Effect of bioimpedance-defined overhydration parameters on mortality and cardiovascular events in patients undergoing dialysis: a systematic review and meta-analysis

Assessment of volume status of pediatric hemodialysis patients

BACKGROUND

Accurate volume status assessment and dry weight achievement are the most challenging goals for a nephrologist. We aimed to evaluate the role of ultrasonographic parameters including lung ultrasound and inferior vena cava (IVC) measurements as practical methods of volume status assessment in children on hemodialysis by comparing them with established techniques, such as clinical evaluation and bioimpedance spectroscopy.

METHODS

A prospective cross-sectional study compared pre- and post-dialysis volume status using bioimpedance spectroscopy (BIS) parameters and clinical data with ultrasonographic lung B-lines and IVC parameters in children on regular hemodialysis.

RESULTS

A total 60 children (mean age 9.4 ± 2.8 years) were enrolled. Twenty patients (33.3%) were clinically overloaded to varying degrees (17 patients had mild to moderate signs of fluid overload and 3 patients had moderate to severe signs of fluid overload). All other patients (66.7%) were clinically euvolemic. Sonographic parameters were significantly lower post-dialysis than pre-dialysis, including lung B-line count and IVC diameter. IVC collapsibility index mean was significantly higher post-dialysis than pre-dialysis. There was a significant correlation between the lung B-line count, IVC parameters, and BIS-measured overhydration both before and after hemodialysis. Nine patients had ≥ 8 B-lines post-dialysis, only three of them were hypertensive.

CONCLUSIONS

Clinical criteria alone are not specific for determining accurate fluid status in pediatric hemodialysis patients. Lung B-line score, IVC parameters, and BIS may be complementary to each other and to clinical data. Lung B-lines outperform IVC measurements and BIS in subclinical volume overload detection in pediatric hemodialysis patients.

Effects of overhydration, Kt/Vurea, β2-microglobulin on coronary artery calcification and mortality in haemodialysis patients

AIM

We studied the effects of overhydration (OH), Kt/Vurea and β2-microglobulin (β2-MG) on coronary artery calcification and mortality in patients undergoing haemodialysis (HD).

METHODS

The Agatston coronary artery calcium score (CACS), postdialysis body composition using bioimpedance analysis, single-pool Kt/Vurea and predialysis β2-MG at baseline were assessed and followed up for 3 years in patients undergoing HD. We performed logistic regression analyses for a CACS ≥400 and Cox proportional hazard analyses for all-cause and cardiovascular mortality.

RESULTS

The study involved 338 patients with a median age of 67 (56-74) years, dialysis duration of 70 (33-141) months and diabetes prevalence of 39.1% (132/338). Patients with a CACS ≥400 (n = 222) had significantly higher age, dialysis duration, male prevalence, diabetes prevalence, C-reactive protein, predialysis β2-MG, OH, extracellular water/total body water and overhydration/extracellular water (OH/ECW) but significantly lower Kt/Vurea than patients with a CACS <400 (n = 116) (p < .05). OH/ECW, Kt/Vurea and predialysis β2-MG were significant predictors of a CACS ≥400 (p < .05) after adjusting for age, dialysis duration, serum phosphate and magnesium. In all patients, cut-off values of OH/ECW, Kt/Vurea and predialysis β2-MG for a CACS ≥400 were 16%, 1.74 and 28 mg/L, respectively. After adjusting for dialysis duration, OH/ECW ≥16%, Kt/Vurea ≥1.74 and β2-MG ≥28 mg/L were significant predictors of 3-year all-cause mortality but not 3-year cardiovascular mortality.

CONCLUSION

Higher OH/ECW, higher predialysis β2-MG and lower Kt/Vurea values are significant risk factors for a CACS ≥400 and 3-year all-cause mortality in patients undergoing maintenance HD.

