Estimation of total body water in very-low-birth-weight infants by using anthropometry with and without bioelectrical impedance and H2[(18)O]

How is bioelectrical impedance used in neonatal intensive care? A scoping review

Poor growth and nutrition management in the neonatal period can have a negative impact upon both the short- and long-term outcomes for the infant. Improvements in bioelectrical impedance technology and accompanying licencing agreements now make this enhanced device available for use in infants as small as 23 weeks gestational age. An exploration of this technology and its use is now timely. The aim of the scoping review was to answer the following question: in preterm and sick term infants in the neonatal intensive care unit, how is bioelectrical impedance being utilized, in what situations, and when? The scoping review was conducted using Arksey and O'Malley's (Int J Soc Res Methodol 8(1):19-32, 2005) framework. Forty-nine papers were initially identified and 16 were included in the scoping review. Three studies were experimental designs, and 13 were observational studies. The review found that BIA was used in neonatal intensive care in three main ways, for, (1) fluid status evaluation, (2) as a measure of adequate nutrition and growth, (3) to validate the technology as an outcome measure in neonates.

CONCLUSION

There is a paucity of recent robust research papers which investigate the use of bioelectrical impedance in preterm neonates. Available evidence spans a range of 30 years, with technological advancement reducing the application of older studies to the modern neonatal setting. Although this technology may be helpful for decision-making around fluid management and nutrition, in preterm infants, robust evidence is needed to demonstrate the clinical benefit of bioelectrical impedance beyond that of usual care.

WHAT IS KNOWN

• Clinical decisions regarding neonatal nutrition and fluid management are currently based upon the interpretation of vital signs, fluid balance, weight trend, biochemical markers, and physical examination. • Bioelectrical Impedance Analysis (BIA) is a non-invasive method of assessing body composition which is now available to be used in infants as small as 23 weeks gestation.

WHAT IS NEW

• Bioelectrical Impedance has been used in three main ways in the NICU, for fluid status evaluation, for measuring nutrition and growth and to validate BIA as an outcome. • There is a lack of recent robust research data to support the use of the device within clinical decision making in neonatal intensive care.

Infant body composition: A comprehensive overview of assessment techniques, nutrition factors, and health outcomes

Body composition assessment is a valuable tool for clinical assessment and research that has implications for long-term health. Unlike traditional measurements such as anthropometrics or body mass index, body composition assessments provide more accurate measures of body fatness and lean mass. Moreover, depending on the technique, they can offer insight into regional body composition, bone mineral density, and brown adipose tissue. Various methods of body composition assessment exist, including air displacement plethysmography, dual-energy x-ray absorptiometry, bioelectrical impedance, magnetic resonance imaging, D3 creatine, ultrasound, and skinfold thickness, each with its own strengths and limitations. In infants, several feeding practices and nutrition factors are associated with body composition outcomes, such as breast milk vs formula feeding, protein intake, breast milk composition, and postdischarge formulas for preterm infants. Longitudinal studies suggest that body composition in infancy predicts later body composition, obesity, and other cardiometabolic outcomes in childhood, making it a useful early marker of cardiometabolic health in both term and preterm infants. Emerging evidence also suggests that body composition during infancy predicts neurodevelopmental outcomes, particularly in preterm infants at high risk of neurodevelopmental impairment. The purpose of this narrative review is to provide clinicians and researchers with a comprehensive overview of body composition assessment techniques, summarize the links between specific nutrition practices and body composition in infancy, and describe the neurodevelopmental and cardiometabolic outcomes associated with body composition patterns in term and preterm infants.

Body composition measurement for the preterm neonate: using a clinical utility framework to translate research tools into clinical care

Body composition analysis to distinguish between fat mass and fat-free mass is an established research approach to assess nutritional status. Within neonatal medicine, preterm infant body composition is linked with later health outcomes including neurodevelopment and cardiometabolic health. Mounting evidence establishing fat-free mass as an indicator of nutritional status, coupled with the availability of testing approaches that are feasible to use in preterm infants, have enhanced interest in measuring body composition in the neonatal intensive care unit (NICU) setting. In this paper, we use the concept of clinical utility-the added value of a new methodology over current standard care-as a framework for assessing several existing body composition methodologies with potential for clinical application to preterm neonates. We also use this framework to identify remaining knowledge gaps and prioritize efforts to advance our understanding of clinically-oriented body composition testing in the NICU.

