Total body water measurement in renal insufficiency

Total body water was measured in 15 children with renal insufficiency (glomerular filtration rate <25 ml/min per 1.73 m²) using deuterium oxide dilution. Total body water was also measured using bioelectrical impedance and skinfold anthropometry in the same 15 children. There was a linear correlation (r=0.98,P<0.01) between total body water measured by deuterium and height²/impedance. The 95% confidence limits for estimates of total body water were –1.5 to 0.9 for impedance and 0.65–3.16 1 for skinfold anthropometry when compared with deuterium dilution. Bioelectrical impedance estimation of total body water is better than the current existing non-invasive method of skinfold anthropometry.     

Noninvasive estimation of total body water in critically ill children after cardiac operations. Validation of a bioelectric impedance method.

The understanding of fluid fluxes in pediatric cardiac critical care is crucial to effective management. Knowledge of variations in total body water in this situation would aid this understanding, but most available methods are unsuitable for routine use. Recently, estimation of total body water by a tetrapolar bioelectric impedance has been validated in older children and adolescents. We undertook a study to validate the method in the taxing conditions of pediatric cardiac critical care. A prospective comparative study was done in 16 children whose ages ranged from 6 days to 10 years (mean 23 months) after a variety of cardiac operations. Total body water was estimated by a standard isotope dilution method (deuterium oxide) and by bioelectric impedance by means of a Holtain body composition analyzer. Individual estimations of total body water were made on two successive days on each patient at varying intervals after a cardiac operation, bioelectric impedance being measured hourly during 4 hourly urine collections for the deuterium oxide method. Thirty-two simultaneous values of total body water (by isotope and by impedance) were collected. Population-specific regression relationship was established by plotting total body water (isotope) against height2/bioelectric impedance. From this data plot r = 0.911, giving this equation: total body water = 0.158 +/- 0.662 x (height2/bioelectric impedance). Levels of agreement of -1.771 to +1.725 were observed, with a standard error of measurement of 16% across the range. The data suggest that bioelectric impedance is a satisfactory and reliable method of estimating total body water in children requiring cardiac critical care. The standard error of 16% suggests that the method may be more useful for measuring trends than absolute values, but the technique should be a valuable noninvasive tool both for continuous monitoring of total body water and in longitudinal research studies of rapid fluid flux and in the assessment of capillary leak.     

Assessment of nutritional status in children with cystic fibrosis: conventional anthropometry and bioelectrical impedance analysis. A cross-sectional study in Dutch patients

BACKGROUND: Assessment of nutritional status in children with cystic fibrosis (CF) is clinically relevant. Methods to measure nutritional status should be reliable and non-invasive, and reference values should be available. AIM: To compare weight and height measurements and measurements of specific body compartments in children with CF. METHODS: In a cross-sectional survey of 58 children with CF (28 females), we compared height and weight (expressed as: weight-for-height, body mass index (BMI), height-for-age and weight-for-age) with fat mass (skinfold sum (SFS)), muscle mass (upper arm circumference (UAC)) and bioelectrical impedance analysis (BIA). Results were expressed as Z-scores, using Dutch reference values. RESULTS: BMI and weight-for-height were within the normal range (mean Z-score (range): -0.13 (-1.5, 2.7) and -0.02 (-1.7, 2.8)). Weight and height corrected for age were below normal (mean Z-score (range): -0.79 (-2.4, -0.05) and -1.2 (-2.8, 1.4) (P<0.01)). Lean body mass by skinfold sum (LBM(sfs)), UAC and BIA were also significantly below reference values (mean Z-score (range): -0.9 (-2.2, 1.8), -0.95 (-2.4, 1.8) and -1.1 (-3.6, 1.0) (P<0.01)). Lean body mass (LBM) by BIA correlated with LBM(sfs). BIA systematically underestimated LBM in both CF patients and in control subjects. CONCLUSION: Nutritional status of children with CF must be evaluated, using age-corrected weight and height expressed in Z-score. LBM estimated by SFS, UAC and by BIA appear to be useful, although longitudinal studies in CF children should be performed to evaluate their clinical significance in detecting changes in nutritional status.     

