Design and performance of blanket heat shields for neonates.

BACKGROUND: Several designs of plastic blanket heat shields are in use. This study was done to compare different designs for their efficiency in reducing heat loss. METHODS: Four heat shield designs were tested by sequentially covering each of 14 infants (wt. 640-2,030 g) cared for under radiant warmers. The power consumption of the radiant warmers was measured as a surrogate for heat loss. All designs were tested for a total of 20 min on all infants. Results were calculated as percent change in power consumption from shield to shield. The most efficient design was further modified and evaluated in another group of 14 infants (wt. 700-1,180 g). RESULTS: The relative reductions in power consumption were: no shield (control) -0%, a plastic foil over the side rails: -17%, a single layer close to the infant but excluding the head: -34%, the same as double layer -37% and the most efficient one, a single layer covering the whole infant -42%. A modification of this design, tested in the second group of infants, reduced power consumption by 13% (95% CI -5.9/-19.7), (p less than 0.004) when compared to the single layer covering the whole infant. It was tucked under the connecting tubes to the ventilator. It also reduced the risk for displacement and allowed for the endotracheal tube to be suctioned without removing the blanket. CONCLUSION: Modifications of the design of heat shield blankets for infants resulted in significant increases in efficiency.     

Reduction of oxygen consumption, insensible water loss, and radiant heat demand with use of a plastic blanket for low-birth-weight infants under radiant warmers

Eight very low-birth-weight premature infants (mean birth weight 1.11 +/- 0.05 [SEM]kg, mean gestation 30 +/- 1 weeks, and mean age 9 +/- 2 days) were studied under servocontrolled radiant warmers with and without a loosely fitted, transparent, and flexible Saran plastic blanket. Metabolic rate was significantly less in all infants when covered by the blanket (oxygen consumption was 7.99 +/- 1.13 mL/kg/min v 9.00 +/- 1.10 mL/kg/min uncovered, P less than .001). There were also significant reductions in insensible water loss (1.86 +/- 0.18 v 1.25 +/- 0.20 mL/kg/h, P less than .01) and in heat demand from the radiant warmer (14.3 +/- 1.3 v 9.9 +/- 1.4 mW/cm2, P less than .001) when infants were nursed under the blanket compared with the control condition, respectively. Covering the critically ill, very low-birth-weight infant nursed under a radiant heater with a thin, transparent layer of Saran is beneficial in reducing oxygen consumption, insensible water loss, and the need for exposure to high levels of radiant heat. Further investigation to confirm the benefits and possible complications of plastic blankets should be conducted before routine use can be recommended.     

Effects of environmental warming on blood components dispensed in syringes for neonatal transfusions

We examined the quality of blood components dispensed in syringes for transfusion into neonates, including the effects on quality of environmental conditions to which blood is exposed when it is transfused into neonates nursed in warm-air incubators or under radiant warmers. Syringes of blood placed in incubators rapidly warmed to 36 degrees C. Blood placed under radiant warmers operated at full power was heated rapidly to temperatures approaching 45 degrees C, and all blood components exhibited evidence of falling pH and cellular damage after 6 hours exposure to radiant energy. Erythrocyte damage was suggested by an increase in plasma hemoglobin, potassium, and lactic dehydrogenase. Platelets lost the ability to recover from hypotonic shock. Granulocytes exhibited a marked defect in the ability to produce superoxide anion after stimulation. The excessive warming and functional abnormalities exhibited by all blood components exposed to infrared energy were abrogated when syringes were shielded by covering them with aluminum foil. The clinical importance of these experimental findings remains to be established. Meanwhile, it would seem prudent either to shield syringes of blood placed under radiant warmers by covering them with aluminum foil or to limit the volume of a single transfusion to a quantity that can be infused within a relatively brief period.     

Thermal support for the very-low-birth-weight infant: role of supplemental conductive heat

Heated water pads were placed underneath very-low-birth-weight preterm infants receiving care under overhead radiant warmers with plastic heat shields to evaluate the effects on their thermal environments. The electrical input (watts) to the overhead warmer was monitored and temperatures at various locations in the environment and on the infants were recorded. The electrical input to the radiant warmers decreased significantly (P = 0.0015) with the introduction of the heated water pads. Several of the temperatures recorded during the study also showed significant changes, including increased abdominal skin temperatures in these prone infants (P = 0.007) and decreased back-to-abdomen skin temperature gradients (P = 0.007). Less marked changes included higher mattress or pad temperatures (P = 0.019), lower ambient air temperatures within the plastic heat shields (P = 0.022), and increased infant foot temperatures (P = 0.036). We believe that conduction has a significant influence on the thermal environment of the VLBW infant cared for under an overhead radiant warmer and that the use of a heated water pad can markedly alter heat transfer. The impact of conduction appears to have been previously underestimated.     