Prediction of fat-free mass in a multi-ethnic cohort of infants using bioelectrical impedance: Validation against the PEA POD

Background

Bioelectrical impedance analysis (BIA) is widely used to measure body composition but has not been adequately evaluated in infancy. Prior studies have largely been of poor quality, and few included healthy term-born offspring, so it is unclear if BIA can accurately predict body composition at this age.

Aim

This study evaluated impedance technology to predict fat-free mass (FFM) among a large multi-ethnic cohort of infants from the United Kingdom, Singapore, and New Zealand at ages 6 weeks and 6 months (n = 292 and 212, respectively).

Materials and methods

Using air displacement plethysmography (PEA POD) as the reference, two impedance approaches were evaluated: (1) empirical prediction equations; (2) Cole modeling and mixture theory prediction. Sex-specific equations were developed among ∼70% of the cohort. Equations were validated in the remaining ∼30% and in an independent University of Queensland cohort. Mixture theory estimates of FFM were validated using the entire cohort at both ages.

Results

Sex-specific equations based on weight and length explained 75-81% of FFM variance at 6 weeks but only 48-57% at 6 months. At both ages, the margin of error for these equations was 5-6% of mean FFM, as assessed by the root mean squared errors (RMSE). The stepwise addition of clinically-relevant covariates (i.e., gestational age, birthweight SDS, subscapular skinfold thickness, abdominal circumference) improved model accuracy (i.e., lowered RMSE). However, improvements in model accuracy were not consistently observed when impedance parameters (as the impedance index) were incorporated instead of length. The bioimpedance equations had mean absolute percentage errors (MAPE) < 5% when validated. Limits of agreement analyses showed that biases were low (< 100 g) and limits of agreement were narrower for bioimpedance-based than anthropometry-based equations, with no clear benefit following the addition of clinically-relevant variables. Estimates of FFM from BIS mixture theory prediction were inaccurate (MAPE 11-12%).

Conclusion

The addition of the impedance index improved the accuracy of empirical FFM predictions. However, improvements were modest, so the benefits of using bioimpedance in the field remain unclear and require further investigation. Mixture theory prediction of FFM from BIS is inaccurate in infancy and cannot be recommended.

Body composition in preterm infants: a systematic review on measurement methods

BACKGROUND

There are several methods to measure body composition in preterm infants. Yet, there is no agreement on which method should be preferred.

METHODS

PubMed, Embase.com, Wiley/Cochrane Library, and Google Scholar were searched for studies that reported on the predictive value or validity of body composition measurements in preterms, up to 6 months corrected age.

RESULTS

Nineteen out of 1884 identified studies were included. Predictive equations based on weight and length indices, body area circumferences, skinfold thickness, bioelectrical impedance, and ultrasound did not show agreement with body composition measured with air displacement plethysmography (ADP), dual-energy x-ray absorptiometry (DXA), magnetic resonance imaging (MRI), or isotope dilution. ADP agreed well with fat mass density measured by isotope dilution (bias -0.002 g/ml, limits of agreement ±0.012 g/ml, n = 14). Fat mass percentage measured with ADP did not agree well with fat mass percentage measured by isotope dilution (limits of agreement up to ±5.8%) and the bias between measurements was up to 2.2%. DXA, MRI, and isotope dilution were not compared to another reference method in preterms.

CONCLUSIONS

DXA, ADP, and isotope dilution methods are considered trustworthy validated techniques. Nevertheless, this review showed that these methods may not yield comparable results.

IMPACT

Based on validation studies that were conducted in a limited number of study subjects, weight and length indices, body area circumferences, skinfold thickness, bioelectrical impedance, and ultrasound seem to be a poor representation of body composition in preterm infants. DXA, ADP, and isotope dilution methods are considered trustworthy and validated techniques. Nevertheless, these methods may not yield comparable results.

Total body water in full-term and preterm newborns: systematic review and meta-analysis

BACKGROUND

Total body water (TBW) is one component of fat-free mass and changes in TBW are influenced by fluid shifts (especially during transition to postnatal life), electrolyte balance and nutritional status. Normal values for term-born neonates and preterm infants at birth have not been defined in large cohorts, limiting investigation into its monitoring and use in clinical practice.

OBJECTIVE

To systematically review the evidence base for percentage of TBW in term-born infants, quantify the effect of prematurity on TBW at birth, and describe normal progression of TBW over time in preterm infants.

METHODS

Systematic review of Medline, Web of Science Core Collection and EBSCO-CINAHL (January 1946 to January 2020). Included articles used dilutional methods to assess TBW.

