Comparison of hemodialysis urea clearance using spent dialysate and Kt/Vurea equations

INTRODUCTION

Dialysis adequacy is traditionally calculated from pre- and post-hemodialysis session serum urea concentrations and expressed as the urea reduction ratio, or Kt/Vurea. However, with increasing hemodiafiltration usage, we wished to determine whether there were any differences between standard Kt/Vurea equations and directly measured spent dialysate urea clearance.

METHODS

Urea clearance was measured from collected effluent dialysate and compared with various other methods of Kt/Vurea calculation, including change in total body urea from measuring pre- and post-total body water with bioimpedance and the Watson equation, by standard Kt/V equations, and online clearance measurements using effective ionic dialysance (OLC).

RESULTS

We compared urea clearance in 41 patients, 56.1% male, mean age 69.3 ± 12.6 years with 87.8% treated by hemodiafiltration. Reduction in total body urea was greater when estimating changes in total body urea, compared to measured dialysate losses of 58.4% (48.5-67.6) vs 71.6% (62.1-78), p < 0.01. Sessional urea clearance (Kt/Vurea) was greater using the online Solute-Solver program compared to OLC, median 1.45(1.13-1.75) vs 1.2 (0.93-1.4), and 2nd generation Kt/V equations 1.3 (1.02-1.66), p < 0.01, but not different from estimated total body urea clearance 1.36 (1.15-1.73) and dialysate clearance 1.36 (1.07-1.76). The mean bias compared to the Solute-Solver program was greatest with OLC (-0.25), compared to second-generation equations (-0.02), estimated total body clearance (-0.02) and measured dialysate clearance (-0.01).

CONCLUSION

This study demonstrated that the result from equations estimating urea clearance indirectly from pre- and postblood samples from hemo- and hemodiafiltration treatments was highly correlated with direct measurements of dialysate urea clearance.

Is the measurement of tissue advanced glycosylation products by skin autofluorescence associated with mortality in patients treated by peritoneal dialysis?

BACKGROUND

Advanced glycosylated end-products (AGEs) have been shown to cause cardiovascular disease, and tissue AGE accumulation can be measured by skin autofluorescence (SAF). AGEs are cleared by the kidney, and thus accumulate in dialysis patients. However, as the results of SAF measurements in peritoneal dialysis patients (PD) have been ambiguous, we examined the association between mortality and SAF.

METHODS

We reviewed SAF measurements in PD patients attending a university associated PD program, along with standard measurements of dialysis adequacy and peritoneal membrane function.

RESULTS

We studied 341 prevalent PD patients, 61.9% male, mean age 61.2 ± 16 years, and 31.4% of all patients died during a median follow-up of 27.2 (23.3-36.3) months. Patients who died were older, mean age 72 ± 10.5 years, were more often diabetic (60.7%), and had higher median SAF 3.8 (3.2-4.5) AU. On logistic regression, mortality was independently associated with age (odds ratio (OR) 1.1 (95% confidence limits 1.06-1.16), diabetes OR 10.1 (3.1-33.4), SAF OR 3.3 (1.8-6.2), all p < 0.001, and male gender OR 5.2 (1.6-17.4), p = 0.007; and negatively associated with weight OR 0.91 (0.86-0.95), p < 0..001, normalised nitrogen appearance rate (nPNA) OR 0.05 (0.01-0.4), p = 0.005 and mean arterial blood pressure (MAP) OR 0.96 (0.93-0.96), p = 0.03.

CONCLUSIONS

In this observational study, SAF was independently associated with mortality. However, other factors were also associated with mortality, including age, diabetes and malnutrition which have all been reported to affect SAF measurements. Thus, the additional predictive value of measuring SAF compared to standard risk factors for mortality remains to be determined.

How Is Body Composition and Nutrition Status Associated with Erythropoietin Response in Hemodialyzed Patients? A Single-Center Prospective Cohort Study

Background: Anemia is the most common finding in patients with end-stage kidney disease undergoing renal replacement therapy. A certain percentage of patients does not respond adequately to erythropoietin (EPO) treatment, not being able to reach desirable hemoglobin levels even when treated with large-dose EPO and intravenous/oral iron. In our study, we wanted to further investigate how nutritional status is associated with erythropoietin responsiveness. To quantify EPO response, we used the Erythropoietin Resistance Index (ERI), which is defined as the weekly weight-adjusted dose of EPO divided by the hemoglobin level. Patients and methods: Seventy-eight patients undergoing hemodialysis were included. All of them were measured by a SECA mBCA body composition analyzer and evaluated by Kalantar-Zadeh’s MIS score. Routine biochemical tests were also taken into account. The Shapiro-Wilk test was used to study the distributions of quantitative variables, which were significantly different from normal (p < 0.05). We used nonparametric Mann-Whitney U-test to compare groups. Correlations were studied by means of Spearman’s rank correlation coefficient. Bonferroni correction for multiple testing was performed. To find independent determinants of ERI, we additionally performed multivariate analysis using the General Linear Model (GLM). Results: In terms of body composition, factors that are associated with high ERI are low BMI, low fat mass, low visceral fat volume, high total body water percentage, low phase angle and low fat-free mass. In addition to body composition parameters, total MIS score and IL-6 serum levels correlated positively with ERI value. IL-6 was an independent determinant of ERI value, based on multivariate analysis. After correction for multiple analysis, BMI and eGFR both remained significant factors associated with EPO response. Conclusions: It seems crucial to prevent inflammatory malnutrition as a part of a holistic approach to anemia treatment in dialysis patients.

