Intraperitoneal fluid overestimates hydration status assessment by bioimpedance spectroscopy

Effect of peritoneal dialysate on bioelectrical impedance analysis variability in pediatric patients receiving peritoneal dialysis

BACKGROUND

Previous adult studies have yielded conflicting results regarding whether the presence (D +) or absence (D-) of peritoneal dialysate affects the accuracy of bioelectrical impedance analysis (BIA) measurements. The aim of this study was to investigate whether the accuracy of BIA data varies between D + and D- measurements in children.

METHODS

This cross-sectional study recruited chronic kidney disease stage 5 patients aged 3 to 18 years who received peritoneal dialysis. Body composition was assessed by multifrequency BIA, and values were compared between D + and D- measurements using the intraclass correlation coefficient (ICC).

RESULTS

Fifty paired BIA measurements were collected from 18 patients with a mean age of 13.6 ± 4.1 years and a mean dialysate fill volume of 1,006 ± 239.7 ml/m2. Sixteen out of 17 BIA parameters (94.1%) exhibited excellent correlations between D + and D- measurements (ICC values = 0.954, 0.998). There was a trend of increased fluid status, including extracellular water, edema index, and overhydration, in D + measurements, with mean differences (95% CIs) of 0.5 (0.4, 0.6) L, 0.002 (0.001, 0.002), and 0.1 (0.1, 0.2) L, respectively. Soft lean mass and fat-free mass were higher in D + measurements, with mean differences (95% CIs) of 1.4 (1.2, 1.6), and 1.6 (1.4, 1.8) kg, respectively. In addition, patients older than 10 years had a stronger correlation between D + and D- measurements than younger patients.

CONCLUSIONS

A total of 94.1% of BIA parameters exhibited excellent correlations between D + and D- measurements, especially patients older than 10 years. We recommend that BIA measurements be collected from children regardless of the presence of peritoneal dialysate.

Nutritional Assessments by Bioimpedance Technique in Dialysis Patients

Bioelectrical impedance analysis (BIA) has been extensively applied in nutritional assessments on the general population, and it is recommended in establishing the diagnosis of malnutrition and sarcopenia. The bioimpedance technique has become a promising modality through which to measure the whole-body composition in dialysis patients, where the presence of subclinical volume overload and sarcopenic obesity may be overlooked by assessing body weight alone. In the past two decades, bioimpedance devices have evolved from applying a single frequency to a range of frequencies (bioimpedance spectroscopy, BIS), in which the latter is incorporated with a three-compartment model that allows for the simultaneous measurement of the volume of overhydration, adipose tissue mass (ATM), and lean tissue mass (LTM). However, clinicians should be aware of common potential limitations, such as the adoption of population-specific prediction equations in some BIA devices. Inherent prediction error does exist in the bioimpedance technique, but the extent to which this error becomes clinically significant remains to be determined. Importantly, reduction in LTM has been associated with increased risk of frailty, hospitalization, and mortality in dialysis patients, whereas the prognostic value of ATM remains debatable. Further studies are needed to determine whether modifications of bioimpedance-derived body composition parameters through nutrition intervention can result in clinical benefits.

Phase Angle as a Risk Factor for Mortality in Patients Undergoing Peritoneal Dialysis

Phase angle (PhA) is measured using bioimpedance analysis and calculated using body reactance and resistance in the waveform at 50 kHz. Further studies are necessary to clarify the predictive efficacy of PhA in the mortality of peritoneal dialysis (PD) patients. The objective of this study was to assess the utility of PhA for predicting patient mortality and technique failure and compare the predictability of PhA with other risk factors. Our study had a retrospective cohort design. Our center routinely evaluates bioimpedance measurements for all prevalent PD patients (n = 199). The PhA was measured using multifrequency bioimpedance analysis. Our study evaluated patient and technique survival. There were 66, 68, and 65 patients in the low, middle, and high tertiles of PhA, respectively. The PhA values of the low, middle, and high tertiles were 3.6° (3.4-3.9), 4.4° (4.2-4.7), and 5.5° (5.2-6.0), respectively. The 5-year patient survival rates for the high, middle, and low tertiles were 100%, 81.7%, 69.9%, respectively (p < 0.001). The 5 year technique survival rates for the high, middle, and low tertiles were 91.9%, 74.8%, 63.7%, respectively (p = 0.004). Patient and technique survival increased as the PhA tertiles increased. Both univariate and multivariate Cox regression analyses demonstrated a consistent pattern. The prediction of patient or technique survival was better in PhA than in the other classical indicators. The present study demonstrated that PhA may be an effective indicator for predicting patient or technique survival in PD patients. Furthermore, it suggests that routine measurement of PhA and pre-emptive intervention to recover PhA according to causes of low PhA may help improve patient or technique survival in PD patients.

