input (which can be produced from a spreadsheet) and generates a separator-delimited output file that can be imported back into a spreadsheet or other database. The program also produces individual patient-by-patient report pages. It typically provides kinetic output for 300 patient treatments in 30-60 seconds. Advantages of this program over previously available equations and algorithms include the capacity to properly model such newer dialysis schedules as 6-times-weekly short daily or nocturnal hemodialysis, as well as account for substantial variation in residual renal function. Ultimately, this effort may promote wider use of formal urea modeling and facilitate research that requires measurement of hemodialysis or hemodialysis adequacy, especially involving the newer expressions of continuous equivalent clearance, and expressions of clearance normalized to body surface area.

Solute clearances and fluid removal in the frequent hemodialysis network trials.

BACKGROUND: The Frequent Hemodialysis Network (FHN) is conducting 2 randomized clinical trials, a daytime in-center trial ("daily") comparing 6 versus 3 treatments/wk, and a home nocturnal trial comparing 6 nocturnal treatments versus 3 conventional treatments/wk. The goal of this study was to project separation between the treatment and control arms of these studies for measures of dialysis dose by using simulations based on 2-compartment variable-volume models. SETTING & PARTICIPANTS: Data from the most recent hemodialysis treatment in 100 patients dialyzed 3 times/wk at facilities of the Renal Research Institute in New York and from 2 data sets (n = 154 and 115 patients) from the Hemodialysis (HEMO) trial. DESIGN: Observational study. PREDICTOR: Dialysis prescriptions for the treatment and control arms in the FHN trials. DIALYSIS REGIMEN OUTCOMES: Treatment time, ultrafiltration rate, standard Kt/V/wk for urea (stdKt/V(urea)), and continuous clearance estimates based on ratios of urea, creatinine, and normalized beta(2)-microglobulin generation rates (denoted by Gn) to time-averaged concentrations (TACs) of these solutes during 1 treatment week. RESULTS: The expected differences between median values in the experimental and control groups were weekly treatment time: daily trial, 29%; nocturnal trial, 234%; ultrafiltration rate: daily, -20%; nocturnal, -69%; stdKt/V(urea): daily, 52%; nocturnal, 133%; Gn(urea)/TAC(urea): daily, 34%; nocturnal, 130%; Gn(cr)/TAC(cr): daily, 31%; nocturnal, 135%; and Gn(beta2)/TAC(beta2): daily, 8%; nocturnal, 67%. LIMITATIONS: Use of simulated data and assumption of equivalent volumes and ultrafiltration rates between treatment arms. CONCLUSIONS: The nocturnal 6-times-weekly regimen produces substantially greater separation between the treatment and control arms than the daytime 6-times-weekly regimen for a wide range of treatment parameters. However, the 6-times-weekly interventions in both FHN trials will produce substantially greater separation than in the HEMO trial, where separations in median weekly treatment time and stdKt/V(urea) between the 3-times-weekly high- and standard-dose groups were 18% and 17%, respectively. The FHN trials will test whether substantial increases in solute clearance and other effects of frequent hemodialysis materially influence selected intermediate outcome measures.

Dosing intermittent haemodialysis in the intensive care unit patient with acute renal failure--estimation of urea removal and evidence for the regional blood flow model.

