Comparison of different measurements of lean body mass in normal individuals and in chronic peritoneal dialysis patients

Clinical and predictive value of simplified creatinine index used as muscle mass surrogate in end-stage kidney disease haemodialysis patients-results from the international MONitoring Dialysis Outcome initiative

Background

Protein-energy wasting, muscle mass (MM) loss and sarcopenia are highly prevalent and associated with poor outcome in haemodialysis (HD) patients. Monitoring of MM and/or muscle metabolism in HD patients is of paramount importance for timely detection of muscle loss and to intervene adequately. In this study we assessed the reliability and reproducibility of a simplified creatinine index (SCI) as a surrogate marker of MM and explored its predictive value on outcome.

Method

We included all in-centre HD patients from 16 European countries with at least one SCI. The baseline period was defined as 30 days before and after the first multifrequency bioimpedance spectroscopy measurement; the subsequent 7 years constituted the follow-up. SCI was calculated by the Canaud equation. Multivariate Cox proportional hazards models were applied to assess the association of SCI with all-cause mortality. Using backward analysis, we explored the trends of SCI before death. Bland–Altman analysis was performed to analyse the agreement between estimated and measured MM.

Results

We included 23 495 HD patients; 3662 were incident. Females and older patients have lower baseline SCI. Higher SCI was associated with a lower risk of mortality [hazard ratio 0.81 (95% confidence interval 0.79–0.82)]. SCI decline accelerated ∼5–7 months before death. Lean tissue index (LTI) estimated by SCI was correlated with measured LTI in both sexes (males: R² = 0.94; females: R² = 0.92; both P < 0.001). Bland–Altman analysis showed that measured LTI was 4.71 kg/m² (±2 SD: −12.54–3.12) lower than estimated LTI.

Conclusion

SCI is a simple, easily obtainable and clinically relevant surrogate marker of MM in HD patients.

Urinary creatinine based equations for estimation of fat free mass in patients with intestinal insufficiency or intestinal failure

BACKGROUND & AIMS

Assessment of body composition is an important aspect of disease management in patients with intestinal insufficiency (INS) or intestinal failure (IF). However, in daily clinical settings most body composition methods are too expensive or impractical, leaving body composition to be assessed by less reliable methods such as skin fold thickness. The aim of this study was to investigate and validate the use of an equation for the estimation of fat-free mass (FFM) with bioelectrical impedance analysis (BIA) as reference method.

METHODS

A literature search for identification of urinary creatinine-based FFM-prediction equations was carried out a long side the creation of an equation by multiple linear regression. The correlation of each equation with FFM (measured by BIA in 277 patients with either INS or IF) was done by Pearson's correlation. Further investigation and validation of performance was done for the equations with the strongest correlation by Bland-Altman analysis, determination of root mean square error (RMSE), and intraclass correlation (ICC). The validation was carried out in a new group of 37 patients with either INS or IF.

RESULTS

A total of 11 prediction equations were correlated with FFM measured by BIA. The equation called FFMmultiple and FFM-5 had the strongest correlation (r = 0.969, p < 0.01 and r = 0.950, p < 0.01, respectively). FFMmultiple was superior to FFM-5 regarding Bland-Altman analysis, RMSE, and ICC in the study group (Mean bias ± Standard Deviation = 0.042 ± 2.352 versus 0.309 ± 3.196; 95% limits of agreement = [-4.568; 4.651] versus [-5.955; 6.578]; RMSE = 0.158 versus 0.236; ICC = 0.969 versus 0.948). Cross-validation resulted in a Bland-Altman analysis with a statistically significant difference between FFMmultiple and FFM by BIA. FFM-5 showed wide 95% limits of agreement ([-6.977; 6.421]).

CONCLUSIONS

Two urinary creatinine-based equations (FFMmultiple and FFM-5) showed promising results as possible substitutes to BIA, however further investigation and cross validation revealed inauspicious results. Thus, the present study cannot recommend the use of a prediction equation instead of BIA for the assessment of FFM in patients with INS and IF.

The Role of Lean Body Mass as a Nutritional Index in Chinese Peritoneal Dialysis Patients—Comparison of Creatinine Kinetics Method and Anthropometric Method

Objective

To compare, in Chinese continuous ambulatory peritoneal dialysis (CAPD) patients, the creatinine kinetics method (LBM-CK) and the anthropometric method (LBM-AM) for determining lean body mass (LBM).

Design

Single-center cross-sectional study.

Patients and Methods

We studied 151 unselected CAPD patients (78 males, 73 females). We calculated LBM-CK and LBM-AM using standard formulas. The results of the two methods were then compared by the Bland and Altman method. Dialysis adequacy and other nutritional indices, including total Kt/V, weekly creatinine clearance (CCr), residual glomerular filtration rate (GFR), protein nitrogen appearance (PNA), subjective global assessment (SGA), and serum albumin, were measured simultaneously.

Results

The mean age of the patients was 55.6 ± 12.2 years, and the mean duration of dialysis was 33.6 ± 28.5 months. The mean body mass index (BMI) was 22.7 ± 3.7. The average LBM-AM was 43.6 ± 8.0 kg; the average LBM-CK was 33.0 ± 9.3 kg. The difference between the calculated LBM-AM and LBM-CK was 10.7 kg, with LBM-AM always giving a higher value; the limits of agreement were –5.8 kg and 27.1 kg. The difference between the two measures correlated with residual GFR (Pearson r = 0.629, p < 0.001). After normalizing for desired body weight, LBM-AM was only modestly correlated with serum albumin level. No correlations were found between overall SGA score or normalized protein nitrogen appearance (nPNA) and LBM-AM or LBM-CK.

Conclusions

In Chinese patients at least, a substantial discrepancy exists between LBM-AM and LBM-CK. The difference is especially marked in patients with significant residual renal function. The optimal method for determining LBM remains obscure in Chinese CAPD patients. Moreover, LBM correlated poorly with other nutritional indices. Multiple parameters should be taken into consideration in an assessment of nutritional status of CAPD patients.

Influence of Fluid Status on Techniques Used to Assess Body Composition in Peritoneal Dialysis Patients

Objective

A reliable assessment of nutritional state in peritoneal dialysis (PD) patients is of great importance. Nevertheless, techniques used to assess body composition in patients on PD may be affected by abnormalities in fluid status. The primary aim of the present study was to compare different techniques used to evaluate body composition and to assess the influence of fluid status on the assessment of body composition. The secondary aim was to assess the relevance of handgrip muscle strength in the nutritional evaluation of the patient.

Methods

In 40 PD patients, dual-energy x-ray absorptiometry (DEXA), multifrequency bioimpedance analysis (MF-BIA), and anthropometry were compared with respect to the evaluation of body composition [fat mass and lean body mass (LBM; by DEXA), and fat-free mass (FFM; by MF-BIA, anthropometry]. The influence of fluid status on the measurement of LBM/FFM by the various techniques was assessed by their relation to left ventricular end-diastolic diameter (LVEDD), assessed by echocardiography, and by estimating the ratio between extracellular water (ECW) and total body water (TBW), assessed by bromide and deuterium dilution, with LBM (DEXA). The relevance of handgrip muscle strength as a nutritional parameter was assessed by its relation to LBM and other nutritional parameters.

