Measurement of peritoneal fluid absorption and ultrafiltration during peritoneal dialysis using segmental bioimpedance.

The aim of this study was to measure intraperitoneal volume (IPV) and ultrafiltration volume (UFV) by monitoring the abdominal resistance using segmental bioimpedance analysis (SBIA, Hydra 4200). Twenty peritoneal dialysis (PD) patients were studied during a fill with 2 L of 2.5% glucose peritoneal dialysate solution. UFVDrain (g) was measured as weight difference between fill and drain dialysate volumes. Ultrafiltration volume (UFVSBIA; ml) and absorption volume were calculated from the IPV curve derived by SBIA. UFVSBIA correlated with UFVDrain ( ). This study may provide actionable clinical insights and help clinicians to better understand the function of the peritoneal membrane in individuals. Clinical Relevance-This technique may support personalized medicine by aiding the prescription of PD therapy on a patient-level.

Identification of fluid overload in elderly patients with chronic kidney disease using bioimpedance techniques.

Diagnosis of fluid overload (FO) in early stage is essential to manage fluid balance of patients with chronic kidney disease (CKD) and to prevent cardiovascular disease (CVD). However, the identification of fluid status in patients with CKD is largely dependent on the physician's clinical acumen. The ratio of fluid overload to extracellular volume (FO/ECV) has been used as a reference to assess fluid status. The primary aim of this study was to compare FO/ECV with other bioimpedance methods and clinical assessments in patients with CKD. Whole body ECV, intracellular volume (ICV), total body water (TBW), and calf normalized resistivity (CNR) were measured (Hydra 4200). Thresholds of FO utilizing CNR and ECV/TBW were derived by receiver operator characteristic (ROC) analysis based on data from pooled patients with CKD and healthy subjects (HSs). Clinical assessments of FO in patients with CKD were performed by nephrologists. Patients with CKD (stage 3 and stage 4) (n = 50) and HSs (n = 189) were studied. The thresholds of FO were ≤14.3 (10-2 Ωm3/kg) for females and ≤13.1 (10-2 Ωm3/kg) for males using CNR and ≥0.445 in females and ≥0.434 in males using ECV/TBW. FO was diagnosed in 78%, 62%, and 52% of patients with CKD by CNR, FO/ECV, and ECV/TBW, respectively, whereas only 24% of patients with CKD were diagnosed to be FO by clinical assessment. The proportion of FO in patients with nondialysis CKD was largely underestimated by clinical assessment compared with FO/ECV, CNR, and ECV/TBW. CNR and FO/ECV methods were more sensitive than ECV/TBW in identifying fluid overload in these patients with CKD.NEW & NOTEWORTHY We found that fluid overload (FO) in patients with nondialysis CKD was largely underestimated by clinical assessment compared with bioimpedance methods, which was majorly due to lack of appropriate techniques to assess FO. In addition, although degree of FO by bioimpedance markers positively correlated with the age in healthy subjects (HSs), no difference was observed in the three hydration markers between groups of 50 ≤ age <70 yr and age ≥70 yr in the patients with CKD.

Estimation of fluid status using three multifrequency bioimpedance methods in hemodialysis patients.

INTRODUCTION: Segmental eight-point bioimpedance has been increasingly used in practice. However, whether changes in bioimpedance analysis components before and after hemodialysis (HD) using this technique in a standing position is comparable to traditional whole-body wrist-to-ankle method is still unclear. We aimed to investigate the differences between two eight-point devices (InBody 770 and Seca mBCA 514) and one wrist-to-ankle (Hydra 4200) in HD patients and healthy subjects in a standing position. METHODS: Thirteen HD patients were studied pre- and post-HD, and 12 healthy subjects once. Four measurements were performed in the following order: InBody; Seca; Hydra; and InBody again. Electrical equivalent models by each bioimpedance method and the fluid volume estimates by each device were also compared. FINDINGS: Overall, total body water (TBW) was not different between the three devices, but InBody showed lower extracellular water (ECW) and higher intracellular water (ICW) compared to the other two devices. When intradialytic weight loss was used as a surrogate for changes in ECW (∆ECW) and changes in TBW (∆TBW), ∆ECW was underestimated by Hydra (-0.79 ± 0.89 L, p < 0.01), InBody (-1.44 ± 0.65 L, p < 0.0001), and Seca (-0.32 ± 1.34, n.s.). ∆TBW was underestimated by Hydra (-1.14 ± 2.81 L, n.s.) and InBody (-0.52 ± 0.85 L, p < 0.05) but overestimated by Seca (+0.93 ± 3.55 L, n.s.). DISCUSSION: Although segmental eight-point bioimpedance techniques provided comparable TBW measurements not affected by standing over a period of 10-15 min, the ECW/TBW ratio appeared to be significantly lower in InBody compared with Seca and Hydra. Results from our study showed lack of agreement between different bioimpedance devices; direct comparison of ECW, ICW, and ECW/TBW between different devices should be avoided and clinicians should use the same device to track the fluid status in their HD population in a longitudinal direction.

