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Bioelectrical impedance spectroscopy (BIS) in young children with acute and semi-acute hydration disorders: Potentials and limitations
~
Pergamon
PII:
Appl. Radiat. lsot. Vol. 49, No. 5/6. pp. 611 614, 1998 © 1998 ElsevierScienceLtd. All rights reserved Printed in Great Britain S0969-8043(97)00267.-4 0969-8043/98 $19.00+ 0.00
Bioelectrical Impedance Spectroscopy (BIS) in Young Children with Acute and Semi-acute Hydration Disorders: Potentials and Limitations M A N O L O M A Z A R I E G O S 1, C H R I S T I A N E P I T H A N 2, A N D R E A M E Y E W , I V A N M E N D O Z A I, P E T E R F O R S T 2 a n d N O E L W. S O L O M O N S ~ ~Center for Studies of Sensory Impairment, Aging and Metabolism (CeSSIAM), Diagonal 21, 19-19 zona 11, Guatemala City, C.A. 01011, Guatemala and 21nstitute of Biological Chemistry and Nutrition, University of Hohenheim, GarbenstraBe 30, 70599, Stuttgart, Germany This study aimed to evaluate the feasibility and reliability of bioelectrical impedance spectroscopy in young children suffering of acute hydrational disorders. Whole body and segmental measurements were carried out in a group of 42 of children aged 4 to 147 months, using a BIS analyzer (Xitron 4000B). This phase of the study involved several hundred of B1S measurement, which showed the feasibility of using this technique in young children. Using the sweep mode and the modeling software provided for the manufacturer of the instrument, the resistance of the extracellular (RECW) and intracellular (RICW) compartment was calculated. Correlation coefficient (r) and technical error of measurement (TEM) were obtained from paired BIS measurements. RECW showed to be highly reproducible (r = 0.99), with a relatively low TEM (from 1 to 3.5%), across all segments. The reliability was markedly lower respect to RICW, which shows the potential application of BIS technique even in critically ill young child populations. ~) 1998 Elsevier Science Ltd. All rights reserved
Introduction
determination of the reliability of the measurement for both whole body and segmental assessments.
Bioelectrical impedance spectroscopy (BIS) has been proposed as a non-invasive technique to assess body composition and to determine fluid distribution across cell membranes (Kanai et al., 1987). Several reports about the use of BIS have been published in the literature (Cornish et al., 1994; De Lorenzo et al., 1995; Chumlea and Guo, 1994), and preliminary results in adult populations seem to be promising. However, very little information exists about the use of BIS in children, and even less is known about the potential application of such a technique in young children suffering from severe malnutrition, such as marasmus or kwashiorkor, or from acute dehydration due to diarrhoeal disease. Although BIS has the advantages of being non-invasive and the equipment is portable, the technique requires good cooperation from the subject. In young children, the small size of the body segments (small conductor length), lack of spontaneous cooperation and acute illnesses associated with water distribution disorders are some of the factors that may impose a great challenge to the BIS technique. The present study explores the usefulness of BIS in these populations with respect to: (a) feasibility studies of its application; and (b) the
Subjectsand Methods Population
A group of 42 children from 4 to 147 months of age (27 boys and 15 girls) was studied; a group of children who were admitted to the General Hospital 'San Juan de Dios' in Guatemala City, either for acute malnutrition (n = 22) or acute dehydration associated with diarrhoeal disease (n = 20). The former group was composed of 22 members with either marasmic malnutrition, severe malnutrition associated with oedema (kwashiorkor), or a mixed type. In the second group of 20, nine had moderate dehydration and 11 were severely dehydrated. Procedures
Weight and height were measured at admission and then at intervals according to the therapy protocol. BIS measurements were taking using a Xitron 4000B analyzer (Xitron Technologies, CA, U.S.A.), at the level of whole body as reported in the literature (Lukaski et al., 1985) and segmental measurements at the level of arm, trunk ipsilateral and medial, leg and 611
Manolo Mazariegos et al.