Results

Despite highly significant correlations, wide limits of agreement between the various techniques were present with respect to assessment of body composition (expressed as % body weight) and were most pronounced for anthropometry: LBM (DEXA) – FFM (MF-BIA) = 3.4% ± 12.2%; LBM (DEXA) – FFM (anthropometry) = –5.7% ± 7.8%; fat mass (DEXA – MF-BIA) = –4.2%± 7.9%; fat mass (DEXA – anthropometry) = 2.9% ± 7.2%. The ratio between ECW and LBM (DEXA) was 0.36 ± 0.08 L/kg (range 0.25 – 0.67 L/kg), and the ratio between TBW and LBM was 0.75 ± 0.06 L/kg (range 0.63 – 0.86 L/kg), which shows the variability in hydration state of LBM/FFM between individual patients. LBM/FFM measured by all three techniques was significantly related to LVEDD, suggesting an important influence of hydration state on this parameter. Handgrip muscle strength was significantly related to LBM/FFM, as measured by all three techniques, but not to other nutritional parameters.

Conclusion

Wide limits of agreement were found between various techniques used to assess body composition in PD patients. The assessment of body composition was strongly influenced by hydration state. The handgrip test is related to body composition, but not to other nutritional parameters.

Nutritional Markers during Peritoneal Dialysis: Data from the 1998 Peritoneal Dialysis Core Indicators Study

Objective

This analysis explores the nutritional status of adult U.S. peritoneal dialysis (PD) patients.

Design

The Peritoneal Dialysis Core Indicators Study is a prospective cross-sectional prevalence survey describing the care provided to a random sample of adult U.S. PD patients.

Methods and Population

Prevalence data were collected from a national random sample of 1381 adult PD patients participating in the United States End Stage Renal Disease (ESRD) program.

Results

The median age of these patients was 55 years, 61% were Caucasian; the leading cause of ESRD was diabetes mellitus. Age, sex, size, peritoneal permeability, dialysis adequacy, and nutritional indices did not differ between patients on continuous ambulatory PD and patients on automated PD. The dialysis prescriptions employed achieved mean weekly Kt/V urea (wKt/V) and creatinine clearance (wCCr) values of 2.22 ± 0.57 and 67.8 ± 22.5 L/1.73 m2/week, respectively. The PD patients were large, with a mean body weight of 77 ± 21 kg and body mass index (BMI) of 27 ± 8.6 kg/m2. The mean serum albumin of these patients was 3.5 ± 0.51 g/dL, and 43% of values fell below the National Kidney Foundation Dialysis Outcomes Quality Initiative's desired range. The PD patients had a normalized protein equivalent of nitrogen appearance (nPNA) of 1.0 ± 0.57 g/kg/day, a normalized creatinine appearance rate (nCAR) of 17 ± 7.3 mg/kg/day, and an estimated lean body mass (%LBM) of 62% ± 18% of body weight. Serum albumin correlated positively with patient size, nCAR, and nPNA, but negatively with age, the presence of diabetes mellitus, female gender, erythropoietin dose, the creatinine dialysate-to-plasma ratio results of peritoneal equilibration testing, and the dialysis portion of the wCCr. The duration of ESRD experience correlated negatively with both serum albumin and patient size, although these relationships were complex.

Conclusion

Peritoneal dialysis patients generally have marginal serum albumin levels, a finding incongruent with alternative measures of nutritional status, such as weight, BMI, and creatinine generation. Serum albumin is reduced in patients with high peritoneal permeability ( i.e., rapid transporters) and, because these patients generally have higher than average wCCr values, serum albumin is inversely correlated with the dialysis component of the wCCr. The presumptive nutritional indicators (BMI, %LBM, nPNA, and serum albumin) provide disparate estimates, varying from 10% to 50% for the prevalence of nutritionally stressed PD patients.

An Elevated Ratio of Measured to Predicted Creatinine Production in Capd Patients is Not a Sensitive Predictor of Noncompliance with the Dialysis Prescription

Objective

To determine the effect a period of “intentional noncompliance” in stable continuous ambulatory peritoneal dialysis (CAPD) patients has on the ratio of measured to predicted creatinine generation.

Design

Prospective study that compares baseline to noncompliant periods in individual CAPD patients.

Patients

Nine chronic, stable CAPD patients.

Study Design

At baseline, measured creatinine production and adequacy parameters (KT/V, creatinine clearance, lean body mass, and protein equivalent of nitrogen appearance) were calculated from 24-hour collections of dialysate and urine while patients were performing their routine dialysis prescriptions. After three days of intentional noncompliance (one less exchange/day) the patients repeated their 24-hour collections, again performing their routine number of exchanges. Measured creatinine production and adequacy parameters were again calculated. Predicted creatinine production for each patient was calculated from standard equations. All parameters at baseline were compared to corresponding parameters after intentional noncompliance.

Results

In all patients, except one where there was no change, there was a statistically significant increase in not only the ratio of measured to predicted creatinine production but also all other parameters.

Conclusion

As suspected by previous investigators, this study suggests that one cause of an elevated ratio of measured to predicted creatinine production may be a recent period of noncompliance with the patient's dialysis prescription. However, these data suggest that an isolated ratio of measured to predicted creatinine generation is not a sensitive predictor of noncompliance with the peritoneal dialysis prescription.

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.

Can Malnutrition be Prevented? Nutrition and Dialysis Adequacy

As chronic renal failure (CRF) worsens, the nutritional balance is disrupt ed at several different levels that are normally responsible for maintaining metabolic homeostasis (1–3). These abnormalities may remain constant, improve, or worsen once dialysis is initiated. The success of dialytic intervention in correcting these abnormalities depends not only on the actual dose of delivered therapy, but also on the availability of nutrient substrate and the ease of modulating body composition.

In the general population body composition has long been used as a predictor for mortality (4). Several different approaches have been taken to identify individuals at risk for a poor outcome (5). These techniques may examine specific serological parameters or actual components of body composition thought to more precisely depict nutritional balance.

Historically, many reports have stressed the link between serum albumin levels and patient survival for both hemodialysis and peritoneal dialysis (6–11). However, some authors have questioned the usefulness of this marker (12–14). Based on these concerns, defining nutritional status through body composition measurements may offer a more meaningful assessment than standard serological parameters. Furthermore, in the setting of uremia the ability to successfully modulate body composition may denote the essence of what aptimal dialysis should signify. Conceptually, optimal dialysis represents the therapeutic return of an individual to nutritional balance, with an expected survival comparable to that of age, gender, and disease-matched nonuremic individuals. Because of the complexity of maintaining nutrient balance, the definition of adequate dialysis should be re-evaluated. Contemporary dialysis practice should extend beyond solely quantitating dialysis to include an understanding of nutrient balance, regulation of food intake, and the application of surveillance tools for identifying abnormalities in body composition. Only through expanding the end points of adequate dialysis can we move closer to optimal dialysis synonymous with long-term treatment survival.

Predicted and Measured Daily Creatinine Production in CAPD: Identifying Noncompliance

Objective

To evaluate the ratio of measured creatinine (Cr) production to predicted creatinine production as an index of noncompliance in patients on continuous ambulatory peritoneal dialysis (CAPD).

Design

A cross-sectional analysis.

Patients

One hundred and twenty-one patients on CAPD.

Measurements

We have calculated Cr production from measured Cr outputs in 24-hour collections of urine and dialysate. Predicted Cr productions were calculated from standard tables. Weekly KTN urea and weekly Cr clearances were determined from the same 24-hour urine and dialysate collections. Lean body mass (LBM) was calculated from the Cr production. Serum albumin concentration was measured.