BACKGROUND: Blood-side dosing methods may overestimate urea removal in comparison to dialysate-side measurements during intermittent HD (IHD) for acute renal failure (ARF). The present study sought to quantify this mass balance error (MBE) and explore potential explanatory factors. METHODS: Prospective, formal, blood-side urea kinetic modelling was performed in serial sessions (n = 42) in 18 intensive care unit ARF patients. Three blood-side estimates of urea removal were calculated and these were compared to urea removal derived from fractional dialysate sampling and use of an on-line urea monitor. We also examined urea rebound in these patients, as expressed by the intercompartmental urea clearance (Kc), and in a subset of patients examined the relation of Kc to cardiac output and systemic vascular resistance (SVR). RESULTS: The mean % MBE (MBE = blood - dialysate-estimated urea removal) was about 9% using conventional two-pool modelling based on a 60-min post-dialysis blood urea nitrogen (BUN) with or without the use of one or more intra-dialytic BUN values. The extent of MBE could not be explained by the clinical or dialytic variables that were measured. Part of the MBE error was due to overestimation of the intradialytic BUN profile, because model-independent profiling of intra-dialytic BUN values to compute urea removal reduced the MBE to approximately 6%. The log Kc was correlated with cardiac output and showed trends towards an inverse correlation with SVR. CONCLUSIONS: Classical, two-pool, blood-side UKM produces a modest overestimate of urea removal in IHD for critically ill ARF patients. The source of this small, residual MBE is unknown. The amount of urea rebound, as reflected by Kc, varied among patients and associated with cardiac output and SVR, as predicted by the regional blood flow model.

Comparison of proposed alternative methods for rescaling dialysis dose: resting energy expenditure, high metabolic rate organ mass, liver size, and body surface area.

A number of denominators for scaling the dose of dialysis have been proposed as alternatives to the urea distribution volume (V). These include resting energy expenditure (REE), mass of high metabolic rate organs (HMRO), visceral mass, and body surface area. Metabolic rate is an unlikely denominator as it varies enormously among humans with different levels of activity and correlates poorly with the glomerular filtration rate. Similarly, scaling based on HMRO may not be optimal, as many organs with high metabolic rates such as spleen, brain, and heart are unlikely to generate unusually large amounts of uremic toxins. Visceral mass, in particular the liver and gut, has potential merit as a denominator for scaling; liver size is related to protein intake and the liver, along with the gut, is known to be responsible for the generation of suspected uremic toxins. Surface area is time-honored as a scaling method for glomerular filtration rate and scales similarly to liver size. How currently recommended dialysis doses might be affected by these alternative rescaling methods was modeled by applying anthropometric equations to a large group of dialysis patients who participated in the HEMO study. The data suggested that rescaling to REE would not be much different from scaling to V. Scaling to HMRO mass would mandate substantially higher dialysis doses for smaller patients of either gender. Rescaling to liver mass would require substantially more dialysis for women compared with men at all levels of body size. Rescaling to body surface area would require more dialysis for smaller patients of either gender and also more dialysis for women of any size. Of these proposed alternative rescaling measures, body surface area may be the best, because it reflects gender-based scaling of liver size and thereby the rate of generation of uremic toxins.

Surface-area-normalized Kt/V: a method of rescaling dialysis dose to body surface area-implications for different-size patients by gender.

Dialysis is measured as Kt/V, which scales the dose (Kt) to body water content (V). Scaling dialysis dose to body surface area (S(dub)) has been advocated, but the implications of such rescaling have not been examined. We developed a method of rescaling measured Kt/V to S(dub) and studied the effect of such alternative scaling on the minimum adequacy values that might then be applied in male and female patients of varying body size. We examined anthropometric estimates of V and S (Watson vs. Dubois estimates) in 1765 patients enrolled in the HEMO study after excluding patients with amputations. An S-normalized target stdKt/V was defined, and an adequacy ratio (R) was computed for each patient as R = D/N where D = delivered stdKt/V (calculated using the Gotch-Leypoldt equation for stdKt/V) and N = the S-normalized minimum target value. In the HEMO data set, we determined the extent to which baseline (prerandomization) stdKt/V values would have exceeded such an S-based minimum target stdKt/V. The median V(wat):S(dub) ratios were significantly higher in men (21.34) than in women (18.50). The average of these (20) was used to normalize the current suggested minimally adequate value (stdKt/V > or = 2.0/week) to the S-normalized target value (stdKt/S > or = 40 L/M(2)), assuming that average modeled V = average anthropometric V. To achieve this S-normalized target, the required single-pool (sp) Kt/V was always higher in women than in men at any level of body size. For small patients (V(wat) = 25L), required stdKt/V values were 2.05 and 2.21/week for men and women, respectively, corresponding to spKt/V values of 1.31 and 1.52/session. On the other hand, large (V(wat) = 50L) male patients would need spKt/V values of only 1.0/session. Prerandomization baseline dialysis sessions in the HEMO study were found to meet such a new S-based standard in almost all (766/773) men and in 885/992 women. An analysis of scaling dose to anthropometrically estimated liver size (L) showed similar gender ratios for V(wat):L and V(wat):S(dub), providing a potential physiologic explanation underpinning S-based scaling. S-based scaling of the dialysis dose would require considerably higher doses in small patients and in women, and would allow somewhat lower doses in larger male patients. Current dialysis practice would largely meet such an S-based adequacy standard if the dose were normalized to a V(wat):S(dub) ratio of 20.

