Bioelectrical impedance parameters in critically ill children: importance of reactance and resistance

Phase angle and its determinants among adolescents: influence of body composition and physical fitness level

To examine the association between levels of physical fitness, parameters of body composition and phase angle (PhA) amongst adolescents. A total of 152 adolescents (84 girls) aged 11-16 years were included in this study. Weight and height were measured and the body mass index (BMI) was calculated. Bioelectrical impedance analysis (BIA) provided resistance and reactance parameters to calculate fat-free mass (FFM), PhA and fat mass (%FM). The following physical fitness variables were analysed: flexibility, abdominal muscular endurance, upper and lower limb explosive strength, agility, speed and cardiorespiratory fitness. Generalized Linear Models were applied to verify differences across sexes. Stepwise linear regression was used to establish an association between the variables studied. The study established an association between PhA and weight, FFM, BMI, FM, %FM and medicine ball throw (MBT) for girls. As for the boys, an association was verified between PhA and weight, FFM, BMI, standing long jump (SLJ), MBT and the three allometric VO2peak variables analyzed. An association was found between PhA and the boys' 4-m shuttle run test (4SRT) and 20-m sprint test (20SRT). Boys showed a greater phase angle than girls; In girls, BMI and %FM, were determinant of 32.4% (r = 0.57). PhA variability which is influenced by physical fitness, body composition and, therefore, the tissues electrical conductivity. Furthermore, boys' height, FFM, upper limb strength, and agility account for 58.4% (r = 0.76) PhA variability. There was a positive correlation between the physical fitness tests and the PhA.

Body composition in pediatric patients

Undernutrition is highly prevalent in children who are critically ill and is associated with increased morbidity and mortality, including a higher risk of infection due to transitory immunological disorders, inadequate wound healing, reduced gut function, longer dependency on mechanical ventilation, and longer hospital stays compared with eutrophic children who are critically ill. Nutrition care studies have proposed that early interventions targeting nutrition assessment can prevent or minimize the complications of undernutrition. Stress promotes an acute inflammatory response mediated by cytokines, resulting in increased basal metabolism and nitrogen excretion and leading to muscle loss and changes in body composition. Therefore, the inclusion of body composition assessment is important in the evaluation of these patients because, in addition to the nutrition aspect, body composition seems to predict clinical prognosis. Several techniques can be used to assess body composition, such as arm measurements, calf circumference, grip strength, bioelectrical impedance analysis, and imaging examinations, including computed tomography and dual-energy x-ray absorptiometry. This review of available evidence suggests that arm measurements seem to be well-established in assessing body composition in children who are critically ill, and that bioelectrical impedance analysis with phase angle, handgrip strength, calf circumference and ultrasound seem to be promising in this evaluation. However, further robust studies based on scientific evidence are necessary.

Pathobiology, Severity, and Risk Stratification of Pediatric Acute Respiratory Distress Syndrome: From the Second Pediatric Acute Lung Injury Consensus Conference

OBJECTIVES

To review the literature for studies published in children on the pathobiology, severity, and risk stratification of pediatric acute respiratory distress syndrome (PARDS) with the intent of guiding current medical practice and identifying important areas for future research related to severity and risk stratification.

DATA SOURCES

Electronic searches of PubMed and Embase were conducted from 2013 to March 2022 by using a combination of medical subject heading terms and text words to capture the pathobiology, severity, and comorbidities of PARDS.

STUDY SELECTION

We included studies of critically ill patients with PARDS that related to the severity and risk stratification of PARDS using characteristics other than the oxygenation defect. Studies using animal models, adult only, and studies with 10 or fewer children were excluded from our review.

DATA EXTRACTION

Title/abstract review, full-text review, and data extraction using a standardized data collection form.

DATA SYNTHESIS

The Grading of Recommendations Assessment, Development, and Evaluation approach was used to identify and summarize relevant evidence and develop recommendations for clinical practice. There were 192 studies identified for full-text extraction to address the relevant Patient/Intervention/Comparator/Outcome questions. One clinical recommendation was generated related to the use of dead space fraction for risk stratification. In addition, six research statements were generated about the impact of age on acute respiratory distress syndrome pathobiology and outcomes, addressing PARDS heterogeneity using biomarkers to identify subphenotypes and endotypes, and use of standardized ventilator, physiologic, and nonpulmonary organ failure measurements for future research.

CONCLUSIONS

Based on an extensive literature review, we propose clinical management and research recommendations related to characterization and risk stratification of PARDS severity.

