Acta Paediatr 81: 764-8. 1992
Insensible water loss from the skin during phototherapy in term and preterm infants S Kjartansson, K Hammarlund and G Sedin Depurtment of Puediuirics, Universiiy Hospital, Uppsulu. Sweden
Kjartansson S, Hammarlund K, Sedin G . Insensible water loss from the skin during phototherapy in term and preterm infants. Acta Prediatr 1992;81:76&8. Stockholm. ISSN 0803-5253 The rate of evaporation from the skin was measured before and during phototherapy in 10 full-term and seven preterm infants (gestational age 29-33 weeks). The method for measurement of rate of evaporation was non-invasive and was based on determination of the water vapour pressure gradient close to the skin surface. All infants were studied naked in an incubator with an ambient relative humidity of 50% and with a controlled environmentwith respect to temperature and air velocity. In the term infants the mean rate of evaporation, measured from an interscapular skin area, was 3.1 g/m2h both before and after 30 min of phototherapy. In the preterm infants the corresponding value was 9.8 g/m2h before and 9.7 g/m2h after 120 min of phototherapy. Thus, in thermally stable infants, nonionizing radiation from phototherapy equipment does not increase water loss from the skin. 0 Evaporation rate, heat balance, insensible water loss, newborn infants, phototherapy, transepidermal water loss, water balance G Sedin, Department of Paediatrics, University Hospital, S-75185 Uppsala, Sweden
There have been several reports indicating a substantial increase in insensible water loss during phototherapy (1-4). This has been assumed to be due to increased water loss from the skin because of altered barrier properties, or increased respiratory water loss. In the above-mentioned studies, insensible water loss was measured as insensible weight loss, making it difficult to ascertain whether the observed increase derived from an increase in water loss from the skin or from the respiratory tract. In addition, phototherapy may cause an increase in sensible loss of water in the stools (1, 5). We have shown previously that both the water loss from the skin and from the respiratory tract increase during heat stress and during increased motor activity ( 6 , 7). It is therefore possible that the previously reported (1-4) increase in insensible water loss during phototherapy is due to heat stress (6, 7) caused by the heat generated by the phototherapy equipment. The aim of the present study was to study the water loss from the skin in thermally stable and calm newborn infants during short periods of exposure to non-ionizing radiation from phototherapy equipment. Measurements of the evaporation rate were made directly from the skin area exposed to phototherapy. The method is non-invasive and allows direct, quick and repeated measurements of the rate of evaporation from the skin without causing discomfort to the infant or interfering with nursing routines (8-10). The method has been used previously in studies of water loss from the skin of newborn infants (1 1). Measurements of the evaporation rate are not influenced by the radiative energy from the
phototherapy equipment ( 1 2). A preliminary report on evaporation rate from the skin during phototherapy has been published ( I 3).
Subjects and methods Measurements of the rate of evaporation (ER) from the skin were made in 10 full-term and seven preterm infants. All infants had a birth weight appropriate for gestational age. The full-term infants were born after a mean gestation of 39 weeks (range 37-41 weeks), with a mean birth weight of 3.363 kg (range 2.750-4.010 kg) and had a mean postnatal age of four days (range 2-7 days) at the time of measurements. They were treated with phototherapy for “physiological” hyperbilirubinaemia but were otherwise healthy. The preterm infants were born after a mean gestation of 31 weeks (range 29-33 weeks), with a mean birth weight of 1.548 kg (range 1.420-1.787 kg) and had a mean postnatal age of four days (range 2-7 days) at the time of measurements. Their condition was stable and they received phototherapy for hyperbilirubinaemia of prematurity. One of the preterm infants was receiving CPAP, but the others received no ventilatory support. Three of the infants were quadruplets. Measurements were started on 10 further infants (six term and four preterm) but had to be discontinued because of increased motor activity (crying) or nursing interventions. The study was approved by the Ethics Committee of
ACTA PEDIATR 81 (1992)
Water loss during phototherapy
765