Application of the Clinical Frailty Score and body composition and upper arm strength in haemodialysis patients

Background

To improve outcomes, simple screening tests are required to detect patients at increased risk of mortality. As patients with muscle weakness and wasting are at increased risk of death, we wished to review the use of the Clinical Frailty Score (CFS).

Patients and methods

Dialysis staff graded haemodialysis (HD) patients attending for routine outpatient sessions using the CFS, a functional scoring scale, for patients who require help with their instrumental activities of daily living, classified as clinically frail with scores >4, which were compared with contemporaneous Stoke–Davies comorbidity scores, post-HD body composition measured by bioimpedance, hand grip strength (HGS) and standard laboratory investigations.

Results

The results from 2089 patients (60.2% male) were reviewed, with 890 (42.6%) classified as frail. Frail patients were older [mean ± standard deviation (SD) 71.5 ± 15.6 versus 59.1 ± 15.6 years) and female (50.7% versus 37.3%) and had greater comorbidity {median 2 [interquartile range (IQR) 1–3] versus 1 [0–2]}, body mass index (BMI) (26.0 ± 6.7 versus 25.5 ± 5.4 kg/m²),  C-reactive protein (CRP) [8 (IQR 3–20) versus 5 (2–11) mg/L], lower serum albumin (37.6 ± 4.7 versus 40.1 ± 4.7 g/L),  lean BMI (8.9 ± 1.7 versus 9.7 ± 1.6 kg/m²) and HGS [13.4 (IQR 9.6–18.8) versus 20.9 (14.5–29) kg] (all P < 0.001). Frailty was independently associated in a multivariable logistic model with age {odds ratio [OR] 2.33 [95% confidence limit (CL) 2.01–2.7]}, body fat mass [OR 1.02 (CL 1.01–1.03)], log CRP [OR 1.63 (CL 1.28–2.07)] (all P < 0.001) and comorbidity [OR 1.45 (CL 1.17–1.8); P = 0.001] and negatively associated with albumin [OR 0.95 (CL 0.92–0.98) and HGS [OR 0.91 (CL 0.9–0.93)] (both P < 0.001).

Conclusion

Frail patients are at increased risk of mortality and, as such, simple reliable screening tools are required to rapidly detect patients at risk. The CFS is a useful screening tool that can be readily performed by dialysis staff to identify frail patients. Frailty in HD patients was associated with increasing age, comorbidity, fat weight and inflammation and reduced muscle strength and muscle mass. There is an overlap between frailty and both sarcopenia and protein energy wasting, which requires additional assessments, potentially including body composition, strength, dietary assessments and laboratory investigations. In addition, as the CFS offers a scale, patient trajectories can potentially be serially monitored over time, thus allowing patient-specific interventions or holistic care plans.

Dialysis of the Obese Patient: Meeting Needs for a Growing Epidemic

Increasing population obesity and associated metabolic consequences has led to increased number of obese patients with chronic kidney disease and end-stage renal disease. While obesity is associated with increased cardiovascular morbidity and mortality, obese dialysis patients present a seeming paradox for survival benefit, given other acute intervening illnesses for those on dialysis with loss of lean body mass overtime. Challenges remain in providing adequate renal replacement options and therapy for this growing segment of obese patients on dialysis which are discussed in this article.

Hemodialysis (HD) dose and ultrafiltration rate are associated with survival in pediatric and adolescent patients on chronic HD-a large observational study with follow-up to young adult age

BACKGROUND

Hemodialysis (HD) dose targets and ultrafiltration rate (UFR) limits for pediatric patients on chronic HD are not known and are derived from adults (spKt/V>1.4 and <13 ml/kg/h). We aimed to characterize how delivered HD dose and UFR are associated with survival in a large cohort of patients who started HD in childhood.

METHODS

Retrospective analysis on a cohort of patients <30 years, on chronic HD since childhood (<19 years), having received thrice-weekly HD 2004-2016 in outpatient DaVita centers.

OUTCOME

Survival while remaining on HD.

PREDICTORS

(I) primary analysis: mean delivered dialysis dose stratified as spKt/V ≤1.4/1.4-1.6/>1.6 (Kaplan-Meier analysis), (II) secondary analyses: UFR and alternative dialysis adequacy measures [eKt/V, body-surface normalized Kt/BSA] on continuous scale (Weibull regression model).

RESULTS

A total of 1780 patients were included (age at the start of HD: 0-12y: n=321, >12-18y: n=1459; median spKt/V=1.55, eKt/V=1.31, Kt/BSA=31.2 L/m², UFR=10.6 mL/kg/h). (I) spKt/V<1.4 was associated with lower survival compared to spKt/V>1.4-1.6 (P<0.001, log-rank test), and spKt/V>1.6 (P<0.001), with 10-year survival of 69.3% (59.4-80.9%) versus 83.0% (76.8-89.8%) and 84.0% (79.6-88.5%), respectively. (II) Kt/BSA was a better predictor of survival than spKt/V or eKt/V. UFR was additionally associated with survival (P<0.001), with increased mortality <10/>18 mL/kg/h. Associations did not alter significantly following adjustment for demographic characteristics (age, etiology of kidney disease, and ethnicity).

CONCLUSIONS

Our results suggest usefulness of targeting Kt/BSA>30 L/m² for best long-term outcomes, corresponding to spKt/V>1.4 (>12 years) and >1.6 (<12 years). In contrast to adults, higher UFR of 10-18 ml/kg/h was not associated with greater mortality in this population.