Association of electrical bioimpedance vectors with the nutritional classification of vulnerable multiethnic children

BACKGROUND & AIMS

Monitoring growth and body composition in childhood is vital for early detection of health and nutrition problems during child development. The bioelectrical impedance vector analysis (BIVA) revealed its effectiveness as an indicator of nutritional status. This study aimed to measure the bioimpedance vectors of a sample of multiethnic children and evaluate the utility of BIVA for the classification of the nutritional status in a group of children with greater vulnerability, including in the presence of obesity.

METHODS

This is a cross-sectional study that analyzed the bioelectrical impedance of a sample of 321 children from public daycare centers, aged 1-4 years, using the RXc graph method (tetrapolar analysis at 50 kHz frequency). The 95%, 75%, and 50% tolerance ellipses were plotted by age group. The Z-scores of bioimpedance parameters (Xc/H-Z and R/H-Z) were calculated regarding age, which were used to build reference tolerance ellipses for a single group, regardless of age. Such ellipses were evaluated for their ability to recognize the pattern and classify the deviations, using individual vectors of obese children.

RESULTS

The mean impedance vectors showed progressively higher reactances and lower resistances with age. In the group of obese children, the individual vectors located outside the 95% baseline tolerance ellipse were 12.5%, 18.75%, and 11.1% of the cases for the WHZ, WAZ, and BMIZ criteria, respectively, all above the expected 5%, but much below expectations. This may be a problem with the obesity criteria used, as WHZ, WAZ, and BMIZ do not differentiate fat from lean mass.

CONCLUSION

Bioimpedance vector analysis reflects differences in the bioelectric patterns of children classified as obese. Provided the obesity criteria are constructed based on fat measurements, rather than lean mass, the use of tolerance ellipses in the BIVA chart is promising as a tool for monitoring nutritional status where measuring body composition is difficult, because constant tissue hydration cannot be assumed.

The association of bioimpedance analysis parameters with the outcomes of critically ill patients

BACKGROUND

The association between bioimpedance analysis (BIA) parameters and the outcomes of critically ill patients was explored through a retrospective investigation.

METHODS

The study enrolled patients in the intensive care units of our hospital who had a record of BIA measurements as well as disease severity scores assessed by Acute Physiology and Chronic Health Evaluation II (APACHE II), Simplified Acute Physiology Score II (SAPS II) and Sequential Organ Failure Assessment (SOFA). The associations between clinical conditions, outcomes and BIA parameters were analysed. The relationship between individual bioimpedance values and the current frequencies fit well to a natural logarithmic function, providing a regression coefficient S value. Other parameters obtained from the BIA measurements included phase angle (PA), the ratio of bioimpedance at high and low frequencies (IR), extracellular water (ECW), intracellular water (ICW) and total body water (TBW).

RESULTS

Among 201 enrolled patients, the 90-day in-hospital mortality was 35.8%. Compared to the survivors at 7-days, for the non-survivors, the IR, S value, ratio of ECW/weight and ratio of ECW/TBW were higher, and the PA was lower (P < 0.05). Compared to the survivors at 90-days, for the non-survivors, the IR, S value and ratio of ECW/weight were higher, and the PA was lower (P < 0.05). Multinomial logistic regression analysis results showed that only SAPS II and S value were independent risk factors for 7-day and 90-day death (P < 0.01). When analysed by ROC, the AUC of the S value for predicting 7-day and 90-day death was non-significantly lower than SAPS II (S vs. SAPS II, 0.729 vs. 0.747 (7-day); 0.701 vs. 0.779 (90-day), P > 0.05). Importantly, both the 7-day and the 90-day mortality in patients with S values ≤-25.5 were 0; for the others, the mortality increased with the rise of S value. For patients with SAPS II ≤33, the mortality varied minimally; and for patients with SAPS II >55, the mortality was 100%.

CONCLUSIONS

The S value and SAPS II are independent risk factors for 7-day and 90-day death in critically ill patients; the former may have a greater negative predictive value, while the latter may have a greater positive predictive value.

The importance of bioelectrical impedance in the critical pediatric patient

BACKGROUND & AIMS

Sepsis is still a significant cause of death in the Intensive Care Unit and its early diagnosis is vital. Changes in cell permeability have been observed early in sepsis. Lower values of bioelectrical impedance (BIA) such as reactance adjusted by height (Xc/H) and phase angle (PA) have already been studied as a prognostic biomarker for many diseases and may indicate cell injury. BIA is a low cost, practical, noninvasive method that can be measured at bedside. This study investigated the utility of PA and Xc/H raw values in the pediatric critical care unit as predictors of progression to septic shock, as a clinical monitoring tool and to support the diagnosis of septic shock.

