Insensible
Water
Loss in Preterm
Infants:
Changes
With
Postnatal
Development
and
Non-ionizing
Radiant
Energy
Paul V. K. Wu., M.B., B.S., and
Joan
E. Hodgman, M.D.From the Department of Pediatrics, Los Angeles County-University of Southern California Medical Genter,
and the University of Southern California School of Medicine.
ABSTRACT. Insensible water loss (IWL) was measured by an Electronic Potter Baby Scale in 170 healthy preterm in-fants, with birthweights ranging from 800 to 2,000 gin, who were appropriate for gestational age. IWL was found to
in-crease with decreasing birth weight, i.e., from a mean of 0.7 mi/kg/hr in infants weighing 1,751 to 2,000 gm to 2.67 mi/kg/hr in infants weighing <1,000 gm. This correlation between IWL and birthweight was high (r 0.91; P = <0.001). In infants < 1,500 gm, IWL decreased with
post-natal age while in infants > 1,500 gm, IWL increased in the second week and was stable in the third and fourth weeks. Exposure to non-ionizing radiant energy from three
radiant heat warmers was found to increase IWL by 50% to 190% depending on the maturity of the infant and the type of warmers. Phototherapy was associated with a twofold to threefold increase in IWL, which can be minimized by care-ful temperature control of the infant. The magnitude of
in-crease in IWL in response to exposure to non-ionizing radiant
energy, both from radiant heat warmers and phototherapy was greater in infants with birthweight > 1,500 gm than in infants <1,500 gm. Pediatrics, 54:704, 1974, INSENSIBLE WATER LOSS IN PRETERM INFANTS, POSTNATAL CHANGE IN IWL, IWL ANI) NON-IONIZING RAI)IANT ENERGY, IWL AND PHOTOTHERAPY.
Insensible (or nonvisible) loss of water (IWL) to the environment from skin and respiratory tract constitutes a major factor in thermoregulation and
fluid balance. Although the importance of IWL
and its relation to metabolic rate was recognized as early as 1907 by Benedict’ and by Soderstrom and Dubois in 1917,2 until recently there has been very little data on IWL in neonates, and still less
in small preterm infants. The rapid changes in
techniques and new instruments for supportive care of neonates, such as elimination of added humidity in incubators, use of various radiant heat
warmers and phototherapy, may affect IWL
sig-mficantly. A recent report by Fanaroff et al.3
mdi-#{176}Potter,J. A.: Linear Variable Differential Transformer (LVDT) Bulletin JAP 5/21/73 and Description of Scale Prin-ciples, Bulletin JAP 5/22/73, 12 Green House Blvd., West Hartford, Connecticut 06110.
cated that infants with birthweights tmder 1,250 gm have a much higher IWL than those reported by Levine (1930) and Hey (1969). This, coupled with clinical observations that small immature in-fants and infants under phototherapy4-5 require proportionately larger amounts of fluid to main-tam water balance, prompted us to study in great-er detail IWL in preterm infants.
METHODS
Insensible water loss (IWL) was measured by an Electronic Potter Baby Scale. The scale was de-signed for continuous automatic weight monitor-ing of babies in incubators. Essentially, it consists of a mechanical balance and an electronic compo-nent. The mechanical balance consists of a load plate attached to a lever subsystem. The lever sub-system is connected to a linear variable
differen-tial This is an electromechanical
transducer which produces an electrical output proportional to the displacement of a separate movable core. The electrical signal is an analog of the mechanical deflection of the levers, and caus-es the electrical indicating instrument to show in-cremental or decremental weight changes contin-uously as soon as they occur. Thus, after the infant is placed on the load plate, with the initial adjust-ment of zero, the indicating pointer automatically follows changes in weight of the infant. The mea-suring capacity is 10.01 kg with a resolution of 0.5 gm on the indicating scale.
(Received August 31, 1973; revision accepted for publication April 3, 1974.)
Supported in part by a grant from Mead Johnson Laborato-ries.