Patient-reported symptoms during dialysis: the effect of pre-dialysis extracellular water and change in extracellular water post-dialysis

Background

Quality of life for haemodialysis (HD) patients may be affected by symptoms during dialysis treatments, and patient groups have highlighted the need to improve post-dialysis fatigue and dialysis-related symptoms. As changes in extracellular water (ECW) may lead to cramps and other symptoms, we wished to determine whether there was an association between ECW and intra-dialytic symptoms.

Methods

We reviewed the hospital records of HD patients who completed a self-reported intra-dialytic symptom questionnaire, using a visual analogue scale, who had contemporaneous pre- and postdialysis bioimpedance ECW measurements adjusted to height (aECW).

Results

We studied dialysis sessions of 506 patients, 314 (62.1%) male, 226 (44.7%) diabetic, mean age 64.6 ± 15.7 years, weight 69.9 ± 17.4 kg, and duration of dialysis treatment 26 (9.6–60.1) months. We divided patients into three groups according to pre-dialysis aECW, and total dialysis symptom scores were greater for those in the lower tertile (25 (10–41) vs middle 18 (8.5–34) vs upper 20 (7–31), p < 0.05). Only feeling cold, dizziness, and low blood pressure were statistically different between the three pre-dialysis aECW groups, and there was no difference in post-dialysis recovery times.

We analysed the effect of the fall in aECW pre-to post-dialysis. Patients in the group with the greatest fall in aECW did not report more intra-dialytic symptoms or longer recovery times.

Conclusion

We found that patients starting dialysis with lower relative ECW were more likely to report intra-dialytic symptoms than those with greater amounts of fluid to remove, and most commonly reported symptoms were associated with intra-vascular volume depletion.

The association of standard Kt/V and surface area-normalized standard Kt/V with clinical outcomes in hemodialysis patients

INTRODUCTION

A previous study demonstrated that the surface area-normalized standard Kt/V (SAstdKt/V) was better associated with mortality than standard Kt/V (stdKt/V). This study investigates the association of SAstdKt/V and stdKt/V with mortality, anemia, and hypoalbuminemia in a larger patient cohort with a longer follow-up period.

METHODS

We included adult patients on thrice-weekly hemodialysis in the USRDS database and excluded amputated patients. StdKt/V and SAstdKt/V were calculated from the available single-pool Kt/V. Patients were categorized into five groups according to their stdKt/V and SAstdKt/V: <2.00, 2.00-2.19, 2.20-2.39, 2.40-2.59, and ≥2.60. Hazard ratios (HR) and odds ratios (OR) were calculated using Cox and logistic regression analysis respectively.

FINDINGS

There were 507,656 patients included in the analysis. The patients had a median age of 65.5 years with a median follow-up period of 2 years. Thirty-four percent died during follow-up. HRs for mortality progressively decreased as SAstdKt/V increased in both unadjusted and adjusted models. Unlike SAstdKt/V, HRs were the lowest in the categories with stdKt/V of 2.40-2.59 and they increased in the higher stdKt/V category. The adjusted HR for SAstdKt/V vs. stdKt/V were 0.68 vs. 0.62 in the category of 2.40-2.59, and 0.63 vs. 0.73 in the category of ≥2.60. The adjusted ORs for anemia progressively decreased as SAstdKt/V increased, whereas ORs decreased to the lowest in stdKt/V category 2.40-2.59 and increased in the ≥2.60 category. The adjusted ORs for hypoalbuminemia progressively decreased as SAstdKt/V and stdKt/V increased which were both 0.45 in 2.40-2.59 category and decreased to 0.29 and 0.42 in the ≥2.60 category.

DISCUSSION

SAstdKt/V is better associated with mortality, anemia, and hypoalbuminemia than stdKt/V. SAstdKt/V is a better parameter in defining hemodialysis dosing which can be calculated by an available online tool. Further studies to determine the optimal SAstdKt/V dose required to achieve improved clinical outcomes with better cost-effectiveness are needed.

Impact of obesity on dialysis and transplant and its management

Obesity is increasing to unprecedented levels, including in the end-stage kidney disease population, where upwards of 60% of kidney transplant patients are overweight or obese. Obesity poses additional challenges to the care of the dialysis patient, including difficulties in creating vascular access and inserting Tenckhoff catheters, higher rates of catheter malfunction and peritonitis, the need for longer and/or more frequent dialysis (or peritoneal dialysis [PD] exchanges) to achieve adequate clearance, increased metabolic complications particularly with PD, and obesity is a barrier to kidney transplantation. In this article, we review special considerations in performing PD, hemodialysis and transplant in the obese patient, as well as the evidence behind medical and surgical management of obesity in dialysis patients.

Telenephrology and on-site nephrology: Comparable adequate dialysis care to patients living in remote Pacific Islands

Introduction

End-stage renal disease is a major public health concern in New Caledonia and in Wallis and Futuna (prevalence value: 2542 per million population in 2017). Spread over the territory, 594 dialysis patients are followed up by nephrologists and partially by telemedicine due to the distance. The aim of our this study was to evaluate the quality of care provided by telemedicine for chronic dialysis patients on Wallis Island, a dialysis unit remote from Noumea (2100 km).

Methods

We compared two populations of haemodialysis patients, one based in Poindimie in New Caledonia and followed by monthly physical consultation, the other based on Wallis Island and followed by monthly teleconsultation and quarterly on-site consultation.