Bioelectrical impedance can be used to predict muscle mass and hence improve estimation of glomerular filtration rate in non-diabetic patients with chronic kidney disease.

BACKGROUND: In this article (the second of two companion studies), we report whether bioelectrical impedance analysis (BIA) can be used to predict muscle mass in patients with chronic kidney disease (CKD), and whether using this predicted muscle mass can improve the estimation of glomerular filtration rate (GFR). METHODS: Seventy five non-diabetic patients with CKD (mean age +/- SD, 65.1 +/- 12.0 years; mean GFR 45.9 +/- 28.8 ml/min/1.73 m2) underwent body composition analysis by dual energy X-ray absorptiometry to provide a criterion marker of skeletal muscle mass (appendicular lean mass, ALM). Validity of a published BIA equation to predict ALM was evaluated and a new BIA equation was generated (ALM(BIA)) and cross-validated by the leave-one-out procedure. Renal inulin clearance provided a criterion measure of GFR (GFR(inu)). The performance of the equation including ALM(BIA) to estimate GFR(inu) was compared with demographic variables as used in the modification of diet in renal disease (MDRD) equation, by determining bias, limits of agreement and accuracy. RESULTS: The previously published BIA equation to predict ALM was not valid in these patients with CKD. In contrast, our new ALM(BIA) equation cross-validated successfully. Compared with the MDRD demographic variables, using ALM(BIA) to predict GFR(inu) improved estimation performance, showing reduced bias (4.3 vs 15.6 ml/min) and improved limits of agreement (41.1 vs 59.2 ml/min) and accuracy (69.7 vs 39.4% of patients' predicted GFR did not deviate by more than 30% of GFR(inu)). CONCLUSIONS: ALM(BIA) provides a clinically obtainable and valid method to predict muscle mass in patients with CKD, and using ALM(BIA) improves the estimation of GFR(inu). Researchers developing future GFR estimation equations should consider including ALM(BIA).     

Evaluation of measurement of fat mass reduction after liposuction in obese patients

Abstract

Body composition measurements are used to evaluate surgical treatment, such as bariatric surgery in overweight patients. Nowadays, there are many different methods to measure body composition available. However, none of them has been validated for use in patients after operation. The aim of the present study was to compare the amount of surgically removed fat with two different methods, bioelectrical impedance analysis (BIA) and total body potassium (TBK). Amount of removed fat during liposuction was measured 1, 2, 3, 4, 14 days, and 1 year postoperatively in 27 obese patients after liposuction. The results were compared with actual removed fat during the operation. The median fat mass removed was 4020 grams (range 1954–9655). Postoperatively there was a varying reduction in fat mass, as measured with BIA and with TBK. There was a clear difference between the range of amounts removed measured with BIA and the range of amount removed measured with TBK. This study indicates that BIA, but not TBK, is an appropriate method to measure fat mass in obese subjects in a surgical setting. BIA seems to underestimate the amount of fat removed, whereas TBK seems to overestimate it.     

Body composition following hemodialysis: Studies using dual-energy X-ray absorptiometry and bioelectrical impedance analysis

