A proposed glossary for dialysis kinetics

The Rationale and Ultimate Limitations of Urea Kinetic Modelling in the Estimation of Nutritional Status

Objective

This paper reviews protein flux and amino acid metabolism and the potential inaccuracies inherent in using urea kinetics as an estimate of these processes, particularly in the patient undergoing peritoneal dialysis. The problems of extrapolating these estimates back to the whole patient are examined, addressing assumptions about neutral nitrogen balance, and the difficult issue of normalizing urea-derived indices to body size.

Conclusions

Urea kinetics can be a helpful tool for assessing nutritional indices, but there are many caveats and many pitfalls that must be kept in mind to avoid being lulled into a false sense of confidence by the comfort of numbers.

Solute Clearance Approach to Adequacy of Peritoneal Dialysis

To investigate the effect of dialysis prescription on patient outcome for peritoneal dialysis patients, the relationship between total solute clearance and the relative risk of death has been investigated. Preliminary studies have suggested that more clearance is better and that patient outcome is predicted by total solute clearance. The recently published Canada-U.S.A. (CANUSA) multicenter study, evaluating adequacy of dialysis and nutrition in peritoneal dialysis patients, has further defined this relationship. Although these publications allow us to establish guidelines for the treatment of peritoneal dialysis patients, they also define the limitations of our knowledge and raise new questions.

In this article we review our current knowledge regarding the predicted value of total solute clearance with patient outcome and nutritional status. Furthermore, we attempt to outline a practical approach for optimizing total solute clearance in peritoneal dialysis patients.

Based on a review of the published literature and clinical recommendations, we feel that the minimal target total solute clearance for continuous forms of peritoneal dialysis is a weekly total KTN > 2.0 and/or a weekly total creatinine clearance >60 L/week/1.73 m2. For intermittent therapies, a weekly total KTN > 2.2 and/or a weekly total creatinine clearance >70 L/week/1.73 m2 is recommended.

Nutrition Indices in Obese Continuous Peritoneal Dialysis Patients with Inadequate and Adequate Urea Clearance

♦ Objective

To test whether better nutrition is associated more with adequate urea clearance than with inadequate urea clearance in obese patients on continuous peritoneal dialysis (CPD).

♦ Design

Retrospective analysis of clearance and nutrition indices in obese CPD patients. Only obese patients were analyzed. Obesity was defined as a ratio of actual weight to desired weight (W/DW) ≥ 1.2. The dose of dialysis was considered adequate at weekly Kt/V urea ≥ 2.0. Small solute clearances and nutrition indices were compared between patients with weekly Kt/V urea < 2.0 and patients with weekly Kt/V urea ≥ 2.0 at the first clearance study.

♦ Setting

Four university-affiliated and two private dialysis units in Canada and the United States.

♦ Patients

A total of 270 CPD patients with W/DW ≥ 1.2 at the first clearance study.

♦ Results

Among the 270 obese CPD patients, 157 (58.1%) were underdialyzed (weekly Kt/V urea 1.66 ± 0.22) and 113 (41.9%) had adequate dialysis (weekly Kt/V urea 2.51 ± 0.47) at the first clearance study. Creatinine clearance values also differed between the underdialyzed and adequately dialyzed obese groups (55.6 ± 15.2 vs 87.6 ± 29.8 L/1.73 m2 weekly, respectively, p < 0.001). The underdialyzed group contained fewer women (39.5% vs 60.2%, p < 0.001) and more patients with anuria (35.0% vs 8.8%, p < 0.001), and had higher serum urea (20.7 ± 6.9 vs 18.2 ± 5.3 mmol/L, p = 0.001) and serum creatinine (974 ± 283 vs 734 ± 275 μmol/L, p < 0.001), marginally lower serum albumin (35.8 ± 5.2 vs 37.2 ± 6.4 g/L, p = 0.082), lower urea nitrogen excretion (5778 ± 2290 vs 7085 ± 2238 mg/24 hr, p < 0.001) and indices derived from urea nitrogen excretion (protein nitrogen appearance and normalized protein nitrogen appearance), and lower creatinine excretion (1034 ± 349 vs 1217 ± 432 mg/24 hr, p < 0.001) and indices derived from creatinine excretion (lean body mass normalized to actual or desired weight) than the adequately dialyzed group.

♦ Conclusion

Nutrition indices derived from urea nitrogen and creatinine excretion are worse in underdialyzed than in adequately dialyzed obese CPD patients. This finding may have clinical importance, despite the mathematical coupling between small solute clearances and excretion rates in cross-sectional studies, because of evidence from other studies that small solute excretion rate in cross-sectional studies is a robust independent predictor of outcome in CPD.

Toward Targets for Initiation of Chronic Dialysis

Objectives

To better defaine the targets for initiation of chronic dialysis, we compared the relationship between the normalized protein equivalent of nitrogen appearance (nPNA, g/kg standard weight/day) and weekly urea clearance (Kt) normalized to total body water (V) in predialysis chronic renal failure (CRF) patients and in patients on continuous ambulatory peritoneal dialysis (CAPD) and hemodialysis (HD). We also studied the relationships of other nutritional parameters to weekly Kt/Vurea in CRF patients.

Design

This cross-sectional study was a prospective observational design meant to study each patient once.

Setting

The University Hospital and Clinics and Harry S. Truman VA Medical Center, Columbia, Missouri.

Patients

Forty-five consecutive predialysis CRF patients were enrolled and the results compared with patients on CAPD and HD.

Results

In CRF, the nPNA calculated from urea appearance correlated with the weekly Kt/Vurea (r = 0.57, p < 0.0001) and, using exponential best-fit, nPNA = 1.217 x (1 - e-0.769Kt/v). This exponential relationship was similar to that for CAPD and both were different from that in patients on HD. Likewise, nPNAs, calculated from Kjeldahl nitrogen output, and weekly Kt/Vurea were correlated (r = 0.37, p = 0.014) and, using exponential best-fit, nPNA = 1.102(1 - e-0.867Kt/v), similar to the relationship in patients on CAPD. Evidence is presented that these relationships are not explained only by mathematical coupling. There was a significant correlation between the weekly Kt/Vurea and 24-hour urinary creatinine excretion.

Conclusions

The findings suggest that in CRF, as in CAPD, a weekly Kt/Vurea less than 2.0 is likely to be associated with a nPNA less than 0.9 g/kg standard weight. In CRF patients, initiation of chronic dialysis should be considered if weekly renal Kt/Vurea falls below 2.0 and a nPNA greater than 0.8 is desired.

Suitable Dialytic Indicators for Pediatric Peritoneal Dialysis Patients: The Alternative to Creatinine Clearance

← Objective

Owing to the discord between body weight and body surface area (BSA), creatinine clearance (CCr) is predisposed to be small in pediatric patients on peritoneal dialysis (PD). Alternatively, Kt/V creatinine (Kt/V creat), which is normalized to total body water (TBW) rather than BSA, could be a better dialytic indicator. In this study, the efficiency of dialysis and the nutritional status of pediatric patients on chronic PD were examined, and the utility of dialytic indicators was evaluated.

← Patients and Methods

49 patients under 20 years old, in stable condition, and on PD were analyzed. Weekly total Kt/V of urea (Kt/V urea), CCr, Kt/V creat, and normalized protein equivalent of nitrogen appearance (nPNA) were measured for all patients and for patients under 6 years old. The target value was 2.0/week for Kt/V urea and 60 L/week/1.73 m2 for CCr, as recommended by the Kidney Disease Outcomes Quality Initiative guidelines. The target value for Kt/V creat was set as 1.52/week, using a male model with a height of 170 cm and a body weight of 65 kg.