METHODS

We prospectively analyzed bioelectrical impedance in 145 children aged between one month and six years who were not in septic shock on admission to the intensive care unit Serial bioelectrical impedance analysis (BIA) measures were analyzed to determine the sensitivity and specificity of accurately identifying children who subsequently developed septic shock. Kaplan-Meier septic shock-free survival curves modeled by Xc/H and PA were done.

RESULTS

The free-septic shock survival curve analysis showed that patients with the lowest median values of Xc/H and PA were associated with the highest percentage of occurrence of septic shock (p = 0.0001 for Xc/H and <0.0006 for PA) and longest length of stay in the intensive care unit (p < 0.0011 for Xc/H and p < 0.004 for PA). Values of Xc/H below 48.63 Ohm/m at admission showed statistically significant odds ratio (OR) of 3.72 for developing septic shock any time during the hospitalization period, with a 87% sensitivity, 35% specificity and an area under the curve (AUC) of 0.62. The PA at admission did not show significant results. During hospitalization, patients with Xc/H below 35.72 Ohm/m were 3.38 times more likely to develop septic shock in the next day, with a sensitivity of 66.7%, a specificity of 62.3% and AUC of 0.65. PA values below 3.27 had an OR of 9.58 for a septic shock the next day with a sensitivity of 95.8%, specificity of 29.4% and AUC of 0.62. The presence of a value of Xc/H below 33 Ohm/m showed a strong association with the occurrence of septic shock on the same day of the measurement, with an OR of 11.7, as well as a value of PA below 2.64, showed an OR of 14.2.

CONCLUSIONS

The bioelectrical parameters Xc/H and phase angle have limitations in predicting septic shock as isolated biomarkers, but have a potential role as a monitoring tool in the pediatric intensive care unit. The comparative value with other biomarkers remains to be elucidated.

Bioelectric impedance vector analysis (BIVA) in hospitalised children; predictors and associations with clinical outcomes

BACKGROUND

Clinical use of bioelectric impedance is limited by variability in hydration. Analysis of raw bioelectric impedance vectors (BIVA), resistance (R), reactance (Xc) and phase angle (PA) may be an alternative for monitoring disease progression/treatment. Clinical experience of BIVA in children is limited. We investigated predictors of BIVA and their ability to predict clinical outcomes in children with complex diagnoses.

METHODS

R, Xc and PA were measured (BODYSTAT Quadscan 4000) on admission in 108 patients (4.6-16.8 years, mean 10.0). R and Xc were indexed by height (H) and BIVA-SDS for age and sex calculated using data from healthy children. Potential predictors and clinical outcomes (greater-than-expected length-of-stay (LOS), complications) were recorded.

RESULTS

Mean R/H-SDS was significantly higher (0.99 (SD 1.32)) and PA-SDS lower (-1.22 (1.68))) than expected, with a wide range for all parameters. In multivariate models, the Strongkids risk category predicted R/H-SDS (adjusted mean for low, medium and high risk = 0.49, 1.28, 2.17, p = 0.009) and PA-SDS (adjusted mean -0.52, -1.53, -2.36, p = 0.01). BIVA-SDS were not significantly different in patients with or without adverse outcomes.

CONCLUSIONS

These complex patients had abnormal mean BIVA-SDS suggestive of reduced hydration and poor cellular health according to conventional interpretation. R/H-SDS was higher and PA-SDS lower in those classified as higher malnutrition risk by the StrongKids tool. Further investigation in specific patient groups, including those with acute fluid shifts and using disease-specific outcomes, may better define the clinical role of BIV.

Body Composition Technology: Implications for the ICU

Malnutrition continues to be highly prevalent in hospitalized and critically ill patients and is associated with significant morbidity and mortality. Additionally, survivors of critical illness have an increased risk for sarcopenia, which leads to weakness and physical debilitation that can persist for years. Nutrition risk assessment tools have been developed and validated in critically ill patients but have limitations. Variables such as body weight, body mass index, weight change, or percentage of food intake can be difficult to obtain in critically ill patients and may be misleading given changes in body composition, such as an increase in body water. Assessment of body composition through new techniques provides a unique opportunity to counter some of these limitations and develop improved methods of nutrition risk assessment based on objective data. The present manuscript provides a review of the most commonly available clinical technology for assessment of body composition (bioimpedance, computed tomography, and ultrasound), including data from trials in critically ill patients highlighting the benefits and weaknesses of each modality.