Prevalence of fluid overload in an urban US hemodialysis population: A cross-sectional study.

INTRODUCTION: Inadequate fluid status remains a key driver of cardiovascular morbidity and mortality in chronic hemodialysis (HD) patients. Quantification of fluid overload (FO) using bioimpedance spectroscopy (BIS) has become standard in many countries. To date, no BIS device has been approved in the United States for fluid status assessment in kidney patients. Therefore, no previous quantification of fluid status in US kidney patients using BIS has been reported. Our aim was to conduct a cross-sectional BIS-based assessment of fluid status in an urban US HD population. METHODS: We determined fluid status in chronic HD patients using whole body BIS (Body Composition Monitor, BCM). The BCM reports FO in liters; negative FO denotes fluid depletion. Measurements were performed before dialysis. Post-HD FO was estimated by subtracting the intradialytic weight loss from the pre-HD FO. FINDINGS: We studied 170 urban HD patients (age 61 ± 14 years, 60% male). Pre- and post-HD FO (mean ± SD), were 2.2 ± 2.4 and -0.2 ± 2.7 L, respectively. Pre-HD, 43% of patients were fluid overloaded, 53% normally hydrated, and 4% fluid depleted. Post-HD, 12% were fluid overloaded, 55% normohydrated and 32% fluid depleted. Only 48% of fluid overloaded patients were hypertensive, while 38% were normotensive and 14% hypotensive. Fluid status did not differ significantly between African Americans (N = 90) and Caucasians (N = 61). DISCUSSION: While about half of the patients had normal fluid status pre-HD, a considerable proportion of patients was either fluid overloaded or depleted, indicating the need for tools to objectively quantify fluid status.

Monitoring of Intraperitoneal Fluid Volume during Peritoneal Equilibration Testing using Segmental Bioimpedance.

BACKGROUND: Ultrafiltration failure and fluid overload are common in peritoneal dialysis (PD) patients. Knowledge of intraperitoneal volume (IPV) and time to peak IPV during a dwell would permit improved PD prescription. This study aimed to utilize trunk segmental bioimpedance analysis (SBIA) to quasi-continuously monitor IPV (IPVSBIA) during the peritoneal dwell. METHODS: IPVSBIA was measured every minute using lower-trunk SBIA (Hydra 4200; Xitron Technologies Inc., CA, USA) in 10 PD patients during a standard 240-min peritoneal equilibration test (PET). The known dialysate volume (2 L) rendered IPVSBIA calibration and calculation of instantaneous ultrafiltration volume (UFVSBIA) possible. UFVSBIA was defined as IPVSBIA - 2 L. RESULTS: Based on dialysate-to-plasma creatinine ratio, 2 patients were high, 7 high-average, and 1 low-average transporters. Technically sound IPVSBIA measurements were obtained in 9 patients (age 59.0 ± 8.8 years, 7 females, 5 African Americans). Drained ultrafiltration volume (UFVdrain) was 0.47 ± 0.21 L and correlated (r = 0.74; p < 0.05) with end-dwell UFVSBIA (0.55 ± 0.17 L). Peak UFVSBIA was 1.04 ± 0.32 L, it was reached 177 ± 61 min into the dwell and exceeded end-dwell UFVSBIA by 0.49 ± 0.28 L (95% CI: 0.27-0.7) and UFVdrain by 0.52 ± 0.31 L (95% CI: 0.29-0.76), respectively. CONCLUSION: This pilot study demonstrates the feasibility of trunk segmental bioimpedance to quasi-continuously monitor IPVSBIA and identify the time to peak UFVSBIA during a standard PET. Such new insights into the dynamics of intraperitoneal fluid volume during the dwell may advance our understanding of the underlying transport physiology and eventually assist in improving PD treatment prescriptions.