the Medical Faculty of Uppsala University and from the phototherapy light by a paper hood. Twallwas informed parental consent was obtained for all infants measured from the centre of the inner surface of the incubator wall, opposite the front opening, and Troofwas studied. The evaporation rate was measured by a method based measured from the inner surface of the incubator roof, on determination of the water vapour pressure gradient above the infant. RHamband PH20amb were measured in the air layer close to the skin surface (Evaporimeter about 10 cm above the infant and about 10 cm distal to EPI, ServoMed AB, Stockholm, Sweden (9)). The the place where Tambwas measured. During measureequipment for measurement of ER also gives data on ments the infants were mostly asleep and showed little relative humidity (RH %) and water vapour pressure motor activity. In full-term infants measurements were made before, (PH~okPa). In the preterm infants the heart rate (HR beats/min) was recorded with an ECG monitor (Hellige, during and after 30 min of phototherapy. The infants Freiburg, FRG) and the respiratory rate (RR breaths/ had not received phototherapy before the start of the min) was estimated by 1-min counting. The ambient air measurements. During the measurement period RH,,b temperature in the incubator (Tamb"C), skin temperature was maintained at 50% and T a m b was not altered. Ln preterm infants, measurements were made before, (Tskin "C), deep rectal temperature (Tbody"C) and the temperatures of the incubator walls (TWa""C) and roof during and after 120 min of phototherapy. If the skin or (Tro,foC)were measured with a YSI telethermometer (43 body temperature of the infant increased, Tambwas TA, using probes 405, 427 and 402, Yellow Springs, adjusted manually to keep the infant in thermal balance. Ohio, USA). The air-flow velocity in the incubator was RHambwas 50% at the start of the measurements, but if measured with an air velocity meter (Omnisensor, model T a m b was lowered during the measurement period, 1640, TST Incorporated, St. Paul, MN, USA). Photo- PHZOamb, not RHamb,was kept constant. When necessary, therapy was given with standard phototherapy equip- the infants were given breast milk through an indwelling ment (Bililite, Olympic Medical, Seattle, USA). This orogastric catheter during the measurement period. equipment provides blue light radiation with a wave- Four of the infants had not received phototherapy prior length mainly between 440 and 470 nm. Spectral to the study and in the remaining three infants photoirradiance was measured with a phototherapy radi- therapy was withheld for at least 5 h before the ometer (PR3, Air Shields, Hatboro, PN, USA). The measurements were started. irradianceat thelevel oftheinfant was 8-12pW/cm2/nm. All recordings were made with a Watanabe recording Statistical analysis system (Watanabe Instruments Corporation, Tokyo, Data were obtained for ER, RHamb, PH2Oamb, Tamb, Tbdy, Japan). Tskin, Troof, Twa1l, H R and RR. Statistical analysis was performed using the Student's t-test on paired Measurement procedure observations. The values for the preterm infants were After feeding, the naked infant was placed in the prone interpolated to fixed times. position in an incubator (AGA MK241, AGA Medical, Lidingo, Sweden). At least 30 min were allowed for the infant to settle down and for the environmental condi- Results tions in the incubator to stabilize. The air-flow to the incubator was 8-10 I/min and the air velocity above the Full-term infants infant was less than 0.1 m/s. The system for servo In each infant, ER remained at the same level during control of skin temperature, supplied with the incuba- exposure to phototherapy. The mean ER was 3.1 (SD tor, was used to regulate Tambto the desired T a m b by 0.7) g/m2h at the start of the measurements and 3.1 (0.5) suspending the sensing thermistor in the centre of the g/m2h after 30 min of phototherapy (Fig. l), giving a incubator above the infant. The phototherapy equip- mean difference of 0.0 (confidence limits -0.20 and ment was placed above the incubator. ER was measured 0.20). This difference was not statistically significant. from an interscapular skin area. ER was first measured Table 1 shows the temperatures and RH before and before the start of phototherapy, and repeated measure- after 30 min of phototherapy. NOsignificant change was ments were made during phototherapy. The last noted in Tbody,Tskin,T a m b or RH. Troorincreased from measurement was made after switching off the photo- 29.6 to 33.0 "C. This caused a decrease in the radiative therapy equipment. Before each ER measurement, heat loss from the skin area facing the roof from 37.8 to readings of ambient relative humidity (RHamb),ambient 15.9 W/m2 ( I 4). water vapour pressure (PH2Oarnb), Tbody,Tskin, TambrTwall and Troofand, in the preterm infants, H R and RR were made. Tskinwas measured close to the site at which the Preterm infants ER measurements were made. Tambwas measured in the In each infant ER remained at the same level during centre of the incubator, about 10 cm above the infant. exposure to phototherapy. The level of ER depended on The thermistor for measurement of Tamb was protected the infant's gestational age at birth and postnatal age.