With the assistance of our electronic engineer the accuracy and stability of the scale was tested by a series of addition and subtraction of known weights. Although the resolution on the indicating scale is 0.5 gm, constant reproducible deflections were obtained with weights as small as 0.25 gm. The mean settling time to a stable reading after a change in load weight was 20 ± 4 seconds. In
ad-dition, a series of IWL measurements were made
in 14 infants as outlined below. Each infant was studied twice on the same day. The correlation coefficient between the IWL results of the first set of measurements to the second set of measure-ments was 0.82 (P<0.001). Three-hour tests were run to evaluate the stability of the scale. The scale was found to be stable inside the proportional
ser-vocontrolled incubator following 15 minutes of
stabilization. Care was taken to prevent wires
from touching the load plate since they can cause deviations in deflection on the read-out scale. In
between studies the accuracy of the scale was
checked. We found that care had to be taken to
ensure that the movable core in the linear variable differential transformer was properly centered,
since it may accidentally be displaced during
cleaning and in moving the scale from one infant
to another. When measurements were made in
ra-diant heat warmers, the scale was allowed to sta-bilize under the radiant heat for half an hour prior to placing the infant on the load plate.
Each study consisted of four consecutive half-hour periods, starting 30 to 60 minutes following a feed. This time elapse after handling was neces-sary to allow stabilization of the infant’s environ-ment. At this time also, the infant was most likely to be quiet during observation periods. During the study, the infant was kept naked on the load plate and, apart from a single sheet on top of the load plate, was not in contact with any other moisture-absorbing material. The infant generally did not void or stool during the study period. When the in-fant voided or stooled during a particular period, that period was at once terminated and discarded.
The baby was then wiped dry and the sheet
changed. The pointer was then adjusted to zero
and a new period recorded. This obviated the ne-cessity of stool and urine collection with its atten-dant difficulties and inaccuracies.
At the beginning and end of each period, tem-peratures of the abdominal skin, rectum and am-bient air were recorded with a multichannel Ye!-low Springs Recorder. Ambient relative humidity
was measured by an Airguide hygrometer at the
infant’s side. Heart rate and respiratory rate were also recorded.
IWL was determined in three groups of healthy
preterm infants, i.e., infants without respiratory distress, breathing room air, without overt signs of illness. The infants were appropriate for gestation. Gestational age was calculated from the first day of the last menstrual cycle from maternal history, with birthweight falling within the 10th and 90th
percentile when plotted on the Lubchenko
In-trauterine Growth Curve.6
Group I
IWL of infants in incubators. This group was
subdivided according to birthweight into five
subgroups viz
(
1)1,000,
(2) 1,001 to 1,250, (3) 1,251 to 1,500, (4) 1,501 to 1,750, (5) 1,751 to 2,000 gm (Table I). A total of 54 infants was studied. Mean postnatal age was 4.9 days. Measurements were made with the infant lying naked on the load plate of the scale inside an incubator (Isolette,Model C-86) with proportional servocontrol and
abdominal skin temperature set at 36.5 C.
Group 2
IWL of infants exposed to non-ionizing radiant energy. Sixty preterm infants, mean postnatal age 4.8 days, were divided into two groups according to birthweight: (1) below 1,500 gm and (2) more than 1,500 gm. Ten infants from each group were placed under one of three types of radiant heat warmers currently used in our nurseries:
1. The IMI heat shield, in which heat source is
from a heat element laminated between two
sheets of carbon impregnated fiberglass.
2. The Air Shield Radiant Warmer, in which
the heat source is from a nichrome wire coiled in a quartz tube envelope, housed in a parabolic re-flector.
3. The KDC Radiant Warmer, in which the
heat source is from four infrared lamps directed at the infant, with four intervening light-opaque, heat-transmitting lenses.
Skin temperature was set at 36.5 C and was
ser-vocontrolled. Measurements were made
begin-fling after one hour of exposure under the heat
source. The IWL values were compared with
those obtained from comparable infants in incuba-tors.
