Utility of Volume Assessment Using Bioelectrical Impedance Analysis in Critically Ill Patients Receiving Continuous Renal Replacement Therapy: A Prospective Observational Study

Nutritional management of children with acute kidney injury-clinical practice recommendations from the Pediatric Renal Nutrition Taskforce

The nutritional management of children with acute kidney injury (AKI) is complex. The dynamic nature of AKI necessitates frequent nutritional assessments and adjustments in management. Dietitians providing medical nutrition therapies to this patient population must consider the interaction of medical treatments and AKI status to effectively support both the nutrition status of patients with AKI as well as limit adverse metabolic derangements associated with inappropriately prescribed nutrition support. The Pediatric Renal Nutrition Taskforce (PRNT), an international team of pediatric renal dietitians and pediatric nephrologists, has developed clinical practice recommendations (CPR) for the nutritional management of children with AKI. We address the need for intensive collaboration between dietitians and physicians so that nutritional management is optimized in line with AKI medical treatments. We focus on key challenges faced by dietitians regarding nutrition assessment. Furthermore, we address how nutrition support should be provided to children with AKI while taking into account the effect of various medical treatment modalities of AKI on nutritional needs. Given the poor quality of evidence available, a Delphi survey was conducted to seek consensus from international experts. Statements with a low grade or those that are opinion-based must be carefully considered and adapted to individual patient needs, based on the clinical judgment of the treating physician and dietitian. Research recommendations are provided. CPRs will be regularly audited and updated by the PRNT.

Applying bio-impedance vector analysis (BIVA) to adjust ultrafiltration rate in critically ill patients on continuous renal replacement therapy: A randomized controlled trial

BACKGROUND

Bioimpedance vector analysis (BIVA) has been suggested as a valuable tool in assessing volume status in critically ill patients. However, its effectiveness in guiding fluid removal by continuous renal replacement therapy (CRRT) has not been evaluated.

METHODS

In this randomized controlled trial, 65 critically ill patients receiving CRRT were allocated on a 1:1 ratio to have UF prescribed and adjusted using BIVA fluid assessment in the intervention group (32 patients) or conventional clinical parameters (33 patients). The primary outcome was the lean body mass (LBM) water content at CRRT discontinuation, and the secondary outcomes included the mortality rate, urinary output, the duration of ventilation support, and ICU stay.

RESULTS

The study group was associated with a lower water content of LBM (80.7 ± 9.4 vs. 85.9 ± 10.4%; p < 0.05), and a higher mean UF-rate and urinary output (1.5 ± 0.8 vs. 1.2 ± 0.5 ml/kg/h and 0.9 ± 0.9 vs 0.5 ± 0.6 ml/kg/h, both: p < 0.05). The mortality rate, the length of ICU stay, and ventilation support duration were similar.

CONCLUSION

BIVA guided UF prescription may be associated with a lower rate of fluid overload. Larger studies are required to evaluate its impact on patients' outcomes.

Fluid Overload and Precision Net Ultrafiltration in Critically Ill Patients

BACKGROUND

Fluid overload is present in two-thirds of critically ill patients with acute kidney injury and is associated with morbidity, mortality, and increased healthcare resource utilization. Kidney replacement therapy (KRT) is frequently used for net fluid removal (i.e., net ultrafiltration [UFNET]) in patients with severe oliguric acute kidney injury. However, ultrafiltration has considerable risks associated with it, and there is a need for newer technology to perform ultrafiltration safely and to improve outcomes.

SUMMARY

Caring for a critically ill patient with oliguric acute kidney injury and fluid overload is one of the most challenging problems. Although diuretics are the first-line treatment for management of fluid overload, diuretic resistance is common. Various clinical practice guidelines support fluid removal using ultrafiltration during KRT. Emerging evidence from observational studies in critically ill patients suggests that both slow and fast rates of net fluid removal during continuous kidney replacement therapy are associated with increased mortality compared with moderate UFNET rates. In addition, fast UFNET rates are associated with an increased risk of cardiac arrhythmias. Randomized trials are required to examine whether moderate UFNET rates are associated with a reduced risk of hemodynamic instability, organ injury, and improved outcomes in critically ill patients. There is a need for newer technology for fluid removal in patients who do not meet traditional criteria for initiation of KRT. Emerging newer and miniaturized ultrafiltration devices may address an unmet clinical need.