Effect of dialysis dose and membrane flux in maintenance hemodialysis.

BACKGROUND: The effects of the dose of dialysis and the level of flux of the dialyzer membrane on mortality and morbidity among patients undergoing maintenance hemodialysis are uncertain. METHODS: We undertook a randomized clinical trial in 1846 patients undergoing thrice-weekly dialysis, using a two-by-two factorial design to assign patients randomly to a standard or high dose of dialysis and to a low-flux or high-flux dialyzer. RESULTS: In the standard-dose group, the mean (+/-SD) urea-reduction ratio was 66.3+/-2.5 percent, the single-pool Kt/V was 1.32+/-0.09, and the equilibrated Kt/V was 1.16+/-0.08; in the high-dose group, the values were 75.2+/-2.5 percent, 1.71+/-0.11, and 1.53+/-0.09, respectively. Flux, estimated on the basis of beta2-microglobulin clearance, was 3+/-7 ml per minute in the low-flux group and 34+/-11 ml per minute in the high-flux group. The primary outcome, death from any cause, was not significantly influenced by the dose or flux assignment: the relative risk of death in the high-dose group as compared with the standard-dose group was 0.96 (95 percent confidence interval, 0.84 to 1.10; P=0.53), and the relative risk of death in the high-flux group as compared with the low-flux group was 0.92 (95 percent confidence interval, 0.81 to 1.05; P=0.23). The main secondary outcomes (first hospitalization for cardiac causes or death from any cause, first hospitalization for infection or death from any cause, first 15 percent decrease in the serum albumin level or death from any cause, and all hospitalizations not related to vascular access) also did not differ significantly between either the dose groups or the flux groups. Possible benefits of the dose or flux interventions were suggested in two of seven prespecified subgroups of patients. CONCLUSIONS: Patients undergoing hemodialysis thrice weekly appear to have no major benefit from a higher dialysis dose than that recommended by current U.S. guidelines or from the use of a high-flux membrane.

Effect of change in vascular access on patient mortality in hemodialysis patients.

BACKGROUND: Hemodialysis patients using a catheter have a greater mortality risk than those using an arteriovenous (AV) access (fistula or graft). However, catheter-dependent patients also differ from those with an AV access in several clinical features, and these differences may themselves contribute to their excess mortality. METHODS: The current study evaluates whether a change in vascular access affects risk for mortality in patients enrolled in the Hemodialysis Study. Time-dependent Cox regression was used to relate mortality risk to current type of access and change in access type during the preceding 1 year. RESULTS: Compared with patients who dialyzed using an AV access at both the beginning and end of the preceding 1-year interval, relative risks for mortality were 3.43 (95% confidence interval [CI], 2.42 to 4.86) in patients who dialyzed with a catheter at both times; 2.38 (95% CI, 1.76 to 3.23) in patients switching from an AV access to a catheter, and 1.37 (95% CI, 0.81 to 2.32) in patients switching from a catheter to an AV access. Change from AV access to a catheter was associated with an antecedent decrease in serum albumin level (odds ratio, 1.25; 95% CI, 1.09 to 1.45 per 0.5 g/dL; P = 0.002), weight loss (odds ratio, 1.14; 95% CI, 1.06 to 1.22 per 2 kg; P < 0.001), and decreases in equilibrated normalized protein catabolic rate (odds ratio, 2.22; 95% CI, 1.41 to 3.57 per 0.25 g/kg/d; P < 0.001) and non-access-related hospitalization (odds ratio, 1.19; 95% CI, 1.06 to 1.32 per 1 additional hospitalization over 4 months; P = 0.002). Change from a catheter to AV access was predicted by only the antecedent non-access-related hospitalization rate (odds ratio, 0.93; 95% CI, 0.87 to 0.97 per 1 additional hospitalization over 4 months; P < 0.001). CONCLUSION: Change from a catheter to AV access is associated with a substantial decrease in mortality risk.