Comparison of whole body versus thoracic bioimpedance in relation to ultrafiltration volume and systolic blood pressure during hemodialysis

In contrast to whole body bioimpedance, which estimates fluid status at a single point in time, thoracic bioimpedance applied by a wearable device could enable continuous measurements. However, clinical experience with thoracic bioimpedance in patients on dialysis is limited. To test the reproducibility of whole body and thoracic bioimpedance measurements and to compare their relationship with hemodynamic changes during hemodialysis, these parameters were measured pre- and end-dialysis in 54 patients during two sessions. The resistance from both bioimpedance techniques was moderately reproducible between two dialysis sessions (intraclass correlations of pre- to end-dialysis whole body and thoracic resistance between session 1 and 2 were 0.711 [0.58-0.8] and 0.723 [0.6-0.81], respectively). There was a very high to high correlation between changes in ultrafiltration volume and changes in whole body thoracic resistance. Changes in systolic blood pressure negatively correlated to both bioimpedance techniques. Although the relationship between changes in ultrafiltration volume and changes in resistance was stronger for whole body bioimpedance, the relationship with changes in blood pressure was at least comparable for thoracic measurements. These results suggest that thoracic bioimpedance, measured by a wearable device, may serve as an interesting alternative to whole body measurements for continuous hemodynamic monitoring during hemodialysis.NEW & NOTEWORTHY We examined the role of whole body and thoracic bioimpedance in hemodynamic changes during hemodialysis. Whole body and thoracic bioimpedance signals were strongly related to ultrafiltration volume and moderately, negatively, to changes in blood pressure. This work supports the further development of a wearable device measuring thoracic bioimpedance longitudinally in patients on hemodialysis. As such, it may serve as an innovative tool for continuous hemodynamic monitoring during hemodialysis in hospital or in a home-based setting.

Bioimpedanciometry in nutritional and hydration assessments in a single dialysis center

BACKGROUND

Bioimpedance analysis (BIA) has been demonstrated to add accuracy to nutritional and volume status assessments in dialysis (HD) patients.

AIM

to describe a sample of dialysis patients from a single center on their demographics and BIA of volume distribution and nutritional status, and mortality during 12-month follow-up.

METHODS

prospective observational cohort study to evaluate vintage HD patients with single-frequency BIA.

RESULTS

we evaluated 82 patients, 29% over 65 years old. Elderly patients had higher ECW/TBW (0.51 vs. 0.44, p < 0.0001), and narrower phase angle (PhA) (4.9 vs. 6.4º, p < 0.0001). Fifteen patients (18.2%) died during follow-up, eight (53%) were elderly. Death was associated with age (62.6 vs. 50.2 years, p = 0.012), post-HD PhA (4.8 vs. 6.2º, p = 0.0001), and post-HD ECW/TBW (0.50 vs. 0.45, p = 0.015). The ROC curve analysis to predict mortality found ECW/TBW ≥ 0.47 and PhA ≤ 5.5º to have the best sensitivity and specificity. One-year patient survival was lower with post-HD ECW/TBW ≥ 0.47 (69.5% vs. 90.6%, p = 0.019), age ≥ 65 years (64.2%, vs. 86.2%, p = 0.029), and PhA ≤ 5.5º (68.2 vs. 91.0%, p = 0.002). Cox regression analysis demonstrated that PhA [HR 5.04 (95%CI 1.60-15.86), p = 0.006] remained associated with death after adjusting for age and ECW/TBW.

CONCLUSION

BIA is useful in assessing volume distribution and nutrition in HD patients, and combined with clinical judgement, may help determine dry weight, especially in elderly patients. Narrower PhA and higher ECW/TBW after HD were associated with poorer one-year survival.