The detection, prevention and treatment of disease is greatly facilitated by the availability of accurate and non-invasive techniques for measuring the amount and regional distribution of fat mass and fat-free mass. As differing degrees of hydration may influence these measurements, we used dual-energy X-ray absorptiometry (DXA) and bioelectrical impedance analysis (BIA) to detect changes in hydration following hemodialysis, and to determine whether fat mass, fat-free mass and bone density measurements were affected by these fluid changes. Ten subjects (7 men, 3 women) mean age 46.2 years (range 25–68 years), with renal failure had bone density, fat-free mass and fat mass measured by DXA, and total body water and fat-free mass measured by BIA, before and after hemodialysis. Thirty-two subjects had fat-free mass measured by DXA and BIA in an attempt to derive new equations (using fat-free mass measured by DXA as the reference standard) to improve the predictive value of BIA. The new equations were then used to derive the changes in fat-free mass following hemodialysis measured using BIA. In absolute terms, total tissue measured by DXA (r=0.99,p=0.01) and total body water measured by BIA (r=0.91,p=0.01) correlated with gravimetric weight. Following hemodialysis, fat mass and bone density measured by DXA were unaffacted by the fluid changes. The change in gravimetric weight was 1.8±0.3 kg,p=0.01 (mean±SEM). This change was measured as 1.9±0.3 kg by DXA, –0.9±1.0 kg by BIA using the published equation for fat-free mass, and 3.2±0.4 kg using the new equation for fat-free mass. The change in fat-free mass measured by DXA (r=0.75,p=0.01), and the change in total body water measured by BIA (r=0.70,p=0.02), correlated with the change in gravimetric weight. The change in fat-free mass measured by BIA did not correlate with the change in gravimetric weight. With the new equation, the change in fat-free mass measured by BIA correlated with the change in gravimetric weight (r=0.74,p=0.02). We conclude that absolute values, and changes in fluid in the range observed in this study, can be detected reliably by DXA. They are reflected in the fat-free mass measurement and do not confound measurements of fat mass and bone density. Although absolute values are reliably measured by BIA, the technique may have limited usefulness in detecting fluid changes. DXA thus provides a practical, non-invasive, precise and accurate method of measuring body composition which can be used as a gold standard for validating other techniques.     

Validity of Bioelectrical Impedance Analysis for Measuring Changes in Body Water and Percent Fat After Bariatric Surgery

Background

Few studies have validated bioelectrical impedance analysis (BIA) following bariatric surgery.

Methods

We examined agreement of BIA (Tanita 310) measures of total body water (TBW) and percent body fat (%fat) before (T0) and 12 months (T12) after bariatric surgery, and change between T0 and T12 with reference measures: deuterium oxide dilution for TBW and three-compartment model (3C) for %fat in a subset of participants (n?=?50) of the Longitudinal Assessment of Bariatric Surgery-2.

Results

T0 to T12 median (IQR) change in deuterium TBW and 3C %fat was ?6.4 L (6.4 L) and ?14.8 % (13.4 %), respectively. There were no statistically significant differences between deuterium and BIA determined TBW [median (IQR) difference: T0 ?0.1 L (7.1 L), p?=?0.75; T12 0.2 L (5.7 L), p?=?0.35; Δ 0.35 L(6.3 L), p?=?1.0]. Compared with 3C, BIA underestimated %fat at T0 and T12 [T0 ?3.3 (5.6), p?<?0.001; T12 ?1.7 (5.2), p?=?0.04] but not change [0.7 (8.2), p?=?0.38]. Except for %fat change, Bland-Altman plots indicated no proportional bias. However, 95 % limits of agreement were wide (TBW 15–22 L, %fat 19–20 %).

Conclusions

BIA may be appropriate for evaluating group level response among severely obese adults. However, clinically meaningful differences in the accuracy of BIA between individuals exist.     

Assessment of total body water from anthropometry-based equations using bioelectrical impedance as reference in Korean adult control and haemodialysis subjects.