KEY MESSAGES

Among critically ill patients with acute kidney injury and fluid overload requiring continuous kidney replacement therapy, use of higher and slower UFNET rates compared with moderate UFNET rates might be associated with poor outcomes. Newer minimally invasive technologies may allow for safe and efficient UFNET in patients with acute kidney injury who do not meet criteria for initiation of KRT.

The Use of Bioelectrical Impedance Analysis Measures for Predicting Clinical Outcomes in Critically Ill Children

Background

The study aimed to investigate the association of bioelectrical impedance analysis (BIA) for predicting clinical outcomes in critically ill children.

Methods

This single-center prospective observational study included patients admitted to a mixed Pediatric Intensive Care Unit (PICU). All patients underwent anthropometric measurement and BIA measurements in the first 24 h of admission. The patients were classified into different groups based on body mass index (BMI) for age. Electronic hospital medical records were reviewed to collect clinical data for each patient. All the obtained data were analyzed by the statistical methods.

Results

There were 231 patients enrolled in our study, of which 31.6% were diagnosed with malnutrition. The phase angle (PhA) of 90-day survivors was significantly higher than that of the non-survivors (4.3° ± 1.1°vs. 3.1° ± 0.9°, P = 0.02). The age-adjusted Spearman partial correlation analysis showed a weak negative correlation between PhA and duration of medical ventilation (r_s = -0.42, P < 0.05). Furthermore, length of stay in PICU has a very weak correlation with ECW/TBW (r_s = 0.29, P < 0.05), and a negative correlation with protein (r_s = -0.27, P < 0.05). Multivariate analysis found that PhA was a significant predictor associated with the 90-day mortality when it was adjusted for PRISM III score (adjusted OR = 1.51, CI: 1.10–2.07, p = 0.01). The area under the ROC (AUROC) of PhA for predicting 90-day mortality was 0.69 (95% CI: 0.53–0.85, p < 0.05), and the cutoff value of PhA was 3.0°, with a sensitivity and specificity of 83 and 53%, respectively.

Conclusion

BIA-derived PhA was found to be an independent predictor of 90-day mortality among critically ill children. A low PhA was associated with a prolonged duration of medical ventilation.

Bioimpedance as a measure of fluid status in critically ill patients: A systematic review

OBJECTIVE

Precise measurements of fluid status lack valid methods. Bioimpedance is an attractive diagnostic tool because it is noninvasive, quick, and relatively cheap. This systematic review aims to assess the existing evidence of bioimpedance as an accurate measure of fluid status in critically ill patients.

DATA SOURCES

PubMed and Embase up till March 2021 were systematically searched (PROSPERO: CRD42020157436).

STUDY SELECTION

Eligibility criteria were studies reporting original data from cohorts of adult patients in intensive care units and doing at least one whole-body bioimpedance and one reference test. In addition, studies assessing internal reproducibility were included.

DATA EXTRACTION

An extraction form was designed for the purpose.

DATA SYNTHESIS

Nine hundred five studies were screened for eligibility, and 28 studies, comprising 1482 individual patients, were included in the final analysis. Eight studies compared bioimpedance with a gold standard, and two of those reported the results adequate. We found a low mean difference, but the 95% limits of agreements had wide limits. The remaining studies applied different surrogates as reference tests. Correlations ranged from 0.05 to 0.99. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) certainty of evidence for all outcomes was very low.

CONCLUSIONS

The accuracy of bioimpedance as a measure for fluids in critically ill patients in the intensive care unit cannot be determined. Due to the lack of a gold standard, numerous studies compared bioimpedance with surrogate outcomes with great variability in both designs and results. Assessing the internal reproducibility of bioimpedance had the same limitations, but the studies overall reported good internal reproducibility.