Results

The ratio of measured/predicted Cr production correlated positively and significantly with weekly KTN urea, the protein equivalent of nitrogen appearance (PNA), weekly Cr clearance, and LBM. There was a decline in serum albumin concentration at ratios greater than 1.24, supporting the opinions of previous authors who have suggested that ratios greater than 1.24 are highly suggestive of noncompliance with the dialysis prescription. Defining noncompliance as a ratio greater than 1.24 implied that at least 5% of the female and 17% of the male patients were noncompliant.

Conclusions

Declining serum albumin concentrations at higher ratios of measured/predicted Cr production support the opinion that this is an index of noncompliance. However, not all noncompliant patients necessarily have a ratio greater than 1.24. Weekly KTN urea, weekly Ccr and LBM are all artifactually increased by “washout effects” if all exchanges are done only or mainly on the collection day.

Influence of Initial Nutritional Status on Continuous Ambulatory Peritoneal Dialysis Patient Survival

Objectives

To evaluate the influence of initial nutritional status on continuous ambulatory peritoneal dialysis (CAPD) patient survival and to identify factors determining initial nutritional status and patient mortality.

Design

Prospective single-center study.

Setting

Kidney Center, Soon Chun Hyang University Hospital.

Patients

A total of 91 consecutive CAPD patients, who underwent initial nutritional assessment at Soon Chun Hyang University Hospital, Seoul, Korea, between September 1994 and January 1999, was included in this study. All patients were assessed at a mean of 7 days after beginning CAPD (range 3 – 24 days). Forty-eight patients were male, 50 were diabetics, and their mean age was 53.9 years (range 22 – 76 years).

Methods

Nutritional status was assessed by subjective global assessment (SGA), biochemical and anthropometric measurements, fat-free edema-free (FFEF) body mass by creatinine kinetics, urea kinetic studies, and calculation of the normalized protein equivalent of total nitrogen appearance (nPNA).

Results

By SGA, 55% were classified as having normal nutrition while 45% had signs of malnutrition; 61% of female and 31% of male patients, and 54% of diabetics and 34% of nondiabetics were classified as malnourished. Initial FFEF body mass, blood urea nitrogen (BUN), serum albumin (sAlb), residual renal function (RRF), and weekly total creatinine clearance were significantly lower in the malnourished patients than in the patients with normal nutrition. On multiple regression analysis, only FFEF body mass was an independent determinant of SGA score. On 31 January 1999, 41 patients were still on CAPD, 15 patients had died, and 27 patients had been transferred to hemodialysis. Those who died during observation were older and had lower initial FFEF body mass, % lean body mass, BUN, sAlb, RRF, and SGA score. The 2-year patient survival rate was significantly lower in the malnourished than in normal patients (67.1% vs 91.7%, p = 0.02). On Cox proportional hazards analysis, initial age, malnutrition assessed by SGA, and FFEF body mass were identified as factors determining death.

Conclusion

Malnutrition was present in 45% of patients commencing CAPD when assessed by SGA. Initial FFEF body mass was a determinant of SGA score and predicted death. Malnutrition as assessed by SGA was also an independent predictor of death. Initial nutritional status, therefore, appears to exert a powerful influence on CAPD patient survival.

1996 Peritoneal Dialysis Core Indicators Study: Report on Nutritional Indicators

Objective

The 1996 Peritoneal Dialysis Core Indicators Study illustrates the conduct of peritoneal dialysis in the United States during 1996.

Design and Patient Population

The survey is a medical records audit of 1317 randomly selected adult U.S.A. Medicare patients using peritoneal dialysis during 1996.

Outcome Measures

Abstracted data included basic demographic characteristics, dialysis prescription, delivered dialysis dose, residual renal function, serum albumin, hematocrit, anemia management, and patient status.

Results

The survey included 785 patients using continuous ambulatory peritoneal dialysis (CAPD) and 423 using automated peritoneal dialysis (APD) primarily in the form of continuous cycling peritoneal dialysis (CCPD). Except for the prescription mechanics and a greater likelihood that African-Americans would use CAPD, the groups did not differ substantially from one another. Evaluation of patient weight (W), body mass index (BMI), residual renal function, average serum albumin, protein equivalent of nitrogen appearance (nPNA), and dialysis efficiency as weekly fractional urea nitrogen removal (wKt/V urea) and weekly creatinine clearance (wCrCI) revealed a picture of reasonable dialysis delivery and marginal protein nutrition. Additionally, there was little evidence that “dialysis efficiency,” over the range assessed, had a major influence on nutritional status. Despite a tendency toward obesity (body weight = 76.6 ± 20.0 kg and BMI = 27 ± 7), 47% of patients had an average serum albumin below “normal” (3.5 g/dL by bromcresol green) and 70% had a nPNA below 1.0 g/kg/day.

Conclusions

Peritoneal dialysis patients appear to have marginal protein reserves despite surfeit energy stores.

Effect of Dialysis Modality and Membrane Transport Characteristics on Dialysate Protein Losses of Patients on Peritoneal Dialysis

Objective

To determine if peritoneal dialysis modality has an impact on protein losses in dialysate.

Design

Retrospective, cross-sectional study.

Patients

190 patients who had selected peritoneal dialysis were classified into one of four transport categories (high, high-average, low-average, or low) based on standard peritoneal equilibration test results. Patients were then assigned to continuous ambulatory peritoneal dialysis (CAPD) or nightly intermittent peritoneal dialysis (NIPD) based on membrane transport characteristics and individual preferences.

Results

Patients with similar membrane transport characteristics had essentially no differences in dialysate protein and albumin losses whether treated with CAPD or NIPD.

Conclusions

Although high transporters may be better managed with short -dwell therapies such as nocturnal intermittent peritoneal dialysis or daily ambulatory peritoneal dialysis, consistent marked decreases in protein losses cannot be cited as a benefit of NIPD over CAPD.

A Novel Objective Nutritional Score for Children on Chronic Peritoneal Dialysis

Objectives

To establish a novel nutritional score based on a series of objective parameters capable of detecting protein-calorie malnutrition in children being treated with chronic peritoneal dialysis (CPD), to test the score in a healthy pediatric population, and to apply it to children on CPD to evaluate their nutritional status.

Study Population

264 healthy school children (mean age 8.69 ± 3.26 years, range 3.05 – 14.98 years) and 29 patients treated with CPD for 1.75 ± 1.02 years (mean age 10.54 ± 6.28 years, range 2.8 – 15.24 years).

Methods

Nutritional status was evaluated by means of three sets of measurements: anthropometric (A1 and A2) and bioimpedance analysis (BIA) measurements. Anthropometry included two sets of measures: set A1 consisted of height (H), weight (W), and body mass index (BMI); set A2 consisted of midarm muscle circumference (MAMC), arm muscle area (AMA), and arm fat area (AFA). The BIA measurements included reactance, phase angle, and distance. All parameters are expressed as standard deviation scores (SDS). Tanner's, Rolland–Cachera's, and Frisancho's data were used as references for H, W, BMI, MAMC, AMA, and AFA; personal data obtained from 551 healthy boys and girls were used for the BIA indices. The nine anthropometry and BIA parameters were given scores of 1 to 5: 5 = > 0 SDS, 4 = ≤ 0 and > –1 SDS, 3 = ≤ –1 and > –2 SDS, 2 = ≤ –2 and > –3 SDS, and 1 = ≤ –3 SDS. Average scores were established for each of A1, A2, and BIA, and then summed to obtain the anthropometry–BIA nutrition (ABN) score. To establish the cutoff value between normal nutritional status and malnutrition, the method was first applied to the 264 healthy children; distribution percentiles were calculated for each area score and the ABN score. The ABN score corresponding to the 3rd percentile was considered the limit of normality and then applied three times to the 29 children on CPD, for a total of 87 nutritional assessments.