612
Table I. Mean comparisons, correlation coefficients and TEM for Recw and Rlcw by body segments between first and second measurement in malnourished children Body segment Whole body (n = 142) Armless body (n = 138) Leg (n = 142)
BIS index (f2)" Re~ R~w Rec~ R~c~ REcw
Rww Arm (n = 139) Trunk ipsilateral (n = 138) Trunk medial (n = 138)
Recw R~c~ Recw R~cw Recw
R,cw
Mean _+ SD measure 1b 697 ± 1147 + 336 ± 559 ± 271 ± 625 ± 358 ± 819 ± 69 ± 57 ± 46 ± 55 ±
(r) ~
144 ns 474 ns 97 ns 175 ns 90 ns 190 ns 70 ns 436 ns 13 ns 26 ns 10 ns 22 ns
TEM (~)
0.99*** 0.64*** 0.99*** 0,64*** 0.99*** 0.70*** 0.99*** 0.44** 0.98*** 0.69*** 0.99*** 0.81"**
TEM (%)
12.2 352 3 102 3 98 5 301 2 16 1 9
1.8 30.7 0.8 18.3 1.0 15.7 1.4 36.8 2.2 28.7 2.1 16.2
"R~cw = resistance of the extracellular space; R~cw= resistance of the intracellular space. ~Comparison of means of measurement I with mean of measurement 2 by paired t-test: + , p < 0.05; ns, not significant. 'Pearson correlation coefficient between measurement 1 and measurement 2: ***, p < 0.001: **, p < 0.01.
a n k l e - s h o u l d e r ( a r m l e s s b o d y ) as d e s c r i b e d in Fig. 1, which represents a slight m o d i f i c a t i o n to the a p p r o a c h s u g g e s t e d by O r g a n et al. (1994). T r u n k i p s i l a t e r a l a n d m e d i a l r e l a t e t o d i f f e r e n t r e g i o n s o f t he c h e s t a n d differ a l s o in t e r m s o f t he d i s t a n c e b e t w e e n the
inner
electrodes.
Measurements
were
made
s e q u e n t i a l l y in d u p l i c a t e . T o o b t a i n p r o p e r m e a s u r e m e n t s in c h i l d r e n w i t h v e r y little a b i l i t y t o c o o p e r a t e , it w a s n e c e s s a r y t o w r a p t he c h i l d in a b l a n k e t , leaving exposed
o n l y t he
specific s e g m e n t
to
be
a s s e s s e d . F o r t h e p u r p o s e s o f t hi s s t u d y , t he s k i n electrodes (BIS4000 electrodes, Xitron Technologies, C A , U . S . A . ) w e r e k e p t in p o s i t i o n w h i l e d u p l i c a t e m e a s u r e m e n t s w e r e in p r o g r e s s . B IS i n d i c e s s u c h a s extracellular
resistance
(Recw)
and
intracellular
r e s i s t a n c e (R,cw) w e r e c a l c u l a t e d u s i n g t he C o l e - C o l e m o d e l i n g a p p r o a c h i n c o r p o r a t e d w i t h i n t he m a n u f a c Fig. 1. Electrode position for whole body and segmental BIS measurements. Segments measured (broken lines): a = arm; L = leg; ti = trunk ipsilateral; and tm = trunk medial. For whole body measurements both current and voltage electrodes were positioned on the wrist and ankle on the right side. For arm-less body segment, one voltage electrode was positioned at the level of shoulder and the other on the ankle, on the right side. Dark circles (O) represent current electrodes, which remained fixed at the level of wrist and ankle on the right side for whole body and all segmental configurations. Dark squares (11), at the extremes of each broken line, represent the pair of voltage electrodes for each segmental measurement. Each voltage cable was moved proximally according to each segmental configuration.
turer's software.
Statistical analysis Mean
c o m p a r i s o n s were done between pairs of
measurements
by
using
a
paired
t-test.