Future lines of research on phase angle: Strengths and limitations

Bioelectrical impedance analysis (BIA) is the most widely used technique in body composition analysis. When we focus the use of phase sensitive BIA on its raw parameters Resistance (R), Reactance (Xc) and Phase Angle (PhA), we eliminate the bias of using predictive equations based on reference models. In particular PhA, have demonstrated their prognostic utility in multiple aspects of health and disease. In recent years, as a strong association between prognostic and diagnostic factors has been observed, scientific interest in the utility of PhA has increased. In the different fields of knowledge in biomedical research, there are different ways of assessing the impact of a scientific-technical aspect such as PhA. Single frequency with phase detection bioimpedance analysis (SF-BIA) using a 50 kHz single frequency device and tetrapolar wrist-ankle electrode placement is the most widely used bioimpedance approach for characterization of whole-body composition. However, the incorporation of vector representation of raw bioelectrical parameters and direct mathematical calculations without the need for regression equations for the analysis of body compartments has been one of the most important aspects for the development of research in this area. These results provide new evidence for the validity of phase-sensitive bioelectrical measurements as biomarkers of fluid and nutritional status. To enable the development of clinical research that provides consistent results, it is essential to establish appropriate standardization of PhA measurement techniques. Standardization of test protocols will facilitate the diagnosis and assessment of the risk associated with reduced PhA and the evaluation of changes in response to therapeutic interventions. In this paper, we describe and overview the value of PhA in biomedical research, technical and instrumental aspects of PhA research, analysis of Areas of clinical research (cancer patients, digestive and liver diseases, critical and surgical patients, Respiratory, infectious, and COVID-19, obesity and metabolic diseases, Heart and kidney failure, Malnutrition and sarcopenia), characterisation of the different research outcomes, Morphofunctional assessment in disease-related malnutrition and other metabolic disorders: validation of PhA with reference clinical practice techniques, strengths and limitations. Based on the detailed study of the measurement technique, some of the key issues to be considered in future PhA research. On the other hand, it is important to assess the clinical conditions and the phenotype of the patients, as well as to establish a disease-specific clinical profile. The appropriate selection of the most critical outcomes is another fundamental aspect of research.

Bioimpedance spectroscopy fluid analysis in acute high-risk abdominal surgery, a prospective clinician-blinded observational feasibility study

Objective assessment of fluid status in critical surgical care may help optimize perioperative fluid administration and prevent postoperative fluid retention. We evaluated the feasibility of hydration status and fluid distribution assessment by Bioimpedance spectroscopy Analysis (BIA) in patients undergoing acute high-risk abdominal (AHA) surgery. This observational study included 73 patients undergoing AHA surgery. During the observational period (0-120 h), we registered BIA calculated absolute fluid overload (AFO) and relative fluid overload (RFO), defined as AFO/extracellular water ratio, as well as cumulative fluid balance and weight. Based on RFO values, hydration status was classified into three categories: dehydrated (RFO <  - 10%), normohydrated (- 10% ≤ RFO ≤  + 15%), overhydrated RFO > 15%. We performed a total of 365 BIA measurements. Preoperative overhydration was found in 16% of patients, increasing to 66% by postoperative day five. The changes in BIA measured AFO correlated with the cumulative fluid balance (r2 = 0.44, p < .001), and change in weight (r2 = 0.55, p < .0001). Perioperative overhydration measured with BIA was associated with worse outcome compared to patients with normo- or dehydration. We have demonstrated the feasibility of obtaining perioperative bedside BIA measurements in patients undergoing AHA surgery. BIA measurements correlated with fluid balance, weight changes, and postoperative clinical complications. BIA-assessed fluid status might add helpful information to guide fluid management in patients undergoing AHA surgery.

Perioperative changes in fluid distribution and haemodynamics in acute high-risk abdominal surgery

BACKGROUND

Understanding the pathophysiology of fluid distribution in acute high-risk abdominal (AHA) surgery is essential in optimizing fluid management. There is currently no data on the time course and haemodynamic implications of fluid distribution in the perioperative period and the differences between the surgical pathologies.

METHODS

Seventy-three patients undergoing surgery for intestinal obstruction, perforated viscus, and anastomotic leakage within a well-defined perioperative regime, including intraoperative goal-directed therapy, were included in this prospective, observational study. From 0 to 120 h, we measured body fluid volumes and hydration status by bioimpedance spectroscopy (BIA), fluid balance (input vs. output), preload dependency defined as a > 10% increase in stroke volume after preoperative fluid challenge, and post-operatively evaluated by passive leg raise.

RESULTS

We observed a progressive increase in fluid balance and extracellular volume throughout the study, irrespective of surgical diagnosis. BIA measured variables indicated post-operative overhydration in 36% of the patients, increasing to 50% on the 5th post-operative day, coinciding with a progressive increase of preload dependency, from 12% immediately post-operatively to 58% on the 5th post-operative day and irrespective of surgical diagnosis. Patients with overhydration were less haemodynamically stable than those with normo- or dehydration.