Group
3IWL of infants on phototherapy. A series of IWL determinations were made in 56 icteric pre-term infants who required phototherapy for clini-cal reasons, i.e., serum bilirubin > 10 mg/ 100 ml. Mean postnatal age was 4.6 days. The infants were divided into two weight groups: (a) under 1,500 gm and (b) over 1,500 gm. Two sets of IWL
TABLE I
INSENSIBLE WATER Loss (IWL): INCUBATOR CHARACTERISTICS OF INFANTS
Weight of No. Birthweight Gestational Surface Age
GroUps of Sex (iii ± SD) Age Area’ (th ± SD)
(gin) infants M:F (gm) (iii ± SD) (#{241}#{236}± SD,) (days)
(weeks) (sq cm)
< 1,000 8 5:3 917.5 ± 103.9 27.9 ± 0.9 902.7 ± 103.9 4.8 ± 0.6 1,001 - 1,250 10 5:5 1,158.5 ± 64.1 28.8 ± 0.4 1,158.5 ± 64.1 5.0 ± 0.6
1,2,51 - 1,500 12 7:5 1,396.17 ± 70.4 33.3 ± 0.9 1,396.2 ± 70.4 4.9 ± 0.9
1,501 - 1,750 12 6:6 1,617.08 ± 61.3 35.3 ± 0.5 1,638.0 ± 49.6 4.9 ± 0.9
1,751 - 2,000 12 5:7 1,877.1 ± 96.9 35.8 ± 0.6 1,835.5 ± 70.2 4.9 ± 0.8
‘Surface area calculated from Boyd’s formula.
TABLE II
INSENSIBLE WATER Loss (IWL): INCUBATOR
Skin Rectal
Weight of Relative Incubator Temper- Temper- IWL IWL
(;roiip.s Ilunndity Temperature attire ature (mI/kg! (mi/sq ;n/
(gui) (%) (C) (C) (C) HR. R.R. 24 hr) 24 hr,)
-
<1,000 351±1.4 34.9 ± 0.2 36.5 ± 0.1 36.7 ± 0.2 166.0 ± 3.1 53.7 ± 3.5 64.2 ± 4.4 651.7 ± 58.71,001 - 1,25() 34.9 ± 1.2 .33.9 ± 0.3 36.5 ± 0.2 36.8 ± 0.3 163.6 ± 3.5 59.8 ± 2.9 55.7 ± 7.4 523.9 ± 96.6
1,251 - 1,500 34.7 ± 1.1 33.6 ± 0.6 36.4 ± 0.1 36.9 ± 0.2 161.9 ± 4.1 55.3 ± 6.2 .38.4 ± 7.1 369.1 ± 68.5
1,5()l - 1,750 35.1 ± 1.5 33.7 ± 0.8 36.5 ± 0.2 37.0 ± 0.2 152.6 ± 6.6 53.1 ± 5.7 22.1 ± 6.1 218.4 ± 60.7
1,751 -2,001) 35.0 ± 1.4 33.7 ± 1.1 36.5 ± 0.2 37.0 ± 0.3 156.8 ± 6.1 50.4 ± 4.1 16.7 ± 3.6 170.6 ± 37.1
TABLE III
INSENSIBLE WATER Loss (IWL): POSTNATAL CHANGES’
Incubator Skin Rectal
Body Relative Temper- Temper- Temper- IWL IWL
Weight Age Ifumubty attire attire attire (nil/kg/ (ml/kg/
Week
_
(gin) (days) (%) (C) (C) (C) H.R. R.R. hr) 24 hr)< 1,500 gm (7 infants)
1st 1194.3±156.9 5.1±0.7 34.8±1.3 34.1±0.5 36.5±0.1 36.7±0.3 166.3±2.1 60.9±2.2 2.4±0.4 56.6±10.4 2nd 1288.0± 172.9 13.0± 1.0 35.5±2.4 33.7±0.5 36.4±0.2 36.9±0.2 146.9±5.9 47.1 ±5.6 2.1 ±0.3 49.6± 7.2 3rd 1428.1 ± 178.5 19.7±0.8 35.1 ±2.2 32.6±0.3 36.4±0.1 36.9±0.2 145.4±6.2 36.9±0.2 1.7±0.3 40.8± 6.3 4th 1588.4± 175.7 27.4±0.8 34.9± 1.9 32.7±0.4 36.5±0.2 36.9±0.2 145.4±6.9 29.4±4.8 1.6±0.2 38.4± 4.8
> 1,500 g; (9 infants)
1st 1765.0±160.4 4.9±0.8 35.4±1.9 33.3±0.3 36.5±0.1 37.0±0.1 156.3±3.6 51.9±3.1 0.8±0.3 20.0± 6.3 2nd 1844.7±159.8 12.2±1.1 35.3±1.9 33.2±0.2 36.4±0.2 37.1±0.1 150.6±6.2 44.0±0.5 1.3±0.2 31.5± 4.2 3rd 2032.7±133.9 19.7±0.9 35.4±2.5 32.8±0.4 36.4±0.2 37.1±0.1 144.4±4.7 30.0±3.9 1.3±0.1 30.1± 2.7 4th 2195.8±124.9 26.8±0.8 35.4±2.3 32.6±0.5 36.4±0.2 37.1±0.1 140.4±8.4 31.0±6.0 1.2±0.1 29.9± 3.0
‘All values expressed as mean ± SD.