A comparison of fluid status determination using bioelectric impedance and the isotope dilution method in hemodialysis and peritoneal dialysis patients

We aimed to compare fluid status as determined by multifrequency bioimpedance spectroscopy (MF-BIS, Xitron 4200, USA) with that determined by the isotope dilution method among a contemporary Chinese cohort. Healthy Chinese subjects (HS, n = 30) were recruited in Zhengzhou. Hemodialysis (HD, n = 49) and peritoneal dialysis (PD, n = 48) patients were screened at the First Affiliated Hospital of Zhengzhou University. Total body water (TBW) and extracellular water (ECW) were measured by deuterium (TBW_D) and bromide (ECW_Br) dilution, respectively, and by MF-BIS using the Moissl equation (ME). The results of MF-BIS were compared to the reference method by Pearson analysis and Bland–Altman analysis in the three groups. The accuracy of overhydration as determined by MF-BIS was analyzed by receiver operating characteristic (ROC) curves. The TBW_D and TBW_ME values were 34.67 ± 7.31 and 35.41 ± 5.76 L, 37.30 ± 8.58 and 37.02 ± 8.10 L, and 38.61 ± 10.02 and 38.44 ± 7.59 L in the HS, HD and PD groups, respectively. The ECW_Br and ECW_ME values were 14.88 ± 3.33 and 15.53 ± 2.39 L, 16.24 ± 5.08 and 16.90 ± 3.93 L, and 19.08 ± 6.41 and 18.23 ± 3.61 L in the HS, HD and PD groups, respectively. The mean bias between TBW_D and TBW_ME was −0.74 L, 0.28 L, and 0.17 L in the HS, HD and PD groups, respectively. The mean bias between ECW_Br and ECW_ME was −0.65 L, −0.66 L, and 0.85 L in the HS, HD and PD groups, respectively. Compared to the ECW_Br/TBW_D ratio, the area under the ROC curve (AUC) of the ECW_ME/TBW_ME ratio for the diagnosis of overhydration was 0.76 and 0.68 in the HD and PD groups, respectively. In summary, MF-BIS with ME could be used in Chinese HD and PD patients.

Bioimpedance spectroscopy: Is a picture worth a thousand words?

Volume status can be difficult to assess in dialysis patients. Peripheral edema, elevated venous pressure, lung crackles, and hypertension are taught as signs of fluid overload, but sensitivity and specificity are poor. Bioimpedance technology has evolved from early single frequency to multifrequency machines which apply spectroscopic analysis (BIS), modeling data to physics-based mixture theory. Bioimpedance plots can aid the evaluation of hydration status and body composition. The challenge remains how to use this information to manage dialysis populations, particularly as interventions to improve over hydration, sarcopenia, and adiposity are not without side effects. It is therefore of no surprise that validation studies for BIS use in peritoneal dialysis patients are limited, and results from clinical trials are inconsistent and conflicting. Despite these limitations, BIS has clinical utility with potential to accurately evaluate small changes in body tissue components. This article explains the information a BIS plot ("picture") can provide and how it can contribute to the overall clinical assessment of a patient. However, it remains the role of the clinician to integrate information and devise treatment strategies to optimize competing patient risks, fluid and nutrition status, effects of high glucose PD fluids on membrane function, and quality of life issues.

Assessment of Hydration Status in Peritoneal Dialysis Patients: Validity, Prognostic Value, Strengths, and Limitations of Available Techniques

BACKGROUND

The majority of patients undergoing peritoneal dialysis (PD) suffer from volume overload and this overhydration is associated with increased mortality. Thus, optimal assessment of volume status in PD is an issue of paramount importance. Patient symptoms and physical signs are often unreliable indexes of true hydration status.

