Estimation of total body water from bioelectrical impedance spectroscopy in oncology outpatients receiving radiotherapy and agreement with three prediction equations

Background: Bioelectrical impedance spectroscopy (BIS) may be more accurate in determining total body water (TBW) than bioelectrical impedance analysis (BIA). The present study compared the agreement between three TBW prediction equations developed using BIA and BIS‐derived TBW in oncology outpatients. Methods: A cross‐sectional, observational study was conducted in 37 outpatients receiving radiotherapy (27 males/10 females, aged 68.3 ± 10.2 years). TBW was estimated by BIS (TBW_BIS) and three BIA TBW prediction equations (TBW_ca‐u: underweight cancer patients; TBW_ca‐n: normal‐weight cancer patients; and TBW_rad: patients receiving radiotherapy). Bland–Altman analyses determined agreement between methods. BIS‐derived TBW using new resistivity constants was calculated. Results: The mean ± SD of TBW estimated by BIS was 39.8 ± 8.3 L, which was significantly different from the prediction equations; TBW_rad 35.1 ± 7.9 L, TBW_ca‐u 33.1 ± 7.5 L and TBW_ca‐n 32.3 ± 7.3 L, (P < 0.001). Using new resistivity constants, TBW was 36.2 ± 8.1 L but this still differed from the equations (P < 0.001). Bias between TBW_BIS and that predicted by the equations was in the range 4.7–7.4 L or 1.1–3.9 L using new resistivity constants. Conclusions: TBW estimated by BIS cannot be directly compared with oncology‐specific BIA equations, suggesting that BIS cannot be used at the group level in outpatients receiving radiotherapy. There was a reduced bias with BIS using new resistivity constants; however, further research should determine any advantage of BIS over BIA in this population.     

Bioelectrical impedance: effect of 3 identical meals on diurnal impedance variation and calculation of body composition

BACKGROUND: Bioelectrical impedance analysis (BIA) can be used for estimating body composition. Earlier studies showed that the ingestion of meals lowers bioelectrical impedance, but none studied the effect of repeated ingestion of an identical meal in narrow intervals on impedance measurements during 24 h. OBJECTIVES: The objectives were to study the effect on bioelectrical impedance of 3 identical meals and to compare the results from single-frequency BIA measurements with those from multiple-frequency BIA measurements. DESIGN: Bioelectrical impedance was measured 18 times during 24 h in 18 healthy subjects [10 women and 8 men; x +/- SD age: 31.5 +/- 11.7 y; body mass index (in kg/m(2)): 22.2 +/- 2.7]. An identical meal was given at breakfast, lunch, and dinner. RESULTS: Bioelectrical impedance decreased after ingestion of a standard meal (P < 0.05). The decrease in impedance lasted 2-4 h after each meal. The decrease was additive during the day, although it was more pronounced after the first meal because of the combined effect of rising from the supine position and meal ingestion. This is an important consideration when calculating body composition: percentage of body fat varied by 8.8% from the highest to the lowest measurement in women and by 9.9% from the highest to the lowest measurement in men. The bioelectrical impedance at 50 kHz was identical when measured with multiple frequencies or a single frequency. CONCLUSION: The ingestion of meals leads to an additive decrease in bioelectrical impedance and thus to a decrease in the calculated percentage of body fat.     

The Stayhealthy bioelectrical impedance analyzer predicts body fat in children and adults

Bioelectrical impedance analysis (BIA) is a time-efficient and cost-effective method for estimating body composition. We hypothesized that there would be no significant difference between the Stayhealthy BC1 BIA and the selected reference methods when determining body composition. Thus, the purpose of the present study was to determine the validity of estimating percent body fat (%BF) using the Stayhealthy BIA with its most recently updated algorithms compared to the reference methods of dual-energy x-ray absorptiometry for adults and hydrostatic weighing for children. We measured %BF in 245 adults aged 18 to 80 years and 115 children aged 10 to 17 years. Body fat by BIA was determined using a single 50 kHz frequency handheld impedance device and proprietary software. Agreement between BIA and reference methods was assessed by Bland and Altman plots. Bland and Altman analysis for men, women, and children revealed good agreement between the reference methods and BIA. There was no significant difference by t tests between mean %BF by BIA for men, women, or children when compared to the respective reference method. Significant correlation values between BIA, and reference methods for all men, women, and children were 0.85, 0.88, and 0.79, respectively. Reliability (test-retest) was assessed by intraclass correlation coefficient and coefficient of variation. Intraclass correlation coefficient values were greater than 0.99 (P < .001) for men, women, and children with coefficient of variation values 3.3%, 1.8%, and 1.7%, respectively. The Stayhealthy BIA device demonstrated good agreement between reference methods using Bland and Altman analyses.     