← Results

The mean values of delivered Kt/V urea, CCr, Kt/V creat, and nPNA (and proportion of patients that achieved each target value) for all patients were 2.25 ± 0.57/week (67.4%), 53.8 ± 19.3 L/week/1.73 2m (26.5%), 1.83 ± 0.73/week (65.3%), and 1.11 ± 0.42 g/day, respectively. The values for patients under 6 years old were 2.38± 0.26/week (90.0%), 45.9 ± 12.8 L/week/1.73 2m (10.0%), 1.94 ± 0.51/week (90.0%), and 1.52 ± 0.67 g/day, respectively. Stepwise multiple regression analyses revealed that the relationship between CCr and Kt/V urea was affected by the patient's age.

← Conclusions

Our pediatric patients achieved the recommended target value of Kt/V urea. At the same time, the nPNA results reflected the patient's status well. However, CCr appeared to be inappropriate as an indicator for patients under 6 years old. Kt/V creat is suggested to be a better dialytic indicator for these patients.

Mass Balance Index: An Index for Adequacy of Dialysis and Nutrition

Determining adequacy of dialysis has remained a problem for the nephrologist despite the results of the National Cooperative Dialysis Study published more than 20 years ago. Urea Kinetics Modelling (UKM) which requires computer data entry is time-consuming for the dialysis staff but is the only method that has been rigorously studied. Furthermore, it is unclear today what value of Kt/V represents ideal dialysis; the technique is subject to a number of errors associated with estimation of dialyser clearance (K) and volume of distribution of urea (V) but it is useful for calculating protein catabolic rate (PCR). Methods that use urea reduction ratios (URR) is widely used because it is simpler but not always accurate and suffer from an inability to calculate PCR. Direct dialysis quantification (DDQ) can overcome a number of these problems but it is too cumbersome for routine use. Simpler methods to determine dialysateside kinetics have the advantage of solving a number of these problems and also facilitate the calculation of PCR to determine the patient's nutritional state. In our study, we have demonstrated that by taking two dialysate samples at the beginning and at the end of dialysis (2-DSM), it is possible to determine total urea removal (TUR) which is equivalent to DDQ. By taking blood samples after dialysis and before the next dialysis, it is possible to calculate the total urea generated (TUG). The ratio of TUR/TUG will provide an index of dialysis which places emphasis on removal of solute that has accumulated in the inter-dialytic interval thus re-establishing a state of equilibrium. We refer to this index as the Mass Balance Index (MBI). The MBI is also useful in helping to identify those patients whose PCR is inadequate since the mean MBI for patients with an nPCR <0.8 was 0.93 ± 0.03 vs 1.08 ± 0.02 in those with a PCR >0.8. In these two groups of patients the Kt/V was not significantly different, 1.49 ± 0.07 vs 1.53 ± 0.06, p -0.64. We suggest that the emphasis for adequacy of dialysis should shift away from Kt/V to maintaining a state of equilibrium by removing the solutes that accumulate between dialysis and by identifying those patients with an inadequate PCR.

Protein and Energy Depletion in Chronic Hemodialysis Patients: Clinical Applicability of Diagnostic Tools

Protein and energy depletion states are common and associated with increased morbidity and mortality in chronic hemodialysis (CHD) patients. Therefore, proper use of diagnostic tools to assess depleted states in CHD patients is critical. Assessment of protein and energy status can be done by an array of methodologies that include simple estimates of the visceral and somatic pools of protein to more refined techniques to measure protein and energy balance. The nutritional and metabolic derangements in the CHD population are highly complex and can be confounded by multiple comorbidities and fluid shifts between body compartments. Therefore, assessment of protein and energy status in CHD patients requires a wide range of methodologies that not only identify depleted states but also monitor nutrition therapy and predict clinical outcome. Most important, these methods require cautious and individualized interpretation in order to minimize the interference of comorbid conditions frequently observed in the CHD population. Currently, there is not a single method that can be considered the gold standard for assessment of protein and energy status in CHD patients. Therefore, a combination of methods is recommended. In this review, we describe available methods to assess protein and energy status, with special considerations pertaining to CHD patients.

Assessment of nutritional status in children with chronic kidney disease and on dialysis

Protein-energy wasting (PEW) is defined as a state of decreased body protein mass and fuel reserves (body protein and fat mass) and is a common complication of chronic kidney disease (CKD). It is multifactorial: the main causative factors are hormonal imbalances and a low nutrient intake, but low residual renal function, inadequate dialysis dose, chronic inflammation and metabolic acidosis are other important contributory factors. Adult PEW has been defined, but there is no accepted definition of pediatric PEW and consequently no precise diagnostic criteria. Assessing nutritional status in children is also complicated by the absence of a gold standard, specific abnormalities in body composition, and the slowly progressive course of the disease. The evaluation of PEW should take into account all of its pathogenetic aspects, which include dietary assessment, clinical and anthropometric assessment (based on weight, height, and body mass index), a panel of biochemical parameters, and a normalized protein catabolic rate (in the case of adolescents on hemodialysis). Bioimpedance indices can be used in individual patients on a regular basis in centers with expertise. The longitudinal follow-up data relating to the above parameters are valuable for comparing patient and normative data. Given the complex nature of PEW, only a multidisciplinary approach can provide an accurate assessment of nutritional status and its derangements in children with CKD and on dialysis.

Resistance to erythropoietin-stimulating agents: etiology, evaluation, and therapeutic considerations

Routine clinical and laboratory assessments facilitate diagnosis of erythropoietin (EPO) resistant anemia by allowing early identification of patients with non-adherence. Any new event that impairs response to EPO (e.g., catheter sepsis) must be promptly controlled. Because of the confounding interaction of its risk factors, initial evaluation should include nutrition, dialysis adequacy, hemorrhage, bone mineral metabolism, and inflammation. Prevention of EPO resistance is more cost effective and should include adequate dialysis and nutritional supplements. Blood loss during hemodialysis (HD) procedures should be minimized. If there is laboratory proof of iron deficit intravenous repletion is most effective. Oxidative stress may be attenuated by vitamins E and C, while optimal control of hyperparathyroidism will enhance EPO stimulation. Contaminated dialysates should be suspected if there is EPO-stimulating agents (ESA) resistance at the same time among most members of a dialysis program. Heavy metal toxicity should be suspected in high-risk patients. The impact of co-morbidities such as hemoglobinopathy, glucose 6 phosphate dehydrogenase (G6PD) deficiency and connective tissue diseases must be excluded in an appropriate setting. In conclusion, given the multiple risk factors of EPO resistance promotion of the overall health status will most likely yield an enduring benefit. Finally, there are experimental trials of gene-based (therapy) to stimulate endogenous EPO synthesis with the goal of avoiding the off-target effect of excessive dosing.

The newly identified anorexigenic adipokine nesfatin-1 in hemodialysis patients: Are there associations with food intake, body composition and inflammation?