Evaluation of one year of frequent dialysis on fluid load and body composition using calf bioimpedance technique.

OBJECTIVE: The primary aim of this study was to evaluate the effect of increased frequency of dialysis (FHD) on change in fluid status and body composition using segmental bioimpedance. APPROACH: Twelve stable HD patients were switched from 3 times/week to 6 times/week HD (FHD). Systolic blood pressure (SBP), body mass and body mass index (BMI) were measured pre- and post-HD. Calf resistance (R 5) at 5 kHz was measured using a multifrequency bioimpedance device (Hydra 4200). Calf resistivity (ρ = R 5 * area/length), normalized resistivity (CNR = ρ/BMI) and calf extracellular volume (cECV) were calculated. Fat mass was measured by Futrex body composition analyzers (Futrex 6100, Futrex Tech, Inc.). All measurements were performed at baseline (BL) and monthly for up to one year. MAIN RESULTS: Nine patients completed one year of FHD. Compared to BL, body weight and cECV decreased, and CNR increased significantly by the first month but did not change thereafter. SBP pre-HD decreased significantly by the end of the first month with further reduction until month 12. Additionally, antihypertensive medication decreased significantly from baseline by month 4 and remained stable from month 6 throughout the rest of the study. The post-HD CNR in five of nine patients reached the range of normal (>18.5 10-2 * Ohm * m3 kg-1 for males and >19.1 10-2 * Ohm * m3 kg-1 for females) after 1 year FHD. In patients who returned to 3 times/week dialysis, CNR decreased significantly in the first week, and this was associated with increases in body weight and SBP. SIGNIFICANCE: Reduction of fluid overload with no alteration of body composition was observed in this study. Accordingly, improving fluid status was confirmed by reducing BP and use of antihypertensive drugs together with increase in CNR. Measurement of fluid status by CNR in hemodialysis patients is a new method to quantitatively assess hydration potentially creating a target for volume of fluid removal.

Effect of Change in Fluid Status Evaluated by Bioimpedance Techniques on Body Composition in Hemodialysis Patients.

OBJECTIVE: This prospective study uses calf bioimpedance spectroscopy (cBIS) to guide the attainment of dry weight (DWcBIS) in chronic hemodialysis (HD) patients. The primary aim of this study was to evaluate whether body composition is altered when fluid status is reduced to DWcBIS. METHODS: Target post-HD weight was gradually reduced from baseline (BL) until DWcBIS was achieved. DWcBIS was defined as the presence of both flattening of the curve of extracellular resistance and the attainment calf normalized resistivity in the normal range during the dialysis treatment. Extracellular volume (ECV), intracellular volume, and total body water (TBW) were measured using whole body BIS (Hydra 4200). Fluid overload, lean body mass, and fat mass were calculated according to a body composition model. RESULTS: Seventy-three patients enrolled and 60 completed the study (55 ± 13 years, 49% male). Twenty-eight patients (25% diabetes) achieved DWcBIS, whereas 32 patients (47% diabetes) did not. Number of treatment measurements were 16 ± 10 and 12 ± 13 studies per patient in the DWcBIS and non-DWcBIS groups, respectively. Although significant decreases in body weight and ECV were observed, lean body mass and FM did not differ significantly in both groups from BL to the end of study. ECV, ECV/TBW, and fluid overload were higher in the non-DWcBIS than in the DWcBIS group both at BL and at the end of study. Ratios of intradialytic changes in calf normalized resistivity, ECV, and ECV/TBW to ultrafiltration volume were significantly lower in diabetic than in non-diabetic patients. CONCLUSIONS: This study shows that decreasing fluid status by gradual reduction of post-HD weight in both DWcBIS and Non-DWcBIS groups did not affect body composition significantly over a period of about 4 weeks.

Effect of age and blood pressure on determination of normal fluid status in a general population using whole body and calf bioimpedance techniques.