RESULTS

Searches identified 2349 articles of which 22 included data suitable for analysis. Mean TBW in term-born newborns was 73.8% (95% CI 72.47% to 75.06%, 15 studies, 433 infants). Meta-regression showed that TBW was higher in preterm infants (up to 90% at 26 weeks gestation, dropping to 75% at 36 weeks corrected gestation) and was negatively correlated with gestation at birth, falling 1.44% per week (95% CI 0.63% to 2.24%, 9 studies, 179 infants). Analysis of TBW over time during the ex utero growth of preterm infants was not possible due to paucity of data.

CONCLUSION

This review defines the normal TBW percentage in term-born infants and confirms and quantifies previous findings that preterm infants have a higher TBW percentage.

Bioelectrical impedance analysis for assessment of body composition in infants and young children-A systematic literature review

Bioelectrical impedance analysis (BIA) is an easy to use, portable tool, but the accuracy of the technique in infants and young children (<24 months) remains unclear. A systematic literature review was conducted to identify studies that have developed and validated BIA equations in this age group. MEDLINE, Scopus, EMBASE, and CENTRAL were searched for relevant literature published up until June 30, 2020, using terms related to bioelectrical impedance, body composition, and paediatrics. Two reviewers independently screened studies for eligibility, resulting in 15 studies that had developed and/or validated equations. Forty-six equations were developed and 34 validations were conducted. Most equations were developed in young infants (≤6 months), whereas only seven were developed among older infants and children (6-24 months). Most studies were identified as having a high risk of bias, and only a few included predominantly healthy children born at term. Using the best available evidence, BIA appears to predict body composition at least as well as other body composition tools; however, among younger infants BIA may provide little benefit over anthropometry-based prediction equations. Currently, none of the available equations can be recommended for use in research or in clinical practice.

The influence of body position on bioelectrical impedance spectroscopy measurements in young children

Bioelectrical impedance techniques are easy to use and portable tools for assessing body composition. While measurements vary according to standing vs supine position in adults, and fasting and bladder voiding have been proposed as additional important influences, these have not been assessed in young children. Therefore, the influence of position, fasting, and voiding on bioimpedance measurements was examined in children. Bioimpedance measurements (ImpediMed SFB7) were made in 50 children (3.38 years). Measurements were made when supine and twice when standing (immediately on standing and after four minutes). Impedance and body composition were compared between positions, and the effect of fasting and voiding was assessed. Impedance varied between positions, but body composition parameters other than fat mass (total body water, intra- and extra-cellular water, fat-free mass) differed by less than 5%. There were no differences according to time of last meal or void. Equations were developed to allow standing measurements of fat mass to be combined with supine measurements. In early childhood, it can be difficult to meet requirements for fasting, voiding, and lying supine prior to measurement. This study provides evidence to enable standing and supine bioimpedance measurements to be combined in cohorts of young children.

Bioelectrical Impedance Analysis-An Easy Tool for Quantifying Body Composition in Infancy?

There has been increasing interest in understanding body composition in early life and factors that may influence its evolution. While several technologies exist to measure body composition in infancy, the equipment is typically large, and thus not readily portable, is expensive, and requires a qualified operator. Bioelectrical impedance analysis shows promise as an inexpensive, portable, and easy to use tool. Despite the technique being widely used to assess body composition for over 35 years, it has been seldom used in infancy. This may be related to the evolving nature of the fat-free mass compartment during this period. Nonetheless, a number of factors have been identified that may influence bioelectrical impedance measurements, which, when controlled for, may result in more accurate measurements. Despite this, questions remain in infants regarding the optimal size and placement of electrodes, the standardization of normal hydration, and the influence of body position on the distribution of water throughout the body. The technology requires further evaluation before being considered as a suitable tool to assess body composition in infancy.