once before and once during phototherapy, after at least one hour of exposure. The light source was from ten 20-watt fluorescent lamps. Irradiance measurements taken with filters and the Kendall Mark IV Radiometer at the infant level inside the incubator were 0.245 and 0.227 milliwatts/sq cm
for the 420-460 and 460-500 nm wavebands,
re-spectively.
was set on manual control at a setting to maintain the abdominal skin temperature at 36.5 C initially. No attempt was made to alter incubator settings during the study periods.
In the second set of studies, the infants’ skin temperature was kept constant at 36.5 C with ser-vocontrol, both before and during phototherapy.
IWL recordings were made as above.
Calculations
Calculation of IWL was by a modffied form of
the Isenschmid equation,7 IL = IWL + (CO2
-02), where IL = insensible weight loss in grams;
IWL = insensible water loss in grams; CO2 =
CO2 loss in grams; 02 02 intake in grams.
In our method CO2 + 02 was not measured so
IL = IWL. The methodology overestimates IWL
because
IL is really equal to IWL + (CO2 - 02).Nevertheless, since CO2 - 02 accounts for
approx-imately only 10% of IWL and is relatively
con-stant, this was ignored in the results presented in this paper.
Surface area was calculated from Boyd’s
For-mula8 viz
S = sq cm (W = body
weight in kg)
RESULTS
IWL and Preterm Infants (Group 1)
IWL was found to decrease from a mean of 2.67 ± 0.35
SD
ml/kg/hr (th 64.08 ml/kg/24 hr) in in-fants with birthweights less than 1,000 gm, to 0.7± 0.2 SD ml/kg/hr (ih 16.8 ml/kg/24 hr) in
in-fants in the group with birthweights 1,751 to 2,000
gm (Fig. 1). IWL, expressed as ml/kg/24 hr and
ml/sqm/24 hr, is shown in Table II.
With the skin temperature servocontrolled at
36.5 C the temperature of the incubator in infants below 1,000 gm was significantly higher (P <0.05)
than in the infants over 1,000 gm (see Table II). The rectal temperatures were found to be slightly lower in the group under 1,500 gm when compared to the groups over 1,500 gm. Variations in heart
rate and respiratory rates between the groups
were not significant.
In the infants studied, IWL was found to corre-late highly with body weight. The correlation coefficient = 0.91 with P value = less than 0.001
(Fig. 2).
IWL changes were recorded at weekly
inter-vals in the neonatal period. In seven infants with
birthweights under 1,500 gm, IWL was found to
decrease with postnatal age, while in nine infants with birthweights over 1,500 gm, IWL was found to increase in the second week and was stable in the third and fourth weeks (Table III).
IWL and Non-ionizing Radiant Energy (Group 2)
IWL was recorded in 60 preterm infants under three types of radiant heat warmers. The results were compared with those obtained from compa-rable infants in incubators (Table IV).
