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

Effect of fruits granola (Frugra®) consumption on blood pressure reduction and intestinal microbiome in patients undergoing hemodialysis

Cardiovascular diseases (CVDs) are a major cause of death in patients undergoing hemodialysis (HD). Blood pressure (BP) and uremic toxins are well-known risk factors for CVDs, which are influenced by diet. Dietary fiber supplementation in patients undergoing HD may reduce the risk of CVDs by improving lipid profiles and inflammatory status and lowering the levels of the uremic toxin indoxyl sulfate (IS). In this study, we investigated the relationship between the intestinal microbiota and risk factors for CVDs, such as BP and serum IS, in patients undergoing HD who consumed fruits granola (FGR). The study participants were selected from patients undergoing HD at the Izu Nagaoka Daiichi Clinic and consumed FGR for 2 months. Body composition and blood samples were tested at months 0, 1, 2 and fecal samples were collected at months 0 and 2 for intestinal microbiota analysis. FGR consumption decreased systolic and diastolic BP, estimated salt intake, and serum IS levels and improved the stool characteristics according to the Bristol Stool Form Scale (N = 24). Gut microbiota analysis showed an increase in the alpha diversity and abundance of Blautia and Neglecta. The abundance of lactic acid- and ethanol-producing bacteria also significantly increased, whereas the abundance of indole-producing bacteria significantly decreased. FGR consumption could be a useful tool for salt reduction, fiber supplementation, and improvement of the intestinal environment, thus contributing to improvement of BP and the reduction of other risk factors for CVDs in patients undergoing HD.

Research progress on measurement methods and evaluation of the hemodialysis adequacy index Kt/V

The most common form of replacement therapy for end-stage renal disease (ESRD) is hemodialysis, and the adequacy of hemodialysis is strongly associated with the quality of life and long-term survival of patients. Kt/V is currently one of the most important indicators for evaluating the adequacy of hemodialysis. There are many methods for measuring Kt/V, such as blood collection and measurement, dialysate measurement, bioresistive resistance, WinNonlin software analysis, and artificial intelligence. There are different views on the importance of Kt/V as an indicator of the adequacy of hemodialysis. This article provides a literature review of the various methods of measuring Kt/V and on different perspectives on Kt/V as an evaluation of hemodialysis adequacy.

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.

Dialysis Adequacy: A Cross-Sectional Study to Assess the Reliability of the Online Clearance Monitor to Measure Dialysis Dose

Background Frequent assessment of the dialysis dose delivered to hemodialysis patients might help improve morbidity and mortality. Daugirdas' second-generation formula is the recommended method for calculating dialysis doses. However, urea reduction ratios (URRs) and online clearance monitors (OCMs) are frequently used to assess dialysis adequacy due to their more straightforward concept and ease of use. This study was conducted to determine the most reliable method for measuring dialysis adequacy by comparing the correlation of urea reduction ratio and online clearance monitor measurements with the dialysis dose measured using the recommended Daugirdas' second-generation formula. Methods This study was an observational, cross-sectional, single-center study. The dialysis dose was measured as a urea reduction ratio and by an online clearance monitor simultaneously for 50 patients. It was compared to the dialysis dose measurements obtained using Daugirdas' second-generation formula. Results There was a statistically significant strong positive correlation (r = 0.929; p ≤ 0.001) of the urea reduction ratio and a poor concordance (ρC = 0.401; p ≤ 0.001) of online clearance monitor measurements with the dialysis dose measured using Daugirdas' second generation formula. Conclusion Our findings illustrate that the urea reduction ratio may be a more straightforward and reliable means for assessing the adequacy of intermittent hemodialysis with minimal errors in patients compared to online clearance monitors. Online clearance monitors offer easy estimation and practicality with minimal effort but are prone to multiple errors and may not be accurate in some settings.