Estimation of fat-free mass in Asian neonates using bioelectrical impedance analysis

The aims of this study were to develop and validate a prediction equation of fat-free mass (FFM) based on bioelectrical impedance analysis (BIA) and anthropometry using air-displacement plethysmography (ADP) as a reference in Asian neonates and to test the applicability of the prediction equations in an independent Western cohort. A total of 173 neonates at birth and 140 at two weeks of age were included. Multiple linear regression analysis was performed to develop the prediction equations in a two-third randomly selected subset and validated on the remaining one-third subset at each time point and in an independent Queensland cohort. FFM measured by ADP was the dependent variable, and anthropometric measures, sex and impedance quotient (L2/R50) were independent variables in the model. Accuracy of prediction equations was assessed using intra-class correlation and Bland-Altman analyses. L2/R50 was the significant predictor of FFM at week two but not at birth. Compared with the model using weight, sex and length, including L2/R50 slightly improved the prediction with a bias of 0·01 kg with 2 sd limits of agreement (LOA) (0·18, -0·20). Prediction explained 88·9 % of variation but not beyond that of anthropometry. Applying these equations to the Queensland cohort provided similar performance at the appropriate age. However, when the Queensland equations were applied to our cohort, the bias increased slightly but with similar LOA. BIA appears to have limited use in predicting FFM in the first few weeks of life compared with simple anthropometry in Asian populations. There is a need for population- and age-appropriate FFM prediction equations.

Bioelectrical impedance analysis for assessment of fluid status and body composition in neonates--the good, the bad and the unknown

BACKGROUND/OBJECTIVES

There is a critical need for improved technologies to monitor fluid balance and body composition in neonates, particularly those receiving intensive care. Bioelectrical impedance analysis meets many of the criteria required in this environment and appears to be effective for monitoring physiological trends.

SUBJECT/METHODS

The literature regarding the use of bioelectrical impedance in neonates was reviewed.

RESULTS

It was found that prediction equations for total body water, extracellular water and fat-free mass have been developed, but many require further testing and validation in larger cohorts. Alternative approaches based on Hanai mixture theory or vector analysis are in the early stages of investigation in neonates.

CONCLUSIONS

Further research is required into electrode positioning, bioimpedance spectroscopy and Cole analysis in order to realise the full potential of this technology.

Prediction of fat-free mass and percentage of body fat in neonates using bioelectrical impedance analysis and anthropometric measures: validation against the PEA POD

Accurate assessment of neonatal body composition is essential to studies investigating neonatal nutrition or developmental origins of obesity. Bioelectrical impedance analysis or bioimpedance analysis is inexpensive, non-invasive and portable, and is widely used in adults for the assessment of body composition. There are currently no prediction algorithms using bioimpedance analysis in neonates that have been directly validated against measurements of fat-free mass (FFM). The aim of the study was to evaluate the use of bioimpedance analysis for the estimation of FFM and percentage of body fat over the first 4 months of life in healthy infants born at term, and to compare these with estimations based on anthropometric measurements (weight and length) and with skinfolds. The present study was an observational study in seventy-seven infants. Body fat content of infants was assessed at birth, 6 weeks, 3 and 4·5 months of age by air displacement plethysmography, using the PEA POD body composition system. Bioimpedance analysis was performed at the same time and the data were used to develop and test prediction equations for FFM. The combination of weight+sex+length predicted FFM, with a bias of < 100 g and limits of agreement of 6–13 %. Before 3 months of age, bioimpedance analysis did not improve the prediction of FFM or body fat. At 3 and 4·5 months, the inclusion of impedance in prediction algorithms resulted in small improvements in prediction of FFM, reducing the bias to < 50 g and limits of agreement to < 9 %. Skinfold measurements performed poorly at all ages.

Application of non-invasive cerebral electrical impedance measurement on brain edema in patients with cerebral infarction

OBJECTIVE

To investigate the change of brain edema in patients with cerebral infarction by non-invasive cerebral electrical impedance (CEI) measurements.

METHODS

An invariable secure current at a frequency of 50 kHz and an intensity of 0.1 mA was given into a person's brain. CEI values of the bilateral hemisphere of 200 healthy volunteers and 107 patients with cerebral infarction were measured by non-invasive brain edema monitor. The results of perturbative index (PI) converted from CEI were compared with the volumes of brain edema, which were calculated by an image analysing system according to magnetic resonance imaging or computed tomography.

RESULTS

(1) In the healthy volunteers, PI values in the left and right hemisphere were 7.98 +/- 0.95 and 8.02 +/- 0.71 respectively, and there was no significant difference between the two sides (p>0.05). Age, gender and different measuring times did not obviously affect PI values (p>0.05). (2) In the cerebral infarction group, CEI measurements were more sensitive to the volumes of lesion, which were more than 20 ml. The positive ratio of PI was higher when the volumes of infarction were >20 ml (80.0%): the ratio of PI was 75.9% when the volumes of infarction were 20-50 ml and it was 83.3% when the volumes of lesion were more than 50 ml. PI was lower when the volumes were less than 20 ml. (3) PI of the infarction side increased obviously 3-5 days after onset; the difference of two sides was the most significant. There was a positive correlation between PI of the infarction side and volume of infarction.

