Unlike Kt, high Kt/V is associated with greater mortality: The importance of low V

INTRODUCTION

Kt/V has been used as a synonym for haemodialysis dose. Patient survival improved with a Kt/V>1; this target was subsequently increased to 1.2 and 1.3. The HEMO study revealed no significant relationship between Kt/V and mortality. The relationship between Kt/V and mortality often shows a J-shaped curve. Is V the confounding factor in this relationship? The objective of this study is to determine the relationship between mortality and Kt/V, Kt and body water content (V) and lean mass (bioimpedance).

METHODS

We studied a cohort of 127 prevalent haemodialysis patients, who we followed-up for an average of 36 months. Kt was determined by ionic dialysance, and V and nutrition parameters by bioimpedance. Kt/V, Kt corrected for body surface area (Kt/BSA) and target Kt/BSA were calculated. The mean data from 18,998 sessions were used as haemodialysis parameters, with a mean of 155 sessions per patient.

RESULTS

Mean age was 70.4±15.3 years and 61% were male; 76 were dialysed via an arteriovenous fistula and 65 were on online haemodiafiltration. Weight was 70.6 (16.8)kg; BSA 1.8 (0.25) m²; total body water (V) 32.2 (7.41) l and lean mass index (LMI) 11.1 (2.7)kg/m². Mean Kt/V was 1.84 (0.44); Kt 56.1 (7)l and Kt/BSA 52.8 (10.4)l. The mean target Kt/BSA was 49.7 (4.5)l. Mean Kt/BSA-target Kt/BSA +6.4 (7.0)l. Patients with a higher Kt/V had worse survival rates than others; with Kt this is not the case. Higher Kt/V values are due to a lower V, with poorer nutrition parameters. LMI and serum albumin were the parameters that best independently predicted the risk of death and are lower in patients with a higher Kt/V and lower V.

CONCLUSION

Kt/V is not useful for determining dialysis doses in patients with low or reduced body water. Kt or the Kt/BSA are proposed as an alternative.

Adaptive network based on fuzzy inference system for equilibrated urea concentration prediction

Post-dialysis urea rebound (PDUR) has been attributed mostly to redistribution of urea from different compartments, which is determined by variations in regional blood flows and transcellular urea mass transfer coefficients. PDUR occurs after 30-90min of short or standard hemodialysis (HD) sessions and after 60min in long 8-h HD sessions, which is inconvenient. This paper presents adaptive network based on fuzzy inference system (ANFIS) for predicting intradialytic (Cint) and post-dialysis urea concentrations (Cpost) in order to predict the equilibrated (Ceq) urea concentrations without any blood sampling from dialysis patients. The accuracy of the developed system was prospectively compared with other traditional methods for predicting equilibrated urea (Ceq), post dialysis urea rebound (PDUR) and equilibrated dialysis dose (eKt/V). This comparison is done based on root mean squares error (RMSE), normalized mean square error (NRMSE), and mean absolute percentage error (MAPE). The ANFIS predictor for Ceq achieved mean RMSE values of 0.3654 and 0.4920 for training and testing, respectively. The statistical analysis demonstrated that there is no statistically significant difference found between the predicted and the measured values. The percentage of MAE and RMSE for testing phase is 0.63% and 0.96%, respectively.

Modeling hybrid rough set-based classification procedures to identify hemodialysis adequacy for end-stage renal disease patients

Healthcare problems observed in the majority of end-stage renal disease (ESRD) patients regarding hemodialysis (HD) treatment are serious issues for the Taiwanese healthcare services, and an interesting topic is thus the adequacy of HD therapy. This study successfully models a hybrid procedure to measure HD adequacy to assess therapeutic effects and to explore the relationship between accuracy and coverage for interested parties. The proposed model has better accuracy, a lower standard deviation, and fewer attributes than the listed methods under various evaluation criteria. The study results are useful to subsequent researchers to develop suitable applications, and to ESRD patients and their doctors to ensure satisfactory medical quality.

Altered taste perception and nutritional status among hemodialysis patients

OBJECTIVE

The objective of this study was to examine the association between altered taste perception and nutritional status among hemodialysis patients.

DESIGN

We performed a post hoc analysis of data from the Hemodialysis study (n = 1,745). Taste perception was assessed at baseline and then updated annually using an item from a quality of life survey that asked "During the past 4 weeks, to what extent were you bothered by loss of taste?" Responses were categorized as normal taste perception if subjects answered "not at all" or altered taste perception if they reported any degree of bother. Time-updated logistic regression models were used to evaluate predictors of altered taste perception. Time-updated linear regression models were used to examine the association between altered taste perception and indices of nutritional status. Multivariable proportional hazards and Poisson models were used to assess association between altered taste perception and mortality and hospitalization, respectively.