Results

The score corresponding to the 3rd percentile in the population of healthy children was 10.33. Among the CPD-treated children, 41.4% of the ABN scores were higher than 10.33 (indicating a state of normal nutrition) and 58.6% were lower (indicating various degrees of malnutrition). Severe malnutrition was found in only 1.1% of the cases. The values of all nine A1, A2, and BIA parameters, as well as serum albumin levels, were significantly higher in patients with an ABN score > 10.33 than in those with a score < 10.33.

Conclusion

The ABN score is a simple and objective method of assessing, in clinical practice, the nutritional status of children on CPD.

Bioelectrical Impedance Analysis and Dual Energy X-Ray Absorptiometry to Monitor Nutritional Status

There exists an imperative to monitor changes in body composition in all dialysis patients on a regular basis to avoid overt malnutrition. In this regard, the absolute measurement of the fat-free mass assessment may not be as crucial as the serial measurement of fat-free mass with the same modality. A significant difference in measured fat and fat-free mass should be expected if different techniques are employed. Therefore, when attempting to monitor patients over time or to assess the effects of changes in therapeutic regimens, a single methodology should be employed. Our data validate the use of BIA in the stable PD patient, indicating that BIA can predict the DXA results. Considering the ease with which

BIA measurements can be obtained and the lack of dependency on operator interpretation, BIA is an ideal technique for use in the clinical setting. The applicability of this technique for use in monitoring longitudinal changes in body composition has, in fact, been well established (25,30,31). BIA appears to be an excellent method for routine fat-free mass measurement in dialysis patients. In as much as malnutrition continues to remain a significant problem in PD patients, measuring and monitoring body composition is strongly recommended.

Comparison of Measured and Predicted Creatinine Excretion is An Unreliable Index of Compliance in Pd Patients

Objective

To evaluate the use of the ratio of measured to predicted creatinine excretion as an index of compliance in peritoneal dialysis (PD) patients.

Design

A prospective analysis.

Setting

Academic teaching hospital dialysis unit.

Patients

Forty-three patients on PD.

Measurements

Creatinine excretion in daily dialysate and urine collections was measured on one occasion in 10 patients and on two occasions in 33 patients, and, after adding an estimate for extrarenal creatinine degradation, was divided by predicted creatinine excretion to give a creatinine excretion ratio, which has been proposed as an index of compliance with exchanges in PD patients. Values above 1.24 have been suggested to indicate non-compliance. Lean body mass was also estimated from creatinine excretion.

Results

The mean creatinine excretion ratio was 1.12, and 30% of patients had a value above 1.3. Only one patient admitted noncompliance. Studies on four consecutive days of guaranteed compliance in 7 patients with high ratios showed that creatinine excretion remained constant, suggesting that the patients were high creatinine producers rather than noncompliant. Creatinine excretion was stable when measured at intervals of days, but over months it tended to change markedly in many patients. Lean body mass estimations using creatinine excretion were low in most patients.

Conclusion

Comparison of measured and predicted creatinine excretion is not a reliable indicator of noncompliance because many compliant patients consistently excrete more creatinine than predicted. The standard formulas were not validated in dialysis patients and underestimate creatinine excretion significantly in many PD patients. Existing estimates in the literature of non-compliance, using this methodology, may not be accurate. Better methods of detecting this problem are required.

The Impact of Equations on Calculation of Lean Body Mass by Bioelectrical Impedance Analysis in RDT Patients

Several equations are available to derive lean body mass (LBM) from bioelectrical impedance analysis (BIA). The purpose of this study was to investigate in dialysis patients the impact of the equation used on the outcome of LBM assessment. To avoid dyshydration as a confounder, vena cava diameter measurement was used to assess normohydration in the 21 patients studied. Five equations were compared.

In a previously published study to assess total body water using antipyrine as a gold standard, Deurenberg's formula was advocated to be used in the estimation of LBM by BIA. Therefore, this formula was used as a basis for comparison with the other four equations.

One equation gave results comparable to those obtained by Deurenberg's formula. Despite high correlations and agreement according to Bland and Altman analysis, the other three equations showed a significant difference with Deurenberg-derived LBM. Thus, the equation used has a major impact on the outcome of LBM estimations. (Int J Artif Organs 2000; 23: 168–72)

Reproducibility of serial creatinine excretion measurements in peritoneal dialysis

AIM

To test whether muscle mass evaluated by creatinine excretion (EX_Cr) is maintained in patients with end-stage kidney disease (ESKD) treated by peritoneal dialysis (PD), we evaluated repeated measurements of EX_Cr in a PD population.

METHODS

One hundred and sixty-six PD patients (94 male, 72 female) receiving the same PD dose for the duration of the study (up to approximately 2.5 years) had repeated determinations of total (in urine plus spent dialysate) 24-h EX_Cr (EX_Cr T) to assess the adequacy of PD by creatinine clearance. All 166 patients had two EX_Cr T determinations, 84 of the 166 patients had three EX_Cr T determinations and 44 of the 166 patients had four EX_Cr T measurements. EX_Cr T values were compared using the paired t test in the patients who had two studies and by repeated measures ANOVA in those who were studied three or four times.

RESULTS

In patients who were studied twice, with the first and second EX_Cr T measurements performed at 9.2 ± 15.2 mo and 17.4 ± 15.8 mo after onset of PD, respectively, EX_Cr T did not differ between the first and second study. In patients studied three times and whose final assessment occurred 24.7 ± 16.3 mo after initiating PD, EX_Cr T did not differ between the first and second study, but was significantly lower in the third study compared to the first study. In patients who were studied four times and whose fourth measurement was taken 31.9 ± 16.8 mo after onset of PD, EX_Cr T did not differ between any of the studies. The average EX_Cr T value did not change significantly, with the exception of the third study in the patients studied thrice. However, repeated determinations of EX_Cr T in individuals showed substantial variability, with approximately 50% of the repeated determinations being higher or lower than the first determination by 15% or more.

CONCLUSION

The average value of EX_Cr T remains relatively constant for up to 2.5 years of follow-up in PD patients who adhere to the same PD schedule. However, repeated individual EX_Cr T values vary considerably in a large proportion of the patients. Further studies are needed to evaluate the clinical significance of varying EX_Cr T values and the stability of EX_Cr T beyond 2.5 years of PD follow-up.

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.

Validity of anthropometry- and impedance-based equations for the prediction of total body water as measured by deuterium dilution in Cameroonian haemodialysis patients

BACKGROUND & AIMS

There is no available information on the validity of anthropometry- and impedance-based equations for predicting total body water (TBW) in Cameroonian haemodialysis patients. This study aimed to validate and develop predictive equations of TBW for Cameroonian haemodialysis patients.