In infants under 1,500 gm, IWL was greater by 50.3%, 58. 1% and 100.6% under the IMI radiant heat shield, the nichrome wire radiant warmer, and the infrared radiant warmer, respectively,
when compared to IWL of comparable infants in
incubators (Fig. 3). Similarly, in infants over 1,500
gm, the IWL was increased by 82.4%, 101.3% and
190.5% in the three types of radiant heat warmers, when compared to comparable infants in
incuba-tors, in a thermal environment to maintain
ab-dominal skin temperature at 36.5 C.
IWL and Phototherapy (Group 3)
Study 1. In infants below 1,500 gm, IWL in-creased from a mean of 1.24 ± 0.25 SD mi/kg/hr
prephototherapy to a mean of 2.24 ± 0.26 SD
mi/kg/hr during phototherapy, representing an
incremental rise of 80.6% (Fig. 4). In infants
over 1,500 gm, IWL increased from a mean of
0.73 ± 0.2 prephototherapy to a mean of 2. 14 ± 0.32 mi/kg/hr during phototherapy, representing
an increase of 192.3%. Concomitant increases
were observed in the temperatures in the incuba-tor, skin and rectum, as well as in the heart rate and respiratory rate (Table V).
Study 2. The skin temperature was kept con-stant at 36.5 C before and during phototherapy with servocontrol. In this case, in infants below 1,500 gm, IWL was found to increase from a
pre-phototherapy mean value of 1.3 ± 0. 16 SD
mi/kg/hr to a mean of 1.85 ± 0.15 SD mi/kg/hr during phototherapy, i.e. an increase of 42.4% (Fig. 4). In infants over 1,500 gm, IWL increased from a mean of0.82 ± 0.26 SD mi/kg/hr prepho-totherapy to a mean of 1.75 ± 0.30 SD mi/kg/hr during phototherapy, or an increase of 113.4%. No changes were observed in heart rate and res-piratory rate (Table VI).
DISCUSSION
Insensible water loss (IWL) in infants and chil-dren has been estimated indirectly from insensible weight loss and directly in specially constructed
chambers.92 The results and many of the
prob-iems encountered by these investigators were
summarized by Bruck25 and Zeymuiler24 in their
reports on IWL in newborn infants. One of the
major sources of error in the indirect balance method is the exchange of water between the
INSENSIBLE WATER LOSS OWL)
4
3
I
1
±SD( ) N0.OF INFANTS
,; AGE 4-SD.
.f-(8)
-I-(10)
-F
(12
Fic. 2. Relation of insensil)le water loss to body weight.
IWL - BODY WEIGHT
NO. OF INFANTS =54
CORn. COEFF.= 0.91 ( p<0.001)
4
3
-I
C
0 C
C
C
1000 1500
WEIGKT (Gm.)
2000
1ooo 1251-1500 1751-2000 1001-1250 1501-1750
BIRTH WEIGHT (Gm.)
FIG. 1. InSensible water loss in 54 healthy preterm infants,
mean postnatal age 4.9 days, managed in Isolette C-86 in-cul)atOrS with skin temperature maintained at 36.5C with
servocontrol.
the infant. By using a stainless steel balance with the infant lying naked on a single towel this source of error was minimized. Repeated weighing of the
towel did not show any significant change in
weight before and after each period.
Activity and crying increase IWL in
neo-nates.23-24 By taking measurements between feed-ings, when the infant was quiet, we were able to obtain more consistent results. These results, when extrapolated for a 24-hour period, represent basal evaporative losses, and may be lower than
theactual IWL since IWL may be increased
dur-ing periods when the infant is awake. However, since these small premature infants are asleep
most of the time, the IWL would be less
influ-enced than in larger more active infants. The re-suits also leave out the weight of CO2 excreted minus the 02 consumed. These two factors would be expected to offset each other, leaving results close to the actual IWL. In addition, the balance sensitivity of 0.25 to 0.5 gm renders it suitable for insensible weight loss recordings over compara-tively short periods, interfering minimally with care of the infant. One other major advantage of the Potter’s Electronic Balance is the fact that we are able to measure IWL under usual nursery con-ditions for these small preterm infants.