Pearson
c o r r e l a t i o n c oe ffi c i e nt s w e r e c a l c u l a t e d b e t w e e n t he first a n d s e c o n d m e a s u r e m e n t . T h e t e c h n i c a l e r r o r o f the estimate (TEM)
w a s c a l c u l a t e d b y u s i n g t he
a p p r o a c h s u g g e s t e d by L o h m a n et al. (1988). T h i s a p p r o a c h is b a s e d o n t h e di ffe re nc e s b e t w e e n t h e first a n d s e c o n d m e a s u r e m e n t s t a k e n c l o s e to e a c h o t h e r
Table 2. Mean comparisons, correlation coefficients and TEM for Recw and Rtcw by body segments between first and second measurement in dehydrated children Body segment Whole body (n = 142) Armless body (n = 138) Leg (n = 142) Arm (n = 139) Trunk ipsilateral (n = 138) Trunk medial (n = 138)
BIS index (f~)~
Mean + SD measure I b
(r) ~
REcw Rj~w REcw R,cw
812 ± 119 932 ± 624 438 _+ 104 42t + 209 362 + 102 425 ± 211 402 ± 87 572 ± 325 78 ± 12 51 ± 19 55 + 8 57 ± 28
0.97*** 0.55*** 1.0"** 0.84*** 0.99*** 0.71"** 0.99*** 0.83*** 0.99*** 0.79*** 0.98*** 0.76***
REcw Rjcw Recw Rjcw Recw Rjcw Recw
R~cw
TEM (~) 22.3 397 4.4 91.9 12.4 112.6 6.7 128.7 1.5 9.9 1.1 13.3
"Recw = resistance of the extracellular space; Rtcw = resistance of the intracellular space. "Comparison of mean of measurement I with mean of measurement 2 by paired t-test: + , p < 0.05; ns, not significant. 'Pearson correlation coefficient between measurment 1 and measurement 2: ***, p < 0.001; **, p < 0.01.
TEM (%) 2.8 41.5 1.0 21.1 3.4 26.6 1.7 30.2 1.9 18.0 2.0 24.1
BIS for hydration disorders and applying the equation proposed by Lohman et al. (1988). As the TEM is an estimate, in the units of measurement, of the variable in question, in this paper it was expressed as a percentage in respect of its corresponding mean. In general, TEM indicates the permissible limits of the magnitude of the difference between two consecutive measurements. If the difference between replicates is greater than expected, investigators should correct or remake the measurements.
Results A total of about 1200 pairs of measurements was performed across all segments in the study population. Table l and Table 2 show the means +_ SD for the BIS indices for the first measurement, at both whole body and segments, in malnourished and dehydrated children. The first measurement was compared with the second measurement (the latter not shown) by a t-test. In most cases, the means + SD between the first and second measurements were almost identical in all types of measurements. The range of mean differences between paired measurements was within 3 fL however it varied across segments. The same tables show the Pearson correlation coefficients between the first and second measurements. In most cases, highly significant r values were documented. TEM, as an indicator of the reliability of the BIS method, is presented in the same tables. The magnitude of TEM ranged from 0 to 22 f2. However, when TEM was expressed as a percentage in respect of the mean for each segment, it ranged from 0.8 to 3.4%. Another piece of evidence to support the validity of the segmental BIS measurement with respect to the more conventional whole body is that in most cases the sum of the segmental BIS indices equals the whole body approach (Organ et al., 1994). In addition, segmental measurements were highly correlated (r values around 0.8) with whole body measurements (data not shown), with segments such as leg and armless body showing the highest r values.