Nesfatin-1 is a recently identified anorexigenic peptide that has been implicated in appetite regulation, weight loss and/or malnutrition. Anorexia and malnutrition are common features of chronic kidney disease (CKD) that predispose patients to worse outcomes. However, the reasons for the occurrence of anorexia in CKD patients are not fully elucidated. The aim of this study was to investigate the association between nesfatin-1 and protein intake and body composition in patients undergoing hemodialysis (HD). Twenty five HD patients from a private Clinic in Rio de Janeiro, Brazil were studied and compared with 15 healthy subjects that were matched for body mass index (BMI), % body fat mass (by anthropometrics) and age. Appetite was measured using a specific questionnaire, and food intake was evaluated based on 3-day food records. Nesfatin-1 levels were measured by ELISA and leptin, TNF-α and IL-6 levels were determined by a multiplex assay kit. Serum nesfatin-1 levels did not differ between HD patients (0.16±0.07ng/mL) and healthy subjects (0.17±0.10ng/mL). Nesfatin-1 levels showed significant negative correlations with protein intake (r=-0.42; p=0.03), but did not associate with inflammatory markers or appetite scores. Combining patients and controls, we observed positive correlations with BMI (r=0.33; p=0.03), % body fat (r=0.35; p=0.03), leptin (r=0.45; p=0.006) and the triceps skinfold thickness (r=0.36; p=0.02). In multivariate analysis % body fat was the main determinant of nesfatin-1 variance. In conclusion, nesfatin-1 levels did not differ between HD patients and healthy subjects and negatively correlated with protein intake. This pathway is likely not dysregulated in uremia.

Relationship between total ghrelin and inflammation in hemodialysis patients

In hemodialysis (HD) patients studies have shown that plasma ghrelin is increased and it has been speculated that ghrelin levels might be related to systemic inflammation. The present study attempted to correlate the serum levels of total ghrelin with serum TNF-α and IL-6, and with nutritional status and body composition in HD patients. Forty-seven HD patients from a single dialysis unit (18 women, mean age 55.3±12.2 yr; BMI 24.4±4.2kg/m(2); % body fat 29.4±7.4%) were studied and compared to 21 healthy subjects (12 women, 50.7±15.7 yr and BMI 25.6±4.0kg/m(2); % body fat 30.0±5.7%). Biochemical data, serum total ghrelin, TNF-α and IL-6 levels were measured. The body composition was evaluated by dual energy X-ray absortiometry (DEXA) and energy and protein intake were evaluated. Patients showed elevated plasma ghrelin levels when compared to healthy subjects (1.14±1.0ng/mL vs 0.58±0.4; p<0.001). There was a positive correlation between ghrelin levels and TNF-α (r=0.25; p<0.04), IL-6 (r=0.42; p<0.02), and a negative correlation between TNF-α and protein intake (r=-0.28; p<0.03), and energy intake (r=-0.34; p<0.01). No correlation was observed with any aspect of body composition. Plasma ghrelin levels are elevated in HD patients and associated with the state of systemic inflammation. We suggest that the inflammatory state may affect ghrelin bioactivity and metabolism in hemodialysis patients.

Evaluation of neopterin levels in patients undergoing hemodialysis

Neopterin is a diagnostic or a prognostic biomarker for several pathologies including renal diseases. However, the association between neopterin status and causative main reasons such as diabetes and hypertension for renal disease remains unclear. The aim of the study was to evaluate neopterin levels in diabetes and hypertension patients treated with/without hemodialysis. According to primary renal disorders, the patients undergoing hemodialysis were classified into 4 groups as diabetic nephropathy, hypertensive nephropathy, reflux nephropathy or interstitial nephritis, and others. The controls consisted of healthy subjects, hypertensive subjects, and diabetic individuals without any renal disorder. In the study, both urinary and serum neopterin levels were measured using high performance liquid chromatography and enzyme-linked immunosorbant assay in patients undergoing regular hemodialysis therapy (n=71). The effects of the duration of hemodialysis and treatment of erythropoietin and/or iron on neopterin levels were also evaluated. Neopterin levels were found to be higher in hemodialysis patients than in the healthy controls (P<0.05). A significant difference in neopterin levels was also found between diabetic control patients and diabetic nephropathy patients (P<0.05). A similar significant difference was detected in neopterin levels between hypertensive patients with/without nephropathy (P<0.05). Neopterin may be an early critical marker for progression of nephropathy in diabetic and hypertensive patients in early stages.

Are ghrelin and leptin involved in food intake and body mass index in maintenance hemodialysis?

OBJECTIVES

Both leptin and ghrelin (in the forms of acyl ghrelin and des-acyl ghrelin) are involved in food intake, and appear to be dysregulated in chronic kidney disease. This study describes plasma leptin, acyl, and des-acyl ghrelin concentrations in relation to protein intake and body mass index (BMI) in hemodialysis (HD) patients.

DESIGN

This was a cross-sectional study.

SETTING

This study was conducted during the baseline phase of the French multicenter Influence of a High-Flux Dialyzer on Long-Term Leptin Levels Study.

PATIENTS

We studied 125 HD patients (aged 72.5+/-11.7 years; 59% males).

MAIN OUTCOME MEASURE

Blood samples were collected during fasting, and before a regular HD session. Plasma ghrelin and leptin were evaluated. The protein equivalents of total nitrogen appearance and BMI were calculated.

RESULTS

Patients demonstrated elevated serum leptin (48.0+/-49.0 ng/mL) and des-acyl ghrelin (646.6+/-489.5 pg/mL) levels, and low acyl ghrelin levels (29.8+/-58.5 pg/mL), according to normal values. Acyl ghrelin was negatively correlated with C-reactive protein (r=-0.34, P < .001). The des-acyl to acyl ghrelin ratio was negatively correlated with protein intake, as estimated by normalized Protein Nitrogen Appearance (r=-0.22, P=.01). Serum leptin exhibited its well-described positive correlation with BMI and waist circumference, but the other hormones did not.

CONCLUSIONS

This study reports high des-acyl ghrelin and leptin levels and low acyl ghrelin levels in HD patients, a finding potentially associated with inflammation and food intake.

Methods for determining healthy body weight in end stage renal disease

Several formulas for calculating desirable body weight are used in chronic kidney failure patients. Ideal body weight (IBW) derived from Metropolitan Life Insurance tables has been available since the 1950s. The Hamwi formula was proposed in the 1960s as a simple tool for quickly estimating desirable body weight, especially in people with diabetes. Since the 1970s, National Health and Nutrition Evaluation Surveys I, II, and III have provided an in-depth evaluation of the average body weights of Americans. These standard body weights (SBW) are often interpreted to be normal and healthy weight goals. Body mass index (BMI) has also been studied for decades and is used internationally as the standard for determining healthy weight, especially in relationship to obesity. These 4 methods are discussed and compared along with a brief review of the history of using the adjusted body weight (ABW) formulas, followed by recommendations for clinical practice.

Longitudinal associations between dietary protein intake and survival in hemodialysis patients

BACKGROUND

Decreased dietary protein intake may be associated with increased mortality risk in individuals with kidney failure undergoing maintenance hemodialysis (MHD). We hypothesized that longitudinal changes in dietary protein intake have independent associations with survival in MHD patients.

METHODS

The relation between urea kinetic-based normalized protein nitrogen appearance (nPNA) and all-cause and cardiovascular mortality was examined in a 2-year (July 2001 to June 2003) cohort of 53,933 MHD patients from virtually all DaVita dialysis clinics in the United States, using both conventional and time-dependent (repeated-measure) Cox models to estimate death hazard ratios for quarterly averaged nPNA categories controlled for case-mix, comorbidity, dialysis dose (Kt/V), and available markers of malnutrition-inflammation complex syndrome (MICS).