BACKGROUND: Several indirect prediction equations to estimate total body water (TBW) with simple demographic and anthropometric data are commonly used by researchers and dialysis units. These equations are largely based on observations in subjects of the Western hemisphere. The purpose of this study was to investigate the possible application of anthropometry-based TBW equations to a Korean adult control population and maintenance haemodialysis (HD) patients using multifrequency bioelectrical impedance analysis (BIA) as reference. METHODS: We performed BIA and anthropometric measurements in 67 healthy adults and 101 HD patients. Four anthropometry-based equations were used: 58% of actual body weight (TBW-58), the Watson formula (TBW-W), the Hume formula (TBW-H), and the Chertow formula (TBW-C). Multifrequency BIA was performed at fasting state in controls and after HD. RESULTS: TBW-BIA was 34.6+/-6.9 l in control and 29.9+/-5.1 l in HD patients. TBW-58 and TBW-C gave significantly greater TBWs than TBW-BIA in both control and HD subjects. The correlation coefficients of TBW-BIA with calculated TBWs were lowest in TBW-58 (0.754 in control and 0.856 in HD subjects), and highest in TBW-C (0.944 in control and 0.916 in HD subjects). Mean prediction error was greatest in the Chertow formula for control and HD patients. Mean prediction error, limits of agreement, and root mean square error were lowest between TBW-BIA and TBW-H in control and between TBW-BIA and TBW-W in HD subjects. The correlation coefficient in the Bland-Altman plot was closer to zero and parallel with TBW-W than TBW-H in control and HD subjects. CONCLUSION: Currently available TBW equations overestimate TBW in both Korean normal control subjects and HD patients. Among them, the Watson formula appears to be the closest to TBW and to have the least bias. Based on this analysis, it is reasonable to use the Watson formula for the calculation of TBW in Korean adult control and HD subjects until an Asian-based TBW equation is available.     

Agreement of bioelectric impedance analysis and dual-energy X-ray absorptiometry for body composition evaluation in adults with cystic fibrosis

Malnutrition in cystic fibrosis (CF) is associated with increased mortality and can lead to fat-free (FFM) and fat mass (FM) loss. Dual-energy X-ray absorptiometry (DXA) is used and validated to measure FFM and FM. DXA's high cost has led to the utilization of less costly techniques such as bioelectrical impedance analysis (BIA). The aim of this study was to determine the agreement of FFM, FM and %FM measurements taken with DXA and BIA in adults with CF. We measured FFM, FM and %FM in 34 adults with CF with a leg-to-leg BIA and an iDXA and determined agreement using Bland–Altman analysis. While DXA and BIA measurements were well correlated (r > 0.8), mean biases between both methods were between 8 and 11%. BIA underestimated FM and %FM and overestimated FFM. In a clinical research setting where these measurements are used to phenotype patients, BIA cannot replace DXA.     

Assessment of human brain water content by cerebral bioelectrical impedance analysis: a new technique and its application to cerebral pathological conditions

OBJECTIVE: Total brain water content changes in several cerebral pathological conditions and the measurement of brain water content are important for the selection of appropriate therapeutic procedures. We present a quantitative, in vivo, bioelectrical impedance analysis (BIA) method and propose its use for the accurate assessment of brain water content among human subjects. METHODS: Cerebral BIA is based on the conduction of an applied current in the brain parenchyma. Application of an excitatory current of 800 microA at 50 kHz, via two electrodes placed on the eyelids with the eyes closed, and detection of the voltage drop with two electrodes placed in the suboccipital region allow brain resistance and reactance to be measured. By means of an equation that considers cranial circumference and resistance, it is possible to quantify the total brain water content, expressed as the bioelectrical volume. Cerebral BIA was performed with a series of healthy volunteers (n = 100), for determination of average brain water content values. The method was then applied to 50 patients with brain tumors (n = 20), intracranial hemorrhage (n = 16), or hydrocephalus (n = 14), for assessment of changes in global brain water contents. Data were compared with those obtained for healthy volunteers. RESULTS: Statistically significant differences (P < 0.001) were observed between the two groups. Mean brain water content values (expressed as bioelectrical volume values) were 38.2 +/- 3.9 cm2/Omega for healthy volunteers and 67.7 +/- 13.1 cm2/Omega for patients with cerebral pathological conditions. Statistically significant differences (P < 0.05) were also observed among patients with cerebral pathological conditions. CONCLUSION: The results of this study suggest that BIA, applied to the cerebral parenchyma, is a valid method for the prediction of brain water contents under both normal and pathological conditions. However, further studies are needed to establish whether it is sensitive and reliable enough for future clinical applications.     