METHOD

TBW in 40 Cameroonian haemodialysis patients (28 men and 12 women) was measured by deuterium dilution and compared with the one predicted by 7 anthropometric and 9 BIA equations. Multiple linear regression analysis was used to develop an equation for predicting TBW as measured by deuterium, from anthropometric parameters.

RESULTS

Pure errors in predicting TBW showed unacceptable value for all equations tested. In all the cases, unacceptable discrepancies at individual level for clinical purposes were noted. The following equation was developed and showed a better agreement with the deuterium dilution method: TBW = 13.8994 + 0.0017 × Age +0.3190 × Weight +1.8532 × Sex.

CONCLUSION

Further development and cross-validation of anthropometric and BIA prediction equations specific to African heamodialysis patient are needed. Meanwhile, the equation developed in this study which provided a better agreement with the isotope dilution could be use for Cameroonian haemodialysis patients.

Ethnic differences in creatinine kinetics in a New Zealand end-stage kidney disease cohort

BACKGROUND

Recent data have suggested that glomerular filtration rate (GFR) is better predicted in New Zealand (NZ) Māori and Pacific People using the equations for Black people that predict higher GFR for any given serum creatinine. We hypothesized that this might be due to a higher rate of creatinine generation in NZ Māori and Pacific People.

AIM

To compare creatinine kinetics between different ethnic groups in a cohort of NZ peritoneal dialysis patients.

METHODS

In this retrospective single-centre observational study, creatinine kinetics in 181 patients were determined from timed serum samples, peritoneal dialysate and urine collections between 1 October 2004 and 31 July 2011. Ethnicity was classified as Asian, NZ European, NZ Māori and Pacific People.

RESULTS

A total of 799 samples from 181 patients were analysed: 194 in Asians, 127 in NZ Europeans, 268 in NZ Māori, 207 in Pacific People. Pacific People had the highest serum creatinine and lean body mass, and the highest creatinine generation rate at 1349 mg/day, compared with 1049 for Asians, 1186 for NZ Europeans and 1094 for NZ Māori (P = 0.0001). After adjustment for confounding factors, Pacific People had a greater creatinine generation by 140 mg/day compared with NZ Europeans (P = 0.047).

CONCLUSION

Pacific People on peritoneal dialysis in NZ have higher serum creatinine, lean body mass and creatinine generation than other ethnic groups. This is consistent with previous observations that equations for predicting GFR in Black people may have increased accuracy in some Australasian non-White non-Asian populations.

Novel equations to estimate lean body mass in maintenance hemodialysis patients

BACKGROUND

Lean body mass (LBM) is an important nutritional measure representing muscle mass and somatic protein in hemodialysis patients, for whom we developed and tested equations to estimate LBM.

STUDY DESIGN

A study of diagnostic test accuracy.

SETTING & PARTICIPANTS

The development cohort included 118 hemodialysis patients with LBM measured using dual-energy x-ray absorptiometry (DEXA) and near-infrared (NIR) interactance. The validation cohort included 612 additional hemodialysis patients with LBM measured using a portable NIR interactance technique during hemodialysis.

INDEX TESTS

3-month averaged serum concentrations of creatinine, albumin, and prealbumin; normalized protein nitrogen appearance; midarm muscle circumference (MAMC); handgrip strength; and subjective global assessment of nutrition.

REFERENCE TEST

LBM measured using DEXA in the development cohort and NIR interactance in validation cohorts.

RESULTS

In the development cohort, DEXA and NIR interactance correlated strongly (r = 0.94, P < 0.001). DEXA-measured LBM correlated with serum creatinine level, MAMC, and handgrip strength, but not with other nutritional markers. Three regression equations to estimate DEXA-measured LBM were developed based on each of these 3 surrogates and sex, height, weight, and age (and urea reduction ratio for the serum creatinine regression). In the validation cohort, the validity of the equations was tested against the NIR interactance-measured LBM. The equation estimates correlated well with NIR interactance-measured LBM (R² ≥ 0.88), although in higher LBM ranges, they tended to underestimate it. Median (95% confidence interval) differences and interquartile range for differences between equation estimates and NIR interactance-measured LBM were 3.4 (-3.2 to 12.0) and 3.0 (1.1-5.1) kg for serum creatinine and 4.0 (-2.6 to 13.6) and 3.7 (1.3-6.0) kg for MAMC, respectively.

LIMITATIONS

DEXA measurements were obtained on a nondialysis day, whereas NIR interactance was performed during hemodialysis treatment, with the likelihood of confounding by volume status variations.

CONCLUSIONS

Compared with reference measures of LBM, equations using serum creatinine level, MAMC, or handgrip strength and demographic variables can estimate LBM accurately in long-term hemodialysis patients.

Sources of variation in estimates of lean body mass by creatinine kinetics and by methods based on body water or body mass index in patients on continuous peritoneal dialysis

OBJECTIVE

We identified factors that account for differences between lean body mass computed from creatinine kinetics (LBM(cr)) and from either body water (LBM(V)) or body mass index (LBM(BMI)) in patients on continuous peritoneal dialysis (CPD).

DESIGN

We compared the LBM(cr) and LBM(V) or LBM(BMI) in hypothetical subjects and actual CPD patients.

PATIENTS

We studied 439 CPD patients in Albuquerque, Pittsburgh, and Toronto, with 925 clearance studies.

INTERVENTION

Creatinine production was estimated using formulas derived in CPD patients. Body water (V) was estimated from anthropometric formulas. We calculated LBM(BMI) from a formula that estimates body composition based on body mass index. In hypothetical subjects, LBM values were calculated by varying the determinants of body composition (gender, diabetic status, age, weight, and height) one at a time, while the other determinants were kept constant. In actual CPD patients, multiple linear regression and logistic regression were used to identify factors associated with differences in the estimates of LBM (LBM(cr)<LBM(V), or LBM(cr)<LBM(BMI)).

MAIN OUTCOME MEASURE

We sought predictors of the differences LBM(V) - LBM(cr) and LBM(BMI) - LBM(cr).

RESULTS

Both LBM(V) (regardless of formula used to estimate V) and LBM(BMI) exceeded LBM(cr) in hypothetical subjects with average body compositions. The sources of differences between LBM estimates in this group involved differences in the coefficients assigned to gender, age, height, weight, presence or absence of diabetes, and serum creatinine concentration. In CPD patients, mean LBM(V) or LBM(BMI) exceeded mean LBM(cr) by 6.2 to 6.9 kg. For example, the LBM(V) obtained from one anthropometric formula was 50.4+/-10.4 kg and the LBM(cr) was 44.1+/-13.6 kg (P < .001), whereas among the 925 clearance studies, only 216 (23.3%) had LBM(cr)>LBM(V). The differences in determinants of body composition between groups with high versus low LBM(cr) were similar in hypothetical and actual CPD patients. Multivariate analysis in actual CPD patients identified serum creatinine, height, age, gender, weight, and body mass index as predictors of the differences LBM(V)-LBM(cr) and LBM(BMI)-LBM(cr).

CONCLUSIONS

Overhydration is not the sole factor accounting for the differences between LBM(cr) and either LBM(V) or LBM(BMI) in CPD patients. These differences also stem from the coefficients assigned to major determinants of body composition by the formulas estimating LBM.