CONCLUSION

Despite increased fluid balance and extracellular volumes, preload dependency increased progressively during the post-operative period. Our observations indicate a post-operative physiological incoherence between changes in the extracellular volume compartment and inadequate physiological preload control in patients undergoing AHA surgery. Considering the increasing overhydration during the observational period, our findings show that an indiscriminate correction of preload dependency with intravenous fluid bolus could lead to overhydration. Trial registration clinicaltrials.gov. (NCT03997721), Registered 23 May 2019, first participant enrolled 01 June 2019.

Ratio of extracellular water to intracellular water and simplified creatinine index as predictors of all-cause mortality for patients receiving hemodialysis

The bioelectrical impedance analysis-measured ratio of extracellular water (ECW) to intracellular water (ICW) reflects fluid volume and malnutrition. It may be an indicator of protein-energy wasting and muscle wasting in hemodialysis patients. We examined the association between the ECW/ICW ratio and simplified creatinine index, which is a new surrogate marker of protein-energy wasting and muscle wasting, and whether their combination can accurately predict mortality. A total of 224 patients undergoing hemodialysis for more than 6 months and having undergone bioelectrical impedance analysis for the assessment of body composition were included. Patients were divided into two groups based on the cut-off values of the ECW/ICW ratio (0.57) and simplified creatinine index (20.4 mg/kg/day) for maximumly predicting mortality. Thereafter, they were cross-classified into four groups with each cut-off point. The ECW/ICW ratio was independently associated with the simplified creatinine index (β = -0.164; P = 0.042). During a follow-up of 3.5 years (2.0-6.0 years), 77 patients died. A higher ECW/ICW ratio (adjusted hazard ratio, 3.66, 95% confidence interval 1.99-6.72, P <0.0001) and lower simplified creatinine index (adjusted hazard ratio, 2.25, 95% confidence interval 1.34-3.79, P = 0.0021) were independently associated with an increased risk of all-cause mortality. The adjusted hazard ratio for the higher ECW/ICW ratio and lower simplified creatinine index group vs. the lower ECW/ICW ratio and higher simplified creatinine index group was 12.22 (95% confidence interval 3.68-40.57, p <0.0001). Furthermore, the addition of the ECW/ICW ratio and simplified creatinine index to the baseline risk model significantly improved the C-index from 0.831 to 0.864 (p = 0.045). In conclusion, the ECW/ICW ratio may be a surrogate marker of muscle wasting. Moreover, combining the ECW/ICW ratio and simplified creatinine index may improve the accuracy of predicting all-cause mortality and help stratify the mortality risk of hemodialysis patients.

Bioimpedanciometria em avaliações nutricionais e de hidratação em um único centro de diálise

RESUMO Antecedentes: Análise de bioimpedância (BIA) demonstrou adicionar acurácia às avaliações de estado nutricional e de volume em pacientes em diálise (HD). Objetivo: descrever amostra de pacientes em diálise de um único centro quanto aos aspectos demográficos e BIA na distribuição de volume e no estado nutricional, e a mortalidade em 12 meses de acompanhamento. Métodos: estudo de coorte observacional prospectivo para avaliar pacientes prevalentes em HD com BIA de frequência única. Resultados: avaliamos 82 pacientes, 29% acima de 65 anos. Pacientes idosos apresentaram maior AEC/ACT (0,51 vs. 0,44; p < 0,0001), e ângulo de fase mais estreito (PhA) (4,9 vs. 6,4º; p < 0,0001). Quinze pacientes (18,2%) foram a óbito durante acompanhamento, oito (53%) eram idosos. Óbito foi associado à idade (62,6 vs. 50,2 anos, p = 0,012), PhA pós-HD (4,8 vs. 6,2º; p = 0,0001), e AEC/ACT pós-HD (0,50 vs. 0,45, p = 0,015). A análise da curva ROC para prever mortalidade constatou que AEC/ACT ≥ 0,47 e PhA ≤ 5,5º apresentam melhor sensibilidade e especificidade. Sobrevida do paciente em um ano foi menor com AEC/ACT pós-HD ≥ 0,47 (69,5% vs. 90,6%; p = 0,019), idade ≥ 65 anos (64,2% vs. 86,2%; p = 0,029), e PhA ≤ 5,5º (68,2 vs. 91,0%; p = 0,002). A análise de regressão de Cox demonstrou que PhA [HR 5,04 (IC 95% 1,60–15,86); p = 0,006] permaneceu associado ao óbito após ajuste para idade e AEC/ACT. Conclusão: BIA é útil ao avaliar distribuição de volume e nutrição em pacientes em HD, e juntamente com julgamento clínico, pode ajudar a determinar o peso seco, principalmente em pacientes idosos. PhA mais estreito e maior AEC/ACT pós-HD foram associados a pior sobrevida em um ano.