RESULTS

The best survival was associated with nPNA between 1.0 and 1.4 g/kg/d, whereas nPNA less than 0.8 or greater than 1.4 g/kg/d was associated with greater mortality in almost all models. Adjustment for MICS mitigated the associations substantially. A decrease in protein intake during the first 6 months in patients with an nPNA in the 0.8- to 1.2-g/kg/d range was associated incrementally with greater death risks in the subsequent 18 months, whereas an increase in nPNA tended to correlate with reduced death risk.

CONCLUSION

Low daily protein intake or decrease in its magnitude over time is associated with increased risk for death in MHD patients. Whether the association between time-varying protein intake and survival is causal or a consequence of anorexia secondary to MICS or other factors needs to be explored further in interventional trials.

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

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

Effect of prescribing a high protein diet and increasing the dose of dialysis on nutrition in stable chronic haemodialysis patients: a randomized, controlled trial

BACKGROUND

Protein requirements in stable, adequately dialysed haemodialysis patients are not known and recommendations vary. It is not known whether increasing the dialysis dose above the accepted adequate level has a favourable effect on nutrition. The aim of this study was to determine whether prescribing a high protein diet and increasing the dose of dialysis would have a favourable effect on dietary protein intake and nutritional status in stable, adequately dialysed haemodialysis patients. Effects on hyperphosphataemia and acidosis were also studied.

METHODS

Patients were randomized to a high dialysis dose (HDD) group (target Kt/V(eq) of 1.4) or a regular dialysis dose (RDD) group (target Kt/V(eq) of 1.0). All patients were prescribed a high protein (HP) diet [1.3 g/kg of ideal body weight (IBW)/day] and a regular protein (RP) diet (0.9 g/kg/day), each during 40 weeks in a crossover design. In 50 patients, 23 in the HDD and 27 in the RDD group follow-up was > or =10 weeks. These patients, aged 56+/-15 years, were included in the analysis. Nutritional status was assessed by anthropometry, plasma albumin and a nutritional index.

RESULTS

Delivered Kt/V(eq) in the HDD group (1.26+/-0.14) was significantly higher than in the RDD group (1.02+/-0.08). Protein intake estimated from total nitrogen appearance (PNA) measurements and food records (DPI) was significantly higher during the HP diet (PNA(IBW), 1.01+/-0.18 g/kg/day; DPI(IBW), 1.15+/-0.18 g/kg/day) than during the RP diet (PNA(IBW), 0.90+/-0.14 g/kg/day; DPI(IBW), 0.94+/-0.11 g/kg/day). Increasing the dialysis dose did not increase protein intake either during the HP or RP diet. Plasma albumin (41.9+/-3.0 g/l) lean body mass (107+/-15% of normal values) and the nutritional index did not differ between the dialysis dose groups or protein diets and remained stable overtime. Dry body weight (97+/-14%) and total fat mass increased over time in the HDD group, but remained stable in the RDD group suggesting an effect of dialysis dose on energy balance. There was no effect of the protein diets on dry body weight or total fat mass. Plasma phosphate levels and oral bicarbonate supplements were lower in the HDD group, but were comparable between the protein diets.

CONCLUSIONS

Prescribing a HP diet resulted in a modest increase in actual protein intake, but increasing dialysis dose did not have a contributing effect. A HP diet or increasing the dialysis dose did not have a favourable effect on the nutritional status. A dietary protein intake of at least 0.9 g/kg IBW/day appears to be sufficient for adequately dialysed haemodialysis patients without overt malnutrition.

On-line monitoring of solutes in dialysate using absorption of ultraviolet radiation: technique description

PURPOSE

The aim of this work was to describe a new optical method for monitoring solutes in a spent dialysate using absorption of UV radiation.

METHOD

The method utilises UV-absorbance determined in the spent dialysate using a spectrophotometrical set-up. Measurements were performed both on collected dialysate samples and on-line. During on-line monitoring, a spectrophotometer was connected to the fluid outlet of the dialysis machine, with all spent dialysate passing through a specially-designed cuvette for optical single-wavelength measurements. The concentrations of several substances of various molecular sizes, electrical charge, transport mechanism, etc. were determined in the dialysate and in the blood using standard laboratory techniques. The correlation coefficient between UV-absorbance of the spent dialysate and concentration of the substances in the spent dialysate and in the blood was calculated from data based on the collected samples.

RESULTS

The obtained on-line UV-absorbance curve demonstrates the possibility to follow a single hemodialysis session continuously and to monitor deviations in the dialysator performance using UV-absorbance. The experimental results indicate a very good correlation between UV-absorbance and several small waste solutes removed such as urea, creatinine and uric acid in the spent dialysate and in the blood for every individual treatment at a fixed wavelength of 285 nm. Moreover, a good correlation between the UV-absorbance and substances like potassium, phosphate and beta2-microglobulin was obtained. The lowest correlation was achieved for sodium, calcium, glucose, vitamin B12 and albumin.

CONCLUSIONS

A technique for on-line monitoring of solutes in the spent dialysate utilising the UV-absorbance was developed. On-line monitoring during a single hemodialysis session exploiting UV-absorbance represents a possibility to follow a single hemodialysis session continuously and monitor deviations in dialysis efficiency (e.g. changes in blood flow and clearance). The UV-absorbance correlates well to the concentration of several solutes known to accumulate in dialysis patients indicating that the technique can be used to estimate the removal of retained substances.

Observations with regard to the National Kidney Foundation K/DOQI clinical practice guidelines concerning serum transthyretin in chronic renal failure

The National Kidney Foundation K/DOQI Guidelines state that, "Serum prealbumin is a valid and clinically useful measure of protein-energy nutritional status in maintenance dialysis (MD) patients." Prealbumin, also known as serum transthyretin (TTR), was not recommended as a nutritional parameter of the same usefulness as the serum albumin. This decision was made, in part, because published research at that time suggested that serum TTR was not a more sensitive index of nutritional status than serum albumin and there was much more clinical and research experience with serum albumin as a nutritional and inflammatory marker. Evidence, including more recently published research data, which is reviewed in this paper has led to the following conclusions by the current authors: 1) In MD patients either protein-energy malnutrition or inflammation can lead to a reduction in serum TTR concentrations. 2) Hence, in MD patients, serum TTR concentrations can be used as a measure of both nutritional and inflammatory status. 3) Serum TTR concentrations are typically increased in MD patients. 4) In maintenance hemodialysis (MHD) patients, serum TTR is a risk factor for mortality that is somewhat independent of serum albumin. 5) Current epidemiological evidence suggests that a serum TTR value of 25 or 30 mg/dl or greater is associated with increased survival and, hence, is desirable in MHD patients. 6) MHD patients with serum TTR levels less than 25-30 mg/dl should be evaluated for protein-energy malnutrition and inflammation.