Normal fluid status (dry weight) can be identified by hydration markers established in the healthy population. The general population average could be influenced by age with its accompanying physiological changes and/or illness. The aims of this study were (1) to evaluate the effect of age and systolic blood pressure (SBP) on these markers; (2) to compare mean values of hydration markers as assessed by different bioimpedance techniques. Subjects from the general population (n = 212, males 105, 57.1% White, 31.6% Black, and 11.3% others) were studied. Body weight, height and SBP were measured. Whole body and calf bioimpedance (Hydra 4200) methods were utilized with subjects in the supine position. Calf normalized resistivity (CNR), fluid overload (FO), extracellular (ECV) and intracellular (ICV) volume measurements ECV/total body water (TBW) were calculated. Subjects were stratified by age; young (Group1): 18-35 years; middle (Group2): 36-60 years, senior (Group3): 61-80 years. Body mass index (BMI), CNR, and ECV/TBW differed significantly between age groups, and genders. ECV and FO increased with age in males. Decreased CNR (indicating relative increased fluid load) (p < 0.001) and increased SBP (p < 0.001) were associated with age in all three groups. CNR in Group1 was the same as in 36.0% of subjects in Group2 and 12.5% of subjects in Group3. In those subjects in Group2 and Group3, with CNR levels comparable to Group1 subjects, SBP was lower than in their peers in each respective age group. In conclusion average CNR in Group1 represents the range of healthy subjects. Since CNR is correlated with age, subjects in Group2 and Group3 are more likely to have fluid overload. Although about a third of subjects in Group2 and Group3 were in the range of Group1, the age and associated factors should be considered when CNR is used to identify fluid status in senior patients.

A Randomized Crossover Trial of Dietary Sodium Restriction in Stage 3-4 CKD.

BACKGROUND AND OBJECTIVES: Patients with chronic kidney disease (CKD) are often volume expanded and hypertensive. Few controlled studies have assessed the effects of a sodium-restricted diet (SRD) in CKD. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: We conducted a randomized crossover trial to evaluate the effect of SRD (target <2 g sodium per day) versus usual diet on hydration status (by bioelectrical impedance spectroscopy) and blood pressure (BP) between May of 2009 and May of 2013. A total of 58 adults with stage 3-4 CKD were enrolled from two academic sites: University of Michigan (n=37) and University of North Carolina at Chapel Hill (n=21); 60% were men, 43% were diabetic, 93% were hypertensive, and mean age was 61 years. Participants followed SRD or usual diet for 4 weeks, followed by a 2-week washout period and a 4-week crossover phase. During the SRD, dieticians provided counseling every 2 weeks, using motivational interviewing techniques. RESULTS: Whole-body extracellular volume and calf intracellular volume decreased by 1.02 L (95% confidence interval [95% CI], -1.48 to -0.56; P<0.001) and -0.06 L (95% CI, -0.12 to -0.01; P=0.02), respectively, implying decreased fluid content on the SRD compared with usual diet. Significant reductions in urinary sodium (-57.3 mEq/24 h; 95% CI, -81.8 to -32.9), weight (-2.3 kg; 95% CI, -3.2 to -1.5), and 24-hour systolic BP (-10.8 mmHg; 95% CI, -17.0 to -4.6) were also observed (all P<0.01). Albumin-to-creatinine ratio did not change significantly and mean serum creatinine increased slightly (0.1 mg/dl; 95% CI, -0.01 to 0.2; P=0.06). No period or carryover effects were observed. Results were similar when analyzed from phase 1 only before crossover, although P values were modestly larger because of the loss of power. CONCLUSIONS: In this randomized crossover trial, implementation of SRD in patients with CKD stage 3-4 resulted in clinically and statistically significant improvement in BP and hydration status. This simple dietary intervention merits a larger trial in CKD to evaluate effects on major clinical outcomes.

Calf Resistivity Values in Chronic Kidney Disease in a Caucasian Population.