766
S Kjartansson et a/.
ACTA PRDIATR 81 (1992)
Tahle 1. Mean (+SD) rectal (Tbody)and skin (T,t,")temperatures, and temperatures of the incubator air (Tamb)and of the incubator roof (Troor) and relative humidity of the incubator air (RH) before the start of phototherapy (Pt) and after 30 min of phototherapy (30 min Pt) in term infants (n= 10).
35.4k0.2 35.5k0.2 ns
36.6 k0.I 36.7 + O . 1 ns
Before Pt 30 min Pt p value
32.7k0.6 32.6+0.5 ns
29.6k0.7 33.0k0.9 < 0.00 I
50+ 1 50+ I
ns
Tahle 2. Mean ( f SD) rectal (Tbdy)and skin (Tskln) temperatures, and temperatures of the incubator air (Tamb) and of the incubator roof (T,oof) and relative humidity of the incubator air (RH). heart rate (HR) and respiratory rate (RR) before the start of phototherapy (Pt) and after 120min of phototherapy (120 min Pt) in preterm infants (n = 7).
Before Pt 120 min Pt p value
.
Troor ("C)
RH ("A,)
35.7k 1.2 33.6+ 1.0
31.1 & 1.0 38.6k2.3
54k 1
Insensible water loss from the skin during phototherapy in term and preterm infants S Kjartansson, K Hammarlund and G Sedin Depurtment of Puediuirics, Universiiy Hospital, Uppsulu. Sweden
Kjartansson S, Hammarlund K, Sedin G . Insensible water loss from the skin during phototherapy in term and preterm infants. Acta Prediatr 1992;81:76&8. Stockholm. ISSN 0803-5253 The rate of evaporation from the skin was measured before and during phototherapy in 10 full-term and seven preterm infants (gestational age 29-33 weeks). The method for measurement of rate of evaporation was non-invasive and was based on determination of the water vapour pressure gradient close to the skin surface. All infants were studied naked in an incubator with an ambient relative humidity of 50% and with a controlled environmentwith respect to temperature and air velocity. In the term infants the mean rate of evaporation, measured from an interscapular skin area, was 3.1 g/m2h both before and after 30 min of phototherapy. In the preterm infants the corresponding value was 9.8 g/m2h before and 9.7 g/m2h after 120 min of phototherapy. Thus, in thermally stable infants, nonionizing radiation from phototherapy equipment does not increase water loss from the skin. 0 Evaporation rate, heat balance, insensible water loss, newborn infants, phototherapy, transepidermal water loss, water balance G Sedin, Department of Paediatrics, University Hospital, S-75185 Uppsala, Sweden
There have been several reports indicating a substantial increase in insensible water loss during phototherapy (1-4). This has been assumed to be due to increased water loss from the skin because of altered barrier properties, or increased respiratory water loss. In the above-mentioned studies, insensible water loss was measured as insensible weight loss, making it difficult to ascertain whether the observed increase derived from an increase in water loss from the skin or from the respiratory tract. In addition, phototherapy may cause an increase in sensible loss of water in the stools (1, 5). We have shown previously that both the water loss from the skin and from the respiratory tract increase during heat stress and during increased motor activity ( 6 , 7). It is therefore possible that the previously reported (1-4) increase in insensible water loss during phototherapy is due to heat stress (6, 7) caused by the heat generated by the phototherapy equipment. The aim of the present study was to study the water loss from the skin in thermally stable and calm newborn infants during short periods of exposure to non-ionizing radiation from phototherapy equipment. Measurements of the evaporation rate were made directly from the skin area exposed to phototherapy. The method is non-invasive and allows direct, quick and repeated measurements of the rate of evaporation from the skin without causing discomfort to the infant or interfering with nursing routines (8-10). The method has been used previously in studies of water loss from the skin of newborn infants (1 1). Measurements of the evaporation rate are not influenced by the radiative energy from the
phototherapy equipment ( 1 2). A preliminary report on evaporation rate from the skin during phototherapy has been published ( I 3).