CONCLUSIONS

PI may be a sensitive parameter for non-invasive monitoring of the change of brain edema in patients with cerebral infarction. CEI is a valuable method for the early detection of brain edema.

Prediction of fat-free body mass from bioelectrical impedance among 9- to 11-year-old Swedish children

AIM

Predictive equations for estimating body composition from bioelectrical impedance analysis (BIA) among Scandinavian children are lacking. In the present study, equations for estimation of fat-free body mass (FFM) and lean tissue mass (LTM) were developed and cross-validated from BIA using dual-energy X-ray absorptiometry (DXA) as the reference measurement of body composition.

METHODS

The study population consisted of 49 girls and 52 boys aged 9-11 years from Malmö, Sweden. Bioelectrical impedance was measured between hand and foot at 50 kHz. Predictive equations were developed by multiple linear regression and cross-validated against DXA measurements of body composition.

RESULTS

FFM was predicted from BIA and anthropometric variables with an adjusted R(2)= 0.95 and root mean square error (RMSE) = 0.84 kg, and LTM was predicted with an adjusted R(2)= 0.95 and RMSE = 0.87 kg. Cross-validation revealed a mean RMSE = 0.95 kg FFM and a mean RMSE = 0.96 kg LTM. Prediction of body composition from equations developed in previous literature was mixed when applied to the present cohort of children.

CONCLUSIONS

FFM and LTM are predicted with sufficient accuracy at the population level. We recommend that the predictive equations developed in the present study are used in prepubescent European children aged 9-11 years only in order to minimize confounding of results because of possible differences in population samples.

Evaluation of body composition in neonates and infants

A better understanding of the nutritional needs of both healthy and sick infants is important. Not only does too much or too little nutrition during early life have long-term effects on health, but periods of rapid growth during the first year of life also have long-term consequences. Knowledge of the changes in body composition in early life can help to better define nutritional needs at these ages. Several methods are available for measuring body composition of neonates and infants. Most focus on an assessment of either body fatness or bone mineralization; only a few can monitor the quality of the non-fat lean tissues. This paper provides an evaluation of the different approaches currently available to monitor infant body composition, identifying both their strengths and limitations.

Reference values for whole body and cerebral multi-frequency bio-impedance data in neonates less than 12 h postpartum

Multiple frequency bio-electrical impedance analysis (MFBIA) may be useful for monitoring fluid balance in newborn infants or to provide early prediction of the outcome following perinatal asphyxia. A reference range of data is needed for identification of babies with abnormal impedance values. This was a cross-sectional observational study in 84 term and near-term healthy neonates less than 12 h postpartum. Whole body and cerebral MFBIA measurements were performed at the bedside in the post-natal ward. Gestational age, post-natal age, gender, birthweight, head circumference and foot length measures were recorded. Reference values for impedance at the characteristic frequency (Z(C)) and resistance at zero frequency (R(0)) are reported for whole body and cerebral impedance. Significant correlations (p < 0.05) were observed between whole body impedance and birthweight, footlength and head circumference. Females had a significantly higher whole body R(0) than males. Cerebral impedance did not correlate significantly with any of the demographic measures and there were no gender differences observed for cerebral impedance. The reference range for whole body multi-frequency bio-impedance values in term and near-term infants within the first 12 h postpartum can be calculated from the footlength (FL) using the following equations: Z(C) = (942.9 - 4.818*FL) +/- 124.6 Omega; R(0) = (1042 - 4.520*FL) +/- 135.5 Omega. For cerebral impedance the reference range is 29.5-48.7 Omega for Z(C) and 33.7-58.0 Omega for R(0).

Bioelectrical impedance spectroscopy for the assessment of body fluid volumes of term neonates