Correlations of lean body mass with nutritional indicators and mortality in patients on peritoneal dialysis

Detection of malnutrition in dialysis patients is important since this is a predictor of morbidity and mortality. Lean body mass (LBM) reflects the somatic protein store and this was measured by creatinine kinetics, anthropometry, and biometric impedance in 210 incident Chinese patients on continuous ambulatory peritoneal dialysis. The study was started in the third month of dialysis and the patients were followed for an average of 29 months. We devised three models of survival by combining the three different LBM measures with several nutritional markers and recognized outcome predictors. Follow-up was censored for transplantation or transfer to hemodialysis with an end point of death while on peritoneal dialysis. Statistical correlations were observed among the LBM values determined by all the three methods and these correlated significantly with both left and right hand grip strength but not with nutritional markers. LBM by creatinine kinetics, mean arterial pressure, and the calcium-phosphorus product were significant, independent predictors of death in one survival model. Anthropometry and bioelectric impedance were not significant predictors of death in the other two models. Our study suggests that LBM measured by creatinine kinetics, anthropometry, and bioelectrical impedance correlates well with the somatic protein store but not with the general nutritional status.

Early changes in bioelectrical estimates of body composition in chronic kidney disease

The aim of this study was to detect the potential occurrence of early abnormalities of body composition in patients with chronic kidney disease (CKD) at first referral to an outpatient nephrology clinic. Eighty-four patients with CKD (49 men and 35 women) were compared with 604 healthy control subjects (298 men and 306 women). Anthropometry and bioelectrical impedance analysis (BIA) were performed in all participants, whereas renal function, laboratory tests for nutritional status, and nutrient intake were assessed in the CKD group only. Creatinine clearance was 27.8 +/- 13.8 and 27.4 +/- 13.0 ml/min per 1.73 m(2) in male and female patients with CKD, respectively. No patient showed peripheral edema; frank malnutrition, defined by presence of serum albumin <3.5 g/dl plus body mass index <20 kg/m(2); or protein intake <0.6 g/kg per d. At the BIA, patients with CKD showed lower resistance (R) and abnormal mean impedance vectors for the bivariate normal distribution of R/height and reactance/height. Phase angle also was reduced (-22%), especially in patients with diabetes. When BIA-derived data were considered, total body water was slightly higher (+4.3% in men; +3.5% in women) and body cell mass was lower (-6.7% in men; -7.7% in women) in patients with CKD. No difference in either BIA parameters or nutritional indexes was observed among various CKD stages. Despite the absence of overt malnutrition, patients with CKD exhibit altered BIA variables from the early phases of renal disease. These alterations are related to the renal dysfunction, are more marked in the presence of diabetes, and mainly indicate the presence of overhydration in the absence of edema. Therefore, BIA represents an attractive clinical tool to detect impairment of body composition from the early stages of CKD.

Nutrition and Metabolism in Kidney Disease

Nutritional and metabolic derangements are highly prevalent in patients with chronic kidney disease (CKD) and patients on renal replacement therapy. These derangements, which can be termed uremic malnutrition, significantly affect the high morbidity and mortality rates observed in this patient population. Uremic malnutrition clearly is related to multiple factors encountered during the predialysis stage and during chronic dialysis therapy. Several preliminary studies suggested that interventions to improve the nutritional status and metabolic status of uremic patients actually may improve the expected outcome in these patients, although their long-term efficacy is not well established. It therefore is important to emphasize that uremic malnutrition is a major comorbid condition in CKD and renal replacement therapy patients, and that all efforts should be made to try to understand better and treat these conditions effectively to improve not only mortality but also the quality of life of chronically uremic patients. In this article we review the current state of knowledge in the field of nutrition and metabolism in all stages of CKD and renal replacement therapy, including kidney transplant. We also address questions that face investigators in this field and suggest where future research might be headed.

Assessment of body composition by dual energy X-ray absorptiometry, skinfold thickness and creatinine kinetics in chronic kidney disease patients

BACKGROUND

Finding a method that can be routinely used to assess body composition with minimum error is still a challenge for those who work with chronic kidney disease (CKD) patients. This study aimed to compare the value of two surrogate techniques, skinfold thickness (SKF) and creatinine kinetics (CK) with dual energy X-ray absorptiometry (DEXA) as the reference method for measuring body fat and fat-free mass in non-dialysed CKD patients.

METHODS

The body fat and fat-free mass of 50 non-dialysed CKD patients (38 male, 12 female) were measured by DEXA and compared with measurements obtained by SKF and CK.

RESULTS

The mean values of body fat and fat-free mass obtained by SKF and CK differed significantly from measurements made by DEXA. The intra-class correlation coefficient (r) for body fat between SKF and DEXA (r = 0.74) and between CK and DEXA (r = 0.47) indicated a moderate degree of reproducibility. A Bland and Altman plot analysis showed a better agreement between SKF and DEXA [5.8 +/- 3.9% (-2.0 to 13.6)] than between CK and DEXA [8.8 +/- 8.8% (-8.8 to 26.4)]. Regarding fat-free mass, the intra-class correlation coefficient (r) between SKF and DEXA (r = 0.85) indicated a good degree of reproducibility, while that between SKF and CK (r = 0.57) indicated a moderate degree of reproducibility. The Bland and Altman plot analysis for fat-free mass showed that DEXA agreed better with SKF [-3.1 +/- 3.4 kg (-9.9 to 3.7)] than with CK [-5.5 +/- 6.4 kg (-18.2 to 7.3)].

CONCLUSION

Skinfold thickness seems to be the method of choice for evaluating body fat. The limitations inherent to DEXA in evaluating fat-free mass makes it difficult to designate an alternate method of choice for assessing this body compartment.

Métodos de avaliação da composição corporal em pacientes submetidos à hemodiálise

A avaliação da composição corporal de pacientes com insuficiência renal crônica em hemodiálise é de suma importância para propiciar uma conduta clínica e nutricional adequada, de forma a contribuir para a redução da elevada taxa de morbidade e mortalidade observada nesta população. No entanto, fatores relacionados à doença tais como anormalidades no estado de hidratação e presença de osteodistrofia renal, podem afetar a validade das técnicas de avaliação da composição corporal de pacientes com insuficiência renal crônica. Apesar dos inúmeros métodos de análise de composição corporal existentes, a maioria apresenta limitações para utilização na prática clínica da população em hemodiálise. Este artigo tem como objetivo revisar os métodos de composição corporal de fácil aplicabilidade na rotina clínica dos pacientes em hemodiálise tais como a somatória de pregas cutâneas, a bioimpedância elétrica e a interactância do infravermelho próximo.

Comparison of three methods for the determination of body fat in patients on long-term hemodialysis therapy

OBJECTIVE

To compare three simple methods of body composition analysis for the assessment of body fat in patients on long-term hemodialysis therapy.

DESIGN

Cross-sectional study using the skinfold thickness, bioelectrical impedance analysis, and near-infrared interactance techniques after a hemodialysis session.

SUBJECTS/SETTING

Ninety clinically stable patients (57 male/33 female) undergoing hemodialysis at the Dialysis Unit of the Federal University of São Paulo.

STATISTICAL ANALYSIS

Analysis of variance, intraclass correlation coefficient, and Bland-Altman plot analysis were used for the comparative analysis between the methods.