Non-fasting bioelectrical impedance analysis in cystic fibrosis: Implications for clinical practice and research

BackgroundNutritional status affects pulmonary function in cystic fibrosis (CF) patients and can be monitored by using bioelectrical impedance analysis (BIA). BIA measurements are commonly performed in the fasting state, which is burdensome for patients. We investigated whether fasting is necessary for clinical practice and research.MethodsFat free mass (FFM) and fat mass (FM) were determined in adult CF patients (n = 84) by whole body single frequency BIA (Bodystat 500) in a fasting and non-fasting state. Fasting and non-fasting BIA outcomes were compared with Bland-Altman plots. Pulmonary function was expressed as Forced Expiratory Volume at 1 s percentage predicted (FEV1%pred). Comparability of the associations between fasting and non-fasting body composition measurements with FEV1%pred was assessed by multiple linear regression.ResultsFasting FFM, its index (FFMI), and phase angle were significantly lower than non-fasting estimates (−0.23 kg, p = 0.006, −0.07 kg/m², p = 0.002, −0.10°, p = 0.000, respectively). Fasting FM and its index (FMI) were significantly higher than non-fasting estimates (0.22 kg, p = 0.008) 0.32%, p = 0.005, and 0.07 kg/m², (p = 0.005). Differences between fasting and non-fasting FFM and FM were <1 kg in 86% of the patients. FFMI percentile estimates remained similar in 83% of the patients when measured after nutritional intake. Fasting and non-fasting FFMI showed similar associations with FEV1%pred (β: 4.3%, 95% CL: 0.98, 7.70 and β: 4.6%, 95% CI: 1.22, 8.00, respectively).ConclusionDifferences between fasting and non-fasting FFM and FM were not clinically relevant, and associations with pulmonary function remained similar. Therefore, BIA measurements can be performed in a non-fasting state.     

Comparing different methods of assessing body composition in end-stage renal failure

BACKGROUND: Accurate measurement of nutritional status in patients with end-stage renal disease is important because of its clear association with prognosis. Total body water (TBW) has additionally been recently recognized as an independent prognostic value because of its relationship with hypertension and cardiac morbidity. The current study was designed to assess the utility of surrogate markers of nutritional state and TBW in patients with end-stage renal disease. METHODS: Fifty-four patients with renal disease were studied. TBW obtained using the deuterium dilution technique was compared with estimates derived from anthropometric measures of TBW, including 58% body weight, Watson equations, and bioelectrical impedance analysis (BIA). Anthropometrically derived fat-free mass (FFM) was compared with BIA-derived estimates. Total body nitrogen (TBN) measurements were correlated with TBW estimates and BIA-derived resistance. RESULTS: TBW was significantly underestimated by the Watson equation (mean difference, -1.751 L, P = 0.01) and the 58% body weight approximation significantly overestimated it (mean difference, 1.792 L, P = 0.04). The Kushner BIA estimation of TBW did not significantly differ from that of the gold standard determined from D2O dilution (mean difference, -1.221 L, P = 0.12) and was also the method that showed the best agreement with the D2O estimate. However, the limits of agreement were large. Accurate prediction equations for FFM (FFM = -21.768 + 0.001 x ht2 + 6630.669 x 1/R + 0.312 x wt, R2 = 0.95) and TBN (TBN = -668.324 - 3.963 x age + 10.133 x wt + 0. 045 x ht2 + 32141.457 x 1/R, R2 = 0.91) were derived from BIA obtained resistance. CONCLUSIONS: The estimation of TBW varies significantly depending on the method of calculation. BIA is the most accurate surrogate marker for the measurement of both TBW and other parameters of body composition.     