BACKGROUND: Continuous intradialytic calf bioimpedance spectroscopy (cBIS) allows assessment of changes in calf extracellular fluid volume (ECV) to determine dry weight (DW) in hemodialysis patients. During dialysis, calf ECV decreases until excessive ECV has been removed and normalized resistivity ρN,5 rises to values comparable to those of a normal population (cBIS-DW). It is not clear whether chronic kidney disease (CKD) itself influences ρN,5 and whether normal values depend on race and ethnicity. METHODS: Therefore, we determined ρN,5 in 2 populations consisting of 35 healthy Caucasians and 37 with CKD in KDIGO stages G2-G4. Calf resistivity was determined using a bioimpedance spectrum analyzer (Xitron Technologies, San Diego, CA, USA) and was normalized for body mass index. RESULTS: ρN,5 was significantly higher in healthy subjects than in CKD patients (males: 18.2 ± 2.2 vs. 15.0 ± 2.8 × 10-2·Ωm3kg-1, p < 0.001; females: 19.7 ± 3.2 vs. 16.4 ± 3.3 × 10-2·Ωm3kg-1, p = 0.009). ρN,5 in Caucasians was significantly lower than in previously examined North American healthy subjects with prevailing African American race or Hispanic ethnicity (males: 18.2 ± 2.2 vs. 20.5 ± 2.0 × 10-2·Ωm3kg-1, p < 0.001; females: 19.7 ± 3.2 vs. 21.7 ± 2.6 × 10-2·Ωm3kg-1, p = 0.026). CONCLUSION: We present the first determination of ρN,5 values in a Caucasian healthy as well as a non-dialysis dependent CKD population. Both groups differ significantly. Due to higher amounts of extracellular water, subclinical fluid overload already occurs in pre-dialysis stages of CKD. ρN,5 in Caucasians differs significantly from previously established normal ranges in other races/ethnicities. Population-based reference ranges should be established and used in the future to determine DW by means of cBIS.

Validating Body Fat Assessment by Bioelectric Impedance Spectroscopy in Taiwanese Hemodialysis Patients.

OBJECTIVE: Obesity is becoming increasingly common in hemodialysis (HD) patients and is associated with inflammation and increased mortality. The primary aim of the present study was to evaluate the accuracy and variability of the bioimpedance device in measuring body fat in Taiwanese dialysis patients. DESIGN: Cross-sectional study. SUBJECTS: One hundred twenty-two adult patients receiving HD in a single hospital in Taiwan. SETTING: We compared the results of fat mass (FM) measured by dual-energy x-ray absorptiometry (DEXA) and bioelectrical impedance spectroscopy device (Body composition monitor, BCM). MAIN OUTCOME MEASUREMENT: FM measured by BCM was calculated by subtracting fat-free mass (FFM) from body mass assuming fractional hydration of FFM of 0.73 or the proprietary prediction equations from the BCM model. RESULTS: Assessment of whole-body composition showed that percentage FM measured using the 2 techniques was highly correlated when using the BCM model or estimating from total body water using constant (0.73) hydration (r = 0.87, P < .001). There was no evident difference in measurement between patients gender. The Bland-Altman plot also showed good agreement of percentage of FM (t = 3.82; P < .001). In female patients, it was found that BCM significantly underestimated mean FM as compared to DEXA. However, the mean differences of the estimates between the methods were small (0.35 ± 3.00 kg) and with Bland-Altman plot the limits of agreements were -5.5 to 6.2 kg (P = .40) for FM in female patients. CONCLUSIONS: Using DEXA as the reference test, BCM is a valid tool for the assessment of total body fat in HD patients. Hence, it may provide a more accessible tool for early detection of changes in body composition in these high-risk patients.

Techniques for assessing fluids status in patients with kidney disease.

PURPOSE OF REVIEW: The aim of this article is to present current information on techniques for fluid status assessment in patients with kidney disease. The methods can be broadly categorized into biomarkers, ultrasound, blood volume monitoring, and bioimpedance. RECENT FINDINGS: Biomarkers including atrial natriuretic peptide and B-type natriuretic peptide have been shown to provide information about relative changes in fluid status. Ultrasound is applied to measure inferior vena cava indices, pulmonary indicators, and vascular indicators of fluid overload. Relative blood volume monitoring is used to measure change in intravascular fluid during hemodialysis. While in principle appealing, measurement of absolute blood volume has seen limited use to date. Bioimpedance techniques such as vector analysis, whole body, and regional bioimpedance spectroscopy, have shown their ability to estimate fluid status. SUMMARY: The interpretation of biomarkers is complicated by the presence of cardiac disease. All ultrasound methods have some correlation with fluid status; however, operator dependency limits their routine use. Bioimpedance methods and relative blood volume monitoring are increasingly used to assess fluid status in patients with acute or chronic kidney disease. Measurement of absolute blood volume holds promise for the future.