RESULTS

Body fat measurements obtained by skinfold thickness (13.5+/-6.2 kg) and bioelectrical impedance analysis (13.7+/-6.7 kg) were similar, whereas those measured by near-infrared interactance (11.3+/-5.1 kg) were significantly lower in comparison with skinfold thickness and bioelectrical impedance analysis (P<.001). The strongest intraclass correlation coefficient was found between bioelectrical impedance analysis and skinfold thickness (r=0.87), and near-infrared interactance vs skinfold thickness and bioelectrical impedance analysis methods yielded r=0.78 and r=0.76, respectively. Near-infrared interactance showed a progressive underestimation of body fat values in comparison with the bioelectrical impedance analysis technique in patients with higher amount of adiposity.

CONCLUSION

In our study, we cannot consider that one method of body composition analysis is more accurate than the other because we did not apply a gold standard method. However, the most simple, long-established, and inexpensive method of skinfold thickness seems to be still very useful to the dietitians' routine for assessing body fat in patients on long-term hemodialysis therapy.

Near infra-red interactance for longitudinal assessment of nutrition in dialysis patients

OBJECTIVE

Serial nutritional assessment of dialysis patients is important because of the high incidence and prevalence of malnutrition in these patients. Near-infrared interactance (NIR) technology may provide a practical and reliable method to evaluate body fat and its changes over time in dialysis patients.

DESIGN

Longitudinal study consisting of 2 cross-sectional measurements, 2 months apart.

SETTING

Outpatient dialysis unit affiliated to a tertiary care community medical center.

PATIENTS

Seventy-one dialysis patients (35 men, 36 women), 57 +/- 15 years old, who have been on dialysis between 5 months and 11 years (43 +/- 30 months). Twelve additional patients with similar features were studied during the second round.

INTERVENTION

None.

MAIN OUTCOME MEASURES

NIR was used to estimate the body fat percentage. Other simultaneous measurements included subjective global assessment, anthropometric indices including midarm circumference, triceps and biceps skinfold thickness, and body mass index, and some laboratory values including albumin, transferrin, and cholesterol. NIR measurement was performed by placing a Futrex sensor on the nonaccess upper arm for several seconds, after logging the required individual data (sex, weight, height, and body frame), along with uniform physical activity levels for all patients, into a mini-computer.

RESULTS

Seventy-one dialysis patients underwent nutritional and laboratory measurements. A second measurement round was performed 8 to 9 weeks after the first one and included 12 additional patients. Within each cross-sectional round, Pearson correlation coefficients (r) between the NIR score and nutritionally relevant variables were significant for anthropometric values (0.56 to 0.82) as well as low cholesterol and creatinine (0.22 to 0.30). The two serial NIR measurements on the same patients were highly consistent over the 2-month study interval (r = 0.96), whereas anthropometric values showed greater variability. The within-person coefficient of variation for NIR was low, indicating high consistency between 2 measurements. Moreover, the timing of the NIR measurement (predialysis v postdialysis) did not have any impact on consistency of the NIR results. The longitudinal changes of NIR had significant correlations with anthropometric and laboratory changes over time.

CONCLUSION

The NIR, which can be performed within seconds, may serve as a reliable and practical tool for objective measurements of nutritional status in hemodialysis patients. The NIR not only seems to have a high degree of reproducibility but may also be an optimal tool to detect longitudinal changes in body fat over time. The NIR measurement is independent of the fluid status in dialysis patients. More comparative and longitudinal studies are needed to confirm the validity of NIR measurements in longitudinal evaluation of dialysis patients.

1997 Peritoneal Dialysis-Core Indicators Study: Dialysis Adequacy and Nutritional Indicators Report

The 1997 Peritoneal Dialysis-Core Indicators Study: Dialysis Adequacy and Nutritional Indicators Report documents the current status of peritoneal dialysis within the United States. A national random sample of adult peritoneal dialysis (PD) patients participating in the United States End Stage Renal Disease (ESRD) program was surveyed. PD subjects were large, with a mean body weight of 76 +/- 18.9 kg (mean +/- 1 SD) and a body mass index (BMI) of 27 +/- 6.4. The dialysis prescriptions documented achieved a mean weekly Kt/Vurea (wKt/V) and weekly creatinine clearance (wCrCl) of 2. 45 +/- 2.29 and 65.5 +/- 35.2 L/wk/1.73m2, respectively. The serum albumin of these patients was 3.5 +/- 0.48 g/dL, their normalized protein equivalent of nitrogen appearance (nPNA) 1.0 +/- 0.63 g/kg/d, and their normalized creatinine appearance rate (nCAR) 14 +/- 6.0 mg/kg/d. Serum albumin correlated meagerly but in a positive fashion with BMI, nPNA, and nCAR, and negatively with wCrCl. Among adult US PD patients, serum albumin values appear to correlate poorly with alternative measures of nutritional status and are inversely related to the intensity of renal replacement therapy. The presumptive dietary protein intake (nPNA) and creatinine appearance rate (nCAR) derived for PD patients do correlate in a positive fashion with dialysis delivery, at least up to a wCrCl of 60 to 80 L/wk/1.73 m2 and wKt/V = 2.1, but their values suggest that 30% to 50% of PD patients have marginal nutritional status.

Bioelectrical impedance plethysmographic analysis of body composition in critically injured and healthy subjects

BACKGROUND

Determination of body composition during critical illness is complex because of various patient-related and technical factors. Bioelectrical impedance is a promising technique for the analysis of body composition; however, its clinical utility in critically injured patients is unknown.

OBJECTIVE

The purpose of this study was to compare bioelectrical impedance with metabolic activity in healthy and critically injured patients. If bioelectrical impedance accurately determines body composition during critical illness, the slope between body-composition variables and oxygen consumption would be the same in critically injured and healthy subjects.

DESIGN

There is a strong linear relation between body composition and metabolic activity. In the present study, body composition (fat-free mass and body cell mass) was determined by using bioelectrical impedance and resting metabolic activity (metabolic rate and oxygen consumption) by using gas exchange analysis in a group of healthy and critically injured subjects. The relation between these variables was compared by using linear regression to a similar relation established by hydrostatic weighing in a large historical control group.

RESULTS

The slope of the line relating fat-free mass to resting metabolic rate was the same in the healthy and critically ill groups (P = 0.62) and each was similar to the slope of the line for the control group. However, in 37% of the critically injured group, overhydration contributed to an increase in fat-free mass, disturbing the relation with resting metabolic rate. The slope of the line relating body cell mass to oxygen consumption in our healthy and critically ill groups was almost identical.

CONCLUSION

These results support the use of bioelectrical impedance to determine body cell mass in healthy and critically ill subjects.

Quantification of creatinine kinetic parameters in patients with acute renal failure

BACKGROUND

Urea kinetic modeling (UKM) and creatinine (Cr) kinetic modeling (CKM) are used in the nutritional evaluation of end-stage renal disease (ESRD) patients. Both the UKM-derived normalized protein catabolic rate (nPCR) and the CKM-derived estimate of lean body mass (LBM) may also provide important information in critically ill acute renal failure (ARF) patients. Estimation of LBM may be particularly useful as previous data demonstrate that malnutrition adversely influences outcome in ARF patients.

METHODS

Eleven critically ill ARF patients (age 52 +/- 21 years; mean +/- SD) treated with continuous venovenous hemofiltration (CVVH) were the study group. They were analyzed at steady state with a single-pool variable-volume model that determined the creatinine generation rate (GCr) by a methodology that we have previously described.