Urea space and total body water measurements by stable isotopes in patients with acute renal failure

BACKGROUND: Knowledge of urea volume of distribution (Vurea) in patients with acute renal failure (ARF) is critical in order to prescribe and monitor appropriate dialytic treatment. We have recently shown that in ARF patients, Vurea estimation by urea kinetic modeling is significantly higher than total body water (TBW) by anthropometric estimation. However, these estimates of Vurea and TBW have not been validated by isotopic methods, considered as reference measurement standards. METHODS: In this study, we measured Vurea by [13C]urea and TBW by deuterium oxide (D2O) in 21 patients with ARF (14 males, 7 females, age 62.0 +/- 10.6 years old, 83% Caucasian, 17% African American) at three different centers. These measurements were compared to TBW estimates from anthropometric and bioelectrical impedance (BIA) measurements. RESULTS: Our results show that Vurea by [13C]urea (51.0 +/- 11.7 L) is significantly higher than TBW estimated by all other methods (TBW by D2O: 38.3 +/- 9.8 L, P < 0.001; TBW by BIA: 45.7 +/- 15.7 L, P= 0.08; TBW by Watson formula: 38.3 +/- 7.3 L, P < 0.001; TBW by Chertow formula: 39.3 +/- 7.8 L, P= 0.002, all versus Vurea). Despite significant overestimation of the absolute value and considerable variation, Vurea significantly correlated with TBW by BIA (r= 0.66, P < 0.01) and TBW by D2O (r= 0.5, P= 0.04). There was also significant correlation between D2O and BIA determined TBW (r= 0.8, P < 0.001). CONCLUSION: In terms of useful guidelines to prescribe a specific dose of dialysis in patients with ARF, conventional estimates of TBW as surrogates for Vurea should be used with caution. We propose that these conventional estimates of TBW should be increased by approximately 20% (a factor of 1.2) to avoid significant underdialysis.     

Volume status and body composition of chronic dialysis patients: utility of bioelectric impedance plethysmography

We assessed the utility of bioelectric impedance plethysmography (BIA) for measuring acute volume changes and body composition in patients with renal disease. Chronic hemodialysis and peritoneal dialysis patients were evaluated before and after dialysis. Total body water, as measured by BIA, predicts body weight. Acute changes in body water, induced by dialysis, are not predicted well by data derived from BIA. Body fat (%) and fat-free mass (%), determined by anthropometry, are predicted well by body composition data derived by BIA. BIA is useful for assessing body composition in this population, but must be cautiously applied to the measurement of acute volume changes.     

Measurements of extracellular water volume by bioelectrical impedance analysis during perioperative period of esophageal resection

Segmental bioelectrical impedance analysis (BIA) was conducted in five patients who underwent esophageal resections. Resistance values fitted at zero frequency (R0) in each body segment (arm, trunk and leg) were determined before the induction of anesthesia, at the end of surgery and on the second or third postoperative day. Extracellular water volume (ECW) in each body segment was estimated using the equation derived from the cell suspension theory. ECW in whole body was obtained from the sum of each body segment. R0 in trunk and leg significantly decreased at the end of surgery compared to the values before the induction of anesthesia (P < 0.05). The change ratio of R0 in trunk before the induction of anesthesia was significantly lower at the end of surgery than that in arm (P < 0.05), resulting from the most striking fluid accumulation in the trunk. Postoperatively, R0 in all body segments, however, appeared to decrease similarly compared to the values before the induction of anesthesia, suggesting the redistribution phenomena of extracellular water among body segments. The correlation (r = 0.90, P < 0.001) and good agreement [bias = 0.01 (L)] between net fluid balances and estimates of ECW changes in whole body suggest that BIA allows close monitoring of tissue hydration during perioperative period by providing estimates of ECW in body segments.     

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.     

Performance of Bioelectrical Impedance Analysis in the Estimation of Bone Mineral Content in Healthy Children Aged 6–12 Years