Results

From January 2012–December 2017, dialysis adequacy and survival data were recorded for 84 patients: 44 in Poindimie, 40 on Wallis Island. Dialysis adequacy (i.e. clinical, biological parameters) as well as occurrence of vascular access complications were no different regardless of the means of follow-up. During the study, 23 deaths occurred (11 in Poindimie, 12 on Wallis Island; p = 0.464). We did not find any difference in survival at one and six years ( p = 0.46) between the two dialysis units. Evaluation for transplantation was lower for Wallisian patients ( p = 0.042), without impact on the number of patients being transplanted ( p = 0.678).

Conclusion

Telemedicine is a valuable opportunity for the follow-up of remote chronic haemodialysis patients, allowing them to be treated close to home while ensuring optimal quality of care

The effect of gender on survival for hemodialysis patients: Why don't women live longer than men?

Women in the general population have a survival advantage over men, but this advantage is not sustained in end-stage kidney disease (ESKD) patients treated by hemodialysis. To understand why gender may affect survival we need to understand confounders which may affect dialysis practices. The current paradigm is to prescribe hemodialysis to achieve a target dialyzer urea clearance adjusted to total body water volume (Kt/V_urea ). Estimated glomerular filtration calculated from serum creatinine is often used to determine when patients start dialysis; as creatinine generation rates are lower in women, this may potentially result in a lead time bias with male patients starting dialysis earlier than females. When hemodialysis dose is scaled to total body water (Kt/V_urea ) women receive shorter dialysis session times. Scaling dialysis for body surface area may be more appropriate since urea generation (a surrogate for uremic toxin production) depends upon resting energy expenditure (ie, cellular metabolism) which reflects internal organ sizes. Resting energy expenditure is proportionally greater for smaller people. Women are generally smaller than men and as such have smaller sized internal organs. However, when comparing individuals, then internal organ size is best adjusted for using body surface area, not body water. The shorter, resultant dialysis session also results in lower middle molecule clearances, increases fluid removal rates and the risk of intra-dialytic hypotension; the latter potentially results in earlier loss of residual renal function. Observational studies report that the association between survival and dialyzer Kt/V_urea is improved after adjustment for body surface area, or energy expenditure. These studies also demonstrated that the conventional prescription of hemodialysis based on current Kt/V_urea targets leads to less treatment delivered to women. These multiple consequences of the generally smaller size of women compared with men may account for the unexpectedly higher relative mortality for women. As such, prospective studies investigating alternative scaling parameters are required to confirm that increasing dialysis treatments for women improves survival.

A swan song for Kt/Vurea

Dialyzer clearance of urea multiplied by dialysis time and normalized for urea distribution volume (Kt/V_urea or simply Kt/V) has been used as an index of dialysis adequacy since more than 30 years. This article reviews the flaws of Kt/V, starting with a lack of proof of concept in three randomized controlled hard outcome trials (RCTs), and continuing with a long list of conditions where the concept of Kt/V was shown to be flawed. This information leaves little room for any conclusion other than that Kt/V, as an indicator of dialysis adequacy, is obsolete. The dialysis patient might benefit more if, instead, the nephrology community concentrates in the future on pursuing the optimal dialysis dose that conforms with adequate quality of life and on factors that are likely to affect outcomes more than Kt/V. These include residual renal function, volume status, dialysis length, ultrafiltration rate, the number of intra-dialytic hypotensive episodes, interdialytic blood pressure, serum potassium and phosphate, serum albumin, and C reactive protein.

Prescribing Hemodialysis or Hemodiafiltration: When One Size Does Not Fit All the Proposal of a Personalized Approach Based on Comorbidity and Nutritional Status

There is no simple way to prescribe hemodialysis. Changes in the dialysis population, improvements in dialysis techniques, and different attitudes towards the initiation of dialysis have influenced treatment goals and, consequently, dialysis prescription. However, in clinical practice prescription of dialysis still often follows a "one size fits all" rule, and there is no agreed distinction between treatment goals for the younger, lower-risk population, and for older, high comorbidity patients. In the younger dialysis population, efficiency is our main goal, as assessed by the demonstrated close relationship between depuration (tested by kinetic adequacy) and survival. In the ageing dialysis population, tolerance is probably a better objective: "good dialysis" should allow the patient to attain a stable metabolic balance with minimal dialysis-related morbidity. We would like therefore to open the discussion on a personalized approach to dialysis prescription, focused on efficiency in younger patients and on tolerance in older ones, based on life expectancy, comorbidity, residual kidney function, and nutritional status, with particular attention placed on elderly, high-comorbidity populations, such as the ones presently treated in most European centers. Prescription of dialysis includes reaching decisions on the following elements: dialysis modality (hemodialysis (HD) or hemodiafiltration (HDF)); type of membrane (permeability, surface); and the frequency and duration of sessions. Blood and dialysate flow, anticoagulation, and reinfusion (in HDF) are also briefly discussed. The approach described in this concept paper was developed considering the following items: nutritional markers and integrated scores (albumin, pre-albumin, cholesterol; body size, Body Mass Index (BMI), Malnutrition Inflammation Score (MIS), and Subjective Global Assessment (SGA)); life expectancy (age, comorbidity (Charlson Index), and dialysis vintage); kinetic goals (Kt/V, normalized protein catabolic rate (n-PCR), calcium phosphate, parathyroid hormone (PTH), beta-2 microglobulin); technical aspects including vascular access (fistula versus catheter, degree of functionality); residual kidney function and weight gain; and dialysis tolerance (intradialytic hypotension, post-dialysis fatigue, and subjective evaluation of the effect of dialysis on quality of life). In the era of personalized medicine, we hope the approach described in this concept paper, which requires validation but has the merit of providing innovation, may be a first step towards raising attention on this issue and will be of help in guiding dialysis choices that exploit the extraordinary potential of the present dialysis "menu".