Discussion Although unstable clinical conditions associated with fluid disorders, such as severe malnutrition and dehydration in young children, may provide a good opportunity for testing and/or using BIS, many researchers are reluctant to apply this technique in young and sick populations arguing methodological difficulties. First, the small size of the children with malnutrition because of severe growth retardation and depletion of muscle and fat mass reduces ostensibly the length and volume of the conductor and also impairs the conventional position of input-voltage electrodes suggested for older populations. The second argument is the lack of cooperation of the children which may make the ARI 49/5-6---G
613
quality of the measurements dubious. We have to recognize that performing BIS measurements in this particular group of children with acute life-threatening clinical conditions was not free of inconvenience, but can be performed with high reliability if we are careful and dedicate enough time to obtaining the children's cooperation. In the present study about 2500 BIS measurements were carried out, and therefore we feel confident that this technique has a potential in this particular group. The calculation of TEM allowed us to establish in practical terms the permissible difference between two consecutive BIS measurements carried out in the same subject within a short time (excluding biological factors). The magnitude of TEM for REcw was lower compared with some anthropometric procedures (Lohman et al., 1988). With respect to Rlcw the correlation coefficients and TEM are poor. These data are consistent throughout all studies carried out in our Center. We have documented unusual, very high critical frequencies (Fc) in these young populations. Although we do not have a clear explanation, it may be related to segment size, capability of both hardware and software, or the environment. In conclusion, based on the high comparability of two sets of pair measurements, the highly significant r values (mostly r = 0.99) and the relatively low TEM with respect to REcw (1 to 3.5% with respect to the mean), it is believed that the application of BIS in this type of population is feasible. However, at this stage of development of BIS, Third World countries may have only limited access to this promising technique. Finally, this study showed that only REcw proved to be sufficiently stable to be used to predict extracellular water, a relevant determinant of quality of fat-free mass, and of great importance in clinical medicine. The use of the remaining BIS indices is still uncertain. Acknowledgements--We would like to thank the Director, medical staff and nurses of the General Hospital 'San Juan de Dios' in Guatemala City, for their support whilecarrying out the study. We are also grateful for the instrumental support of Mr. James Matthie, from Xitron Technologies, Inc. (San Diego, CA, U.S.A.) who provided the BIS analyzer and supplies.
References Chumlea, W. C. and Guo, S. S. (1994) Bioelectrical impedance and body composition: present status and future directions. Nutrition Reviews 52, 123-131. Cornish, B. H., App, M., Ward, L. C. and Thomas, B. J. (1994) Alterations of the extracellular and total body water volumes measured by multiple frequency bioelectrical impedance analysis (MFBIA). Nutrition Research 14, 717 727. De Lorenzo, A., Candeloro, N., Andreoli, A. and Deurenberg, P. (1995) Determination of intracellular water by multifrequency bioelectrical impedance. Annals o f Nutrition and Metabolism 39, 177-184.
614
Manolo Mazariegos et al.
Kanai, H., Haeno, M. and Sakamoto, K. (1987) Electrical measurements of fluid distribution in legs and arms. Medical Progress Through Technology 4, 281 311. Lohman, T. G.. Roche, A. F. and Martorell, R. (1988) Anthropometrie Standarization Reference Manual. Human Kinetics Books, Champaign, I1. Lukaski, H. C., Johnson, P. E., Bolonchuk, W. W. and
Lykken, G. (1985) Assessment of fat-free mass using bioelectrical impedance measurements of the human body. A merican Journal of Clinical Nutrition 41, 810-817. Organ, L. W., Bradman, G. B., Gore, D. T. and Lozier, S. L. (1994) Segmental bioelectrical impedance analysis: theory and application of the technique. American Journal of Applied Physiology, 77(1), 98-112.
Pergamon
PII:
Appl. Radiat. lsot. Vol. 49, No. 5/6. pp. 611 614, 1998 © 1998 ElsevierScienceLtd. All rights reserved Printed in Great Britain S0969-8043(97)00267.-4 0969-8043/98 $19.00+ 0.00
Bioelectrical Impedance Spectroscopy (BIS) in Young Children with Acute and Semi-acute Hydration Disorders: Potentials and Limitations M A N O L O M A Z A R I E G O S 1, C H R I S T I A N E P I T H A N 2, A N D R E A M E Y E W , I V A N M E N D O Z A I, P E T E R F O R S T 2 a n d N O E L W. S O L O M O N S ~ ~Center for Studies of Sensory Impairment, Aging and Metabolism (CeSSIAM), Diagonal 21, 19-19 zona 11, Guatemala City, C.A. 01011, Guatemala and 21nstitute of Biological Chemistry and Nutrition, University of Hohenheim, GarbenstraBe 30, 70599, Stuttgart, Germany This study aimed to evaluate the feasibility and reliability of bioelectrical impedance spectroscopy in young children suffering of acute hydrational disorders. Whole body and segmental measurements were carried out in a group of 42 of children aged 4 to 147 months, using a BIS analyzer (Xitron 4000B). This phase of the study involved several hundred of B1S measurement, which showed the feasibility of using this technique in young children. Using the sweep mode and the modeling software provided for the manufacturer of the instrument, the resistance of the extracellular (RECW) and intracellular (RICW) compartment was calculated. Correlation coefficient (r) and technical error of measurement (TEM) were obtained from paired BIS measurements. RECW showed to be highly reproducible (r = 0.99), with a relatively low TEM (from 1 to 3.5%), across all segments. The reliability was markedly lower respect to RICW, which shows the potential application of BIS technique even in critically ill young child populations. ~) 1998 Elsevier Science Ltd. All rights reserved
Introduction
determination of the reliability of the measurement for both whole body and segmental assessments.