Radiant heat loss versus radiant heat gain in premature neonates under radiant warmers

Premature infants nursed on open radiant warmer beds are exposed to short-wavelength infrared power density distributed evenly over the bed surface. Additionally, infants' sides are exposed to relatively cooler nursery walls, and to the radiant warmer bed platform which may heat and reradiate to the baby. Therefore, infants may not only gain heat from the warmer (Q radiant warmer) but lose or gain radiant heat to the sides as well (+/- Q radiant loss). In order to quantitate these parameters, ten premature newborn infants nursed under radiant warmers servocontrolled to 36.5 degrees C skin temperature (weight 1.27 +/- 0.24 SD kg, gestation 31 +/- 3 weeks) were investigated, and partitional calorimetry previously reported. In the present study, calculation of net rate of radiant heat transfer (Q net radiant) was made from these data (-2.63 +/- -1.52 kcal/kg/h), and compared to direct measurements of Q radiant warmer (-2.49 +/- -0.90 kcal/kg/h). The present report further partitions net radiant heat transfer to evaluate Q radiant loss: -0.13 +/- 1.82 kcal/kg/h (range -3.16 to 1.93). From these calculations mean radiant temperature of this environment was estimated (45.3 +/- 4.3 degrees C) and compared to the radiant warmer temperature received (45.0 +/- 2.9 degrees C). This information suggests other strategies to reduce radiant heat loss as well as convective and evaporative losses in premature neonates nursed on open radiant warmer beds.     

WATER REQUIREMENT OF PREMATURE NEWBORN INFANTS

Bell, E. F. and Oh, W. (Department of Pediatrics, Women and Infants Hospital of Rhode Island, and the Program in Medicine, Brown University, Providence, Rhode Island, USA). Water requirement of premature newborn infants. Acta Paediatr Scand, Suppl. 305: 21–26, 1983.—Two groups of studies related to the water requirement of premature infants are reviewed. The first examined the effects of several environmental factors on insensible water loss (IWL) and oxygen consumption of 20 low-birth-weight infants. Incubator air temperature above the neutral zone increased IWL, as did the use of a radiant heat source instead of a conventional incubator. A plastic heat shield slightly reduced IWL of infants in incubators. The second group of studies examined the effects of excess water intake in premature infants. 170 infants were randomly assigned to receive "low" (average estimated requirement for birth weight and age) or "high" (excess) volume water intake. The high-volume group became dehydrated less often but had a greater incidence of patent ductus arteriosus and necrotizing enterocolitis.     

Thermal stability of premature infants during routine care under radiant warmers.

The body temperatures of infants weighing less than 1500 g under radiant warmers during routine care were documented in the first week of life. Ten infants (median gestational age 28 weeks, median birthweight 913 g) were studied. During 30 nursing interventions (mean 9.2 minutes) mean oesophageal and foot temperature changed 0 degrees C and -0.11 degrees C, respectively. A radiant warmer may limit heat loss during interventions because of easy access and rapid radiant warmer responsiveness.     

Techniques for warming red blood cells packaged in different containers for neonatal use

Essential to the management of the sick, low birth weight infant is maintenance of a neutral thermal environment by use of convection incubators and radiant warmers. Manipulation of the infant in preparation for transfusion and the transfusion of cold blood could theoretically lower the infant's body temperature, subsequently contribute to cold stress, and concomitantly increase metabolic demands and oxygen requirements. The authors evaluated different pretransfusion manipulations of syringe aliquots and bags of blood in an effort to provide a clinically acceptable product for transfusion to sick, very low birth weight infants.     