Hepatocyte growth factor and soluble cMet levels in plasma are prognostic biomarkers of mortality in patients with severe acute kidney injury

Background

Hepatocyte growth factor (HGF)/cMet pathway is necessary for repair and regeneration following acute kidney injury (AKI). We evaluated the clinical potential of plasma HGF and soluble cMet as prognostic biomarkers for severe AKI requiring continuous renal replacement therapy (CRRT).

Methods

One hundred thirty-six patients with severe AKI who participated in the VENUS (volume management under body composition monitoring in critically ill patients on CRRT) trial between 2017 and 2019 were enrolled in this study. We investigated associations between plasma HGF and cMet concentrations and all-cause mortality.

Results

Plasma HGF and soluble cMet levels were positively correlated. Patients were divided into three groups based on their HGF and soluble cMet concentrations. The day D 0, D2, and D7 highest concentration HGF groups had significantly higher in-hospital mortality after adjusting for sex, body mass index, Acute Physiology and Chronic Health Evaluation II, and age-adjusted Charlson comorbidity index score, especially on D7 (hazard ratio, 4.26; 95% confidence interval, 1.71–10.62; p = 0.002). D7 soluble cMet level was also associated with mortality. Receiver operating characteristic curve analysis indicated that D7 HGF and soluble cMet levels were best at predicting mortality. Addition of plasma HGF and soluble cMet to conventional prognostic indices significantly improved the predictive value for mortality on D7. However, plasma HGF and soluble cMet were not associated with fluid status.

Conclusion

Plasma HGF and soluble cMet levels were significant predictors of the outcomes of severe AKI patients undergoing CRRT. There was no correlation between plasma HGF and soluble cMet levels and fluid balance.

Bioelectric impedance analysis for body composition measurement and other potential clinical applications in critical illness

PURPOSE OF REVIEW

Insight into body composition is of great value in the ICU. Bioelectric impedance analysis (BIA) is the most applicable bedside technique. However, bioimpedance has not been validated in the critically ill, and the interpretation of the measurements poses challenges. This review discusses the potential clinical applications of BIA and explores caveats and solutions to its use in the intensive care setting.

RECENT FINDINGS

A correlation is repeatedly found between raw impedance parameters, fluid ratios, overhydration, and adverse outcome of critical illness. However, cut-off and reference values remain elusive. Experience with BIA-guided fluid management in the ICU is limited. BIA-derived muscle mass appears a promising biomarker for sarcopenia, correlating well with CT-analysis. Body cell mass and fat-free mass provide potential use in estimation of metabolic rate, protein requirements and pharmacokinetics. Several methods of reducing bias in BIA parameters in critical illness require validation.

SUMMARY

There are currently too many uncertainties and discrepancies regarding interpretation of bioimpedance in critical illness, to justify therapeutic consequences. However, there are several promising areas of research, concerning some of the most urgent clinical problems in intensive care, emphasizing the need to evaluate further the use and interpretation of bioimpedance in the intensive care setting.

Usefulness of bioelectrical impedance analysis and ECW ratio as a guidance for fluid management in critically ill patients after operation

We determined the relationship between changes in bioelectrical impedance analysis (BIA) parameters and response of critically ill patients to fluid therapy during early postoperative period. Associations between BIA values indicating volume status of postoperative patient and clinical outcomes were also evaluated. From May 2019 to April 2020, patients who were admitted to the surgical intensive care unit (SICU) of our institution at more than 48 h after surgery were enrolled. Volume status was measured with a portable BIA device every morning for five days from SICU admission. Overhydration was defined as the case where extracellular water (ECW) ratio > 0.390 measured by BIA. Participants were daily classified into an overhydration or a normohydration group. The relationship between daily hydration status and postoperative outcome was evaluated. Most of the 190 participants showed the overhydration status in the first 48 h after surgery. The overhydration status on day 3 was significant predictor of postoperative morbidities (OR 1.182) and in-hospital mortality (OR 2.040). SOFA score was significant factor of postoperative morbidities (OR 1.163) and in-hospital mortality (OR 3.151) except for the overhydration status on day 3. Cut-off values of overhydration status by ECW ratio at day 3 for predicting postoperative morbidities and in-hospital mortality were > 0.3985 and > 0.4145, respectively. BIA would be a useful and convenient tool to assess the volume status of patients requiring intensive fluid resuscitation in early postoperative period. Overhydration status by ECW ratio on postoperative day 3 needs careful monitoring and appropriate interventions to improve clinical outcomes.