Bioelectrical impedance spectroscopy (BIS) has been proposed as a non-invasive technique to assess body composition and to determine fluid distribution across cell membranes (Kanai et al., 1987). Several reports about the use of BIS have been published in the literature (Cornish et al., 1994; De Lorenzo et al., 1995; Chumlea and Guo, 1994), and preliminary results in adult populations seem to be promising. However, very little information exists about the use of BIS in children, and even less is known about the potential application of such a technique in young children suffering from severe malnutrition, such as marasmus or kwashiorkor, or from acute dehydration due to diarrhoeal disease. Although BIS has the advantages of being non-invasive and the equipment is portable, the technique requires good cooperation from the subject. In young children, the small size of the body segments (small conductor length), lack of spontaneous cooperation and acute illnesses associated with water distribution disorders are some of the factors that may impose a great challenge to the BIS technique. The present study explores the usefulness of BIS in these populations with respect to: (a) feasibility studies of its application; and (b) the
Subjectsand Methods Population
A group of 42 children from 4 to 147 months of age (27 boys and 15 girls) was studied; a group of children who were admitted to the General Hospital 'San Juan de Dios' in Guatemala City, either for acute malnutrition (n = 22) or acute dehydration associated with diarrhoeal disease (n = 20). The former group was composed of 22 members with either marasmic malnutrition, severe malnutrition associated with oedema (kwashiorkor), or a mixed type. In the second group of 20, nine had moderate dehydration and 11 were severely dehydrated. Procedures
Weight and height were measured at admission and then at intervals according to the therapy protocol. BIS measurements were taking using a Xitron 4000B analyzer (Xitron Technologies, CA, U.S.A.), at the level of whole body as reported in the literature (Lukaski et al., 1985) and segmental measurements at the level of arm, trunk ipsilateral and medial, leg and 611
Manolo Mazariegos et al.
612
Table I. Mean comparisons, correlation coefficients and TEM for Recw and Rlcw by body segments between first and second measurement in malnourished children Body segment Whole body (n = 142) Armless body (n = 138) Leg (n = 142)
BIS index (f2)" Re~ R~w Rec~ R~c~ REcw
Rww Arm (n = 139) Trunk ipsilateral (n = 138) Trunk medial (n = 138)
Recw R~c~ Recw R~cw Recw
R,cw
Mean _+ SD measure 1b 697 ± 1147 + 336 ± 559 ± 271 ± 625 ± 358 ± 819 ± 69 ± 57 ± 46 ± 55 ±
(r) ~
144 ns 474 ns 97 ns 175 ns 90 ns 190 ns 70 ns 436 ns 13 ns 26 ns 10 ns 22 ns
TEM (~)
0.99*** 0.64*** 0.99*** 0,64*** 0.99*** 0.70*** 0.99*** 0.44** 0.98*** 0.69*** 0.99*** 0.81"**
TEM (%)
12.2 352 3 102 3 98 5 301 2 16 1 9
1.8 30.7 0.8 18.3 1.0 15.7 1.4 36.8 2.2 28.7 2.1 16.2
"R~cw = resistance of the extracellular space; R~cw= resistance of the intracellular space. ~Comparison of means of measurement I with mean of measurement 2 by paired t-test: + , p < 0.05; ns, not significant. 'Pearson correlation coefficient between measurement 1 and measurement 2: ***, p < 0.001: **, p < 0.01.
a n k l e - s h o u l d e r ( a r m l e s s b o d y ) as d e s c r i b e d in Fig. 1, which represents a slight m o d i f i c a t i o n to the a p p r o a c h s u g g e s t e d by O r g a n et al. (1994). T r u n k i p s i l a t e r a l a n d m e d i a l r e l a t e t o d i f f e r e n t r e g i o n s o f t he c h e s t a n d differ a l s o in t e r m s o f t he d i s t a n c e b e t w e e n the
inner
electrodes.
