Assessment of total body water using bioelectrical impedance analysis in neonates receiving intensive care
a Department of Paediatrics and Neonatal Medicine, b Department of Medical
Statistics, Royal Postgraduate Medical School,
Hammersmith Hospital, Du Cane Road, London W12 0NN
Correspondence to: Dr Neena Modi.
Accepted 4 March 1997
AIMS
To determine the most suitable
anthropometric and impedance measures and current frequency for the
application of bioelectrical impedance to neonates receiving intensive
care; and to derive predictive models for the estimation of total body water.
METHODSTwenty eight babies (median gestational
age 30.5 weeks, range 24-38; median birthweight 1.388 kg, range
0.690-3.510) were each studied once during the first week after birth.
Total body water was first measured by the method of dilution of
isotopic water (H218O). Bioelectrical
measurements were made using the tetrapolar surface electrode method
from four main distal limb positions (right hand-right foot; right
hand-left foot; left hand-left foot; left hand-right foot), the left
upper arm-left thigh position and the left scapula-right buttock
position, and using six frequencies ((500, 250, 100, 50, 10 and 5 kHz).
Regression models, to predict total body water, which were both
independent and dependent of body weight on the day of study, were derived.
RESULTSResistance readings at 50 kHz obtained
from the distal limb positions performed best. There was no difference
between the distal limb positions. There was no difference in the
goodness of fit of the models when using each of three indices of
conductor length, foot, spine and sternum. The model total body water
(litres) (TBW) = 0.016 + 0.674 bodyweight(kg)
0.038 wt2 + 3.84 foot length (cm)2/resistance (50 kHz in OHMS)
performed best, accounting for 99.5% of the variation in TBW, with a
95% prediction interval of 165 ml. The model TBW = 0.144 + 15.518 foot
length (cm)2/resistance (50 kHz in ohms) accounted for
96.4% of the variation and had a 95% prediction interval of 420 ml.
CONCLUSIONSBioelectrical impedance analysis
is a simple, non-invasive method of estimating total body water in
neonates receiving intensive care. It can be applied to both the
assessment of changes in body water and body composition.
© 1997 by Archives of Disease in Childhood
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