In infants with birthweights more than 1,500
gm, the values for IWL we obtained were
com-parable with those reported in earlier studies by Levin and Hey.”21 In infants with birthweights
under 1,500 gm, the values obtained were much
higher than those reported in the earlier studies by Fanaroff et al.3 These extremely high insen-sible water losses are probably due to dispro-portionately larger water losses from the skin rath-er than to the increase in metabolic rate, since small, immature infants have limited ability to in-crease metabolic rate.2627 Skin factors predispos-ing to larger water loss include larger surface area in relation to weight,28 thinner epidermis,29 in-creased water content,3#{176}increased permeability,3’
and increased blood supply.32 The decrease in
IWL with postnatal age in these small immature infants may be due to the balance between postna-tal maturation of the skin and postnatal rise in basal metabolic rate. In larger infants, the postna-tal rise in IWL may correspond to increase in ac-tivity and basal metabolic rate in the second week of life.33
We found a higher correlation of insensible water loss with birthweight and gestational age
than in the study reported by Hey and Katz.23
However, all the infants selected for the present study were appropriate for gestation and the IWL measurements were limited to very narrow varia-tions in postnatal ages as shown in Table I.
Although relative humidity inside the incuba-tors varied from day to day during the period of the studies, the magnitude of change was relative-ly small. The mean relative humidity inside the
in-cubator was 34%, range was 29% to 38%. The
mean relative humidity in the nursery was 38%,
range 31% to 42%. Changes in humidity within the
range does not appear to influence 1WL24
(Ii, + S.D.)
- L ‘ 1500 Gm.
EJ > isoo
x
C,
Fic. 3. I\VL in infants under three types of radiant heat source. Figures denote the number of infants in each group.
IWL - PHOTO THERAPY
STUDY I STUDY 2
I
.c ,. s.s
rT
<l500Gm. J)i5OONon-ionizing Radiant Energy
IWL-PIONIONIZING RADIANT ENERGY
The mechanisms by which non-ionizing radiant energy can cause increase in IWL is relatively
unknown. The radiant energy from the radiant
heat warmers can produce an effect only when it
is absorbed by matter in accordance to the
Gorth-ers and Draper Law.34 Thus, when the radiant
energies of the electromagnetic spectrum are ab-sorbed on the skin, the energy of the photons is transferred to the absorbing molecules. The re-sultant electron excitation can result in dissocia-tion of the molecule, dissipation of the excitation energy in the form of fluorescence or phosphores-cence, formation of free radicles, and degradation into heat.
There is little evidence, however, that photons in the infrared (IR) bands are capable of entering into photochemical reactions in biological sys-tems. They may be too low in energy to affect the electron energy levels of the atoms, but the reac-tion that does occur upon absorption involves an increase in the kinetic energy of the system
pro-ducing a degradation of the radiant energy to
heat. The resultant thermal effect leads to in-crease in blood flow and insensible water loss.
IWL was found to be increased when the infant
was exposed to the radiant heat warmer. Exposure to radiant energy from infrared lamps was found to elicit greater IWL than exposure to radiant en-ergy from the carbon heat shield and nichrome wire type of warmers. The reasons for this differ-ence are not obvious from these studies.
Phototherapy involves exposure to both the
visible light bands of the electromagnetic spec-trum, as well as some infrared bands. The exis-tence of the infrared energies were confirmed in recent measurements made at the Jet Propulsion
Laboratory in Pasadena, California. These
in-frared energies were not present inside the
incu-bator when the lamps were turned on, but were
present after the lamps were operating for one-half to one hour.35 Thus, observation on the effects of phototherapy should be made after one hour of exposure. Although photons from the visible light of phototherapy lamps have relatively low energy values, 3. 1-1.65eV, they initiate both photochemi-cal reactions as well as interactions with
biologi-cal In addition, energies such as those in
the near UV and JR range are present in
photo-therapy lamps and these may cause changes in
body temperature, peripheral blood flow and
IWL.35
Significant differences in the magnitude of
in-crease in IWL during phototherapy between the
infants with and those without temperature servo-control were observed. In infants without
servo-control, both ambient and body temperature was
found to increase during phototherapy (Table V). Similar increases were observed by Oh and his
as-sociates36 and by Wu et in their studies on
changes in blood flow during phototherapy. The
greater increment in IWL in infants that were not
servocontrolled may be due to increase in skin
blood flow following rise in skin temperature.37
Thus, careful temperature control during
pho-totherapy would minimize excessive IWL.