SUMMARY

Over the past decades, a quest for a valid, reproducible, and easily applicable technique to assess hydration status is taking place. Among existing techniques, inferior vena cava diameter measurements with echocardiography and natriuretic peptides such as brain natriuretic peptide and N-terminal pro-B-type natriuretic peptide were not extensively examined in PD populations; while having certain advantages, their interpretation are complicated by the underlying cardiac status and are not widely available. Bioelectrical impedance analysis (BIA) techniques are the most studied tool assessing volume overload in PD. Volume overload assessed with BIA has been associated with technique failure and increased mortality in observational studies, but the results of randomized trials on the value of BIA-based strategies to improve volume-related outcomes are contradictory. Lung ultrasound (US) is a recent technique with the ability to identify volume excess in the critical lung area. Preliminary evidence in PD showed that B-lines from lung US correlate with echocardiographic parameters but not with BIA measurements. This review presents the methods currently used to assess fluid status in PD patients and discusses existing data on their validity, applicability, limitations, and associations with intermediate and hard outcomes in this population. Key Message: No method has proved its value as an intervening tool affecting cardiovascular events, technique, and overall survival in PD patients. As BIA and lung US estimate fluid overload in different compartments of the body, they can be complementary tools for volume status assessment.

Bioimpedance spectroscopy for fluid status assessment in patients with decompensated liver cirrhosis: Implications for peritoneal dialysis

Bioimpedance spectroscopy (BIS) is routinely used in peritoneal dialysis patients and might aid fluid status assessment in patients with liver cirrhosis, but the effect of ascites volume removal on BIS-readings is unknown. Here we determined changes in BIS-derived parameters and clinical signs of fluid overload from before to after abdominal paracentesis. Per our pre-specified sample size calculation, we studied 31 cirrhotic patients, analyzing demographics, labs and clinical parameters along with BIS results. Mean volume of the abdominal paracentesis was 7.8 ± 2.6 L. From pre-to post-paracentesis, extracellular volume (ECV) decreased (20.2 ± 5.2 L to 19.0 ± 4.8 L), total body volume decreased (39.8 ± 9.8 L to 37.8 ± 8.5 L) and adipose tissue mass decreased (38.4 ± 16.0 kg to 29.9 ± 12.9 kg; all p < 0.002). Correlation of BIS-derived parameters from pre to post-paracentesis ranged from R² = 0.26 for body cell mass to R² = 0.99 for ECV. Edema did not correlate with BIS-derived fluid overload (FO ≥ 15% ECV), which occurred in 16 patients (51.6%). In conclusion, BIS-derived information on fluid status did not coincide with clinical judgement. The changes in adipose tissue mass support the BIS-model assumption that fluid in the peritoneal cavity is not detectable, suggesting that ascites (or peritoneal dialysis fluid) mass should be subtracted from adipose tissue if BIS is used in patients with a full peritoneal cavity.

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.

Classification of Hydration in Clinical Conditions: Indirect and Direct Approaches Using Bioimpedance

Although the need to assess hydration is well recognized, laboratory tests and clinical impressions are impractical and lack sensitivity, respectively, to be clinically meaningful. Different approaches use bioelectrical impedance measurements to overcome some of these limitations and aid in the classification of hydration status. One indirect approach utilizes single or multiple frequency bioimpedance in regression equations and theoretical models, respectively, with anthropometric measurements to predict fluid volumes (bioelectrical impedance spectroscopy-BIS) and estimate fluid overload based on the deviation of calculated to reference extracellular fluid volume. Alternatively, bioimpedance vector analysis (BIVA) uses direct phase-sensitive measurements of resistance and reactance, measured at 50 kHz, normalized for standing height, then plotted on a bivariate graph, resulting in a vector with length related to fluid content, and direction with phase angle that indexes hydration status. Comparison with healthy population norms enables BIVA to classify (normal, under-, and over-) and rank (change relative to pre-treatment) hydration independent of body weight. Each approach has wide-ranging uses in evaluation and management of clinical groups with over-hydration with an evolving emphasis on prognosis. This review discusses the advantages and limitations of BIS and BIVA for hydration assessment with comments on future applications.