The prognostic value of URR equals that of Kt/V for all-cause mortality in Taiwan after 10-year follow-up

Kt/V and URR (urea reduction ratio) measurements represent dialysis adequacy. Single-pool Kt/V is theoretically a superior method and is recommended by the Kidney Disease Outcomes Quality Initiative guidelines. However, the prognostic value of URR compared with Kt/V for all-cause mortality is unknown. The effect modifiers and cut-off values of the two parameters have not been compared. We investigated 2615 incident hemodialysis patients with URR of 72% and Kt/V (Daugirdas) of 1.6. The average patient age was 59 years, 50.7% were female, and 1113 (40.2%) died within 10 years. URR and Kt/V were both positively associated with nutrition factors and female sex and negatively associated with body weight and heart failure. In Cox regression mod-els for all-cause mortality, the hazard ratios (HRs) of high URR groups (65-70%, 70-75%, and > 75%) and the URR < 65% group were 0.748 (0.623-0.898), 0.693 (0.578-0.829), and 0.640 (0.519-0.788), respectively. The HRs of high Kt/V groups (Kt/V 1.2-1.4, 1.4-1.7, and > 1.7) and the Kt/V < 1.2 group were 0.711 (0.580-0.873), 0.656 (0.540-0.799), and 0.623 (0.498-0.779), respec-tively. In subgroup analysis, Kt/V was not associated with all-cause mortality in women. The prognostic value of URR for all-cause mortality is as great as that of Kt/V. URR > 70% and Kt/V > 1.4 were associated with a higher survival rate. Kt/V may have weaker prognostic value for women.

Prediction of end-dialysis serum sodium concentration in severely hyponatremic kidney failure patients undergoing conventional hemodialysis using sodium kinetic equation

Background and Objectives

Conventional hemodialysis (HD) for kidney failure patients with severe hyponatremia may be complicated by rapid correction of hyponatremia, which increases the risk of osmotic demyelination syndrome. A simple sodium kinetic equation was effective in prediction of end-dialysis serum Na+ in severely hyponatremic kidney failure patient treated with continuous venovenous hemofiltration, but was not tested in conventional HD. The aim of this study was to assess the validity of this equation when used in conventional HD.

Methods

Twenty conventional HD sessions were delivered to 12 kidney failure patients with severe hyponatremia (serum Na+  < 120 mEq/L). The target change in serum Na+ was 4 mEq/L. The DNa.t/V that obtained this change was predetermined according to the sodium kinetic equation and monitored in real time by online clearance monitoring software embedded in dialysis machine. The dialysis session was terminated once the target DNa.t/V was achieved.

Results

The mean observed and predicted serum Na+ were 119.80 ± 3.42 mEq/L and 119.45 ± 3.12 mEq/L, respectively. Bland–Altman plot analysis revealed a mean difference ± SD of 0.33 ± 1.26 mEq/L, and 95% limits of agreement of − 2.13 to 2.83. The imprecision in prediction of end-dialysis serum Na+ was 2.52 mEq/L. The small difference and clinically insignificant 95% limits of agreement indicate a good agreement between the observed and predicted serum Na+.

Conclusion

The sodium kinetic equation was effective in prediction of end-dialysis serum Na+ in kidney failure patients with severe hyponatremia.

Inflammation and hemodialysis adequacy: are C-reactive protein levels influenced by the dose of dialysis?

INTRODUCTION

Chronic inflammation and the underlying cardiovascular comorbidity are still current problems in chronic hemodialysis patients. There are few studies comparing the "dialysis dose" with the degree of inflammation in the patient. Our main objective was to determine whether there is a relationship between serum C-reactive protein (CRP) levels and the "dialysis dose" (Kt / V) using ionic dialysance.

METHODS

Multicenter cross-sectional study. 536 prevalent chronic hemodialysis patients were included. CRP levels, neutrophil-lymphocyte ratio (NLR) and platelet-lymphocyte ratio (PLR) were collected. Kt was obtained by ionic dialysance and urea distribution volume was calculated from the Watson's formula. The sample was divided into two groups, taking the median CRP as the cut-off point. Dialysis adequacy obtained in each group was compared. Finally, a logistic regression model was carried out to determine the variables with the greatest influence.

RESULTS

Median CRP was 4.10 mg/L (q25-q75: 1.67-10) and mean Kt/V was 1.48 ± 0.308. Kt/V was lower in the patients included in the high inflammation group (p = 0.01). In the multivariate logistic regression, the "high" levels of CRP were directly correlated with the Log INL (p < 0.001) and inversely proportional with serum albumin values (p = 0.014), Kt/V (p = 0.037) and serum iron (p < 0.001).