Body composition in underweight elderly subjects: reliability of bioelectrical impedance analysis

BACKGROUND AND AIMS: In underweight elderly subjects it is important to estimate body composition and particularly fat-free mass (FFM). Bioelectrical impedance analysis (BIA) is a non-invasive method in determining FFM, but its usefulness in these frail subjects should be verified. The aim of this study is to verify in underweight elderly people the reliability of previously published BIA formulas in detecting FFM. METHODS: Fifty-seven hospitalized elderly subjects (27 males and 30 females) with body mass index <20 kg/m(2) were selected. In all subjects, FFM was detected by dual energy X-ray absorptiometry. Moreover, BIA measurements were performed at standard frequency (50 kHz and 800 microA) and FFM was derived using the main previous published BIA equations. Results: In men, Kyle and Rising equations gave acceptable estimates of FFM with a mean error, respectively, of 1+/-1.9 and 1.4+/-1.7 kg. Also RJL formula could be used after adjusting for a correction factor. In women, no equation seemed sufficiently reliable to estimate FFM. CONCLUSIONS: BIA method seems useful to evaluate body composition in underweight elderly men but it seems to have intrinsic limits in women. Nevertheless, the variability in behavior of the different equations suggests to be careful in adopting BIA equations.     

External cross-validation of bioelectrical impedance analysis for the assessment of body composition in Korean adults

Bioelectrical impedance analysis (BIA) models must be validated against a reference method in a representative population sample before they can be accepted as accurate and applicable. The purpose of this study was to compare the eight-electrode BIA method with DEXA as a reference method in the assessment of body composition in Korean adults and to investigate the predictive accuracy and applicability of the eight-electrode BIA model. A total of 174 apparently healthy adults participated. The study was designed as a cross-sectional study. FM, %fat, and FFM were estimated by an eight-electrode BIA model and were measured by DEXA. Correlations between BIA_%fat and DEXA_%fat were 0.956 for men and 0.960 for women with a total error of 2.1%fat in men and 2.3%fat in women. The mean difference between BIA_%fat and DEXA_%fat was small but significant (P < 0.05), which resulted in an overestimation of 1.2 ± 2.2%fat (95% CI: -3.2-6.2%fat) in men and an underestimation of -2.0 ± 2.4%fat (95% CI: -2.3-7.1%fat) in women. In the Bland-Altman analysis, the %fat of 86.3% of men was accurately estimated and the %fat of 66.0% of women was accurately estimated to within 3.5%fat. The BIA had good agreement for prediction of %fat in Korean adults. However, the eight-electrode BIA had small, but systemic, errors of %fat in the predictive accuracy for individual estimation. The total errors led to an overestimation of %fat in lean men and an underestimation of %fat in obese women.     

Errors in estimating peritoneal fluid by bioelectrical impedance analysis and total body electrical conductivity.

Whole-body bioelectrical impedance analysis (BIA) and total body electrical conductivity (TOBEC) have been used to estimate body composition and generalized changes in total body water (TBW). The sensitivity of these methods to measure small, rapid, localized changes in body water has not been fully evaluated. We compared the prediction of TBW by whole-body and segmental BIA and TOBEC with deuterium oxide dilution (D2O) in 10 control subjects and 7 renal failure patients receiving continuous ambulatory peritoneal dialysis (CAPD) prior to and after dialysate infusion. Using D2O as the reference method, there was no significant mean residual error between TBW predicted by BIA and TOBEC in controls (?1.2 +/? 1.5 and ?0.9 +/? 1.0 kg) and CAPD patients pre-infusion (?1.0 +/? 2.0 and 0.29 +/? 2.01 kg). After infusing 1.9 +/? 0.18 kg dialysate, the mean residual error between change in body weight and the three methods was ?0.44 +/? 0.53 kg for D2O (p < 0.1), ?1.7 +/? 0.25 kg for BIA (p < 0.0001), and 1.2 +/? 0.4 kg for TOBEC (p < 0.001). Segmental BIA detected a 7.6% reduction in trunkal resistance with no significant change across the limbs, consistent with abdominal fluid accumulation. It is concluded that whole-body BIA underpredicts and TOBEC overpredicts small changes in peritoneal fluids.     