Bioimpedance indices of fluid overload and cardiorenal outcomes in heart failure and chronic kidney disease: a systematic review

BACKGROUND

Bioimpedance-based estimates of fluid overload have been widely studied and systematically reviewed in dialysis populations, but data from heart failure or non-dialysis chronic kidney disease (CKD) populations have not.

METHODS AND RESULTS

We conducted a systematic review of studies using whole-body bioimpedance from heart failure and non-dialysis CKD populations which reported associations with mortality, cardiovascular outcomes and/or CKD progression. We searched MEDLINE, Embase databases and the Cochrane CENTRAL registry from inception to 14^th March 2022. Thirty one eligible studies were identified: 20 heart failure and 11 CKD cohorts, with 2 studies including over 1000 participants. A wide range of different bioimpedance methods were used across the studies (heart failure: 8 parameters; CKD: 6). Studies generally reported positive associations, but between-study differences in bioimpedance methods, fluid overload exposure definitions, and modelling approaches precluded meta-analysis. The largest identified study was in non-dialysis CKD (Chronic Renal Insufficiency Cohort, 3751 participants) which reported adjusted hazard ratios (95% confidence intervals) for phase angle <5.59 versus ≥6.4 of 2.02 (1.67-2.43) for all-cause mortality; 1.80 (1.46-2.23) for heart failure events; and 1.78 (1.56-2.04) for CKD progression.

CONCLUSIONS

Bioimpedance indices of fluid overload are associated with risk of important cardiorenal outcomes in heart failure and CKD. Facilitation of more widespread use of bioimpedance needs consensus on the optimum device, standardized analytical methods, and larger studies including more detailed characterization of cardiac and renal phenotypes.

The Extracellular Mass to Body Cell Mass Ratio as a Predictor of Mortality Risk in Hemodialysis Patients

The extracellular mass/body cell mass ratio (ECM/BCM ratio) is a novel indicator of nutritional and hydration status in hemodialysis (HD) patients. This study aimed to explore the ECM/BCM ratio as a predictor of mortality risk with nutritional-inflammatory markers in HD patients. A prospective observational study was conducted in 90 HD patients (male: 52.2%; DM: 25.60%). Clinical and biochemical parameters [serum albumin, serum C-reactive protein (s-CRP), interleukine-6 (IL-6)] were analysed and bioelectrical impedance analysis (BIA) was performed. Protein-energy wasting syndrome (PEW) was diagnosed using malnutrition-inflammation score (MIS). Based on BIA-derived measurements, the ECM/BCM ratio with a cut-off point of 1.20 was used as a PEW-fluid overload indicator. Comorbidity by Charlson index and hospital admissions were measured. Out of 90 HD patients followed up for 36 months, 20 patients (22.22%) died. PEW was observed in 24 survivors (34.28%) and all non-survivors. The ECM/BCM ratio was directly correlated with MIS, s-CRP, Charlson index and hospital admissions but was negatively correlated with phase angle and s-albumin (all, p < 0.001). Values of the ECM/BCM ratio ≥ 1.20 were associated with higher probability of all-cause mortality (p = 0.002). The ECM/BCM ratio ≥ 1.20, IL-6 ≥ 3.1 pg/mL, s-CRP and s-albumin ≥ 3.8 g/dL and Charlson index were significantly associated with all-cause mortality risk in multivariate adjusted analysis. This study demonstrates that the ECM/BCM ratio ≥ 1.20 as a nutritional marker and/or fluid overload indicator had a significant prognostic value of death risk in HD patients.