CONCLUSION

The poorer adequacy in terms of dialysis doses, lower Kt / V values, may contribute to a higher degree of inflammation in chronic hemodialysis patients.

Validation of the SMH Equations for the Estimation of the Total Body Water Volume in Hemodialysis Patients

Background:

Online dialysis clearance monitors typically provide an accurate value for Kt. A value for V (total body water [TBW]) is required to calculate Kt/V, the measure of the adequacy of the delivered dialysis in hemodialysis (HD) patients. Using bioimpedance spectroscopy (BIS), we previously developed 2 sex-specific equations for the estimation of the TBW, which we have chosen to name the St Michael’s Hospital (SMH) equations.

Objective:

The objective of this study was to validate the SMH equations in a second distinct population of patients.

Design:

Cross-sectional study.

Setting:

Single center hemodialysis unit at St Michael’s Hospital, a tertiary care teaching hospital, in Toronto, Canada.

Patients:

Eighty-one adult HD patients who had been receiving conventional maintenance HD for at least 3 months.

Measurements:

Anthropometric measurements including weight, height, and waist circumference were collected. TBW was measured by BIS using the Body Composition Monitor (Fresenius Medical Care, Bad Homburg, Germany).

Methods:

The Bland-Altman method to calculate the bias and limits of agreement and the difference plot analysis were used to evaluate the difference between the BIS-TBW and the TBW derived from our equations (SMH equation) in this validation cohort.

Results:

The TBW values based on our equations had a high correlation with BIS-TBW (correlation coefficients = 0.93, P values < .01, bias = 1.8 [95% CI: 1-2.6] liter). Application of SMH equations closely predicted Kt/V, based on BIS value, in all categories of waist circumference.

Limitations:

Small sample size, single-center, not including peritoneal dialysis patients. A larger and more heterogeneous sample with more patients at the extremes of body mass index would allow for more detailed sub-group analyses in different races and different anthropometric categories to better understand the performance of these equations in discrete sub-groups of patients.

Conclusions:

In maintenance HD patients, our previously derived equations to estimate the TBW using weight and waist circumference appear to be valid in a distinct patient population. Given the centrality of TBW to the calculation of small molecule clearance, the SMH equations may enhance the measurement of dialysis adequacy and inform practice.

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.

What Total Body Water Measurement Should Be Used for Prescribing the Dialysis Dose in Low-Flow Home Daily Dialysis?

INTRODUCTION

In low-flow home daily dialysis (HDD), the dialysis dose is evaluated from the total body water (TBW). TBW can be estimated by anthropometric methods or bioimpedance spectroscopy.

METHODS

A multicentric cross-sectional study of patients in HDD for >3 months was conducted to assess the correlation and the difference between the anthropometric estimate of TBW (Watson-TBW) and the bioimpedance estimate (BIS-TBW) and to analyse the impact on the dialysate volume prescribed.

RESULTS

Forty patients from 10 centres were included. The median BIS-TBW and Watson-TBW were 35.1 (29.1-41.4 L) and 36.9 (32-42.4 L), respectively. The 2 methods had a good correlation (r = 0.87, p < 0.05). However, Bland-Altman analysis showed an overestimation of TBW with Watson's formula, with a bias of 2.77 L. For 4, 5, or 6 sessions per week, the use of Watson-TBW increases the dialysate prescription per week by 100 L, 45 L, or 10 L, respectively, over our entire cohort. There is no increase in the volume of dialysate prescribed with the 7 sessions per week schedule.

CONCLUSION

BIS-TBW and Watson-TBW estimation have a good correlation; however, Watson's equation overestimates TBW. This overestimation is negligible for a prescription frequency of >5 sessions per week.

Inflammation and hemodialysis adequacy: Are C-reactive protein levels influenced by dialysis dose?

INTRODUCTION

Chronic inflammation and the underlying cardiovascular comorbidity are still current problems in chronic hemodialysis patients. There are few studies comparing the "dialysis dose" (Kt/V) with the degree of inflammation in the patient. Our main objective was to determine whether there is a relationship between serum C-reactive protein (CRP) levels and the Kt/V using ionic dialysance.