Fluid management and bioimpedance study in peritoneal dialysis

PURPOSE OF REVIEW

Maintaining euvolaemia is an essential yet challenging objective in management of patients on peritoneal dialysis. Optimal method to assess volume status remains to be determined. In this review, we will discuss the risk factors and clinical outcomes of fluid overload in PD patients, and examine the role of bioimpedance study in fluid management.

RECENT FINDINGS

Applying bioimpedance study to measure body composition has attracted increasing attention because it is noninvasive and provides point-of-care assessment of fluid status. Observational studies suggested that presence of residual renal function did not necessarily protect peritoneal dialysis patients from developing fluid overload. This reinforces the importance of fluid restriction in peritoneal dialysis patients, in whom the thirst sensation could be exacerbated by hyperglycaemia. Notably, fluid overload is present in significant portion of asymptomatic patients. Moreover, bioimpedance-defined fluid overload is associated with increase in all-cause mortality, technique failure and possibly excess peritonitis rate.

SUMMARY

Although future studies should investigate the clinical benefit of bioimpedance-guided fluid management in high-risk subgroup, raising awareness among clinicians, together with structured clinical assessment and dietary counselling are the cornerstone to maintain stable fluid status.

Dialysis vintage stratified comparison of body composition, hydration and nutritional state in peritoneal dialysis and hemodialysis patients

INTRODUCTION

Body mass decomposition and hydration state imbalances affect patients on maintenance dialysis. We compared body composition, hydration and nutritional state of patients on peritoneal dialysis (PD) and hemodialysis (HD) based on dialysis vintage (DV).

MATERIAL AND METHODS

Three hundred and fifty-nine prevalent patients on HD (n = 301) and PD (n = 58) were divided into 3 subgroups depending on DV: < 2 years HD (n = 41) and PD (n = 28), 2-4 years HD (n = 111) and PD (n = 17), > 4 years HD (n = 149) and PD (n = 13). Bioimpedance analysis delivered data including overhydration (OH), Lean (LTM) and adipose lipids mass (FAT). Other measurements included daily diuresis (DD), subjective global assessment (SGA) and serum albumin (alb), C-reactive protein (CRP) and total cholesterol (TChol), and hemoglobin (Hb).

RESULTS

Dialysis vintage < 2 years. Hemodialysis patients were older (65.5 ±18.5 vs. 50.9 ±17.1; p < 0.01) with a higher mortality (28 vs. 1; p < 0.01) and OH (8.0 ±4.3 vs. 1.6 ±3.1; p < 0.001). Hemoglobin (10.6 ±1.5 vs. 11.8 ±1.7; p < 0.05), TChol (180.2 ±47.0 vs. 211.7 ±46.3; p < 0.05), DD (871 ±729 vs. 1695 ±960; p < 0.001) and LTM (46.5 ±12.9 vs. 53.8 ±14.4; p < 0.05) were lower on HD. Dialysis vintage 2-4 years: when compared to PD, HD patients had higher OH (11.7 ±5.9 vs. 2.1 ±3.2; p < 0.001) and lower Hb (10.8 ±1.5 vs. 11.9 ±1.4; p < 0.01). Dialysis vintage > 4 years: compared to PD, HD patients had higher LTM (44.3 ±11.7 vs. 38.6 ±7.9; p < 0.05) and lower FAT (34.4 ±11.1 vs. 42.8 ±6.4; p < 0.01).

CONCLUSIONS

Dialysis patients' body composition depends on dialysis modality and DV. Dialysis vintage < 2 years is associated with better hydration, nutritional state, and survival in PD patients, but longer DV reduces these benefits. Dialysis vintage > 4 years associated with similar hydration and mortality in both PD and HD while body composition was better on HD.

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.

Pedal edema and jugular venous pressure for volume overload in peritoneal dialysis patients

Background

The diagnostic strength of the jugular venous pressure (JVP) and pedal edema as physical examination tools for the assessment of volume status has been minimally studied.