Assessment of Fluid Status by Bioimpedance Analysis and Central Venous Pressure Measurement and Their Association with the Outcomes of Severe Acute Kidney Injury

Background and Objectives: Fluid disbalance is associated with adverse outcomes in critically ill patients with acute kidney injury (AKI). In this study, we intended to assess fluid status using bioimpedance analysis (BIA) and central venous pressure (CVP) measurement and to evaluate the association between hyperhydration and hypervolemia with the outcomes of severe AKI. Materials and Methods: A prospective study was conducted in the Hospital of the Lithuanian University of Health Sciences Kauno Klinikos. Forty-seven patients treated at the Intensive Care Unit (ICU) with severe AKI and a need for renal replacement therapy (RRT) were examined. The hydration level was evaluated according to the ratio of extracellular water to total body water (ECW/TBW) of bioimpedance analysis and volemia was measured according to CVP. All of the patients were tested before the first hemodialysis (HD) procedure. Hyperhydration was defined as ECW/TBW > 0.39 and hypervolemia as CVP > 12 cm H₂O. Results: According to bioimpedance analysis, 72.3% (n = 34) of patients were hyperhydrated. According to CVP, only 51.1% (n = 24) of the patients were hypervolemic. Interestingly, 69.6% of hypovolemic/normovolemic patients were also hyperhydrated. Of all study patients, 57.4% (n = 27) died, in 29.8% (n = 14) the kidney function improved, and in 12.8% (n = 6) the demand for RRT remained after in-patient treatment. A tendency of higher mortality in hyperhydrated patients was observed, but no association between hypervolemia and outcomes of severe AKI was established. Conclusions: Three-fourths of the patients with severe AKI were hyperhydrated based on bioimpedance analysis. However, according to CVP, only half of these patients were hypervolemic. A tendency of higher mortality in hyperhydrated patients was observed.

Ultrafiltration in critically ill patients treated with kidney replacement therapy

Management of fluid overload is one of the most challenging problems in the care of critically ill patients with oliguric acute kidney injury. Various clinical practice guidelines support fluid removal using ultrafiltration during kidney replacement therapy. However, ultrafiltration is associated with considerable risks. Emerging evidence from observational studies suggests that both slow and fast rates of net fluid removal (that is, net ultrafiltration (UFNET)) during continuous kidney replacement therapy are associated with increased mortality compared with moderate UFNET rates. In addition, fast UFNET rates are associated with an increased risk of cardiac arrhythmias. Experimental studies in patients with kidney failure who were treated with intermittent haemodialysis suggest that fast UFNET rates are also associated with ischaemic injury to the heart, brain, kidney and gut. The UFNET rate should be prescribed based on patient body weight in millilitres per kilogramme per hour with close monitoring of patient haemodynamics and fluid balance. Dialysate cooling and sodium modelling may prevent haemodynamic instability and facilitate large volumes of fluid removal in patients with kidney failure who are treated with intermittent haemodialysis, but the effects of this strategy on organ injury are less well studied in critically ill patients treated with continuous kidney replacement therapy. Randomized trials are required to examine whether moderate UFNET rates are associated with a reduced risk of haemodynamic instability, organ injury and improved outcomes in critically ill patients.