Nutritional status in the HEMO Study cohort at baseline. Hemodialysis

The nutritional status of the first 1,000 patients randomized into the Hemodialysis (HEMO) Study was analyzed at baseline when they received their typical dialysis dose (equilibrated Kt/V = 1.30 +/- 0.22) and dialysis membrane. This is the largest study to date of the nutritional status of chronic hemodialysis patients. The mean (+/- SD) values for these parameters included a serum albumin level of 3.65 +/- 0.38 g/dL, a dietary energy intake of 22.9 +/- 8.4 kcal/kg/day, a dietary protein intake of 0.93 +/- 0.36 g/kg/day, and a double pool normalized protein catabolic rate (enPCR) of 1.00 +/- 0.25 g/kg/day. The percentage of patients below HEMO Study nutritional standards of care included 29% of patients with a serum albumin level less than 3.5 g/dL, 76% of patients with a dietary energy intake less than 28 kcal/kg/day, 61% of patients with a dietary protein intake less than 1.0 g/kg/day, and 52% of patients with an enPCR of less than 1.0 g/kg/day. There was a strong correlation between dietary protein intake and dietary energy intake (r = 0.74, P < 0.0001). Significant correlations were also evident between serum albumin and double pool PCR and between dietary protein intake and double-pool PCR. Kt/V and membrane flux were not predictive of baseline dietary protein intake, dietary energy intake, or serum albumin level. Thus, a majority of patients in the HEMO Study had protein and energy intake levels and enPCR levels that were below National Kidney Foundation Kidney Dialysis Outcome Quality Improvement (NKF-K/DOQI) guidelines.

Inflammation, Malnutrition, and Cardiac Disease as Predictors of Mortality in Hemodialysis Patients

ABSTRACT. Various studies suggest a strong association between nutrition and clinical outcome in hemodialysis (HD) patients. Several morbidity factors that per se increase the risk of a poor outcome, such as cardiovascular disease (CVD) and inflammation, may also cause malnutrition. Among laboratory parameters used to assess nutritional status, serum albumin appears to be a particularly strong predictor of morbidity and mortality. This study assessed the importance of nutritional status and inflammation and other comorbidity factors as predictors of mortality in HD patients. Nutritional status was evaluated in 128 HD patients by subjective global nutritional assessment (SGNA) and by measuring several anthropometric markers (actual body weight, percentage of actual body weight to desirable body weight, midarm muscle circumferences, triceps skinfold thickness), and serum albumin, plasma insulin such as insulin growth factor-1 and as a marker of inflammation, serum C-reactive protein (s-CRP) levels. The mortality during the next 36 mo was analyzed in relation to age, gender, CVD, SGNA, serum albumin, CRP, and several other factors by Kaplan-Meier analysis multivariate. Cox proportional hazard analysis was used to identify independent predictors of mortality. After 36 mo, 58 patients were still on HD treatment, 57 patients (45%) had died while receiving treatment, and 13 had received a kidney transplant. The main cause of death was CVD (58%), followed by infection (18%); malnutrition/cachexia was a rare direct cause of death (5%). Kaplan-Meier analysis showed that age, female gender, CVD, diabetes, SGNA, all anthropometric parameters, serum albumin, plasma insulinlike growth factor-1, and s-CRP were significant predictors of mortality. Analysis by the Cox model showed that age, gender, CVD, nutritional status (SGNA), and CRP were independent predictors of mortality at 36 mo. A low albumin level was not an independent predictor, although it was strongly associated with a reduced survival rate in the Kaplan-Meier analysis. Inflammation, malnutrition, and CVD appeared to contribute to increased mortality in a stepwise manner. The mortality at 36 mo was 0% when none of these complications was present, whereas the mortality was 75% in those patients with all three risk factors present at baseline. It is concluded that in addition to malnutrition and comorbidities (CVD, diabetes mellitus), inflammation (elevated s-CRP) is a significant independent risk factor for mortality in HD patients. Inflammation, malnutrition, and CVD appear to be interrelated, each additionally contributing to the high mortality in these patients.

Anthropometry-based equations overestimate the urea distribution volume in hemodialysis patients

BACKGROUND

Protein intake in hemodialysis patients can be estimated indirectly from the protein equivalent of total nitrogen appearance (PNA) during the interdialytic period. A reliable estimate of the patient's urea distribution volume (UDV) is required to assess protein intake from PNA values. UDV values are derived frequently from simple anthropometric equations.

METHODS

UDV values based on anthropometric methods were compared with UDV values determined by direct dialysate quantitation (DDQ) in 54 stable chronic hemodialysis patients. The anthropometric methods included the following: the Watson equations (WAT), a fixed proportion of postdialysis body weight, 58% for males and 55% for females (% body wt), and skinfold thickness measurements (SFT). Postdialysis blood samples were drawn at 15-minutes postdialysis.

RESULTS

UDV(WAT) and UDV(SFT) overestimated UDV(DDQ) by about 8 L [limits of agreement (LOA): 2.6 to 14.2 L] in males and about 6 L (LOA: -0.8 to 12.4 L) in females. The overestimation by UDV(%BW) was even larger: 10.5 L (LOA: 2.0 to 19.0 L) in males and 11.1 L (LOA: 2.1 to 20.1 L) in females. The difference between UDV(%BW) and UDV(DDQ) correlated with the percentage of body fat (r = 0.57) and body mass index (r = 0.48). In a subgroup of seven patients, UDV was also determined by dilution (DIL) of the stable isotope [(13)C]urea. UDV(WAT) and UDV(%BW) overestimated UDV(DIL) significantly. In contrast, UDV(DDQ) was significantly smaller than UDV(DIL), even after correction for incomplete postdialysis equilibration. PNA values calculated using the various UDV estimates were compared with dietary protein intake (DPI) assessed from food records. PNA(DDQ) (61 +/- 10 g/day) did not differ significantly from DPI (63 +/- 13 g/day), but the agreement in individual patients varied considerably (LOA, -24 to 20 g/day). Anthropometric-based PNA values overestimated DPI by 8 to 16 g/day.

CONCLUSIONS

Anthropometry-based equations overestimate UDV values in hemodialysis patients, leading to an overestimation of PNA values. Although PNA measurements by DDQ appear to be more reliable for assessing protein intake, PNA(DDQ) values should be interpreted with caution in individual hemodialysis patients.

Urea and nitrogen excretion in pediatric peritoneal dialysis patients

BACKGROUND

Adequate nutrition is critical to the care of children with end-stage renal disease, and failure to reach the target dietary intake is associated with growth failure. Prospective studies of urea and nitrogen output in adults have led to the derivation of quantitative relationships, which allow assessment of dietary protein intake when only urea appearance is known. Such a clinically useful relationship has not been defined in children receiving chronic peritoneal dialysis (PD).

METHODS

We studied 18 pediatric PD patients (ages 0.8 to 14.3 years) on 132 occasions and determined norms of urea nitrogen appearance (UNA), total nitrogen appearance (TNA), and nonurea nitrogen appearance (NUNA). We stratified data on UNA, TNA, NUNA, nonprotein nitrogen appearance, and the protein equivalent of nitrogen appearance by age groups (0 to 5, 6 to 10, and 11 to 15 years of age) and demonstrated significant differences. In addition, dietary protein and energy intake were measured in the outpatient setting with food scales and dietitian interviews, and the results were stratified by age, presence of residual renal function, and recombinant human growth hormone (rhGH) therapy.

RESULTS

UNA (3.05 +/- 1.38 g/day, 103 +/- 42 mg/kg/day) and TNA (4.67 +/- 1.86 g/day, 159 +/- 52 mg/kg/day) varied significantly between different age groups. NUNA in pediatric subjects (56 +/- 24 mg/kg/day) was significantly greater than previously published adult norms. A linear relationship was defined between UNA and TNA that was specific to pediatric PD patients [TNA (g/day) = 1.26(UNA) + 0.83]. When the relationship was scaled to body mass, the y intercept was significantly different in the youngest subjects [TNA = 1.03 (UNA) + 0.02 (weight in kg) + 0.56 (for subjects age 0 to 5) or 0.98 (for subjects age 11 to 15 or 6 to 10), r2 = 0.91]. Dietary protein intake was significantly greater in subjects receiving rhGH therapy, although nitrogen excretion was unchanged.