Adequacy of quotidian hemodialysis.

BACKGROUND: Several methods exist to quantitate small-solute clearance by daily hemodialysis (HD) regimens, but these have not been empirically applied or compared. METHODS: In the London Daily/Nocturnal Hemodialysis Study, dosing and adequacy of quotidian HD regimens, both short daily HD (n = 11) and long nocturnal HD (n = 12), were compared with conventional thrice-weekly HD (n = 22) using several models. Urea clearance was computed by percentage of reduction in urea, kinetic modeling (single-pool Kt/V [spKt/V]), Daugirdas rate equation (equilibrated Kt/V [eKt/V]), and Gotch standardized Kt/V (stdKt/V). RESULTS: Nocturnal HD patients maintained a mean single-session spKt/V of 1.64 throughout the study, similar to that of conventional HD patients (1.73), whereas daily HD patients showed a significant decrease in mean single-session spKt/V (0.93) compared with baseline (t(0)) values. Mean weekly spKt/V values increased from t(0) for both quotidian HD groups (9.08 for nocturnal HD, 5.55 for daily HD) and were higher in both quotidian HD groups compared with conventional HD patients. Weekly eKt/V, stdKt/V, and normalized protein equivalent of nitrogen appearance values showed similar trends. Comparison of the 3 different adequacy models showed an increase in weekly HD doses for both quotidian HD regimens compared with conventional HD; however, percentages of increases from t(0) to follow-up differed according to the model used. The calculated efficiency of dose delivery at the 10-month follow-up comparing daily HD with conventional HD was 257 +/- 26 minutes versus 306 +/- 17 stdKt/V unit delivered, respectively, amounting to almost 1 dialysis-hour saved per stdKt/V unit delivered for daily HD. CONCLUSION: These results show that both quotidian HD regimens are more effective than conventional HD in improving weekly urea clearance measured by spKt/V, stdKt/V, and eKt/V.

Dose of dialysis: key lessons from major observational studies and clinical trials.

Analyses based on the National Cooperative Dialysis Study (NCDS) provided the impetus for routine quantification of delivered dialysis dose in hemodialysis practice throughout the world, by suggesting minimum targets for small solute (urea) clearance. Morbidity and mortality in dialysis populations remain high despite many technological advances in dialysis delivery. A number of observational studies reported association between higher dose of dialysis as measured by Kt/V urea or urea reduction ratio with lower mortality risk. During the 1990s, a steady increase in dialysis dose and a modest reduction in mortality on dialysis were observed. However, observational studies only reveal associations and are limited by selection bias and confounding. The Kidney Disease Outcomes Quality Initiative guidelines on dialysis adequacy are based on results of observational studies and expert opinion. Since the NCDS, the HEMO Study was the first major randomized clinical trial designed to study the effect of dose of dialysis and dialyzer flux on patient outcomes. Despite adequate separation of dose and flux, however, results of the trial did not prove a beneficial effect of higher dose. The Dialysis Outcomes and Practice Patterns Study (DOPPS), in a major international effort designed to examine the effect of practice patterns on outcomes, has made significant contributions to the topic of dialysis dose. The following review critically examines data from observational studies, including the DOPPS, and from the HEMO Study, emphasizing important lessons from both, and discusses future paradigms for achieving dialysis adequacy to improve patient outcomes.