生物电阻抗技术临床应用现状及探讨

生物电阻抗技术是利用细胞外液、细胞内液的电学性质测量人体成分及其变化。因其有无创、操作简便、测量数据精确等优点,在流行病学研究和临床疾病动态检测中广泛应用。我们通过综述生物电阻抗技术在临床应用开展情况的优点和缺陷,试图探讨其可能的应用潜力。     

Bioelectrical impedance variation in healthy subjects during 12 h in the supine position

BACKGROUND AND AIM: Bioelectrical impedance analysis is used to assess human body composition. Studies have shown that meal ingestion and change of body posture affects bioelectrical impedance, but none has studied bioelectrical impedance variation in supine subjects. The aim was to examine the bioelectrical impedance variation in healthy subjects during 12 h in the supine position. METHODS: Bioelectrical impedance was measured 16 times during 12 h in 18 healthy subjects. An identical meal was given at breakfast, lunch, and dinner. RESULTS: Mean (standard deviation) impedance at 50 kHz increased from 558 (87) omega at study start to 584 (95) Omega at study end (P<0.05). Bioelectrical impedance is reduced after ingestion of the first meal, but not following the meals at 1230 and 1730. Calculated body fat content increased from a baseline mean (SD) of 21.7 (6.1) % body fat to 23.9 (6.7) % body fat at study end (P<0.05). CONCLUSIONS: Bioelectrical impedance increased during 12 h in supine subjects. The increase is probably explained by a shift in body fluids from the extremities to thorax during the day and the importance of strict measurement standardisation both in epidemiological studies and clinical practice is underlined.     

Safety of Bioelectrical Impedance Analysis in Patients Equipped With Implantable Cardioverter Defibrillators

Background. Current guidelines warn of potential electromagnetic interferences (EMI) when using bioelectrical impedance analysis (BIA) to measure body composition in patients equipped with implantable cardioverter‐defibrillators (ICDs). We aimed to test the occurrence of EMI in a setting where this risk was experimentally maximized. Materials and Methods. Outpatients scheduled for routine ICD controls simultaneously underwent a BIA measurement using an electrical current of 0.8 mAmp at frequencies from 5–100 kHz. ICD sensitivity levels were set to maximum levels while therapies were temporarily inactivated. The device electrograms were monitored in real time to detect sensed and/or visible EMI during BIA measurement. Results. A total of 63 patients equipped with single‐chamber (n = 13), dual‐chamber (n = 18), or biventricular (n = 32) ICDs from 5 major manufacturers were included. No EMI were detected by the ICDs in these patients, nor were any artifacts visualized during real‐time electrogram recordings. Conclusion. BIA can be safely performed in patients equipped with ICDs without cardiac monitoring. Current guidelines should be updated accordingly.     

Assessment of fat-free mass from bioelectrical impedance analysis in men and women with Prader-Willi syndrome: cross-sectional study

We have recently shown that population-specific formulae are required to estimate fat-free mass (FFM) from bioelectrical impedance analysis (BIA) in obese women with Prader-Willi syndrome (PWS) matched by age and percent fat mass (FM) to non-PWS women. The present cross-sectional study was aimed at developing generalised BIA equations that could be used in PWS subjects independently of sex and FM. We used dual-energy X-ray absorptiometry to measure FFM and BIA to measure whole-body impedance at 50?kHz (Z₅₀) in 34 women and 21 men with PWS. The impedance index, that is, height (cm)²/Z₅₀ (Ω), explained 77% (BCa-bootstrapped 95% CI 65 to 85%) of the variance of FFM with a root mean squared error of the estimate of 3.7?kg (BCa-bootstrapped 95% CI 3.2 to 4.5?kg). BIA can be used to estimate FFM in obese and non-obese PWS men and women by means of population-specific equations.     