CONCLUSIONS

Markers of protein metabolism in pediatric PD patients are age dependent and differ from adult values. An age-specific relationship between TNA and UNA is defined for pediatric subjects; it does not vary with rhGH or the presence of residual renal function.

Adequacy of peritoneal dialysis

The National Kidney Foundation-Dialysis Outcomes Quality Initiatives guidelines have standardized many aspects of treating end-stage renal disease patients with peritoneal dialysis in an attempt to improve overall patient outcome. While recommending certain total solute clearance goals, the guidelines have also pointed out deficiencies in our knowledge base and precipitated many controversies. Some of these controversies have been resolved while others may have been interpreted wrongly, unnecessarily resulting in transfer of patients from peritoneal dialysis to hemodialysis due to "failure to meet adequacy targets" even when doing well clinically. This report reviews the rationale for the original guidelines and their subsequent modification. It also outlines a rational approach toward prescription modification based on peritoneal physiology. Specific solute clearance target goals discussed are the modifications for continuous ambulatory peritoneal dialysis (CAPD) and cycler peritoneal dialysis (CCPD), and a review of what solute clearance targets subsequent guidelines from other countries have used. Some examples are as follows: new guidelines suggest that solute clearance goals for creatine clearance should differ for low and low-average transporters than for high and high-average transporters (weekly clearance of 50 and 60 1/1.73 m(2), respectively) while Kt/V targets remain unchanged. Also discussed is the rationale for having the same target for patients on CCPD with a mid-day exchange as those for patients on CAPD. We are also reminded that solute clearance is only one aspect of "adequate" dialysis-blood pressure and volume control are equally important, and ways to maintain euvolemia and blood pressure control are discussed in the context of prescription management.

Calculated nitrogen balance in hemodialysis patients: influence of protein intake

BACKGROUND

Optimal nutrient intake is important in the maintenance of a positive nitrogen balance in hemodialysis (HD) patients. The objectives of this study were (1) to assess the influence of two levels of protein intakes on nitrogen balance in stable adult HD patients, and (2) to identify a minimum level of protein intake that would result in a negative nitrogen balance, so that preliminary recommendations may be made in Indian patients on maintenance HD (MHD).

METHODS

Stable, adult, nondiabetic MHD patients were recruited after informed consent into a cross over trial with a high-protein (HP) diet [1.2 g/kg ideal body weight (IBW)/day), followed by a low-protein (LP) diet (0.6 g/kg IBW/day] after appropriate periods of equilibration; for both diets, 50% of protein was of high biological value, and calorie intake was 35 kCal/kg IBW/day. Duplicate meals and residues were weighed, homogenized, and stored at -20 degrees C for analysis of dietary N by the Kjeldahl method, used to check the consistency of the N content of the diet supplied. Pre- and post- (30-minute equilibrated) blood urea samples were drawn, and details of weights and other HD parameters were recorded. Interdialytic urine collections for urea were obtained. N input came from dietary protein calculated as 16% of the weight of biological protein; N output was calculated using blood-side urea measurements and urinary urea excretion and was the sum of urea N (UN) and nonurea N (NUN) losses (assumed to be equal to 0.031 g N/kg/day).

RESULTS

Fifteen patients were recruited. Twelve patients completed both limbs of the study. The mean age was 30.3 +/- 12.7 years. The body mass index was 18.9 +/- 2.4. Serum albumin was 3.8 +/- 0.35 g/dL, and Kt/V (equilibrated) was 1.17 +/- 0.3 g/dL. Protein consumed was 1.06 +/- 0.18 g/kg IBW/day in the HP limb versus 0.61 +/- 0.1 g/kg IBW/day in the LP limb (P = 0.000). Energy intake was 33 +/- 6.5 vs. 32.8 +/- 6. 7 kCal/kg IBW/day, respectively (P = 0.8). The normalized protein N appearance (nPNA) was 0.88 +/- 0.2 g/kg/day in the HP limb versus 0. 78 +/- 0.2 g/kg/day in the LP limb (P = 0.02). Dietary N was 73.5 +/- 15.3 g in the HP week and 42.5 +/- 7.5 g in the LP week (P = 0. 000). The difference between this and the sum of (UN + NUN) losses over the week was 29 +/- 13.2 g versus 1.2 +/- 8.1 g, respectively (P = 0.001), showing a strong, uniformly positive nitrogen balance with HP diet and neutral to negative nitrogen balance with LP diet. The ratio of dietary protein intake (DPI) to nPNA was significantly lower (anabolic) in the HP limb (0.7 +/- 0.2 vs. 1.12 +/- 0.3, P = 0. 000). On a scatter plot of nPNA to DPI, a catabolic relationship was demonstrated below a DPI of 0.75 g/kg/day (95% CI, 0.65 to 0.85 g/kg/day).

CONCLUSION

A DPI of approximately 1.1 g/kg/day produces a positive nitrogen balance and 0.6 g/kg/day a neutral to negative nitrogen balance, demonstrating protein anabolism as a function of protein intake. It is suggested that a protein intake of 0.85 g/kg/day should be considered unsafe. These conclusions apply in stable nondiabetic adult HD patients in the setting of adequate dialysis and adequate calorie intake.

Accuracy of hemodialysis modeling

BACKGROUND

One- and two-compartmental models of hemodialysis (HD) are well known. These models make it possible to analyze the course of treatment and to predict the effect of dialysis procedures. Mathematical modeling helps physicians to match dialysis therapy to the individual needs of the patient; however, the efficiency of the models depends on the accuracy of the coefficients. How to select coefficients in the case of one-compartmental models is known for urea and creatinine. Less information is available for two-compartmental models. Results on modeling of uric acid concentrations have not been published.

METHODS

The identification of the mathematical model coefficients was based on the concentration measurements of three markers of uremic toxicity (urea, creatinine, and uric acid) in both patients' blood and dialysate. Blood samples were taken from the arterial line several times throughout the dialysis period. Simultaneously, dialysate samples were taken from a test port in the dialyzer outflow line. The mathematical model parameters were determined so as to minimize the deviations between the measured points and the calculated curves. In this way, distribution volumes, cellular clearances, and dialyzer mass transfer coefficients were estimated.

RESULTS

For a one-compartmental model, the median value of distribution volume V = 0.56 DW was obtained, where DW is the patient's dry weight. For a two-compartmental model, intercompartment volume Vi = 0.36 DW and extracompartment volume Ve = 0.21 DW. The following median values for cellular clearances were established: urea 415 (mL/min), creatinine 207 (mL/min), and uric acid 257 (mL/min).

CONCLUSIONS

One- and two-compartmental models describe the concentration of the urea, creatinine, and uric acid very effectively, in contrast with phosphorus, in which modeling results are not satisfactory. Although two-compartmental models are more effective, they are much more complicated than one-compartmental models, which justifies using the one-compartmental model for hemodialysis modeling. A two-compartmental model must be used in the case of rebound phenomenon modeling. The total body water values we have obtained are similar to the anthropometrically based values for urea and creatinine and to a lesser degree for uric acid. Distribution volumes for one- and two-compartmental models obtained from patient weight are the simplest coefficients for mathematical models and have sufficient precision as well. The global value of both compartments is slightly greater than the corresponding value for a one-compartmental model. The effectiveness of dialyzers is in practice lower than might be expected on the basis of the data provided by their manufacturers. Urea cellular clearance is two times greater than creatinine and uric acid cellular clearances. The clearance differences are more prominent for the cellular membrane than for artificial semipermeable membranes.

beta(2)-microglobulin kinetics in nocturnal haemodialysis

BACKGROUND

beta(2)-Microglobulin (beta(2)m) is a major component of dialysis-related amyloidosis. The available therapeutic options do not permit normalization of the serum beta(2)m level. In a cross-over trial, we studied the kinetics of beta(2)m during two different dialytic techniques.