Characterising the nutritional status of children with primary ciliary dyskinesia

INTRODUCTION

Primary ciliary dyskinesia (PCD) is a rare, heterogeneous genetic disorder where impaired mucociliary clearance is caused by dysfunctional motile cilia leading to bronchiectasis. There is limited evidence characterising the nutritional status of children with PCD, although lower body mass index (BMI) z-score has been associated with worse lung function (FEV₁).

METHODS

All children (n = 43) with PCD, aged <16 years, from a single tertiary centre were prospectively enrolled. Information on clinical phenotype and nutritional status including bioelectrical impedance spectroscopy (BIS) phase-angle was collected.

RESULTS

There was a weak positive association between height-for-age z-score (HAZ) and FEV₁ z-score (n = 28, r = 0.4, p = 0.049). Those with a low fat free mass index (<-2 z scores) had a lower BMI z score (-1.3 ± 1.2 vs. 0.8 ± 0.7, p = 0.0002). BIS phase angle identified more patients at nutritional risk than using moderate malnutrition cut-offs of either HAZ or BMI ≤ -2 z scores alone (21% vs. 4.6% vs. 6.9% respectively). PCD patients had a higher incidence of vitamin D insufficiency (<50 nmoL/L) (54%) and deficiency (<30 nmoL/L) (26%) than healthy children.

CONCLUSIONS

We have characterised the nutritional phenotype of a cohort of children with PCD. Monitoring vitamin D levels is important in PCD patients. There is a weak association between lung function and nutritional status, and measures of BIS phase-angle. The use of BIS phase-angle may allow for early identification of at risk children and may therefore be of benefit for nutritional assessments in the clinical setting. These findings will help inform a future nutritional intervention strategy in children with PCD.

Preoperative bioelectrical impedance predicts intensive care length of stay in children following cardiac surgery

We have previously shown that children with a bioelectrical impedance spectroscopy phase angle at 50° (PA 50°) of <2.7 on postoperative day 2 had a four-fold increase in the risk of prolonged paediatric intensive care length of stay. In this study, we demonstrate a relationship between a baseline measure of phase angle 200/5° and postoperative length of stay.

Disorders of nutritional status in sepsis - facts and myths

The problem of diagnosing nutritional status disorders in septic patients remains unresolved. This is associated with the necessity of the introduction of newer and newer methods of assessing nutritional status, often requiring precise and expensive equipment as well as employment of professionals in this field in hospital wards, primarily including intensive care units (ICU). Methods that have been applied thus far for assessing nutritional status, also used in severely ill septic patients, have little impact on improving treatment results. This is due to the high dynamics of changes in nutritional status in these patients, healing process variability in individual patients, and the “mismatch” of methods for assessing nutritional status in relation to the patient’s clinical status. The diagnostic value of the traditional methods of assessing nutritional status, i.e. anthropometric analysis and selected laboratory tests, as markers of nutritional status disorders in septic patients, is still debatable. There is still no precise method that could become the “gold standard” allowing for early identification of malnutrition in these group of patients. Phase angle, bioelectrical impedance vector analysis (BIVA), and the “illness marker”, obtained directly from the resistance, reactance, and impedance, can be used as prognostic or nutritional indices in severely ill septic patients, but the intensity of research on this subject needs to be increased. Detailed assessment of nutritional status should include tests of selected inflammation markers (including TLC, HMGB1, IL-6, IL-10, IL-1ra, sTNFRI).

Assessment of Body Composition in a Group of Pediatric Patients With Cancer: A Single Romanian Center Experience

Cancer patients are particularly susceptible to nutritional depletion. From March 2014 to December 2015, we assessed 146 patients consecutively hospitalized in a tertiary emergency pediatric hospital. The patients were divided into 2 groups: group I, patients with cancer (43 patients), and group II, the control group consisting of 103 age-matched and sex-matched healthy patients. The anthropometric parameters (weight-W, height-H, body mass index [BMI], middle upper arm circumference [MUAC], tricipital skinfold thickness [TST]) and biochemical parameters (proteins, albumin) were comparatively evaluated. Fat mass (FM, kg and %), fat-free mass (FFM, kg), muscle mass (MM, kg), and total body water (TBW, %) were measured in both groups using Tanita BC 420 S MA Analyzer. Anthropometric and biochemical parameters in group I were significantly different from those in group II for weight, height, BMI, MUAC, TST, protein, and albumin (P<0.05). In the study group, FM was much lower compared with controls 16.9% (3.4% to 33.3%) versus 20.3% (6.6% to 38.4%); (P=0.001), and TBW was much higher 60.8% (48.8% to 70.6%) versus 58.5% (45.2% to 68.6%) (P=0.004). FFM and MM were not statistically different in the 2 groups. The results highlight the complex changes of nutritional status in pediatric patients with cancer.