Suitability of Bioelectrical Based Methods to Assess Water Compartments in Recreational and Elite Athletes

Objective: It is important for highly active individuals to easily and accurately assess their hydration level. Bioelectrical impedance (BIA) can potentially meet these needs but its validity in active individuals is not well established. We aim to validate total body water (TBW), extracellular water (ECW), and intracellular water (ICW) estimates obtained from 50 kHz BIA, bioelectrical impedance spectroscopy (BIS), and BIA-based models against dilution techniques in 2 populations: active adults and elite athletes.

Methods: Active males (N = 28, 20–39 years) involved in recreational sports and elite athletes (females: N = 57, 16–35 years; males: N = 127, 16–38 years) participated in this study. TBW and ECW were assessed with deuterium and bromide dilution, respectively. ICW was assessed as their difference. Body water compartments were also assessed by BIA (BIA-101), BIS (model 4200), and BIA-based equations.

Results: Small but significant differences were observed between alternative methods and the criterion in all subsamples. In female athletes, r² > 0.69, r² > 0.57, and r² > 0.65 were observed between methods in the TBW, ECW, and ICW estimates. In males, r² > 0.75, r² > 0.65, and r² > 0.68 were found between alternative and reference methods in the TBW, ECW, and ICW estimates, respectively, whereas for male recreational exercisers, r² > 0.58, r² > 0.73, and r² > 0.75 were observed. Pure errors ranged between 0.19 to 3.32 kg for TBW, 0.64 to 1.63 for ECW, and 1.98 to 2.64 in ICW. The highest limits of agreement (LoA) were observed in Van Loan and Mayclin equation and the BIA method, respectively, for TBW and ECW assessment and the lowest LoA were observed in BIS for both TBW and ECW estimates.

Conclusions: The higher accuracy of BIS in predicting individual TBW, ECW, and ICW highlights its utility in water assessment of recreational and elite athletes.     

Bioelectrical impedance analysis during acute changes of extracellular osmolality in man

BACKGROUND & AIMS: Bioelectrical impedance analysis (BIA) is widely used as an inexpensive and noninvasive method to provide estimates of body compartments such as total body water, lean body mass and fat mass. The present study was performed to test the reliability of this method during acute changes of extracellular osmolality in eight young health men. METHODS: Hyperosmolal isohydration was achieved by overnight infusions of hypertonic saline solutions (2 and 5% NaCl) and thirsting, and hypoosmolal hyperhydration by drinking of free water and overnight application of desmopressin. The control study (isoosmolality) consisted of oral water ad libitum. RESULTS: When plasma osmolality and sodium concentrations increased (from 285 +/- 1 to 296 +/- 1 mmol/kg (P<0.001) and from 141.9 +/- 0.7 to 148.3 +/- 0.6 mmol/l (P<0.0001)) and total body water remained unchanged, body impedance decreased and calculated total body water increased from 42.7 +/- 2.7 to 45.6 +/- 2.3 liters (P<0.03). In contrast, during hypoosmolal hyperhydration total body water increased by 1.56 +/- 0.17 kg and plasma osmolality decreased from 285 +/- 1 to 272 +/- 1 mmol/kg (P<0.001) and plasma sodium concentrations from 142 +/- 0.5 to 134.8 +/- 0.4 mmol/l (P<0.0001). In spite of these changes of body water, impedance measurements and calculated total body water remained unchanged. During conditions of isoosmolal isohydration (as demonstrated by unchanged plasma sodium concentrations and osmolality) the measurements by BIA also remained unchanged. CONCLUSIONS: Measurements of total body water using BIA under conditions of unknown hydration status (hyper-, hypo- or isohydration) and unknown osmolality (hyper-, hypo- or isoosmolality) may not be reliable. Therefore bioelectrical impedance analysis is not a suitable bedside method to assess changes of body compartments under unstable hydration status.     

Estimation of total body water from foot-to-foot bioelectrical impedance analysis in patients with cancer cachexia – agreement between three prediction methods and deuterium oxide dilution