METHODS

Ten stable, anuric end-stage renal disease patients were studied during two consecutive weeks of three conventional (CHD) and six nocturnal haemodialysis (NHD) sessions. CHD was performed for 4 h three times weekly using a polysulfone dialyser (F80, surface area of 1.8 m(2)) with a mean blood and dialysate flow rate of 401+/-91.6 and 514+/-10.9 ml/min, respectively. The NHD was done with a smaller dialyser (F40, surface area of 0.7 m(2)) and lower blood (281+/-17 ml/min) and dialysate flow rates (99+/-1.2 ml/min) for 8 h, six nights a week.

RESULTS

Weekly removal of urea (51.6+/-24.6 vs 43.1+/-20.5 g) and creatinine (8501+/-5204 vs 6319+/-4134 mg) were comparable with the two modalities of dialysis but the mass of beta(2)m removed was significantly higher with NHD (127+/-48 vs 585+/-309 mg, P<0.001), with a percentage reduction in serum level of 20.5+/-5.8 vs 38.8+/-7. 1% (P<0.0001) and a Kt/V(beta2m) of 0.21+/-0.09 vs 0.56+/-0.17 (P<0. 0006). The mean post-dialysis beta(2)m (20.8+/-6.3 vs 14.0+/-3.8 mg/dl, P=0.02), Tac(beta2m) (26.2+/-5.2 vs 19.8+/-3.8 mg/dl, P=0.02) and pre-dialysis beta(2)m (beta(2)m(pre)) at the end of 1 week of therapy (24.4+/-7.6 vs 19.0+/-3.4 mg/dl, P=0.02) were lower with NHD. Long-term follow-up data were available in 13 and seven patients at the end of 1 and 2 years, respectively. Serum beta(2)m(pre) levels progressively declined from 27.2+/-11.7 mg/dl at initiation of NHD to 13.7+/-4.4 mg/dl by 9 months, and they remained stable thereafter.

CONCLUSIONS

NHD provides a much higher clearance of beta(2)m than CHD, leading to a long-term decrease in the pre-dialysis concentration of beta(2)m.

Relating protein intake to nutritional status in haemodialysis patients: how to normalize the protein equivalent of total nitrogen appearance (PNA)?

BACKGROUND

The protein equivalent of total nitrogen appearance (PNA) is assumed to be a reliable estimate of dietary protein intake in haemodialysis patients. Protein requirements are related to body size. In order to standardize PNA to individual differences in body size, PNA is normalized to various terms related to the patient's body weight. It is not clear which is the most appropriate method to normalize PNA.

METHODS

We calculated five commonly used variants of normalized PNA and related them to indices of nutritional status in 57 stable chronic haemodialysis patients, 57 +/- 15 (mean +/- SD) years of age. PNA, determined by direct dialysate quantification, was normalized to actual post-dialysis dry body weight (DBW), normal body weight (DBWnormal), lean body mass (LBM), normal lean body mass (LBMnormal), and 'normalized' body weight (N). Nutritional status was assessed using an index of nutrition composed of anthropometry derived parameters and plasma albumin concentration.

RESULTS

PNA(DBW) (0.85 +/- 0.14 g/kg/d) tended to be higher than PNA(DBWnormal) (0.81 +/- 0.14 g/kg/d). PNA(LBM) (1.17 +/- 0.19 g/kg/d) did not differ from PNA(LBMnormal) (1.19 +/- 0.21 g/kg/d). PNA(N) (1.06 +/- 0.14 g/kg/d) was significantly higher than PNA(DBW) and PNA(DBWnormal), but lower than PNA(LBM) and PNA(LBMnormal). Actual PNA (61 +/- 13 g/d) correlated significantly with DBW (r=0.52) and LBM (r=0.63) indicating that large patients eat more protein. Interestingly, actual PNA correlated with plasma albumin (r=0.33) and with the overall index of nutrition (r=0.27) as well. PNA(DBW) correlated negatively with relative DBW (r=-0.32), expressed as a percentage of normal values, indicating that PNA(DBW) is relatively high in underweight patients. In contrast, PNA(DBWnormal) correlated positively with all nutritional parameters as well as with the overall index of nutrition (r=0.33). PNAN and PNA(LBM) did not correlate with the nutritional status, but PNA(LBMnormal) correlated positively with relative DBW (r=0.50) and with overall nutritional status (r=0.34). PNA(DBWnormal) and PNA(LBMnormal) in well-nourished patients showed overlap with the values in patients with evident malnutrition, despite the positive correlation of the normalized PNA values with nutritional status.

CONCLUSIONS

Normalizing PNA by DBWnormal and LBMnormal appeared to be the most appropriate method to standardize protein intake in haemodialysis patients. Since actual PNA is the purest estimate of protein intake that correlated with nutritional status, we recommend to evaluate actual PNA as well in studies that relate protein intake to patient outcome.

Morbidity and mortality in redefining adequacy of peritoneal dialysis: a step beyond the National Kidney Foundation Dialysis Outcomes Quality Initiative

The National Kidney Foundation Dialysis Outcomes Quality Initiative (NKF-DOQI) Peritoneal Dialysis (PD) Adequacy Work Group intentionally limited the scope of its work to address adequacy in terms of small-solute removal. This decision was based on the need for rigorous evidence and that mortality is the most objective parameter in the literature. This review attempts to more broadly redefine the concept of the adequacy of PD, particularly as it relates to the most common general medical problems that PD patients experience; namely, cardiovascular disease and malnutrition. Whereas we are sensitive to the developmental process of the NKF-DOQI, we are critical that the definition of adequacy may be too narrow, leading clinicians to overlook other important morbidities. We have reiterated the evidence that suggests a weekly solute clearance (Kt/Vurea) of 1.7 or greater is associated with better patient survival. The arguments to target a greater Kt/Vurea of 2.0 are challenged, yet the concept is ultimately supported. Because cardiovascular disease is the cause of death in half of all patients with end-stage renal disease, dialysis adequacy must be defined, in part, by the potential of that therapy to diminish cardiovascular maladies. Blood pressure, volume, left ventricular hypertrophy, and dyslipidemias are discussed in this context. Lastly, assumptions that increasing total solute clearance leads to improved nutrition in PD patients are challenged. We have attempted to expand on what the NKF-DOQI did not include, and we urge the dialysis community to seek the answers to the many controversies that remain. We need to redefine the adequacy of PD in a holistic manner and find outcome parameters that are not as final as death.

Is peritoneal dialysis a good option for black patients?