RESULTS

At baseline, 34.6% reported altered taste perception, which was associated with poorer baseline nutritional status. On time-updated analysis, altered taste perception was associated with a persistently higher proportion of subjects requiring enteral nutritional supplements and lower serum albumin, serum creatinine, normalized protein catabolic rate, protein intake, sodium intake, and mid-arm muscle circumference. Altered taste perception at baseline was independently associated with increased all-cause mortality: adjusted hazard ratio (95% confidence interval) of 1.17 (1.01-1.37), although not with increased rate of hospitalization.

CONCLUSION

Altered taste perception was common among prevalent hemodialysis patients and was independently associated with poorer indices of nutritional status and increased all-cause mortality.

Prescribed dietary phosphate restriction and survival among hemodialysis patients

BACKGROUND AND OBJECTIVES

Hyperphosphatemia is common among hemodialysis patients. Although prescribed dietary phosphate restriction is a recommended therapy, little is known about the long-term effects on survival.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We conducted a post hoc analysis of data from the Hemodialysis Study (n = 1751). Prescribed dietary phosphate was recorded at baseline and annually thereafter. Marginal structural proportional hazard models were fit to estimate the adjusted association between dietary phosphate restriction and mortality in the setting of time-dependent confounding.

RESULTS

At baseline, prescribed daily phosphate was restricted to levels ≤ 870, 871 to 999, 1000, 1001 to 2000 mg, and not restricted in 300, 314, 307, 297, and 533 participants, respectively. More restrictive prescribed dietary phosphate was associated with poorer indices of nutritional status on baseline analyses and a persistently greater need for nutritional supplementation but not longitudinal changes in caloric or protein intake. On marginal structural analysis, there was a stepwise trend toward greater survival with more liberal phosphate prescription, which reached statistical significance among subjects prescribed 1001 to 2000 mg/d and those with no specified phosphate restriction: hazard ratios (95% CIs) 0.73 (0.54 to 0.97) and 0.71 (0.55 to 0.92), respectively. Subgroup analysis suggested a more pronounced survival benefit of liberal dietary phosphate prescription among nonblacks, participants without hyperphosphatemia, and those not receiving activated vitamin D.

CONCLUSIONS

Prescribed dietary phosphate restriction is not associated with improved survival among prevalent hemodialysis patients, and increased level of restriction may be associated with greater mortality particularly in some subgroups.

Two Spent Dialysate Samples are Sufficient for Hemodialysis Efficacy Assessment

Introduction

The measure of dialysis efficacy is expressed as Kt/V value (calculated from predialysis and postdialysis blood urea concentration). The aim of this study was to assess the possibility of direct calculation of Kt/V value from two spent dialysate samples by using the regular blood-based Kt/V calculation formula with dialysate samples used as surrogates for blood samples, and to detect the most appropriate couple of dialysate samples for Kt/V estimation.

Patients and Methods

Fifty-two single hemodialysis treatments in 34 anuric patients on chronic bicarbonate low-flux hemodialysis were observed. Kt/V values according to Daugirdas formula from two blood samples and from two dialysate samples were calculated.

Results

Kt/V values calculated according to Daugirdas 2nd generation formula from blood samples (Kt/Vsp Daugirdas) were in significant correlation with all Kt/V values obtained from two spent dialysate samples. The highest correlation coefficient (r = 0.74, p & 0.001) and the least standard error of mean of the differences were found between Kt/Vsp Daugirdas and value obtained with substitution of urea concentration from dialysate samples taken 60 minutes after dialysis start and at the end of the dialysis into Daugirdas 2nd generation formula (Kt/VDCD(60)-CD(e)), which can be expressed as a equation of linear regression y = 0.47 + 0.86x. The highest correlation coefficient (r = 0.74, p & 0.001) was found between Kt/Vsp Daugirdas values equilibrated according to Daugirdas rate formula, and Kt/VDCD(60)-CD(e) value, which can also be expressed as an equation of linear regression y = 0.43 + 0.73x.

Conclusion

The results of this study clearly show the sufficiency of only two spent dialysate samples for direct estimation of the Kt/V values, with no blood sample required.

Catheter performance

Venous catheters differ from peripheral arteriovenous (AV) access devices in many important ways. This discussion focuses on their performance as a conduit for blood flow between the patient and the dialyzer and on how catheter function is both limited and enhanced relative to the more common peripheral accesses. Catheter flow is limited by the high resistance inherent in the extended length of venous catheters relative to dialysis needles, but the high rate of flow in central veins also diminishes the opportunity for access recirculation. Cardiopulmonary recirculation is absent in patients with catheter access unless the patient also has a peripheral access. In the latter case, the same detrimental effect on urea clearance is seen regardless of which access device is used. Flow-dependent recirculation through circuits other than the peripheral AV access reduces the efficiency of dialysis (regardless of the type of access, catheter, or peripheral AV device used) across both catheters and peripheral AV devices. The inside diameter of the catheter plays a sensitive role in determining catheter resistance to flow. Slight increases in diameter under the same pressure head are associated with large increases in flow. Negative pressure at the catheter inflow port generated by the blood pump is magnified relative to peripheral devices, predisposing to partial collapse of the pump tubing segment and erroneous blood flow readings by the pump motor speed indicator. Setting a limit on prepump negative pressure can minimize this error. Future applications of dialysis may require lower pump speeds, which would allow more liberal use of catheter access if their potential for infection and clotting can be reduced.