Background: Bioelectrical impedance analysis (BIA) is a widely available tool which provides mineral estimate. However, BIA is not currently recognized as a bone mineral measuring method. This study aimed to explore the ability of BIA to predict bone mineral content (BMC) in children, using dual-energy X-ray absorptiometry as a gold standard. Methods: Healthy children aged 6–12 years (n = 176) were recruited for BIA and dual-energy X-ray absorptiometry measurements. Predictive models were generated using basic indices (age, height, weight, waist circumference, hip circumference, etc.) and BIA parameters (minerals, fat mass, and fat free mass). Results: The root-mean-square deviation and R² for the total BMC predictive model were 0.089 kg and 0.926, respectively using height and weight as predictors whereas 0.113 kg and 0.886, respectively using minerals by BIA. The root-mean-square deviation and R² for the subtotal BMC predictive model were 0.080 kg and 0.935, respectively using height and weight as predictors whereas 0.098 kg and 0.906, respectively using minerals by BIA. The best predictive models included basic indices and BIA parameters as predictors, but they had only slightly better performance over simple models. Conclusions: Mineral content by BIA was good predictor of total and subtotal BMC in healthy children but with similar overall model performance compared to basic indices. More complex models combined all the predictive variables gave better prediction power, but of little improvement to these simple models. The BIA instrument does not appear to be useful in estimating BMC in healthy children as basic indices are more widely available measures but provide comparable performance. Future studies are needed to determine the clinical usefulness of the more complex prediction model in children with disease or children in other subgroups.     

Weight Loss Composition: The Effects of Exercise following Obesity Surgery as Measured by Bioelectrical Impedance Analysis

Background: Sudden weight loss following bariatric operations for morbid obesity, such as the duodenal switch (DS), can result in a concurrent decrease in lean body mass. Several methods for tracking body composition, such as bioelectrical impedance analysis (BIA), are available to monitor these changes. One method to offset the negative effects of sudden weight loss on body mass composition may be exercise. Methods: 100 patients who had undergone the DS operation for morbid obesity were classified as exercisers and non-exercisers based on self-reporting. Their body mass compositions were measured using BIA preoperatively and at 0.75, 1.5, 3, 6, 9, 12, and 18 months postoperatively. Results: At no study interval did postoperative percent changes in weight loss differ between the exercise and non-exercise groups. At 18 months postoperatively, the exercise group showed a 28% higher loss of fat mass and an 8% higher gain in lean body mass than the non-exercise group. Conclusion: Exercise positively influences body mass composition following the DS. BIA can be successfully employed to monitor changes, diagnose deficiencies, and formulate treatment recommendations.     

Sequential body composition analysis by bioimpedance early post-kidney transplantation

BACKGROUND: While chronic renal failure patients present disturbed body water composition, few studies have been done on its behavior following kidney grafting (Tx). We report the changes associated with a successful Tx on body composition evaluated by bioelectrical impedance analysis (BIA). METHODS: Twelve Tx (seven males, five females) were studied. The BIA was assessed before Tx, at month 1 and at month 3 post-Tx. Total body water (TBW), extracellular water (ECW), intracellular water (ICW), Na:K exchange rate (Nae:Ke) and phase angle (PA) were studied. An healthy group and a HD group were evaluated three times in a year interval. RESULTS: Comparing before Tx with month 1 post-Tx, TBW, ECW and Nae:Ke increased, while ICW and PA decreased significantly. Comparing month 1 with month 3 post-Tx, ECW decreased, while ICW and PA increased. On comparing month 1 post-Tx with the healthy group, Nae:Ke was greater and PA was lower at month 1. CONCLUSIONS: The BIA showed that the different body water compartments of Tx recipients quickly match the constitution of normal individuals, overcoming drug therapy side effects.     

Bioelectrical impedance analysis in the measurement of the body composition of surgical patients.

The evaluation of nutritional status in surgical patients remains a difficult problem. Bioelectrical impedance analysis (BIA) is a new method of body composition analysis which is easily performed at the bedside. This study determined the accuracy of BIA in the measurement of total body water (TBW) and potassium (TBK) in a heterogeneous group of surgical patients. The resistance and reactance components of impedance were measured with a whole body impedance analyser. Tritiated water dilution and whole body monitoring were the reference methods for TBW and TBK analysis. With the BIA technique the coefficient of variation for the estimation of TBW was 8.1 per cent and for TBK was 6.4 per cent. Allowing for the errors of the reference methods these results show that BIA is of limited value in the estimation of TBW but may provide a useful index of TBK.