Blacks are less likely than whites to use peritoneal dialysis (PD) as the initial renal replacement therapy. The reason for the underusage of PD by blacks is unknown. In a cross-sectional multicenter trial, we studied peritoneal transport character, small-molecular-weight solute clearances, and nutritional status in 475 patients undergoing PD (168 whites, 192 blacks, and 115 Asians). The mean age of blacks undergoing PD was significantly younger than that of whites (47.6 +/- 14.7 v 58.2 +/- 16.7 years; P < 0.0001). Target Kt/V and weekly creatinine clearance (WCC) as defined by the Dialysis Outcome Quality Initiative Work Group was achieved by 62.5% of whites, 67.2% of blacks, and 54.8% of Asians (P = 0.05). Total protein (7.25 +/- 0.88 v 6.55 +/- 0.73 g/dL), albumin (3.72 +/- 0.57 v 3.55 +/- 0.53 g/dL), and lean body mass (LBM; 41.7 +/- 15.6 v 33.0 +/- 11.8 kg) were lower in whites compared with blacks (P < 0.001). Although the normalized protein catabolic rate (nPCR) was greater (0.82 +/- 0.24 v 0.90 +/- 0.32 g/kg/d; P = 0.04), total protein (6.24 +/- 0.85 g/dL) and serum albumin levels (3.36 +/- 0.52 g/dL) and LBM (30.1 +/- 8.0 kg) were significantly lower in Asians than blacks (P < 0.0001). The favorable anabolic response in blacks may partially be explained by a higher calorie intake in this group of patients (29.6 +/- 10.7 Cal/kg/d) compared with whites (22.4 +/- 6.8 Cal/kg/d) and Asians (23.9 +/- 9.8 Cal/kg/d; P = 0.03). Multiple regression analysis identified that black race and weight were positively associated, whereas dialysate/plasma creatinine ratio (D/P(Creat)) and age had a negative effect on serum albumin level. Follow-up data indicated that the Kt/V (2.09 +/- 0.50 v 2.39 +/- 0.56; P = 0.02) and WCC (60.8 +/- 4.3 v 70.2 +/- 7.3 L/1.73 m2; P = 0.02) increased significantly from baseline only in blacks. We conclude that PD is an ideal renal replacement therapy in at least a subset of blacks with end-stage renal disease.

Factors predicting malnutrition in hemodialysis patients: a cross-sectional study

Signs of protein-energy malnutrition are common in maintenance hemodialysis (HD) patients and are associated with increased morbidity and mortality. To evaluate the nutritional status and relationship between various parameters used for assessing malnutrition, we performed a cross-sectional study in 128 unselected patients treated with hemodialysis (HD) thrice weekly for at least two weeks. Global nutritional status was evaluated by the subjective global nutritional assessment (SGNA). Body weight, skinfold thicknesses converted into % body fat mass (BFM), mid-arm muscle circumference, hand-grip strength and several laboratory values, including serum albumin (SA1b), plasma insulin-like growth factor I (p-IGF-I), serum C-reactive protein (SCRP) and plasma free amino acids, were recorded. Dose of dialysis and protein equivalence of nitrogen appearance (nPNA) were evaluated by urea kinetic modeling. The patients were subdivided into three groups based on SGNA: group I, normal nutritional status (36%); group II, mild malnutrition (51%); and group III, moderate or (in 2 cases) severe malnutrition (13%). Clinical factors associated with malnutrition were: high age, presence of cardiovascular disease and diabetes mellitus. nPNA and Kt/V(urea) were similar in the three groups. However, when normalized to desirable body wt, both were lower in groups II and III than in group I. Anthropometric factors associated with malnutrition were low body wt, skinfold thickness, mid-arm muscle circumference (MAMC), and handgrip strength. Biochemical factors associated with malnutrition were low serum levels of albumin and creatinine and low plasma levels of insulin-like growth factor 1 (IGF-1) and branched-chain amino acids (isoleucine, leucine and valine). The serum albumin (SAlb) level was not only a predictor of nutritional status, but was independently influenced by age, sex and SCRP. Plasma IGF-1 levels also reflected the presence and severity of malnutrition and appeared to be more closely associated than SAlb with anthropometric and biochemical indices of somatic protein mass. Elevated SCRP (> 20 mg/liter), which mainly reflected the presence of infection/inflammation and was associated with hypoalbuminemia, was more common in malnourished patients than in patients with normal nutritional status, and also more common in elderly than in younger patients. Plasma amino acid levels, with the possible exception of the branched-chain amino acids (isoleucine, leucine, valine), seem to be poor predictors of nutritional status in hemodialysis patients.

Using the hemodialysis prognostic nutrition index and urea reduction ratio to predict morbidity and mortality: a pilot study of the 1995 council on renal nutrition national research question

OBJECTIVE

To validate the use of the hemodialysis prognostic nutrition index (HPNI) in an alternate hemodialysis population and to determine if use of urea reduction ratio would improve use in outcome prediction for morbidity and mortality.

DESIGN

Prospective random cohort.

SETTING

Hospital based non-for-profit outpatient dialysis unit.

PATIENTS

Forty chronic hemodialysis patients, 50% men, 50% black, 16% diabetic, 67.2 mean months on hemodialysis, mean age 54.5 years.

INTERVENTIONS

None; observational; tracking of routinely collected demographic, biochemical, and clinical data.

MAIN OUTCOME MEASURES

Number of times and days hospitalized, mortality

RESULTS

Plotting of HPNI against urea reduction ratio produced risk quadrants for hospitalization that were more predictive than HPNI alone.

CONCLUSION

Application continues as a multicenter collaborative Council on Renal Nutrition National Research Question.

The hemodialysis pilot study: nutrition program and participant characteristics at baseline. The HEMO Study Group

OBJECTIVE

Describe the nutrition program (assessments and interventions) and the participants' baseline nutritional characteristics in the Hemodialysis Pilot Study.

DESIGN

Cross sectional survey in which hemodialysis patients were examined during 10 weeks of baseline (BL), before randomization study interventions (dose and flux).

SETTING

Four hemodialysis centers (eight dialysis units in total).

PATIENTS

Twenty-nine male (mean age, 63 years; range, 34 to 75) and 20 female (mean age, 61 years; range, 29 to 73) hemodialysis patients.

INTERVENTIONS

None during BL.

MAIN OUTCOME MEASURES

Feasibility of implementing the proposed nutrition program before conducting the full-scale trial, and description of baseline characteristics related to nutrition.

RESULTS

A nutrition program was developed to assess nutritional status during BL and follow-up periods and to intervene in patients with weight loss or decreasing serum albumin. Methods for collecting biochemical, dietary and anthropometric data were implemented at four clinical centers. At baseline, mean protein intake estimated by single pool normalized protein catabolic rate was 0.95 +/- 0.21 gm/kg adjusted body weight (ABW) (n = 42) and by diet record assisted recalls (n = 47) 0.94 +/- 0.36 gm/kg ABW/d, respectively. Mean energy intake was 22.8 +/- 8 kcal/kg ABW/day (n = 39). Mean serum albumin concentration using the bromcresol green method was 3.8 +/- 0.4 gm/dL (n = 40). Mean body mass index was within the normal limits of 19-27 kg/m2. Mean skinfold thicknesses in females, but not males, were shifted toward the lower end of usual distributions for healthy individuals.

CONCLUSIONS

The goal of designing, developing, and implementing the diet and nutrition component, and related data collection for the HEMO pilot study was accomplished at four separate clinical centers. Baseline mean protein and energy intake were low, suggesting that continuing dietary surveillance is needed. The ongoing full-scale HEMO study will provide the first prospective analysis of dietary intake, nutritional status, and outcome in maintenance hemodialysis patients as a function of dialysis dose and membrane flux.