Subjects and methods Measurements of the rate of evaporation (ER) from the skin were made in 10 full-term and seven preterm infants. All infants had a birth weight appropriate for gestational age. The full-term infants were born after a mean gestation of 39 weeks (range 37-41 weeks), with a mean birth weight of 3.363 kg (range 2.750-4.010 kg) and had a mean postnatal age of four days (range 2-7 days) at the time of measurements. They were treated with phototherapy for “physiological” hyperbilirubinaemia but were otherwise healthy. The preterm infants were born after a mean gestation of 31 weeks (range 29-33 weeks), with a mean birth weight of 1.548 kg (range 1.420-1.787 kg) and had a mean postnatal age of four days (range 2-7 days) at the time of measurements. Their condition was stable and they received phototherapy for hyperbilirubinaemia of prematurity. One of the preterm infants was receiving CPAP, but the others received no ventilatory support. Three of the infants were quadruplets. Measurements were started on 10 further infants (six term and four preterm) but had to be discontinued because of increased motor activity (crying) or nursing interventions. The study was approved by the Ethics Committee of
ACTA PEDIATR 81 (1992)
Water loss during phototherapy
765
the Medical Faculty of Uppsala University and from the phototherapy light by a paper hood. Twallwas informed parental consent was obtained for all infants measured from the centre of the inner surface of the incubator wall, opposite the front opening, and Troofwas studied. The evaporation rate was measured by a method based measured from the inner surface of the incubator roof, on determination of the water vapour pressure gradient above the infant. RHamband PH20amb were measured in the air layer close to the skin surface (Evaporimeter about 10 cm above the infant and about 10 cm distal to EPI, ServoMed AB, Stockholm, Sweden (9)). The the place where Tambwas measured. During measureequipment for measurement of ER also gives data on ments the infants were mostly asleep and showed little relative humidity (RH %) and water vapour pressure motor activity. In full-term infants measurements were made before, (PH~okPa). In the preterm infants the heart rate (HR beats/min) was recorded with an ECG monitor (Hellige, during and after 30 min of phototherapy. The infants Freiburg, FRG) and the respiratory rate (RR breaths/ had not received phototherapy before the start of the min) was estimated by 1-min counting. The ambient air measurements. During the measurement period RH,,b temperature in the incubator (Tamb"C), skin temperature was maintained at 50% and T a m b was not altered. Ln preterm infants, measurements were made before, (Tskin "C), deep rectal temperature (Tbody"C) and the temperatures of the incubator walls (TWa""C) and roof during and after 120 min of phototherapy. If the skin or (Tro,foC)were measured with a YSI telethermometer (43 body temperature of the infant increased, Tambwas TA, using probes 405, 427 and 402, Yellow Springs, adjusted manually to keep the infant in thermal balance. Ohio, USA). The air-flow velocity in the incubator was RHambwas 50% at the start of the measurements, but if measured with an air velocity meter (Omnisensor, model T a m b was lowered during the measurement period, 1640, TST Incorporated, St. Paul, MN, USA). Photo- PHZOamb, not RHamb,was kept constant. When necessary, therapy was given with standard phototherapy equip- the infants were given breast milk through an indwelling ment (Bililite, Olympic Medical, Seattle, USA). This orogastric catheter during the measurement period. equipment provides blue light radiation with a wave- Four of the infants had not received phototherapy prior length