Effect of polyethylene occlusive skin wrapping on heat loss in very low birth weight infants at delivery: a randomized trial

OBJECTIVE: Significant evaporative heat loss in the very low birth weight infant can occur in the delivery room. We investigated the effect of polyethylene wrap applied immediately at birth (without drying) on rectal temperature measured at nursery admission. STUDY DESIGN: Sixty-two consecutive infants delivered at <32 weeks' gestation were stratified by gestational age and randomly allocated to resuscitation with polyethylene wrap. All infants were resuscitated under radiant warmers. Wraps were removed on nursery admission. Rectal temperature was taken by digital electronic thermometer. RESULTS: Fifty-nine of 62 recruited infants completed the study. Maternal temperature, delivery room temperature, transfer-incubator temperature, and time to admission were recorded. Use of occlusive wrapping resulted in a significantly higher admission rectal temperature in infants <28 weeks' gestation (difference in means = 1.9 C, P <.001). No significant difference was seen in admission rectal temperature in infants of 28 to 31 weeks' gestation (difference in means = 0.17 C, P =.47). All 5 deaths were in the nonwrap group (vs wrap, P =.04); their mean temperature was 35.1 C versus 36.5 C in survivors (P =.001). CONCLUSIONS: Occlusive wrapping of very low birth weight infants at delivery reduces postnatal temperature fall. This may result in a decreased mortality rate.     

Optimal thermal management for low birth weight infants nursed under high-powered radiant warmers

Servocontrol of skin temperature for the critically ill premature neonate nursed on a radiant warmer bed has been assumed to be analogous to skin temperature control for infants nursed in convection-warmed incubators. There are significant differences between these two warming techniques, and no definitive data exist to aid the clinical specialist in governing radiant warmer control. Eighteen low birth weight premature infants less than 2 weeks of age were studied under powerful overhead radiant warmers to determine the optimal skin temperature for servocontrol of radiant heater output. Anterior abdominal wall temperature was servocontrolled at 35.5 degrees, 36.5 degrees, and 37.5 degrees C in a randomized fashion for three periods of 90 minutes each after thermal equilibrium was established. Oxygen consumption was measured during the entire 90-min sample period at each temperature by a computerized metabolic apparatus to determine the optimal thermal neutral control temperature defined as minimal oxygen consumption with normal body temperature. Skin, deep rectal, and environmental temperature measurements, as well as behavior assessments, were made concurrently. Oxygen consumption was significantly elevated at 35.5 degrees C (8.62 +/- 0.73 mL/kg/min, mean +/- SEM) compared with 36.5 degrees C (7.30 +/- 0.55 mL/kg/min). Changing servocontrol temperature to 37.5 degrees C produced no further significant decrease in oxygen consumption (7.41 +/- 0.70 mL/kg/min), and nine infants manifested supranormal deep rectal temperatures (greater than 37.5 degrees C). Optimal abdominal skin temperature control at 36.5 degrees C (slightly warmer than previously reported but less than 37.5 degrees C) is recommended for premature neonates nursed on radiant warmer beds.(ABSTRACT TRUNCATED AT 250 WORDS)     

Thermal balance in term and preterm newborn infants nursed in an incubator equipped with a radiant heat source

A radiant hood warmer, a device that heats the incubator roof independently of the incubator's main heat source, was used to study the thermal balance of 11 full term and 13 preterm (gestational age 25–34 weeks) infants exposed to an isolated elevation of incubator roof temperature at stable ambient air temperature and humidity. After initial measurements without active heating of the incubator roof, the hood warmer was set to 33°C, 36°C and finally (preterm infants only) to 39°C. At least 18 min of measurements with the infant asleep were made at each hood warmer setting. In the term infants an increase in roof temperature from 30.5°C to 35.6°C resulted in an increase in skin temperature from 35.4 to 35.9°C, and a decrease in radiative heat loss from 32.8 to 20.7 W/m² exposed skin. In the preterm infants an increase in roof temperature from 31.0 to 38.4°C led to an increase in skin temperature from 35.7 to 36.3°C and a decrease in radiative heat loss from 34.1 to 13.0 W/m² exposed skin. The increased inner roof surface temperature did not affect evaporative or convective heat loss, skin blood flow, respiratory water loss, oxygen consumption or transepidermal water loss in either group. Thus, at stable ambient air temperature and humidity, the increase in incubator roof temperature resulted in an increase in skin temperature and a decrease in radiative heat loss in both term and preterm infants.     