The assessment of fluid volume in neonates by a noninvasive, inexpensive, and fast method can contribute significantly to increase the quality of neonatal care. The objective of the present study was to calibrate an acquisition system and software to estimate the bioelectrical impedance parameters obtained by a method of bioelectrical impedance spectroscopy based on step response and to develop specific equations for the neonatal population to determine body fluid compartments. Bioelectric impedance measurements were performed by a laboratory homemade instrument. The volumes were estimated in a clinical study on 30 full-term neonates at four different times during the first month of life. During the first 24 hours of life the total body water, extracellular water and intracellular water were 2.09 +/- 0.25, 1.20 +/- 0.19, and 0.90 +/- 0.25 liters, respectively. By the 48th hour they were 1.87 +/- 0.27, 1.08 +/- 0.17, and 0.79 +/- 0.21 liters, respectively. On the 10th day they were 2.02 +/- 0.25, 1.29 +/- 0.21, and 0.72 +/- 0.14 liters, respectively, and after 1 month they were 2.34 +/- 0.27, 1.62 +/- 0.20, and 0.72 +/- 0.13 liters, respectively. The behavior of the estimated volume was correlated with neonatal body weight changes, leading to a better interpretation of such changes. In conclusion, this study indicates the feasibility of bioelectrical impedance spectroscopy as a method to help fluid administration in intensive care neonatal units, and also contribute to the development of new equations to estimate neonatal body fluid contents.

Empirically derived new equations for calculating body fat percentage based on skinfold thickness and midarm circumference in preschool Indian children

We wanted to develop and apply new equations based on skinfold and midarm measurements for estimating %fat in preschool children suitable for field use. Prediction equations were developed on preschool-aged urban boys (n = 100) and girls (n = 84). Skinfolds at four sites and midarm measurements were regressed on %fat derived from equations based on height and weight and from bioelectrical impedance analysis (BIA; resistance at 50 kHz). These equations were applied: 1) to 12 children in whom the %fat was determined using D2O dilution, and 2) to 50 children in whom their %fat was derived using height-weight and BIA equations. The 95% limits of agreement (mean +/- 2 SD) for %fat derived by anthropometry and by new equations were within 1.7% in boys (r = 0.85; P < 0.001) and girls (r = 0.90; P < 0.001) and by BIA and new equations were within 1.5% in boys (r = 0.82; P < 0.001) and 2% in girls (r = 0.88; P < 0.001). For %fat measured by D2O dilution and new equations, 95% limits of agreement was within 1.3% (r = 0.98; P < 0.001). In 50 children 95% limits of agreement between anthropometry and new equations were within 1.8% in boys (r = 0.88; P < 0.001) and 1.4% in girls (r = 0.92; P < 0.001) and between BIA and new equations were within 1% in boys (r = 0.91; P < 0.001) and 1.5% in girls (r = 0.89; P < 0.001). The new equations for measuring %fat based on midarm circumference and skinfold measurements are rapid and accurate for South Asian children and should be useful for prediction of body composition and nutritional survey in field studies.

Bioelectrical impedance vector distribution in the first year of life

OBJECTIVE

We assessed the bioelectrical impedance vector distribution in a sample of healthy infants in the first year of life, which is not available in literature.

METHODS

The study was conducted as a cross-sectional study in 153 healthy Caucasian infants (90 male and 63 female) younger than 1 y, born at full term, adequate for gestational age, free from chronic diseases or growth problems, and not feverish. Z scores for weight, length, cranial circumference, and body mass index for the study population were within the range of +/-1.5 standard deviations according to the Euro-Growth Study references. Concurrent anthropometrics (weight, length, and cranial circumference), body mass index, and bioelectrical impedance (resistance and reactance) measurements were made by the same operator. Whole-body (hand to foot) tetrapolar measurements were performed with a single-frequency (50 kHz), phase-sensitive impedance analyzer. The study population was subdivided into three classes of age for statistical analysis: 0 to 3.99 mo, 4 to 7.99 mo, and 8 to 11.99 mo. Using the bivariate normal distribution of resistance and reactance components standardized by the infant's length, the bivariate 95% confidence limits for the mean impedance vector separated by sex and age groups were calculated and plotted. Further, the bivariate 95%, 75%, and 50% tolerance intervals for individual vector measurements in the first year of life were plotted.

RESULTS

Resistance and reactance values often fluctuated during the first year of life, particularly as raw measurements (without normalization by subject's length). However, 95% confidence ellipses of mean vectors from the three age groups overlapped each other, as did confidence ellipses by sex for each age class, indicating no significant vector migration during the first year of life.

CONCLUSIONS

We obtained an estimate of mean impedance vector in a sample of healthy infants in the first year of life and calculated the bivariate values for an individual vector (95%, 75%, and 50% tolerance ellipses).

The effect of zinc supplementation on linear growth, body composition, and growth factors in preterm infants

OBJECTIVE

The aim of our study was to evaluate the effect of zinc supplementation on linear growth, body composition, and growth factors in premature infants.