METHODS

Multicenter cross-sectional study. A total of 536 prevalent chronic hemodialysis patients were included. CRP levels, neutrophil-lymphocyte ratio and platelet-lymphocyte ratio were collected. Kt was obtained by ionic dialysance and urea distribution volume was calculated from the Watson's formula. The sample was divided into 2 groups, taking the median CRP as the cut-off point. Dialysis adequacy obtained in each group was compared. Finally, a logistic regression model was carried out to determine the variables with the greatest influence.

RESULTS

Median CRP was 4.10mg/L (q25-q75: 1.67-10) and mean Kt/V was 1.48±0.308. Kt/V was lower in the patients included in the high inflammation group (P=.01). In the multivariate logistic regression, the "high" levels of CRP were directly correlated with the Log neutrophil-lymphocyte ratio (P<.001) and inversely proportional with serum albumin values (P=.014), Kt/V (P=.037) and serum iron (P<.001).

CONCLUSION

The poorer adequacy in terms of dialysis doses (lower Kt/V values) may contribute to a higher degree of inflammation in chronic hemodialysis patients.

Are Currently Used Bioimpedance Methods in Hemodialysis Comparable for Calculating Dialysis Dose?

Bioelectrical impedance analysis has increasingly been incorporated into hemodialysis units (HD) as a useful, noninvasive technique for evaluating overall fluid status. The aims of this study were to verify whether the information obtained from two different bioelectrical impedance analysis methods (spectroscopy bioimpedance [BCM] and single-frequency bioelectric impedance vector analysis [SF-BIVA]) was comparable for analyzing fluid status, and to determine their impact when used to calculate dialysis dose. This observational cross-sectional study included 78 HD patients who underwent one measurement with BCM and one with SF-BIVA in the same dialysis session. For calculating the dialysis dose, total body water or urea distribution volume (V) was calculated by the Watson formula and compared with the V obtained from the two devices. The difference in V between the two devices was 5.4 L (P < 0.001). Given the existent correlation between V_BCM and V_SF-BIVA , we were able to apply a formula (corrected V = V_SF-BIVA = 1.04 × V_BCM + 4.85, r = 0.93), allowing comparison of the two bioimpedance methods. The mean dialysis dose for BCM device (Kt_ID /V_BCM ) was 2.49 ± 0.85, much higher than Kt_ID /V_SF-BIVA (2.06 ± 0.72) mainly due to the V obtained with the different devices, with Kt_ID /V_Watson being 2.03 ± 0.67. The results on volume distribution showed an acceptable correlation but the devices were not comparable due to intermethod differences observed. Dialysis centers using SF-BIVA will obtain much lower dialysis dose, but by applying our formula, the Kt/V would resemble that obtained by the BCM device.

Volume of urea cleared as a therapy dosing guide for more frequent hemodialysis

INTRODUCTION

With dialysis delivery systems that operate at low dialysate flow rates, prescriptions for more frequent hemodialysis (HD) employ dialysate volume as the primary parameter for small solute removal rather than blood-side urea dialyzer clearance (K). Such delivery systems, however, yield dialysate concentrations that almost completely saturate with blood (water), suggesting that the volume of urea cleared (the product of K and treatment time or Kt) can be readily estimated from the prescribed dialysate volume to target small solute removal. Methods For more frequent HD, we examined the volume of urea cleared per treatment required to achieve a minimal dose of small solute removal, comparing results based on body surface area (BSA) with those based on KDOQI clinical practice guidelines, that is, a weekly stdKt/V of 2.1. Estimates of the target volume of urea cleared were calculated for 4, 5, and 6 treatments per week, and compared for patients with different anthropometric estimates of total body water volume (V_ant ). BSA was assumed proportional to V_ant ^0.8 , and residual kidney function was neglected. Findings Whether based on BSA or weekly stdKt/V of 2.1, the target volume of urea cleared per treatment required to achieve a minimal dose of small solute removal was lower at higher treatment frequency. As with conventional thrice-weekly HD, target volumes of urea cleared for more frequent HD based on BSA were larger for patients with small V_ant and smaller for patients with large V_ant than those based on a weekly stdKt/V of 2.1. Discussion Prescription of more frequent HD using the volume of urea cleared per treatment, calculated from the prescribed dialysate volume, is simple in principle and can be readily implemented in clinical practice when using dialysis delivery systems that operate at low dialysate flow rates. Other aspects of dialysis adequacy require additional consideration.