The relation of IWL to metabolic rate has been
pointed out previously by several
investiga-2, 22.23 For every gram of water evaporated
ap-proximately 0.58 calories of heat is dissipated.
FIG. 4. IWL in infants under phototherapy. Study I was
per-formed in Isolette C-86 incubator without servocontrol of skin temperature. Study 2 was performed in Isolette C-86
in-cul)ator with servocontrol to maintain skin temperature at 36.5 C. Figures in parentheses denote the number of infants
TABLE IV
IWL: N0N-I0NIzIN; RADIANT ENERGY’
Nichrome Wire
Incubator (IMI) (Air Shield) KDC Infrared Lamps
Group weight < 1,500 > 1,500 < 1,500 > 1,500 < 1,500 > 1,500 < 1,500 >1,500 (gm)
Birthweight (gm) 1,326±192 1,752±204 1,345±202 1,730±235 1,320±214 1,746±226 1,333±228 1,736±218
Gestational age 32.6 ± 0.4 35.6 ± 0.5 32.5 ± 0.4 35.4 ± 0.6 32.5 ± 0.6 35.4 ± 0.5 32.4 ± 0.5 35.5 ± 0.6
(weeks)
Humidity 39.7±2.6 39.5± 1.9 45.2±5.2 47.5±6.2 47.0±6.5 48.2±6.4 47.4±5.5 47.6± 6.2
Temperature, 34.2± 1.1 32.8±0.6 25.2± 1.6 24.6±0.9 24.6± 1.1 24.8±0.8 24.4± 1.2 25.2±0.8
ambient (C)
Skin temperature 36.4 ± 0.3 36.5 ± 0.2 36.5 ± 0.3 36.5 ± 0.3 36.4 ± 0.2 36.5 ± 0.3 36.5 ± 0.4 36.5 ± 0.4 (C)
Rectal tempera- 36.5 ± 0.7 36.7 ± 0.4 36.5 ± 0.7 36.8 ± 0.4 36.6 ± 0.6 36.5 ± 0.6 36.6 ± 0.4 36.8 ± 0.4
ture (C)
Respiratory rate 40.5±6.5 38.2±8.4 42.5±6.2 40.2±5.5 41.5±7.2 41.5±8.0 42.5±8.0 41.2±8.5
Heart rate 138.5 ± 6.5 142.2 ± 8.4 140.5 ± 8.5 138.5 ± 8.5 146.0 ± 8.8 146.0 ± 6.8 148.5 ± 8.8 144.8 ± 8.2
IWL (mi/kg/br) 1.56±0.4 0.74±0.4 2.33±0.5 1.35±0.4 2.45±0.4 1.49±0.4 3.49±0.5 2.15±0.5
‘All values expressed as mean ± SD.
TABLE V
IWL: PHOTOTHERAPY
CHANGES IN HUMIDITY, TEMPERATURE, RESPIRATIoN AND HEART RATE STUDY 1
Prephototherapy Phototherapy
(ni ± SD) (in ± SD)
Weight (gm) <1,500 >1,500 <1,500 >1,500
Humidity (%) 36.6±6.1 36.5±5.8 36.1± 6.8 36.2±6.3
Skin temperature (C) 36.5±0.3 36.5±0.2 37.4± 0.3 37.2±0.3
Rectal temperature (C) 36.7±0.4 36.9±0.2 37.4± 0.2 37.1 ±0.3#{176}
Incubator temperature (C) 35.2±0.6 33.7±0.6 38.5± 0.3 34.2±0.5
Respiratory rate/mm 58.2±8.5 48.5±8.6 66.8± 6.8 62.0± 4.2
Heart rate/mm 154.2±8.6 144.4±8.2 164.3± 10.1 158.5±6.5
‘Differences between prephototherapy and phototherapy were significant P <.05 except 37.1 ± 0.3.