Indexing dialysis dose for gender, body size and physical activity: Impact on survival

Current practice basing dialysis dose on urea distribution volume (V) has been questioned. We explored the impact on survival of scaling dialysis dose (Kt) to parameters reflective of metabolic activity. In a multicentre prospective cohort study of 1500 patients on thrice-weekly haemodialysis, body surface area (BSA) and resting energy expenditure (REE) were estimated using validated equations and physical activity by the Recent Physical Activity Questionnaire. Total energy expenditure (TEE) was estimated from REE and physical activity data. Kt was calculated from delivered (single-pool Kt/V)*Watson V. Kt/BSA, Kt/REE and Kt/TEE were then calculated at baseline and 6 monthly during follow-up for 2 years. In adjusted Cox models Kt/TEE, Kt/BSA, Kt/REE, in that order, had lower hazard ratios for death than single-pool Kt/V. On the basis of adjusted survival differences, putative minimum target doses were estimated for Kt/BSA as 27119 ml/m² and Kt/TEE as 25.79 ml/kcal. We identified spKt/V values equivalent to these estimated targets, ranging from 1.4 to 1.8 in patient groups based on gender, body size and physical activity. For sedentary patients, the minimum target dose was 1.4 for large males, 1.5 for small males and 1.7 for women. For active patients the target was 1.8 irrespective of gender and body-weight. Patients achieving these individualised minimum targets had greater adjusted two-year survival compared to those achieving conventional minimum targets. Metabolic activity related parameters, such as Kt/TEE and Kt/BSA, may have a clinically important role in scaling haemodialysis dose. Using such parameters or their spKt/V equivalents to adjust minimum target doses based on gender, body size and habitual physical activity may have a positive impact on survival.

Age- and weight-based differences in haemodialysis prescription and delivery in children, adolescents and young adults

Background

Limited systematic data are available on prescription and dosing of haemodialysis (HD) in children and adolescents compared with adults. We aimed to characterize age- and weight-based differences in HD delivery in children, adolescents and young adults.

Methods

This is a retrospective observational study including 1852 patients <30 years on chronic HD from childhood (53 903 HD sessions), receiving thrice weekly outpatient HD between 2004 and 2016 in the USA (6075 patient-years, of which 2535 were in patients aged 1-18 years; weight range 8.3-168 kg). Median individual prescriptions per year were calculated and overall 50% (IQR) and 90% distribution ranges over age and weight were derived. Repeated measurements analysis of variance assessed differences between age and weight groups.

Results

Prescriptions significantly differed among age and weight groups (P < 0.001). Lower weight patients (<75 kg) had higher (inter-quartile range, IQR) weight-normalized blood flow rate (highest in <25 kg: QB/kg = 6.5-9.1 mL/min/kg), urea dialytic clearance (KD/kg) and single pool Kt/V (spKt/V) (<25 kg: 1.43-1.78; 25-50 kg: 1.52-1.92; 50-75 kg: 1.43-1.74) than heavier patients (lowest in >100 kg: QB/kg = 3.1-4.0 mL/min/kg, spKt/V = 1.22-1.47, respectively). Adolescents had significantly lower QB/kg, KD/kg and spKt/V (1.34-1.71) compared with adults (1.45-1.79) and children <12 years (range of 25th percentiles: 1.37-1.44). Dialytic clearance derived from a mechanistic equation underpredicted KD in children but not in young adults. Significant growth retardation was observed, with the proportion of patients <3rd percentile (height for age) decreasing from 71% (1-2 years) to 15% (>18 years).

Conclusion

Delivered HD treatment varies with age and weight and is more intensified in children aged <12 years, compared with adolescents and overweight young adults, who appear to be at highest risk of receiving suboptimal treatment. Still, delivery of target or higher spKt/V values did not result in appropriate growth in these children, questioning the value of spKt/V as a measure of HD adequacy in children. Provided ranges of outpatient HD prescription can help clinicians and researchers in personalizing and optimizing delivery of dialysis treatment.

Comparison of methods to estimate haemodialysis urea clearance

INTRODUCTION

Dialysis adequacy is traditionally measured by monthly blood urea sampling and calculating sessional Kt/Vurea. Modern dialysis machines can estimate clearances each session, so we wished to compare online measurements with standard Kt/Vurea.

METHODS

Urea clearance was estimated by intermittent changes in effective ionic dialysance and by continuous ultraviolet light absorption spent during the mid-week dialysis session. Total body water was calculated by the Watson equation and measured by multifrequency bioimpedance.

RESULTS

We compared Kt/Vurea measurements in 162 patients with online assessments: 38 by ultraviolet absorption and 124 by effective ionic dialysance (50 Fresenius 4008 and 74 Fresenius 5008). All online measurements overestimated single-pool Kt/Vurea (ultraviolet absorption mean bias 0.25 ± 0.24, effective ionic dialysance 4008H 0.25 ± 0.21 and 5008H 0.20 ± 0.25; p < 0.001). However, there was no difference between dual-pool Kt/V and ultraviolet absorbance (1.28 ± 0.26 vs 1.29 ± 0.27) or by effective ionic dialysance with the 4008 (1.40 ± 0.26 vs 1.46 ± 0.33), although the effective ionic dialysance 5008 overestimated clearance (1.39 ± 0.27 vs 1.31 ± 0.22; p < 0.01). Similarly, with dual-pool Kt/Vurea, the mean bias for ultraviolet absorption was 0.08 ± 0.35, for effective ionic dialysance (EID) 4008 was 0.13 ± 0.55 and for EID 5008 was -0.2 ± 0.36. Hence, the mean bias was greater with the EID 5008 compared to ultraviolet absorption (0.08 ± 0.35 vs -0.2 ± 0.36 vs p < 0.01).