In vivo effects of dialysate flow rate on Kt/V in maintenance hemodialysis patients

It is generally assumed that hemodialysis adequacy is only minimally affected by increasing the dialysate flow rate (Qd). Recent in vitro studies showed that dialyzer urea clearance (Kd(urea)) may increase substantially more than expected in response to an increase in Qd. Because these studies implied that dialysis efficacy may benefit from greater Qds, we studied in vivo the effects of various Qds on the delivered dose of dialysis in 23 maintenance hemodialysis (MHD) patients. Hemodialysis was performed at Qds of 300, 500, and 800 mL/min for at least 3 weeks each, whereas specific dialysis prescriptions (treatment time, blood flow rate [Qb], ultrafiltration volume, and type and size of dialyzer) were kept constant. Delivered dose of dialysis, assessed by single-pool Kt/V (Kt/V(sp)) and double-pool Kt/V (Kt/ V(dp)), was measured at least three times for each Qd (218 measurements). Mean +/- SEM Kt/V(sp) was 1.19 +/- 0.03 at Qd of 300 mL/min, 1.32 +/- 0.04 at 500 mL/min, and 1.45 +/- 0.04 at 800 mL/min. The relative gains in Kt/V(sp) for increasing Qd from 300 to 500 mL/min and 500 to 800 mL/min were 11.7% +/- 8.7% and 9.9% +/- 5.1%, respectively. Kt/V(dp) increased at a similar percentage (11.2% +/- 8.9% and 10.3% +/- 5.1%, respectively). The observed gain in urea clearance by increasing Qd from 500 to 800 mL/min was significantly greater than the increase in Kd(urea) predicted from mathematical modeling (5.7% +/- 0.4%; P = 0.0008). Removal ratios for creatinine and the high-molecular-weight marker, beta(2)-microglobulin, were not affected by increasing Qd from 500 to 800 mL/min. The proportion of patients not achieving adequacy (Kt/V(sp) >/= 1.2) was reduced from 56% at Qd of 300 mL/min to 30% at 500 mL/min and further to 13% at 800 mL/min. It is concluded that increasing Qd from 500 to 800 mL/min is associated with a significant increase in Kt/V. Hemodialysis with Qd of 800 mL/min should be considered in selected patients not achieving adequacy despite extended treatment times and optimized Qbs.

Use of Systemic Blood Urea Nitrogen Levels Obtained 30 Minutes before the End of Hemodialysis to Portray Equilibrated, Postdialysis Blood Urea Nitrogen Values

Blood urea nitrogen (BUN) levels obtained at 30 minutes before the end of dialysis were found to be closely similar to equilibrated, postdialysis BUN values obtained 30 minutes after the end of dialysis. Because of this similarity, the former BUN values can be used to derive equilibrated urea reduction ratio, or equilibrated Kt/V instead.

Practical guide to measuring adequacy of dialysis

Measurement of adequacy of small solute clearance on hemodialysis (HD) and peritoneal dialysis (PD) is important. In HD, formal urea kinetic modelling (UKM) is recommended because it is theoretically more accurate than the urea reduction ratio (URR) and because it allows prospective selection of an adequate prescription. However, the URR is simpler and has an important role to play. Precise attention to the methodology of sampling the post-HD blood urea is important. In PD, both Kt/V and creatinine clearance should be measured, and the main concerns relate to logistic problems in collection and processing of dialysate samples. In both HD and PD, a well-defined standardized methodology for measuring adequacy indices should be in place in each dialysis unit.

Recirculation, urea disequilibrium, and dialysis efficiency: peripheral arteriovenous versus central venovenous vascular access

When accurate, non-urea-based methods of measuring recirculation are used, recirculation is usually absent in arteriovenous (AV) accesses. When urea-based methods are used to measure recirculation in AV accesses, falsely elevated recirculation rates are common. These errors are due to AV and venovenous disequilibrium (peripheral vein method), delayed systemic sampling (two-needle methods), and errors in urea measurement (all methods). The literature suggests that recirculation in central venovenous (CV) catheters is approximately 5%. The methods used for these determinations have all been urea based. However, there are few theoretical problems in using urea-based measurements for measuring recirculation in this setting, making it more likely that these values are accurate. When hemodialysis via CV and AV accesses are compared, equilibrated Kt/V values differ significantly for the same single-pool Kt/V when 15-second postdialysis blood urea nitrogen values are used for modeling, but differ minimally when 2-minute postdialysis samples are used. The impact of transient retrograde blood flow in the superior vena cava on recirculation and whether dialysis efficiency is influenced by the exact site of CV catheter placement (superior vena cava v right atrium) is uncertain.