Estimation of body composition and normal fluid status using a calf bioimpedance technique.

UNLABELLED: The aims of this study in hemodialysis (HD) patients were: 1. To evaluate the relationship of calf bioimpedance with total body composition and fluid status as measured by gold standard methods. 2. To investigate the ability of calf normalized resistivity (CNR) to predict the normal fluid status (dry weight: DW) in a prospective study. In the body composition study (n = 41), fluid status (ECV(Br)/FFM(MRI)), muscle mass (MM(MRI)), and total adipose tissue (TAT(MRI)) were measured by dilution (D2O and Br) and MRI methods three hours prior to HD treatment. Calf extracellular and intracellular resistance, resistivity, and CNR were measured with a multi-frequency bioimpedance device (Hydra 4200). In the fluid status study (n = 32 with 429 measurements), a nonlinear model based on the differences in CNR between patients and healthy subjects was established to predict DW(cBIS) previously determined by a separate continuous calf bioimpedance spectroscopy (cBIS) method. CNR significantly correlated with a gold standard hydration marker (ECV(Br)/FFM(MRI)). Calf body composition models were highly correlated with MM(MRI) (R(2) = 0.85) and TAT(MRI) (R(2) = 0.85). DW(cBIS) prediction was validated with a CNR model in the degree of differences of 0.94 ± 0.18, 0.39 ± 0.7 and -0.02 ± 0.8 kg from DW(cBIS) when post HD fluid overload was 1.8 ± 1.2, 1.15 ± 0.8 and 0.54 ± 0.5 kg, respectively. These differences are not considered to be clinically significant. CONCLUSION: This practical method of calf bioimpedance is useful to predict body composition and normal fluid status in dialysis patients.

Bioimpedance can solve problems of fluid overload.

Bioimpedance (BI) techniques for measuring normal hydration status (NHS) can be generally classified as (1) by frequency as single frequency at 50 kHz, BI analysis, and multifrequency BI spectroscopy and (2) by method as whole body (wrist to ankle) measurement and calf BI spectroscopy. The aim of this article was to review current BI methods for clinical practice in patients with end-stage of kidney disease. BI vector analysis using whole-body single-frequency BI at 50 kHz may be useful for population studies to indicate a range of degree of fluid loading and of nutritional status. Whole body multifrequency BI spectroscopy is used to estimate extracellular (ECV), intracellular fluid volume, and total body water in dialysis patients. The whole-body BI model is used in the body composition monitor (BCM). The whole-body BI model is established with ECV, intracellular fluid volume, and body weight based on parameters from regression analysis in healthy subjects to calculate fluid overload in dialysis patients. Calf BI methods have been developed to measure NHS by 2 ways: (1) continuous measurement of the intradialytic resistance curve until flattening occurs; (2) calf normalized resistivity in the range of healthy subjects (18.5 × 10(-2) Ω m(3)/kg in male and 19.1 × 10(-2) Ω m(3)/kg in female). In general, for population studies, BI vector analysis or ECV/total body water may be useful; BCM is a commercially available device that can certainly guide volume reduction safely over time. For more exact measure of fluid overload, calf BI methods appear to be most accurate, but these are at present research tools. BI techniques are not only useful in assessing NHS but also in the study of nutrition and body composition.

Agreement of single- and multi-frequency bioimpedance measurements in hemodialysis patients: an ancillary study of the Frequent Hemodialysis Network Daily Trial.