Prevention of neonatal cold injury in preterm infants

In many parts of the world neonatal cold injury still contributes to neonatal death in preterm or growth-retarded neonates. Kangaroo Mother Care might improve the situation and is the only effective, affordable and available method to prevent neonatal hypothermia in most developing countries. In developed countries, highly sophisticated incubators and radiant warmers are available but there is increasing concern about the long-term effects of high levels of sound, disturbing light and unplanned procedures which can have a bearing on the use of these tools. A controlled clinical trial of cot-nursing with a heated, water-filled mattress is presented in this issue of Acta Paediatrica. CONCLUSION: The results from the new trial and the recently published systematic reviews by the Cochrane Library of technologies to provide warmth to preterm infants in modem neonatal intensive care units, makes it possible to suggest the place of available tools: incubators, radiant warmers, heated water-filled mattresses and care in skin-to-skin contact.     

Phototherapy effect on the incidence of patent ductus arteriosus in premature infants: prevention with chest shielding

Patent ductus arteriosus is common among premature neonates, especially those with birth weights less than 1,500 g. In vitro, room light inhibits the contraction of immature piglet's ductal rings. Because phototherapy is used frequently from the first days of life to treat jaundice in preterm neonates, we compared the occurrence of patent ductus arteriosus among premature infants exposed to this intense light source with those whose chests were shielded. Seventy-four babies with respiratory distress syndrome were randomly assigned to either a treatment group (chest shielded with aluminum foil while on phototherapy, 36 babies) or control group (no shield, 38 babies). All were on radiant warmers, received mechanical ventilation for respiratory distress syndrome, and phototherapy (Air Shields model PTU 78-1) from day 1 of life. Irradiance was maintained at greater than 4.0 microW/cm2/nm in all cases. Although both groups had similar birth weights, gestational ages, severity of respiratory distress syndrome, intravenous fluid intake, and duration of phototherapy, the incidence of patent ductus arteriosus was significantly less in the shield group (shield 11/36 v No shield 23/38; P = .009). Patent ductus arteriosus murmurs developed in shielded patients at a later date, they required less vigorous treatment (ie, indomethacin), and they had shorter hospitalizations (74 v 85 days; P less than .05). The significant reduction of patent ductus arteriosus with shielding suggests that phototherapy may play a role in the occurrence of patent ductus arteriosus in premature infants. Shielding may be a practical method to decrease this common complication should this initial observation be confirmed.     

Cardiovascular changes in preterm infants nursed under radiant warmers

Radiant heat is known to increase insensible water loss and, to a certain extent, oxygen consumption. Little is known about its cardiovascular effects. We measured cardiac output, stroke volume, heart rate, and lower limb and skin blood flow in 20 preterm newborn infants nursed in an incubator and under a radiant warmer at an abdominal skin temperature of 36.5 degrees C. Mean (+/- SEM) birth weight was 1.57 (0.06) kg, gestational age 31.7 (0.4) weeks, and weight at examination 1.69 (0.02) kg; median postnatal age was 15 days. Skin and limb blood flow measurements increased by 44% to 55% with radiant heat (P less than .001 and P less than .01, respectively). Cardiac output increased by 5.4% (P less than .02) under the radiant warmer secondary to a small but significant (P less than .05) increase in heart rate. The changes in cardiac output during radiant heat administration are comparable to those reported for oxygen consumption.     

Oxygen consumption and insensible water loss in premature infants under radiant heaters

Oxygen consumption ((Vo2), carbon dioxide production (Vco2), and insensible water loss (IWL) were measured simultaneously in nine nondistressed, appropriately grown, premature infants less than 2 weeks old, nursed in a conventional, blow-warmed incubator, and were compared with measurements made on the same infants under a radiant heater. The infants had a pronounced increase (148% on average) in IWL when under the radiant heater (P < .001) whereas Vo2 increased by only 4.6% (P = .073). Abdominal skin temperature (servocontrolled to maintain 36.5 C) and esophageal temperature were the same under both conditions, but ambient air temperature was 0.7 C higher in the incubator (P < 05). Although a positive correlation was found between the increase in IWL and the change in Vo2 (r = .75, P < .01), the large increase in IWL (and, therefore, evaporative heat loss) under the radiant heater is out of proportion to, and cannot be accounted for, by the change in metabolic heat production. The heat transfer processes involved in maintaining body temperature constant under these conditions require further study.     

Maintaining normothermia: Why and how?