CONCLUSIONS

Online measurements allow dialysis adequacy to be measured every session. We found that although online clearances overestimated single-pool Kt/Vurea measurements, there were no significant differences between the continuous ultraviolet light absorbance method and intermittent effective ionic dialysance.

Should we look beyond Kt/V urea in assessing dialysis adequacy?

Since the advent of maintenance dialysis therapy, our interpretation of what adequate dialysis really is has broadened and become more controversial. This is not only due to our changing and aging dialysis population but also to our evolving knowledge base. As nephrologists, we strive to achieve both quality and (often) quantity of life for our patients and we feel reassured when we have a quantifiable marker to show for our efforts. However, we suggest that adequate dialysis reaches far beyond the realms of attaining a particular biochemical result. Dialysis adequacy should encompass a more comprehensive assessment of patient well-being. This metric could comprise quality of life and patient-specified goals, sufficient small solute and middle molecule clearance, optimal blood pressure control, and effective bone-mineral balance, all in the context of minimizing mortality and morbidity, and a livable dialysis regimen for the patient.

Postdialysis recovery time is extended in patients with greater self-reported depression screening questionnaire scores

INTRODUCTION

Most patients take time to recover after a hemodialysis (HD) session. It has been suggested that recovery time is associated with intradialytic hypotension and rapid solute clearances. Other studies have reported a linkage to depression. We investigated the association between recovery time and intradialytic hypotension and depression.

METHODS

In five UK HD units, we screened for depressive symptoms using the Beck depression inventory-II, Patient Health Questionnaire, and recorded sessional blood pressures and Kt/Vurea.

FINDINGS

Seven hundred and one HD patients were studied; 63.6% male, mean age 64.1 ± 16.6 years, 33.5% diabetic. About 24.1% recovered in <1 hour, 27% 1-4 hours, 15.4% 4-8 hours, 10.7% 8-12 hours, and 22.8% after 12 hours. Systolic blood pressure fell by ≥20 mmHg in 30.9% postdialysis, and to <100 mmHg in 7.6%. In multivariate analysis, patients with recovery times >1 hour were more likely to be female, have high self-reported Beck depression inventory-II scores, a past medical history of depression, and be living without a partner. Longer recovery times were also associated with very low postdialysis systolic blood pressures (<100 mmHg), and higher body weight. However, the model predicted only 18% of the variation in recovery times. We found no association between recovery times and short-term mortality risk.

DISCUSSION

Prolonged postdialysis recovery times are associated with higher self-reported depression scores, and very low postdialysis blood pressure. Future studies investigating changes in dialysis practice and recovery times will need to target strategies to prevent intradialytic hypotension and adjust for patient psychological status.

Volume Estimates in Chronic Hemodialysis Patients by the Watson Equation and Bioimpedance Spectroscopy and the Impact on the Kt/Vurea calculation

Background

Accurate assessment of total body water (TBW) is essential for the evaluation of dialysis adequacy (Kt/V_urea). The Watson formula, which is recommended for the calculation of TBW, was derived in healthy volunteers thereby leading to potentially inaccurate TBW estimates in maintenance hemodialysis recipients. Bioimpedance spectroscopy (BIS) may be a robust alternative for the measurement of TBW in hemodialysis recipients.

Objectives

The primary objective of this study was to evaluate the accuracy of Watson formula-derived TBW estimates as compared with TBW measured with BIS. Second, we aimed to identify the anthropometric characteristics that are most likely to generate inaccuracy when using the Watson formula to calculate TBW. Finally, we derived novel anthropometric equations for the more accurate estimation of TBW.

Design and Setting

This was a cross-sectional study of prevalent in-center HD patients at St Michael's Hospital.

Patients

One hundred eighty-four hemodialysis patients (109 men and 75 women) were evaluated in this study.

Measurements

Anthropometric measurements including weight, height, waist circumference, midarm circumference, and 4-site skinfold (biceps, triceps, subscapular, and suprailiac) thickness were measured; fat mass was measured using the formula by Durnin and Womersley. We measured TBW by BIS using the Body Composition Monitor (Fresenius Medical Care, Bad Homburg, Germany).

Methods

We used the Bland-Altman method to calculate the difference between the TBW derived from the Watson method and the BIS. To derive new equations for TBW estimation, Pearson's correlation coefficients between BIS-TBW (the reference test) and other variables were examined. We used the least squares regression analysis to develop parsimonious equations to predict TBW.

Results

TBW values based on the Watson method had a high correlation with BIS-TBW (correlation coefficients = 0.87 and P < .001). Despite the high correlation, the Watson formula overestimated TBW by 5.1 (4.5-5.8) liters and 3.8 (3.0-4.5) liters, in men and women, respectively. Higher fat mass and waist circumference (general and abdominal obesity) were correlated with the greater TBW overestimation by the Watson formula. We created separate equations for men and women based on weight and waist circumference.

Limitations

The main limitation of our study was the lack of an external validation for our novel estimating equation. Furthermore, though BIS has been validated against traditional reference standards, our assumption that it represents the "gold standard" for body compartment assessment may be flawed.