BACKGROUND: Bioimpedance analysis (BIA) is well established to assess body composition. Agreements between single- and multi-frequency bioimpedance (SF-BIA, MF-BIS) measurements in subjects undergoing 6 or 3 times/week hemodialysis (HD) were analyzed. METHODS: Total body water (TBW) and intra- and extracellular fluid (ICF, ECF) of subjects enrolled in the Frequent Hemodialysis Network (FHN) Daily Trial (www.clinicaltrials.gov No. NCT00264758) were measured with a Hydra 4200 at baseline (BL) and at 5 months (M5). Volumes were computed using SF (at 50 kHz) and MF approaches. Agreement was assessed by means of linear regression and Bland-Altman analysis and treatment effects by t test. RESULTS: 35 subjects (17 on the more frequent regimen, 26 males, 20 African-American, 48 ± 9 years, pre-HD weight 84 ± 19 kg) were studied. Assessments with SF-BIA and MF-BIS correlated significantly at BL and M5 in both arms. No proportional errors, but systematic biases over the entire range of values were found at BL and M5. Agreement did not differ between subjects randomized to either HD treatment arm at both time points. MF-BIS appears to have better precision than SF-BIA allowing the observation of a significant treatment effect by the intervention [-1.5 (95% CI -2.5 to -0.5) l] on ECF, not found for ECF SF-BIA. Precision also affected the statistical power of the SF-BIA data in the current analysis. CONCLUSION: Both methods showed agreement without significant proportional errors regardless of HD frequency and can be used for longitudinal analyses. SF-BIA has lower precision which needs thorough consideration in the design of future trials with similar outcomes.

Effect of change in fluid distribution in segments in hemodialysis patients at different ultrafiltration rates on accuracy of whole body bioimpedance measurement.

This study explored divergence (error) between ultrafiltration volumes (UFV) and intradialytic changes in extracellular volume (ΔECV) in hemodialysis (HD) patients measured by whole body (wBIS) and sum of segmental bioimpedance spectroscopy (sBIS). The primary aim of the study was to evaluate the effect of different ultrafiltration rates (UFR) on error of estimation of ΔECV by changes in their distribution in body segments (arm, trunk, and leg). Forty-four HD patients (26 men, age 63.5 ± 14.3 yr) were studied twice in the same week following high and low UFR treatments. ΔECV and distributions (segmental ΔECV/Σsegmental ΔECV, %) in arm, trunk, and leg were measured. ΔECV by wBIS underestimated UFV (0.58 ± 0.43 in high vs. 0.36 ± 0.5 liters at low UFR; P < 0.001, respectively); however, using sBIS no significant difference between UFV and ΔECV was present. Divergence using wBIS but not sBIS correlated positively with UFR. ΔECV distribution in trunk and leg at high UFR (44.1 ± 8.3, 47.2 ± 8.5, %) differed significantly (P < 0.01) from low UFR (36 ± 15.7, 53.8 ± 14.7) respectively, but in arm did not differ between UFR. Primary sources of whole body resistance are arms and legs. Due to different cross-sectional areas between trunk and limbs, wBIS is insensitive to detection of changes in trunk volume. At higher UFR, plasma water was rapidly and largely removed from the trunk but with only a small change in whole body resistance. As a result, accuracy of estimation of ECV by wBIS is further decreased by high UFR, while sBIS remains accurate using separate measurements of segmental volumes.

Comparison of bioimpedance techniques to detect changes in fluid status in hemodialysis patients.

UNLABELLED: Bioimpedance (BI) is maturing as a clinical technique for assessing fluid volume status. The aim of this study was to compare the sensitivity of four BI methods to detect changes in fluid status in hemodialysis patients. METHODS: Forty-five patients were studied twice in the same week, i.e. once after the long and short interdialytic intervals, respectively. The four BI methods used were: (a) calf normalized resistivity (CNR) at a 5-kHz frequency, (b) whole-body multifrequency BI spectroscopy (MF-BIS) to estimate the normal hydration weight (NHWWBM), (c) whole-body MF-BIS to estimate the ratio of extracellular volume to total body water (wECV/wTBW), and (d) whole-body single-frequency (50 kHz) BI analysis to compute the ratio of ECV (sfECV) to TBW (sfTBW). RESULTS: The relationship (slope of the regressive line) between relative changes (%) in the above mentioned four BI parameters and differences in weight (kg) was most pronounced with CNR (5.2 ± 1.6%/kg), followed by wECV/wTBW (1.7 ± 0.7%/kg) and NHWWBM (0.73 ± 0.2%/kg). Changes in sfECV/sfTBW and differences in weight were not correlated. CONCLUSIONS: CNR is more sensitive than whole-body BIS for detecting differences in fluid status.

The association between arterial stiffness and fluid status in peritoneal dialysis patients.