Measurements
were
made
s e q u e n t i a l l y in d u p l i c a t e . T o o b t a i n p r o p e r m e a s u r e m e n t s in c h i l d r e n w i t h v e r y little a b i l i t y t o c o o p e r a t e , it w a s n e c e s s a r y t o w r a p t he c h i l d in a b l a n k e t , leaving exposed
o n l y t he
specific s e g m e n t
to
be
a s s e s s e d . F o r t h e p u r p o s e s o f t hi s s t u d y , t he s k i n electrodes (BIS4000 electrodes, Xitron Technologies, C A , U . S . A . ) w e r e k e p t in p o s i t i o n w h i l e d u p l i c a t e m e a s u r e m e n t s w e r e in p r o g r e s s . B IS i n d i c e s s u c h a s extracellular
resistance
(Recw)
and
intracellular
r e s i s t a n c e (R,cw) w e r e c a l c u l a t e d u s i n g t he C o l e - C o l e m o d e l i n g a p p r o a c h i n c o r p o r a t e d w i t h i n t he m a n u f a c Fig. 1. Electrode position for whole body and segmental BIS measurements. Segments measured (broken lines): a = arm; L = leg; ti = trunk ipsilateral; and tm = trunk medial. For whole body measurements both current and voltage electrodes were positioned on the wrist and ankle on the right side. For arm-less body segment, one voltage electrode was positioned at the level of shoulder and the other on the ankle, on the right side. Dark circles (O) represent current electrodes, which remained fixed at the level of wrist and ankle on the right side for whole body and all segmental configurations. Dark squares (11), at the extremes of each broken line, represent the pair of voltage electrodes for each segmental measurement. Each voltage cable was moved proximally according to each segmental configuration.
turer's software.
Statistical analysis Mean
c o m p a r i s o n s were done between pairs of
measurements
by
using
a
paired
t-test.
Pearson
c o r r e l a t i o n c oe ffi c i e nt s w e r e c a l c u l a t e d b e t w e e n t he first a n d s e c o n d m e a s u r e m e n t . T h e t e c h n i c a l e r r o r o f the estimate (TEM)
w a s c a l c u l a t e d b y u s i n g t he
a p p r o a c h s u g g e s t e d by L o h m a n et al. (1988). T h i s a p p r o a c h is b a s e d o n t h e di ffe re nc e s b e t w e e n t h e first a n d s e c o n d m e a s u r e m e n t s t a k e n c l o s e to e a c h o t h e r
Table 2. Mean comparisons, correlation coefficients and TEM for Recw and Rtcw by body segments between first and second measurement in dehydrated children Body segment Whole body (n = 142) Armless body (n = 138) Leg (n = 142) Arm (n = 139) Trunk ipsilateral (n = 138) Trunk medial (n = 138)
BIS index (f~)~
Mean + SD measure I b
(r) ~
REcw Rj~w REcw R,cw
812 ± 119 932 ± 624 438 _+ 104 42t + 209 362 + 102 425 ± 211 402 ± 87 572 ± 325 78 ± 12 51 ± 19 55 + 8 57 ± 28
0.97*** 0.55*** 1.0"** 0.84*** 0.99*** 0.71"** 0.99*** 0.83*** 0.99*** 0.79*** 0.98*** 0.76***
REcw Rjcw Recw Rjcw Recw Rjcw Recw
R~cw
TEM (~) 22.3 397 4.4 91.9 12.4 112.6 6.7 128.7 1.5 9.9 1.1 13.3
"Recw = resistance of the extracellular space; Rtcw = resistance of the intracellular space. "Comparison of mean of measurement I with mean of measurement 2 by paired t-test: + , p < 0.05; ns, not significant. 'Pearson correlation coefficient between measurment 1 and measurement 2: ***, p < 0.001; **, p < 0.01.