Methods

We conducted a prospective observational study in an outpatient peritoneal dialysis clinic in Saskatoon, Canada. Patients were adult (age 18 or older) peritoneal dialysis outpatients without any history of cardiac dysfunction, a central line, and current arteriovenous fistula. JVP was assessed by both a resident and a staff nephrologist, while the presence of edema was assessed by the resident only. Likelihood ratios were calculated for the absence or presence of pedal edema as well as the JVP at multiple cutoffs. The criterion standard for volume overload was defined as an overhydration to extracellular water ratio of greater than or equal to 7 % as determined by bioimpedance (Body Composition Monitor—Fresnius Medical Care).

Results

Twenty-five separate patient encounters were assessed. Twelve patients were found to be volume overloaded while 13 were euvolemic. The presence and absence of edema were both significant signs for the presence (+likelihood ratio (LR) 16, 95 % confidence interval (CI) 1.02–260) or absence (−LR 0.44, 95 % CI 0.23–0.83) of volume overload, respectively. The JVP failed to reach statistical significance for the presence or absence of volume overload at any height above the sternal angle, although precision was poor for the positive likelihood ratio at cutoffs above 3 cm and the negative likelihood ratio at the 0 cm cutoff.

Conclusions

The presence of pedal edema is a good indicator of volume overload in peritoneal dialysis patients without cardiac dysfunction, although its absence cannot definitively rule out significant water excess. A JVP of 1 to 3 cm was found to be not a clinically significant sign. We are unable to comment on the diagnostic strength of a low (0 cm) or high (JVP >3 cm) due to poor precision.

Insulin Resistance in Nondiabetic Peritoneal Dialysis Patients: Associations with Body Composition, Peritoneal Transport, and Peritoneal Glucose Absorption

BACKGROUND AND OBJECTIVES

Insulin resistance has been associated with cardiovascular disease in peritoneal dialysis patients. Few studies have addressed the impact of fast transport status or dialysis prescription on insulin resistance. The aim of this study was to test whether insulin resistance is associated with obesity parameters, peritoneal transport rate, and glucose absorption.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Insulin resistance was evaluated with homeostasis model assessment method (HOMA-IR), additionally corrected by adiponectin (HOMA-AD). Enrolled patients were prevalent nondiabetics attending at Santo António Hospital Peritoneal Dialysis Unit, who were free of hospitalization or infectious events in the previous 3 months (51 patients aged 50.4 ± 15.9 years, 59% women). Leptin, adiponectin, insulin-like growth factor-binding protein 1 (IGFBP-1), and daily glucose absorption were also measured. Lean tissue index, fat tissue index (FTI), and relative fat mass (rel.FM) were assessed using multifrequency bioimpedance. Patients were categorized according to dialysate to plasma creatinine ratio at 4 hours, 3.86% peritoneal equilibration test, and obesity parameters.

RESULTS

Obesity was present in 49% of patients according to rel.FM. HOMA-IR correlated better with FTI than with body mass index. Significant correlations were found in obese, but not in nonobese patients, between HOMA-IR and leptin, leptin/adiponectin ratio (LAR), and IGFBP-1. HOMA-IR correlated with HOMA-AD, but did not correlate with glucose absorption or transport rate. There were no significant differences in insulin resistance indices, glucose absorption, and body composition parameters between fast and nonfast transporters. A total of 18 patients (35.3%) who had insulin resistance presented with higher LAR and rel.FM (7.3 [12.3, interquartile range] versus 0.7 [1.4, interquartile range], P<0.001, and 39.4 ± 10.1% versus 27.2 ± 11.5%, P=0.002, respectively), lower IGFBP-1 (8.2 ± 7.2 versus 21.0 ± 16.3 ng/ml, P=0.002), but similar glucose absorption and small-solute transport compared with patients without insulin resistance. FTI and LAR were independent correlates of HOMA-IR in multivariate analysis adjusted for glucose absorption and small-solute transport (r=0.82, P<0.001).

CONCLUSIONS

Insulin resistance in nondiabetic peritoneal dialysis patients is associated with obesity and LAR independent of glucose absorption and small-solute transport status. Fast transport status was not associated with higher likelihood of obesity or insulin resistance.