OBJECTIVES: In this study our aim was to evaluate the relationship between degree of fluid status and arterial stiffness measured by pulse wave velocity (PWV) in peritoneal dialysis (PD) patients. Fluid status was determined by different methods including fluid overload measured by bioimpedance (Body Composition Monitor, BCM), calf normalized resistivity (CNR), plasma N-terminal fragment of B-type natriuretic peptide (NT-proBNP) and extracellular to intracellular water ratio (ECW/ICW). METHODS: Sixty PD patients were evaluated. They were stratified into normo- and hypervolemic groups according to their fluid overload (FO). CNR was calculated from resistance at 5 kHz using calf bioimpedance spectroscopy. Arterial stiffness was assessed by PWV. Additionally, all patients underwent transthoracic echocardiography and had levels of NT-proBNP measured. RESULTS: PWV was higher in the hypervolemic compared to normovolemic patients (9.99 ± 2.4 m/sec vs 7.48 ± 2.3 m/sec, p < 0.001). Hypervolemic patients had higher NT-proBNP levels (3065 ± 981 pg/mL vs 1095 ± 502 pg/mL, p < 0.001), a higher ratio of ECW/ICW; (0.93 ± 0.11 vs 0.81 ± 0.08, p < 0.001) and lower CNR (13.7 ± 2.4 vs 16.0 ± 3.3 W m(3)/kg(*)10(-2), p = 0.005). NT-pro BNP level, ECW/ICW ratio, relative FO, and left ventricular (LV) mass index were positively and CNR negatively correlated with PWV. Relative FO and CNR independently predicted PWV in multivariate analysis adjusted for age, duration of PD, body mass index and mean arterial pressure. CONCLUSIONS: Arterial stiffness is increased in fluid-overloaded PD patients. Our results indicated that fluid status is an independent predictor of PWV.

Comparison of fluid volume estimates in chronic hemodialysis patients by bioimpedance, direct isotopic, and dilution methods.

Bioimpedance analysis (BIA) is accepted for the assessment of total-body water (TBW), intracellular fluid (ICF) and extracellular fluid (ECF). We aimed to compare precision and accuracy of single and multi-frequency-BIA to direct estimation methods (DEMs) of TBW, ECF, and ICF in hemodialysis patients. Linear regression analysis of volume estimates in 49 patients by single- and multi-frequency-BIA correlated significantly with DEMs. Bland-Altman analysis (BAA) found systemic bias for ECF single-frequency-BIA vs. ECF-DEMs. No other systematic biases were found. Proportional errors were found by BAA of ICF and ECF assessments with single- and multi-frequency bioimpedance spectroscopy compared to the DEMs. Comparisons of indirect methods (IEMs) to DEMs showed no significant differences and proportional errors. Root mean-squared-error analysis suggested slightly better accuracy and precision of ICF single-frequency-BIA vs. DEMs over ICF multi-frequency-BIA and IEMs to DEMs, and slightly better performance for ECF multi-frequency-BIA over both respective other methods. Compared to DEMs, there is slightly better accuracy for ECF multi- over single-frequency-BIA and ICF single- over multi-frequency-BIA. However the margin of differences between direct and indirect methods suggests that none of the analyzed methods served as a true "gold standard", because indirect methods are almost equally precise compared to DEMs.

Modeling of change in blood volume and extracellular fluid volume during hemodialysis.

Knowledge of dynamics of shift of fluid volume between intra- and extravascular compartments during hemodialysis (HD) is important for managing HD treatment to help patients approach dry weight without hypotension. The Relative blood volume (RBV) monitor indicates change in plasma volume based on the difference between ultrafiltration rate (UFR) and plasma refilling rate (PRR) during HD. However, the absolute value of PRR cannot be obtained from RBV. The aim of this study was to investigate whether fluid transport from the interstitial to blood spaces can be quantitatively analyzed with a two compartments model. 14 patients (30 measurements) were studied. RBV using a blood volume monitor (BVM, Fresenius) and calf extracellular volumes (ECV) by calf bioimpedance device (Hydra 4200, Xitron) were continuously measured during HD. A mathematic model was established with unknown transport coefficients (k1, k2, α, ß, γ, δ) and these coefficients were estimated using a Least Squares Optimization algorithm by fitting from experimental data. A high correlation (R(2)>0.8) between experimental data and calculation by the model were observed in both RBV and ECV measurements. Coefficients k1 and δ significantly differed with different degree of hydration. This model provides parameters which can used to understand relationships between degree of hydration and refilling rate.