Conclusions

The Watson formula generally overestimates TBW in chronic dialysis recipients, particularly in patients with the highest waist circumference. Widespread reliance on the Watson formula for derivation of TBW may lead to the underestimation of Kt/V_urea..

Is Hemodialysis Patient Survival Dependent upon Small Solute Clearance (Kt/V)?: If So How Can Kt/V be Adjusted to Prevent Under Dialysis in Vulnerable Groups?

Small solute clearance achieved during a single hemodialysis session has been traditionally evaluated by urea clearance, normalized for total body water (Kt/Vurea) for more than 30 years. By consensus, the target sessional KtVurea for thrice weekly treatments has been increased from 0.9 to 1.2 over the years. Although this is supported by observational studies, there is a fundamental lack of prospective studies to support this threshold target. In clinical practice achieving sessional Kt/Vurea targets are most closely followed in the US. Yet there appears to be a paradox in that by following Kt/Vurea targets in the US hemodialysis patient survival is better for men and the obese, the opposite of what is seen in the general population. Delivery of a lower dose of hemodialysis to women and smaller men can be explained by underestimation of total body water. The advent of bioimpedance techniques which can measure both body water and body composition will potentially allow a rescaling and re-evaluation of the importance of small solute clearances (Kt/Vurea) in the hemodialysis patient population.

Measuring residual renal function in dialysis patients: can we dispense with 24-hour urine collections?

Residual renal function is associated with improved survival and quality of life for dialysis patients. Whereas residual renal function is monitored in peritoneal dialysis patients, many hemodialysis centers simply concentrate on achieving dialyzer urea clearance targets. Accurately quantifying residual renal function from urine collections is arduous. Thus, there is a clinical need to develop alternative methods of assessing residual renal function based on serum testing, especially for patients receiving less than thrice weekly dialysis.

Body composition monitoring-derived urea distribution volume in children on chronic hemodialysis

BACKGROUND

Modern hemodialysis (HD) machines are able to measure ionic dialysance online and thereby continuously monitor Kt/V. The accuracy of measurement depends on the input of the correct urea distribution volume (V), available from anthropometric equations and body composition monitoring (BCM). The latter method, however, has not been validated in children.

METHODS

We compared V determined by BCM to that calculated using four different anthropometric formulas (Morgenstern, Mellits and Cheek, Hume-Weyers and Watson equations) in 23 pediatric HD patients. We also compared online Kt/V using BCM-derived V with the Kt/V calculated from pre- and post-dialytic urea concentrations using the single-pool second-generation Daugirdas equation.

RESULTS

The V calculated by the Morgenstern equation was similar to that derived by BCM, with a mean difference of -0.7% (95% limits of agreement -11.7 to 10.3%). In contrast, the V calculated by the other equations was 5.4, 6.2 and 18%, respectively higher than the BCM-derived V. The mean difference between Kt/V calculated using the Daugirdas equation and online Kt/V determination based on BCM-derived V data was 0.10 (95% limits of agreement -0.50 to 0.70%).

CONCLUSIONS

In our pediatric HD patients the V measured by BCM was in agreement with that calculated using the Morgenstern equation, which is the only equation which has been validated to date in children on dialysis. Online determination of Kt/V using a BCM-derived V largely agreed with that calculated by the Daugirdas equation. We therefore conclude that the former approach is suitable for frequent online assessment of dialytic small solute clearance.

Body Composition Affects Urea Distribution Volume Estimated by Watson's Formula

OBJECTIVE

Dialysis machines use the Watson formula (Vwatson) to estimate the urea distribution volume (UDV) to calculate the online Kt/V for each dialysis session. However, the equation could give rise to inaccuracies. The present study analyzes whether body composition affects UDV estimated by Vwatson in comparison to bioimpedance spectroscopy (Vbis) as the reference method.

DESIGN

This is a transversal study performed in the setting of a hemodialysis unit.

SUBJECTS

Prevalent hemodialysis patients.

INTERVENTION

The same day, UDV was measured using Vwatson and Vbis. We compared their results.

MAIN OUTCOME MEASURE

Differences between UDV using Watson equation and Vbis.

RESULTS

We included 144 prevalent patients. Vwatson overestimated the volume with regard to Vbis (Vwatson - Vbis) by 2.5 L (1.8 L; P = .001). We found an excellent correlation between the 2 methods. A higher mean Vwatson - Vbis value was correlated to older age (P = .03), body mass index (P = .01), fat tissue index (P = .001), lower lean tissue index (P = .001), lower extracellular water (P = .01), and intracellular water (P = .001).

CONCLUSION

Body composition affects UDV estimated by Vwatson, thus modifying the result of Kt/V. In young patients who present more lean tissue and less fat tissue, Kt/V is underestimated with Vwatson.

Will incremental hemodialysis preserve residual function and improve patient survival?

The progressive loss of residual renal function in peritoneal dialysis patients is associated with increased mortality. It has been suggested that incremental dialysis may help preserve residual renal function and improve patient survival. Residual renal function depends upon both patient related and dialysis associated factors. Maintaining patients in an over-hydrated state may be associated with better preservation of residual renal function but any benefit comes with a significant risk of cardiovascular consequences. Notably, it is only observational studies that have reported an association between dialysis patient survival and residual renal function; causality has not been established for dialysis patient survival. The tenuous connections between residual renal function and outcomes and between incremental hemodialysis and residual renal function should temper our enthusiasm for interventions in this area.