TEM (%) 2.8 41.5 1.0 21.1 3.4 26.6 1.7 30.2 1.9 18.0 2.0 24.1
BIS for hydration disorders and applying the equation proposed by Lohman et al. (1988). As the TEM is an estimate, in the units of measurement, of the variable in question, in this paper it was expressed as a percentage in respect of its corresponding mean. In general, TEM indicates the permissible limits of the magnitude of the difference between two consecutive measurements. If the difference between replicates is greater than expected, investigators should correct or remake the measurements.
Results A total of about 1200 pairs of measurements was performed across all segments in the study population. Table l and Table 2 show the means +_ SD for the BIS indices for the first measurement, at both whole body and segments, in malnourished and dehydrated children. The first measurement was compared with the second measurement (the latter not shown) by a t-test. In most cases, the means + SD between the first and second measurements were almost identical in all types of measurements. The range of mean differences between paired measurements was within 3 fL however it varied across segments. The same tables show the Pearson correlation coefficients between the first and second measurements. In most cases, highly significant r values were documented. TEM, as an indicator of the reliability of the BIS method, is presented in the same tables. The magnitude of TEM ranged from 0 to 22 f2. However, when TEM was expressed as a percentage in respect of the mean for each segment, it ranged from 0.8 to 3.4%. Another piece of evidence to support the validity of the segmental BIS measurement with respect to the more conventional whole body is that in most cases the sum of the segmental BIS indices equals the whole body approach (Organ et al., 1994). In addition, segmental measurements were highly correlated (r values around 0.8) with whole body measurements (data not shown), with segments such as leg and armless body showing the highest r values.
Discussion Although unstable clinical conditions associated with fluid disorders, such as severe malnutrition and dehydration in young children, may provide a good opportunity for testing and/or using BIS, many researchers are reluctant to apply this technique in young and sick populations arguing methodological difficulties. First, the small size of the children with malnutrition because of severe growth retardation and depletion of muscle and fat mass reduces ostensibly the length and volume of the conductor and also impairs the conventional position of input-voltage electrodes suggested for older populations. The second argument is the lack of cooperation of the children which may make the ARI 49/5-6---G
613
quality of the measurements dubious. We have to recognize that performing BIS measurements in this particular group of children with acute life-threatening clinical conditions was not free of inconvenience, but can be performed with high reliability if we are careful and dedicate enough time to obtaining the children's cooperation. In the present study about 2500 BIS measurements were carried out, and therefore we feel confident that this technique has a potential in this particular group. The calculation of TEM allowed us to establish in practical terms the permissible difference between two consecutive BIS measurements carried out in the same subject within a short time (excluding biological factors). The magnitude of TEM for REcw was lower compared with some anthropometric procedures (Lohman et al., 1988). With respect to Rlcw the correlation coefficients and TEM are poor. These data are consistent throughout all studies carried out in our Center. We have documented unusual, very high critical frequencies (Fc) in these young populations. Although we do not have a clear explanation, it may be related to segment size, capability of both hardware and software, or the environment. In conclusion, based on the high comparability of two sets of pair measurements, the highly significant r values (mostly r = 0.99) and the relatively low TEM with respect to REcw (1 to 3.5% with respect to the mean), it is believed that the application of BIS in this type of population is feasible. However, at this stage of development of BIS, Third World countries may have only limited access to this promising technique. Finally, this study showed that only REcw proved to be sufficiently stable to be used to predict extracellular water, a relevant determinant of quality of fat-free mass, and of great importance in clinical medicine. The use of the remaining BIS indices is still uncertain. Acknowledgements--We would like to thank the Director, medical staff and nurses of the General Hospital 'San Juan de Dios' in Guatemala City, for their support whilecarrying out the study. We are also grateful for the instrumental support of Mr. James Matthie, from Xitron Technologies, Inc. (San Diego, CA, U.S.A.) who provided the BIS analyzer and supplies.
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