TABLE VI IWL: PHOTOTHERAPY
CHANGES IN HUMIDITY, TEMPERATURE, RESPIRATION AND HEART RATE STUDY 2 (SERvOcONTR0L)
Prephototherapy Phototherapy
(fn±SD) (in±SD)
Weight (gm) <1,500 >1,500 <1,500 >1,500
Humidity (%) 36.3 ± 5.4 38.8 ± 6.2 36.2 ± 6. 1 36.5 ± 6.1
Skin temperature (C) 36.5±0.25 36.5± 0.2 36.5±0.3 36.5± 0.25
Rectal temperature (C) 37.0±0.25 37.1 ± 0.4 36.6±0.3#{176} 37.0± 0.2 Incubator temperature (C) 35.4 ± 0.4 33.5 ± 0.4 34.8 ± 0.8 32.8 ± 0.5
Respiratory rate/mm 56.4±8.2 48.5± 10.2 58.2±6.6 52.4± 9.5
Heart rate/mm 150.4±8.8 148.4± 8.2 152.4±9.2 148.2± 12.4
Under basal conditions IWL accounts for approxi-mately 23% to 25% of metabolic rate. It would ap-pear unlikely that the increase in IWL under the radiant heat warmers and photoirradiation repre-sents a proportional increment in metabolic rates of the magnitude recorded in these studies, i.e., a twofold to threefold increase in metabolic rate. Consequently, it must be due to some other mech-anism. It is probable that the local heat produced as a result of photochemical reactions or electron excitation may cause increase in evaporative water losses in order to dissipate the heat.
In infants with birthweights above 1,500 gm
the
magnitude of rise in IWL was found to begreater than those below 1,500 gm when exposed to non-ionizing radiant energy and phototherapy (Figs. 3 and 4). This difference in response appears to be similar to the differences in response in IWL
between mature and immature infants on
expo-sure to changes in environmental temperature re-ported earlier by Hey and Katz.23 Their
explana-tion was that the more mature infants had more
mature sweating mechanism and therefore can re-spond in greater magnitude to environmental
changes. Although visible sweating was not
ob-served in any of the infants in our studies, never-theless this mechanism may account for the great-er IWL response in the more mature infants.
The data from these studies suggests the need to take into account differences in IWL in neonates
of varying maturity and under various modes of
management in the calculation of fluid and cab-ne requirements, particularly in the small pre-term infants in the early neonatal period. Further
studies of IWL in sick infants would provide a
more rational approach to fluid therapy.
SUMMARY
IWL was measured in healthy preterm infants
with birthweights less than 2,000 gm, with the
Electronic Potter Baby Scale. IWL was found to
increase with decreasing birthweight. The
corre-lation between IWL and birthweight was high
(r = 0.91; P = <0.001). In infants with
birth-weights less than 1,500 gm, IWL decreased with
postnatal age, while in infants with birthweights more than 1,500 gm, IWL increased in the second week and was stable in the third and fourth weeks. IWL was found to increase on exposure to
non-ion-izing radiant energy from three radiant heat
sources.
Maximum IWL occurred in infants ex-posed to infrared lamps. Phototherapy was associ-ated with a twofold to threefold increase in IWL. The magnitude of increase in IWL in response to exposure to non-ionizing radiant energy, both from radiant heat sources and phototherapy lamps, wasfound to be greater in infants with birthweights more than 1,500 gm than in infants less than 1,500 gm.
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ACKNOWLEDGMENT
The authors gratefully acknowledge the technical assist-ance of Juan Martinez, Michael Osuna and Felipe Gonzalez. Our thanks to Art Johnson for maintaining and checking the
accuracy of the balance and to Dr. John James and Dr. Paul Wherle, for their helpful suggestions in the preparation of this manuscript.
Barakat, A. Y., Papadopoulou,
Z. L., Chandra,
R.
S., Hollerman,C. E., and
Calcagno, P. L.: Pseudohermaphroditism, nephron disorder, and Wilms’ tumor:
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