RESULTS

The CVVH ultrafiltrate production rate was 913 +/- 49 ml/hr, yielding a blood Cr clearance of 15.2 +/- 0.9 ml/min and a steady state serum Cr of 3.4 +/- 1.7 mg/dl. Daily creatinine generation normalized to body wt (creatinine index: CI) was 6.3 +/- 0.8 and 10.6 +/- 3.0 mg/kg/day for females (N = 4) and males (N = 7), respectively (P < 0.05). Estimated mean LBM was 30.0 +/- 2.0 and 41.2 +/- 7.0 kg in females and males, respectively (P < 0.05), while the same parameter normalized to body wt was 0.50 +/- 0.05 and 0.52 +/- 0.10, respectively. These values are substantially lower than those previously reported for both normal and ESRD patients. Regression analysis demonstrated both GCr (r2 = 0.96; P < 0.001) and LBM (r2 = 0.96; P < 0.001) were significantly correlated with steady state serum Cr in a linear manner. However, no significant correlation (r2 = 0.06; P = 0.24) between nPCR and CI was observed.

CONCLUSIONS

These data suggest critically ill ARF patients have severe somatic protein depletion. This malnourished state is likely due to deficits established prior to the development of ARF, such as those secondary to underlying chronic illnesses or prolonged hospitalization, and deficits related to acute hypercatabolism. Quantitative assessment of malnutrition in ARF patients with this CKM-based methodology may permit a better understanding of predisposing factors and, consequently, facilitate the development of interventions designed to prevent malnutrition in these patients.

Protein catabolic rate over lean body mass ratio: a more rational approach to normalize the protein catabolic rate in dialysis patients

Protein catabolic rate (PCR), equivalent to dietary protein intake in "stable" dialysis patients, is widely accepted as a marker of their protein nutritional status. PCR is usually established from urea generation rate using urea kinetic modeling (UKM), but the normalizing factor is still a matter of controversy. By convention, PCR is expressed in grams of protein degraded daily divided by the dry body weight (BW) (nPCRBW). To be valid, this implies that dry BW is close to ideal BW and that body composition is preserved with a lean body mass (LBM) over BW ratio near 0.73. Such conditions being infrequently found in dialysis patients, it has been proposed to normalize PCR to ideal BW or to total body water, but these correction factors are not really appropriate. A more rational approach would be to express PCR as the ratio of protein degraded to the kilograms of LBM (nPCRLBM), thus offering the main advantage of directly coupling PCR to changes in protein or nitrogen reserve. In this study, we developed a combined kinetic model of urea and creatinine applied to the midweek dialysis cycle in 66 end-stage renal disease (ESRD) patients. UKM provided Kt/V and PCR, whereas creatinine kinetic modeling (CKM) was used to calculate LBM. Thirty-four patients with a preserved LBM (LBM/dry BW ratio equal to or greater than 0.70; mean ratio, 0.81 +/- 0.11) and with a dry/ideal BW ratio of 1.01 +/- 0.16 had a mean PCR of 1.14 +/- 0.30 g/kg/24 h when normalized to BW (nPCRBW) and of 1.40 +/- 0.30 g/kg/24 h when normalized to LBM (nPCRLBM). In the 32 patients with a reduced LBM (LBM/dry BW ratio, below 0.70; mean ratio, 0.60 +/- 0.09) and dry/ideal BW ratio of 1.11 +/- 0.23, the mean nPCRBW was 0.99 +/- 0.31 g/kg/24 h, whereas nPCRLBM was 1.62 +/- 0.32 g/kg/24 h. For both subgroups, Kt/V was similar, with mean values of 1.76 +/- 0.34 and 1.69 +/- 0.27. Normalizing PCR to LBM offers a double benefit: it compensates for the error induced by abnormal body composition (eg, obese patients) and permits PCR to be adjusted for the decrease in LBM that occurs with age. We propose nPCRLBM as a more rational index to express PCR in dialysis patients.

Creatinine generation rate and lean body mass: a critical analysis in peritoneal dialysis patients

Calculation of creatinine generation rate (CGR) has been reintroduced as a method to estimate lean body mass (LBM) in dialysis patients. It has also been suggested that it be used to identify noncompliance with dialysis prescription. In order to evaluate this method, LBM calculated from CGR (LBMCGR) was compared to 48 simultaneous estimations of LBM from measurements of total body potassium (TBK) in 35 patients on peritoneal dialysis (PD). TBK (mmol) was measured in a whole body counter and LBM (kg) was calculated as TBK/68.1 (Forbes). CGR was calculated with and without inclusion of "metabolic degradation" of creatinine. LBMCGR was further estimated using two different equations based on results in healthy subjects, one from a group on an ad libitum diet, the other from a group on a meat-free diet. The intercept of the two equations differs by 13 kg. CGR systematically underestimated LBM when compared to TBK, but to a lesser degree when using the equation based on a meat-free diet. Repeated determinations of CGR in 11 stable patients revealed an unacceptably high coefficient of variation (CV%) for LBM, 14.2%, while body wt CV was 1.4%. We conclude that CGR is not a valid method to monitor LBM in PD patients. CGR is highly variable and in part dependent on meat intake, as is the relation between CGR and LBM. For the same reasons, it seems unwise to draw conclusions of noncompliance of PD-patients from determinations of CGR.

Nutrition in end-stage renal disease

In summary, it is evident that malnutrition is highly prevalent in ESRD patients. This is clearly related to multiple factors encountered during the pre-dialysis stage, as well as during maintenance dialysis therapy. A body of evidence highlights the existence of relationship between malnutrition and outcome in this patient population. Several preliminary studies suggest that interventions to improve the poor nutritional status of the ESRD patients may actually improve the expected outcome in these patients, although their long-term efficacy is not well established. It is therefore important to emphasize that malnutrition is a major co-morbid condition in the ESRD population and that the nutritional status and the treatment parameters of these patients should be altered to improve not only the mortality outcome of ESRD patients but also their quality of life.

Comparison of body composition measured by total body potassium and infrared interactance

OBJECTIVE

The purpose of this study was to find how closely a near infrared instrument (IRI), Futrex 5000, would compare to whole body counting (WBC) of potassium-40 (40K) in assessing body composition.

DESIGN

We measured lean body mass (LBM) and percent total body fat (PCF) in 177 males and 27 females by total body potassium (TBK) and by infrared interactance (IRI). TBK was assessed by 2 pi whole body counter (WBC) and IRI by Futrex (F) instrument. These subjects were measured for TBK and for IRI within 1 week of each other.

RESULT

A large mean difference (p < or = 0.001) was found between the results using the two instruments: IRI data for LBM were higher and PCF lower compared to TBK.

CONCLUSION

As shown by repeated TBK measurements over a 22-year period in these same volunteers, this technique is reliable. The IRI assessments did not come to a close fit with TBK.

The importance of monitoring dialysis adequacy in chronic peritoneal dialysis

The case of a patient who was noted to be malnourished but improved after his dialysis dose was increased is presented. This case and the discussion that follows emphasize the importance of proactively monitoring peritoneal dialysis adequacy and nutritional intake, supporting the notion that the dose of peritoneal dialysis is a major determinant of appetite and, consequently, of nutritional status. In the clinical setting, this influence is best indicated by changes in the serum albumin level and ultimately in long-term patient survival. The case discussion reviews the major principles and supporting literature, describing how we target peritoneal dialysis delivery and optimize nutritional status in an effort to reduce morbidity and mortality.