DESIGN

Thirty-six preterm infants (gestational age: 32.0 +/- 2.1 weeks, birth weight: 1704 +/- 364 g) participated in a longitudinal double-blind, randomized clinical trial. They were randomly allocated either to the supplemental (S) group fed with a standard term formula supplemented with zinc (final content 10 mg/L) and a small quantity of copper (final content 0.6 mg/L), or to the placebo group fed with the same formula without supplementation (final content of zinc: 5 mg/L and copper: 0.4 mg/L), from 36 weeks postconceptional age until 6 months corrected postnatal age. At each evaluation, anthropometric variables and bioelectrical impedance were measured, a 3-day dietary record was collected, and a blood sample was taken. We analyzed serum levels of total alkaline phosphatase, skeletal alkaline phosphatase (sALP), insulin growth factor (IGF)-I, IGF binding protein-3, IGF binding protein-1, zinc and copper, and the concentrations of zinc in erythrocytes.

RESULTS

The S group had significantly higher zinc levels in serum and erythrocytes and lower serum copper levels with respect to the placebo group. We found that the S group had a greater linear growth (from baseline to 3 months corrected age: Delta score deviation standard length: 1.32 +/-.8 vs.38 +/-.8). The increase in total body water and in serum levels of sALP was also significantly higher in the S group (total body water: 3 months; corrected age: 3.8 +/-.5 vs 3.5 +/-.4 kg, 6 months; corrected age: 4.5 +/-.5 vs 4.2 +/-.4 kg; sALP: 3 months; corrected age: 140.2 +/- 28.7 vs 118.7 +/- 18.8 micro g/L).

CONCLUSIONS

Zinc supplementation has a positive effect on linear growth in premature infants.

Cerebral impedance and neurological outcome following a mild or severe hypoxic/ischemic episode in neonatal piglets

Multi-frequency bio-impedance has the potential to identify infants at risk of poor neurodevelopmental outcome following hypoxia by detecting cerebral edema. This study investigated the relationship between the severity of an hypoxic/ischemic episode, neurological outcome following the hypoxia and non-invasively measured cerebral bioelectrical impedance in piglets. One-day-old piglets were anaesthetised and ventilated. Hypoxia was induced by reducing the inspired oxygen concentration to 3-5%. Severe hypoxia was defined as hypoxia resulting in at least 30 min of low amplitude EEG (<5 microV) as well as hypotension and acidosis. Cerebral bio-impedance was measured before, during and for up to 6 h post-hypoxia. Neurological outcome was determined by a neurology score at 24 and 48 h after hypoxia, and by histological examination of the brain at 72 h. There was no increase in cerebral impedance in control animals. Following mild hypoxia cerebral impedance increased transiently. Following severe hypoxia, cerebral impedance increased and remained elevated. Cerebral impedance following severe hypoxia was significantly higher than after mild hypoxia at 10 min and from 2 to 6 h after resuscitation. Cerebral impedance measurements made up to 1 h and between 3 and 6 h after resuscitation were significantly correlated with neurological outcome. Results indicate that non-invasive cerebral impedance measurements are able to discriminate early between those individuals who have suffered a mild, acute hypoxic episode, and those who have suffered a severe hypoxic episode. The technique has the potential to predict which individuals will have a poor neurological outcome.

Reference values of the bioelectrical impedance vector in neonates in the first week after birth

OBJECTIVE

To determine the reference, bivariate, tolerance intervals of the whole-body impedance vector for healthy white neonates, we performed an observational, cross-sectional study in two university hospitals.

METHODS

The impedance vector (standard, tetrapolar analysis at 50-kHz frequency) was measured in 163 consecutive subjects (87 boys and 76 girls) with postnatal ages of 1 to 7 d. Bivariate vector analysis was conducted with the resistance-reactance (RXc) graph method.

RESULTS

The age-specific 95% confidence intervals of mean vectors and the 95%, 75%, and 50% tolerance intervals for individual vector measurements were plotted using R and Xc components standardized by the subject's crown-to-heel length (height). Mean vectors from the groups (1, 2, and 3 to 7 d) with overlapping 95% confidence ellipses were considered representative of only one age class of 1 to 7 d. The impedance vector distribution of neonates also was compared with healthy white children (1014 boys and 1030 girls, age 2-15 y) and adult subjects (354 men and 372 women, age 15-85 y) from the same geographic area. There was a definite, progressive, vector shortening from birth, through ages 2 to 15 y, toward the adults' vector position.