Predialysis NTproBNP predicts magnitude of extracellular volume overload in haemodialysis patients

INTRODUCTION

Increased natriuretic peptides are associated with increased cardiovascular and all-cause mortality for haemodialysis (HD) patients. However, debate continues whether these biomarkers are increased by extracellular water (ECW) excess and can be used to aid clinical assessment of volume status and help determine target weight.

METHODS

We measured N terminal probrain natriuretic peptide (NT-proBNP) predialysis in 375 stable haemodialysis outpatients with corresponding pre and postdialysis multifrequency bioelectrical impedance assessments (MFBIA) of (ECW)/total body water (TBW).

RESULTS

Median age 64 (51-75), 63.9% male, 42.9% diabetic, 43.2% Caucasoid, 14.4% with a history of myocardial infarction, 8.4% coronary artery bypass surgery, dialysis vintage 28.2 (12.3-55.5) months. Median predialysis NT-proBNP 283 (123-989) pmol/l, and predialysis ECW/TBW ratio 0.397 ± 0.029. On multivariate analysis, predialysis log NT-proBNP was associated with predialysis systolic blood pressure (β 0.007, p = 0.000), weight (β -0.008, p = 0.001), valvular heart disease (β 0.342, p = 0.015, ECW/TBW (β 1.3, p = 0.019) and log CRP (β 0.145, p = 0.037). Dividing patients into NTproBNP quartiles, %ECW/TBW and relative ECW overhydration were significantly greater for the highest quartile vs. lowest (40.5 ± 4.1 vs. 39.0 ± 1.1, and 1.51 ± 1.24 vs. 0.61 ± 0.69 l, respectively, p < 0.001).

CONCLUSION

In this study, predialysis NTproBNP values were associated with direct assessments of the extracellular volume excess measured by MFBIA and systolic arterial blood pressure. This suggests that predialysis NTproBNP values can potentially be used to aid clinical assessment of volume status in dialysis patients to determine target weight.

Increased postdialysis systolic blood pressure is associated with extracellular overhydration in hemodialysis outpatients

Recently, intradialytic hypertension was reported to be associated with increased mortality for hemodialysis patients. To determine whether volume status plays a role in dialysis-associated hypertension, we prospectively audited 531 patients that had volume assessments measured by multiple-frequency bioelectrical impedance during their midweek dialysis session. Mean pre- and postdialysis weights were 73.2 vs 71.7 kg, and systolic blood pressures (SBPs) 140.5 vs. 130.3 mm Hg, respectively. Patients were divided into groups based on a fall in SBP of 20 mm Hg or more (32%), an increased SBP of 10 mm Hg or more (18%), and a stable group (50%). There were no differences in patient demographics, dialysis prescriptions, predialysis weight, total body (TBW), and extracellular (ECW) and intracellular water (ICW). However, the change in weight was significantly less in the increased blood pressure group (1.01 kg vs. stable 1.65, and 1.7 hypotensive). The ratio of ECW to TBW was significantly higher in the increased blood pressure group, particularly post dialysis (39.1 vs. stable 38.7% and fall in blood pressure group 38.7%). ECW overhydration was significantly greater in the increased blood pressure group post dialysis (0.7 (0.17 to 1.1) vs. stable 0.39 (-0.2 to 0.95) and fall in blood pressure group 0.38 (-0.19 to 0.86) liter). We found that patients who had increased blood pressure post dialysis had greater hydration status, particularly ECW. Thus, patients who increase their blood pressure post dialysis should have review of target weight, consideration of lowering the post-dialysis weight, and may benefit from increasing dialysis session time or frequency.

Aortic pulse wave velocity in haemodialysis patients is associated with the prescription of active vitamin D analogues

BACKGROUND

Cardiovascular disease remains the most common cause of death for haemodialysis patients. In addition to traditional cardiovascular risk factors, haemodialysis patients have additional risk factors, including vascular calcification. Pulse wave velocity (PWV) is a measurement of arterial stiffness, and we wished to determine whether PWV is affected by different factors in haemodialysis patients compared to the general population.

METHODS

Aortic PWV was measured in 303 adult patients attending for routine outpatient dialysis.

RESULTS

303 patients, 63.4% male, mean age 68.5 ± 15.8 years, 47.5% diabetic with a body mass index of 25.8 ± 5.3 kg/m(2), were studied. Systolic blood pressure (SBP) was 148.7 ± 28.6 mmHg and diastolic 80.4 ± 15.3 mmHg. Aortic PWV was 9.73 ± 2.08 m/s, and was correlated with SBP (β 0.015, F 5.29, p = 0.023), log serum parathyroid hormone (PTH) (β 1.58, F 13.85, p < 0.001) and prescription of alfacalcidol (β -1.11, F 6.81, p = 0.010). 197 patients had corresponding ECHO cardiograms, and in this cohort PWV was associated with SBP (β 0.017, F 7.49, p = 0.006), log serum parathyroid hormone (β 0.85, F 5.99, p < 0.015) and prescription of alfacalcidol (β -0.8, F 4.18, p = 0.042), left ventricular mass index (LVMI) (β 0.01, F 11.4, p = 0.001), and log serum triglycerides (β 1.43, F 4.79, p = 0.03).

CONCLUSIONS

We found that PWV, a measurement of arterial stiffness, was associated with both traditional cardiovascular risk factors, including SBP and LVMI, but also non-traditional risk factors such as prescription of active vitamin D analogues, suggesting a potential link between vascular calcification and arterial stiffness in haemodialysis patients.