mainly between 440 and 470 nm. Spectral to the study and in the remaining three infants photoirradiance was measured with a phototherapy radi- therapy was withheld for at least 5 h before the ometer (PR3, Air Shields, Hatboro, PN, USA). The measurements were started. irradianceat thelevel oftheinfant was 8-12pW/cm2/nm. All recordings were made with a Watanabe recording Statistical analysis system (Watanabe Instruments Corporation, Tokyo, Data were obtained for ER, RHamb, PH2Oamb, Tamb, Tbdy, Japan). Tskin, Troof, Twa1l, H R and RR. Statistical analysis was performed using the Student's t-test on paired Measurement procedure observations. The values for the preterm infants were After feeding, the naked infant was placed in the prone interpolated to fixed times. position in an incubator (AGA MK241, AGA Medical, Lidingo, Sweden). At least 30 min were allowed for the infant to settle down and for the environmental condi- Results tions in the incubator to stabilize. The air-flow to the incubator was 8-10 I/min and the air velocity above the Full-term infants infant was less than 0.1 m/s. The system for servo In each infant, ER remained at the same level during control of skin temperature, supplied with the incuba- exposure to phototherapy. The mean ER was 3.1 (SD tor, was used to regulate Tambto the desired T a m b by 0.7) g/m2h at the start of the measurements and 3.1 (0.5) suspending the sensing thermistor in the centre of the g/m2h after 30 min of phototherapy (Fig. l), giving a incubator above the infant. The phototherapy equip- mean difference of 0.0 (confidence limits -0.20 and ment was placed above the incubator. ER was measured 0.20). This difference was not statistically significant. from an interscapular skin area. ER was first measured Table 1 shows the temperatures and RH before and before the start of phototherapy, and repeated measure- after 30 min of phototherapy. NOsignificant change was ments were made during phototherapy. The last noted in Tbody,Tskin,T a m b or RH. Troorincreased from measurement was made after switching off the photo- 29.6 to 33.0 "C. This caused a decrease in the radiative therapy equipment. Before each ER measurement, heat loss from the skin area facing the roof from 37.8 to readings of ambient relative humidity (RHamb),ambient 15.9 W/m2 ( I 4). water vapour pressure (PH2Oarnb), Tbody,Tskin, TambrTwall and Troofand, in the preterm infants, H R and RR were made. Tskinwas measured close to the site at which the Preterm infants ER measurements were made. Tambwas measured in the In each infant ER remained at the same level during centre of the incubator, about 10 cm above the infant. exposure to phototherapy. The level of ER depended on The thermistor for measurement of Tamb was protected the infant's gestational age at birth and postnatal age.
766
S Kjartansson et a/.
ACTA PRDIATR 81 (1992)
Tahle 1. Mean (+SD) rectal (Tbody)and skin (T,t,")temperatures, and temperatures of the incubator air (Tamb)and of the incubator roof (Troor) and relative humidity of the incubator air (RH) before the start of phototherapy (Pt) and after 30 min of phototherapy (30 min Pt) in term infants (n= 10).
35.4k0.2 35.5k0.2 ns
36.6 k0.I 36.7 + O . 1 ns
Before Pt 30 min Pt p value
32.7k0.6 32.6+0.5 ns
29.6k0.7 33.0k0.9 < 0.00 I
50+ 1 50+ I
ns
Tahle 2. Mean ( f SD) rectal (Tbdy)and skin (Tskln) temperatures, and temperatures of the incubator air (Tamb) and of the incubator roof (T,oof) and relative humidity of the incubator air (RH). heart rate (HR) and respiratory rate (RR) before the start of phototherapy (Pt) and after 120min of phototherapy (120 min Pt) in preterm infants (n = 7).
Before Pt 120 min Pt p value
.
Troor ("C)
RH ("A,)
35.7k 1.2 33.6+ 1.0
31.1 & 1.0 38.6k2.3
54k 1