CONCLUSIONS

We established the reference, bivariate, 95%, 75%, and 50% tolerance intervals of the impedance vector in the first postnatal week for healthy white neonates, with which the vectors from infants with altered body composition can be tested (free software is available from apiccoli@ unipd.it).

Increased parenteral amino acid administration to extremely low-birth-weight infants during early postnatal life

BACKGROUND

Early administration of parenteral amino acids to infants with extremely low birth weight (birth weight < or = 1,000 g) has been encouraged to foster growth. However, excessive intravenous intake of amino acids may cause metabolic acidosis and uremia in extremely low birth weight infants. The hypothesis for this study was that extremely low birth weight infants would tolerate slightly increased early postnatal parenteral amino acid administration and benefit.

METHODS

The peak daily parenteral amino acid dosage was increased from 3 g/kg (standard group) to 4 g/kg (modified group). The corrected parenteral amino acid dosage was computed to account for enteral protein intake and keep the combined daily intravenous amino acid and enteral protein intake at or below 3 g . kg -1 . d -1 in the standard group and 4 g . kg -1 . d -1 in the modified group. The primary outcome measure was plasma bicarbonate concentration as an indicator of acid-base status. Data were collected for patient demographics, nutritional intake, serum bicarbonate and serum urea nitrogen concentrations, and outcome.

RESULTS

The corrected parenteral amino acid intake of the modified group was 16% greater at postnatal week 1 (3.30 +/- 0.83 g . kg -1 . d -1; mean, +/-1 SD) and 18% greater (3.86 +/- 0.94 g . kg -1 . d -1 ) at postnatal week 2 than the parenteral amino acid intake of the standard group. In the modified group, the mean serum bicarbonate concentration was 19.1 +/- 1.8 mEq/dL at week 1 and 23.9 +/- 2.9 mEq/dL at week 2, with no difference between the groups. At week 1, serum urea nitrogen concentrations were the same in both groups. The mean serum urea nitrogen concentration of the modified group at postnatal week 2 (18.2 +/- 8.8 mg/dL) was unchanged from postnatal week 1, but was greater than that of the standard group at postnatal week 2. Weight gain was the same in both groups. Corrected parenteral amino acid intake at postnatal week 1 correlated directly with weight gain from birth to postnatal week 2 ( P < 0.03) in both groups.

CONCLUSIONS

Infants with extremely low birth weight tolerated parenteral amino acid intake of approximately 4 g . kg -1 . d -1. Mild increases of mean serum urea nitrogen concentration and mean weight gain were associated with increased parenteral amino acid administration without significant acidosis.

Measurement of extracellular fluid volume in the neonate using multiple frequency bio-impedance analysis

Bioelectrical impedance analysis may be useful for cot-side monitoring of fluid balance in the neonatal intensive care unit (NICU). However the presence of cardio-respiratory monitoring equipment, non-ideal electrode placement and inability to obtain accurate crown-heel measurements may interfere with the ability to obtain reliable impedance data in this setting. This study aimed to investigate the effects of these factors on impedance analysis and to develop a prediction equation for extracellular fluid volume in the neonate. The study found that cardio respiratory monitoring had no significant effect on multi-frequency impedance measurements. Placement of current delivering electrodes on the ventral rather than dorsal surfaces improved separation of current and voltage electrodes but did not alter impedance results. Contralateral measurements were not significantly different to ipsilateral measurements. In 24 infants, extracellular fluid volume was measured using corrected bromide space (CBS) and simultaneous impedance analysis was performed. There was good correlation between CBS and the impedance quotient FF2/Ro where F is foot length and R0 is resistance at zero frequency. The study concludes that despite many potential difficulties associated with impedance analysis in the NICU, reliable measurements of impedance can be obtained and further work to validate prediction equations for ECF is warranted.

Protein metabolism in the extremely low-birth weight infant

Although extensive data are available on the impact of nutrient and protein administration on growth, plasma amino acids, and nitrogen balance in the newborn and growing infants, relatively few studies have carefully examined the dynamic aspects of protein metabolism in vivo and particularly in the micropremie or ELBW infant. These studies show that the very preterm infants, either because of immaturity or because of the intercurrent illness, have high rates of protein turnover and protein breakdown. This high rate of proteolysis is not as responsive to nutrient administration. Intervention strategies aimed at promoting nitrogen accretion, such as insulin, human growth hormone, or glutamine, have not thus far resulted in enhanced protein accretion and growth. This may be, in part, due to limitations in delivery of adequate calorie and nitrogen.