INTRODUCTION: Bioelectrical impedance analysis (BIA) is a useful bedside measure to estimate total body water (TBW). The aim of this study was to determine the agreement between three equations for the prediction of TBW using BIA against the criterion method, deuterium oxide dilution, in patients with cancer cachexia. METHODS: Eighteen measurements of TBW using foot-to-foot BIA in seven outpatients with cancer cachexia (five male and two female, age 56.4 +/- 6.7 years) at an Australian hospital. Three prediction formulae were used to estimate TBW - TBW(ca-radiotherapy) developed in patients with cancer undergoing radiotherapy, TBW(ca-underweight) and TBW(ca-normal weight) developed in underweight and normal weight patients with cachexia. TBW was measured using the deuterium oxide dilution technique as the gold standard. RESULTS: Mean measured TBW was 39.5 +/- 6.0 L. There was no significant difference in measured TBW and estimates from prediction equations TBW(ca-underweight) and TBW(ca-radiotherapy). There was a significant difference in measured TBW and TBW(ca-normal weight). All prediction equations overestimated TBW in comparison with measured TBW. The smallest bias was observed with TBW(ca-underweight) (0.38 L). The limits of agreement are wide (>7.4 L) for each of the prediction equations compared with measured TBW. CONCLUSIONS: At a group level, TBW(ca-underweight) is the best predictor of measured TBW in patients with cancer cachexia. For an individual however, the limits of agreement are wide for all prediction equations and are unsuitable for use. Practitioners need to be aware of the limitations of using TBW prediction equations for individuals.     

Assessment of intracellular water by whole body bioelectrical impedance and total body potassium in HIV-positive patients

OBJECTIVE: Bioelectrical impedance analysis (BIA) is widely used as bedside assessment of body composition. Body cell mass (BCM) and intracellular water (ICW) are clinically important body compartments. Estimates of ICW obtained from BIA by different calculation approaches were compared to a reference method in male HIV-infected patients. PATIENTS: Representative subsample of clinically stable HIV-infected outpatients, consisting of 42 men with a body mass index of 22.4 +/- 3.8 kg/m(2)(range, 13-l31 kg/m(2)). METHODS: Total body potassium was assessed in a whole body counter, and compared to 50 kHz monofrequency BIA and multifrequency bioelectrical impedance spectroscopy. Six different prediction equations for ICW from BIA data were applied. Methods were compared by the Bland-Altman method. RESULTS: BIA-derived ICW estimates explained 58% to 73% of the observed variance in ICW (TBK), but limits of confidence were wide (-16.6 to +18.2% for the best method). BIA overestimated low ICW (TBK) and underestimated high ICW (TBK) when normalized for weight or height. Mono- and multifrequency BIA were not different in precision but population-specific equations tended to narrower confidence limits. CONCLUSION: BIA is an unreliable method to estimate ICW in this population, in contrast to the better established estimation of total body water and extracellular water. Potassium depletion in severe malnutrition may contribute to this finding but a major part of the residual between methods remains unexplained.     

Accuracy of body fat assessment by bioelectrical impedance in Japanese middle-aged and older people

Bioelectrical impedance analysis (BIA) is commonly used to measure the percentage of body fat (%BF), but its accuracy is controversial. In addition, the equations are specific to the group for which they were established. As far as we know, there is no study examining the accuracy of BIA in Japanese middle-aged and older people. We compared %BF assessed using BIA with that of dual-energy X-ray absorptiometry (DEXA) in 102 female and 51 male local residents aged 40 to 78 y. Simple correlation coefficients were 0.79 for females and 0.69 for males, which are statistically significant (p<0.001). However, BIA tended to overestimate %BF in the lower BF group and underestimate it in the BF higher group, and only 45.1% for female and 47.1% for male subjects were measured accurately, i.e., within 10% of the measurement by DEXA. This result suggests that this model of BIA is an alternative for estimating %BF in Japanese middle-aged and older people as well as when subjects are within a normal body fat range, but greater accuracy is needed for lean and overweight subjects.     

生物电阻抗分析在临床监测中的应用进展与前景

生物电阻抗分析（BIA）作为一种人体成分测量的有效手段,由于能获得细胞内液、细胞外液等有效参数,对营养学和体液平衡控制有重要的临床指导意义,本文叙述了其在临床监测中的应用与进展。     

One-year increment of fat mass and lean body mass of Japanese school children using bioelectrical impedance