Kidney Replacement Therapy for Fluid Management

Emerging evidence from observational studies suggests that both slower and faster net ultrafiltration rates during kidney replacement therapy are associated with increased mortality in critically ill patients with acute kidney injury and fluid overload. Faster rates are associated with ischemic organ injury. The net ultrafiltration rate should be prescribed based on patient body weight in milliliters per kilogram per hour, with close monitoring of patient hemodynamics and fluid balance. Randomized trials are required to examine whether moderate net ultrafiltration rates compared with slower and faster rates are associated with reduced risk of hemodynamic instability, organ injury, and improved outcomes.

Ratio of Overhydration and Extracellular Water Versus Ratio of Extracellular Water and Body Cell Mass in the Assessment of Fluid Status in Patients With Acute Kidney Injury Requiring Kidney Replacement Therapy: A Cohort Study

OBJECTIVES

The aim of this study is to analyze the association between the ratio of overhydration and extracellular water (OH/ECW) and the ratio of extracellular water and body cell mass (ECW/BCM) measured by bioelectrical impedance and outcomes of patients with acute kidney injury (AKI) requiring kidney replacement therapy (KRT).

METHODS

Patients with severe AKI treated with KRT in our hospital between September 2016 and August 2018 were enrolled. These patients were assessed using a body composition monitor before KRT, and on the 3rd day and the 7th day after initiation of KRT. The predictors mainly included OH/ECW and ECW/BCM. The association between all-cause mortality and predictors were analyzed using Cox regression.

RESULTS

A total of 152 patients were included in this study with a median follow-up of 39 (interquartile range 8-742) days. The 28-day mortality, 90-day mortality, and 1-year mortality were 46.7%, 54.6%, and 60.5%, respectively. A high ratio of OH/ECW (adjusted hazard ratio per standard deviation, 1.45; 95% confidence interval = 1.15-1.82, P = .002) and a high ratio of ECW/BCM (adjusted hazard ratio per standard deviation, 1.33, 95% confidence interval = 1.07-1.64, P = .009) before KRT were associated with all-cause mortality during follow-up. Higher ECW/BCM rather than OH/ECW at 7th day was associated with poorer outcomes. Furthermore, a reduction of OH/ECW with an increase of ECW/BCM had higher 1-year mortality as compared to others (85.7% vs. 51.2%, P = .004) in patients who survived 7 days after KRT initiation.

CONCLUSIONS

ECW/BCM performed better than OH/ECW in assessment of fluid status in AKI patients requiring KRT. This study suggested that a simple reduction of OH/ECW without decreasing ECW/BCM may not improve outcomes.

Wireless, Artefact Aware Impedance Sensor Node for Continuous Bio-Impedance Monitoring

Body bio-impedance is a unique parameter to monitor changes in body composition non-invasively. Continuous measurement of bio-impedance can track changes in body fluid content and cell mass and has widespread applications for physiological monitoring. State-of-the-art implementation of bio-impedance sensor devices is still limited for continuous use, in part, due to artefacts arising at the skin-electrode (SE) interface. Artefacts at the SE interface may arise due to various factors such as motion, applied pressure on the electrode surface, changes in ambient conditions or gradual drying of electrodes. This paper presents a novel bio-impedance sensor node that includes an artefact aware method for bio-impedance measurement. The sensor node enables autonomous and continuous measurement of bio-impedance and SE contact impedance at ten frequencies between 10 kHz to 100 kHz to detect artefacts at the SE interface. Experimental evaluation with SE contact impedance models using passive 2R1C electronic circuits and also with non-invasive in vivo measurements of SE contact impedance demonstrated high accuracy (with maximum error less than 1.5%) and precision of 0.6 Ω. The ability to detect artefacts caused by motion, vertically applied pressure and skin temperature changes was analysed in proof of concept experiments. Low power sensor node design achieved with 50mW in active mode and only 143 μW in sleep mode estimated a battery life of 90 days with a 250 mAh battery and duty-cycling impedance measurements every 60 seconds. Our method for artefact aware bio-impedance sensing is a step towards autonomous and unobtrusive continuous bio-impedance measurement for health monitoring at-home or in clinical environments.