Electrode placement in neonatal bioelectrical impedance analysis

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.

Adverse effects of near current-electrode placement in non-invasive bio-impedance measurements

A major problem confronting application of impedance techniques to studies of disease is the extraction of intrinsic properties of the tissue from the measured impedances, which unavoidably involve geometric factors as well. Amongst the foremost are the sizes and locations of the measuring electrode arrays, and this paper addresses one of these, the location of current injecting electrodes. Tetrapolar impedance measurements on a 17.5 cm segment of the thigh gave R and X values three to four times larger when the current injecting electrodes were placed 2.5 cm from the sensing electrodes than when very distant placement was used. The frequency dependences of R and X were affected as well, though the X versus R plots still showed virtually perfect depressed-center semicircles, as in the Cole model. R(f) and X(f) for the set of contiguous 2.5 cm wide sub-segments show that these behaviors can be explained by a combination of the transverse orientation of current flow lines near the injecting electrodes and the anisotropy of the resistivity associated with the bundled fiber structure of muscle tissue. The measured impedance was found to be a separable function of geometric and intrinsic tissue variables, but far more complicated than is implicit in the usual cylindrical models. The results also suggest that many full and segmental body composition studies in the literature may be prone to substantial errors due to too close placement of the current injecting electrodes.

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.

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).

Bioimpedance electrical spectroscopy in the first six months of life: some methodologic considerations

OBJECTIVES

The objectives of this study were to evaluate the feasibility of using multifrequency bioelectrical impedance spectroscopy (BIS) in newborns and first-semester infants and to assess the influence of diverse methodologic and biological factors on BIS measurements.

METHODS

We studied 69 infants of both sexes, from the first day after birth through age 6 mo. They were healthy term infants who had no congenital malformations and were born in a low-income, peri-urban neighborhood of Guatemala City. The design was based on serial, repeated BIS measurements.

RESULTS

Overall mean values of extra- and intracellular resistance (mean+/-standard deviation) were 470.0+/-73.3 Omega and 604.6+/-179.2 Omega, respectively. We found statistical differences in both resistances in relation to advancing age and degree of movement while taking the measurements. With respect to repeat measurements by two separate observers, interobserver differences were a non-significant 7.6 Omega for both resistances. Restraining the infants and previous consumption of milk or formula had a significant effect on extracellular resistance measurements. The mean standard errors of measurement was 4.5 Omega for extracellular resistance and 73.9 Omega for intracellular resistance.

CONCLUSION

The BIS technique is feasible in newborn and young children when physiologic and methodologic aspects are respected or controlled.

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.