Bioelectrical impedance analysis (BIA) and skinfold thickness (SF) (triceps and subscapular) methods were applied to 436 Japanese school children (228 boys and 208 girls) aged from 9 to 11 years with a one-year follow-up to determine changes in body composition. By BIA oneyear increment (Δ) of lean body mass (LBM) for boys increased significantly (p<0.01) and Δ LBM was almost equivalent to that for Δ weight (Wt). Δ Wt and Δ fat mass (FM) between the age 10 (from ages 10 to 11) and age 11 (from ages 11 to 12) groups in girls achieved statistical significance (p<0.01 and p<0.001, respectively) and Δ Wt was almost completely comprised of the Δ FM in these age groups. Δ FM in die age 11 group for girls was statistically higher than that in the age 10 group, and this obvious increase of FM in the age 11 group was presumed to be die effect of menses in consideration of die maximum oneyear increment of Ht (Δ Ht) in die age 10 group. These results of the assessment of body composition by BIA supported those of previous reports, and therefore BIA can be considered as a useful mediod to estimate changes in body composition of school children because it is simple and non-invasive and can be performed rapidly.     

生物电阻抗法与双标水稀释法在人体成分测定中的应用比较

目的 用双标水稀释法验证目前在我国广泛应用的体成分测定方法--生物电阻抗法的准确性.方法 从白求恩军医学院某中队150名学员中根据体质指数(BMI)等指标筛选出16名学员作为受试对象,试验期为14 d,试验期间学员集中管理,统一食宿.试验第1天受试者服用双标水,收集服用前及服用后2 h、4 h、6 h、8 h及第2至第14天的尿液,用质谱分析的方法,得到受试者2H、18O的消除曲线,从而获得受试者的体成分数据.与此同时,从试验第1天开始,每天晚餐后3 h用生物电阻抗仪对每位受试者进行体成分的测定.最后,将2种方法获得的体成分数据加以比对.结果 经统计学分析,生物电阻抗法与双标水稀释法获得的体成分参数值差异无统计学意义,而且高度相关,两种方法测得的总体水、瘦体重、体脂及体脂百分比的相关系数分别为0.556,0.556,0.817,0.606,具有统计学意义.结论 应用生物电阻抗法测定中国人体成分具有较高的准确性.     

Body composition analysis in critically ill survivors: a comparison of bioelectrical impedance spectroscopy devices

Background: Body composition is commonly altered in response to critical illness and can be estimated at the bedside with bioelectrical impedance spectroscopy (BIS). Different electrode configurations may be used to mitigate assumptions of the technique, but the reliability of tetra‐polar and octo‐polar arrangements has yet to be established. This study aimed to compare both configurations, in a prospective observational study of 17 critically ill survivors and 12 healthy controls. Methods: Weight, supine body length, and BIS on both tetra‐polar and octo‐polar configured devices were recorded, then repeated 2 days later. Bioelectrical impedance vector analysis was subsequently performed using data from the tetra‐polar device at a frequency of 50 kHz. Results: Test‐retest agreement was acceptable for the tetra‐polar device (intraclass correlation coefficient range, patients: 0.876–0.988 vs controls: 0.983–0.998, P ≤ 0.001). However, lower and wider ranging test‐retest intraclass correlation coefficients were obtained with the octo‐polar instrument in both groups. Furthermore, there was a difference in the mass/volume of body compartments measured on each device in both patients (P ≤ .017) and controls (P ≤ .045). A change in the composition profile of critically ill males was evident between measurement occasions, which was reflected by a reduction in body weight of 1.6 (1.5) kg (P ≤ 0.001) across the sample over the same period. Conclusions: BIS devices should not be used interchangeably in the clinical setting. The reliability of the tetra‐polar instrument was good, but daily fluctuations in body weight may have affected the results.     

Whole-body and segmental bioelectrical-impedance analysis in patients with cirrhosis of the liver: changes after treatment of ascites.

Bioelectrical impedance analysis (BIA) is a simple technique for determining body water and calculating body composition. It has been validated in healthy control subjects but not in patients with liver disease. We examined the ability of BIA to detect changes in total body water (TBW) due to removal of ascites. In 12 cirrhotic patients, BIA of the whole body and of body segments was performed before and after treatment of ascites with paracentesis (n = 12) and diuretics (n = 2). TBW changes predicted by BIA, by using two prediction equations, were significantly less than body weight changes (51% and 45% of the weight loss). BIA of body segments showed highly significant changes in both the trunk and the leg and small changes in the arm. These data indicate that BIA of the whole body is not a suitable technique for monitoring fluid changes in cirrhotic patients with ascites. Changes in BIA of body segments may be due to mobilization of edema after the removal of ascites.