Optimal Nutrition for Acute Rehabilitation in the PICU

Achieving optimal nutrition for a child who is receiving acute rehabilitation in the pediatric intensive care unit requires an individualized approach. Nutrition screening and assessment is necessary to identify children at high risk for complications who require targeted interventions. Early enteral nutrition can improve outcomes, and is thus preferred over parenteral nutrition in the absence of gastrointestinal contraindications. Measurement of caloric requirements with indirect calorimetry is essential to accurately prescribe nutrition support, while monitoring body composition can determine efficacy of nutrition therapies employed. The complex care of critically ill children receiving acute rehabilitation is composed of treatments that compete with delivery of prescribed nutrition. Repeated feeding interruptions can lead to nutrition deficits and prolonged recovery. Nutrition bundles that incorporate evidenced-based nutrition algorithms, methods to overcome nutrition barriers, and nutrition monitoring parameters can direct and optimize nutrition care for critically ill children in need of acute rehabilitation.

Using skin for drug delivery and diagnosis in the critically ill

Skin offers easy access, convenience and non-invasiveness for drug delivery and diagnosis. In principle, these advantages of skin appear to be attractive for critically ill patients given potential difficulties that may be associated with oral and parenteral access in these patients. However, the profound changes in skin physiology that can be seen in these patients provide a challenge to reliably deliver drugs or provide diagnostic information. Drug delivery through skin may be used to manage burn injury, wounds, infection, trauma and the multisystem complications that rise from these conditions. Local anaesthetics and analgesics can be delivered through skin and may have wide application in critically ill patients. To ensure accurate information, diagnostic tools require validation in the critically ill patient population as information from other patient populations may not be applicable.

The theory and fundamentals of bioimpedance analysis in clinical status monitoring and diagnosis of diseases

Bioimpedance analysis is a noninvasive, low cost and a commonly used approach for body composition measurements and assessment of clinical condition. There are a variety of methods applied for interpretation of measured bioimpedance data and a wide range of utilizations of bioimpedance in body composition estimation and evaluation of clinical status. This paper reviews the main concepts of bioimpedance measurement techniques including the frequency based, the allocation based, bioimpedance vector analysis and the real time bioimpedance analysis systems. Commonly used prediction equations for body composition assessment and influence of anthropometric measurements, gender, ethnic groups, postures, measurements protocols and electrode artifacts in estimated values are also discussed. In addition, this paper also contributes to the deliberations of bioimpedance analysis assessment of abnormal loss in lean body mass and unbalanced shift in body fluids and to the summary of diagnostic usage in different kinds of conditions such as cardiac, pulmonary, renal, and neural and infection diseases.

The differential Howland current source with high signal to noise ratio for bioimpedance measurement system

The stability and signal to noise ratio (SNR) of the current source circuit are the important factors contributing to enhance the accuracy and sensitivity in bioimpedance measurement system. In this paper we propose a new differential Howland topology current source and evaluate its output characters by simulation and actual measurement. The results include (1) the output current and impedance in high frequencies are stabilized after compensation methods. And the stability of output current in the differential current source circuit (DCSC) is 0.2%. (2) The output impedance of two current circuits below the frequency of 200 KHz is above 1 MΩ, and below 1 MHz the output impedance can arrive to 200 KΩ. Then in total the output impedance of the DCSC is higher than that of the Howland current source circuit (HCSC). (3) The SNR of the DCSC are 85.64 dB and 65 dB in the simulation and actual measurement with 10 KHz, which illustrates that the DCSC effectively eliminates the common mode interference. (4) The maximum load in the DCSC is twice as much as that of the HCSC. Lastly a two-dimensional phantom electrical impedance tomography is well reconstructed with the proposed HCSC. Therefore, the measured performance shows that the DCSC can significantly improve the output impedance, the stability, the maximum load, and the SNR of the measurement system.