A high incidence of postnatal hypothermia has been reported in high-as well low-resource countries and it remains an independent predictor of neonatal morbidity and mortality, especially in very preterm infants in all settings. The temperature of newly born infants should be maintained between 36.5 and 37.5 °C after birth through admission and stabilization. Interventions to achieve this may include environmental temperature 23–25 °C, use of radiant warmers, exothermic mattresses, woollen or plastic caps, plastic wraps, humidified and heated gases. Skin-to-skin contact has been used, especially in low-resource settings. The combinations of these interventions applied to quality improvement initiatives, including staff training, use of checklists, and continuous feedback with the staff involved in the management of the neonate, are key factors to prevent heat loss from delivery room to admission to the neonatal intensive care unit. The admission temperature should be recorded as a predictor of outcomes as well as a quality indicator.     

Effect of radiant heat on head temperature gradient in term infants.

AIMS: To test the hypothesis that external radiant heating might lead to significant fluctuations in superficial and core head temperatures in newborn infants. METHODS: In an observation group of 14 term infants nursed under a radiant heater, servo-controlled to the abdominal skin, changes in rectal, core head, and scalp temperatures with heater activation were examined. In a further intervention group of six infants the effect of a reflective head shield on the fluctuations of scalp temperature was also tested. RESULTS: In the observation group, when the heater had been off for 30 minutes, the rectal and scalp temperatures were 36.7 (SD 0.6) and 35.6 (0.6) degrees C, respectively, a difference of 1.2 (0.2) degrees C. After 30 minutes with the radiant heater on this fell to 0.2 (0.5) degrees C. The core head temperature, however, remained similar to the rectal temperature throughout. In the intervention group a reflective shield prevented the loss of the rectal-scalp gradient. CONCLUSION: Overhead heater activation is associated with loss of the core to scalp temperature gradient, but no change in core head temperature in term infants. The clinical relevance of this superficial heating in vulnerable infants warrants further study.     

WATER EVAPORATION AND HEAT EXCHANGE WITH THE ENVIRONMENT IN NEWBORN INFANTS

Hammarlund, K. and Sedin, G. (Department of Paediatrics, University Hospital, Uppsala, Sweden). Water evaporation and heat exchange with the environment in newborn infants. Acta Paediatr Scand, Suppl. 305: 32–35, 1983.—The amount of water evaporated from the skin of newborn infants and the temperatures of the skin, the ambient air and the surfaces facing the infants were measured and used to calculate the evaporative, radiative and convective heat exchange between the infant and the environment in infants of varying gestational ages. Immediately after birth the evaporative heat exchange was very high but it then decreased gradually. The radiative heat exchange was very high in the delivery room but lower in the incubators. In incubators the evaporative heat exchange was high in the most pre-term infants, especially when nursed at a low ambient humidity. Different modes of heat exchange were interrelated, so that when the pre-term infants had a high evaporation rate, a high ambient temperature was needed and the heat exchange through radiation and convection decreased. Net heat exchange was lowest in very pre-term infants at an ambient humidity of 60%.     

Spot the red herring: breastfeeding, fruitpurée, and infant autonomic functioning-the generation R study

Several studies have suggested that breastfeeding is related to infant autonomic functioning. The authors investigated whether this is a causal relation. In all, 444 mothers reported breastfeeding practices 2 mo postpartum. Infant autonomic functioning was assessed by heart rate variability at age 14 mo, after discontinuation of breastfeeding. The dose-dependent association between breastfeeding and infant autonomic functioning was tested with linear regression models adjusted for multiple confounders. The authors investigated the relation of fruitpurée consumption with infant autonomic functioning. Fruitpurée consumption has similar socioeconomic epiphenomena but is not related via the same causal mechanism to autonomic regulation as breastfeeding. Nonbreastfed infants had high sympathetic modulation [7.87 log (ms)/SD, 95% CI: 7.71-8.02], partially breastfed infants had intermediate sympathetic modulation [7.75 log (ms)/SD, 95% CI: 7.51-7.82], sympathetic modulation of exclusively breastfed infants was low [7.63 log (ms)/SD, 95% CI: 7.50-7.77]. However, this association could be explained by socioeconomic confounders. Furthermore, fruitpurée consumption was similarly associated with reduced infant sympathetic modulation. The association between breastfeeding practices and infant sympathetic modulation was accounted for by socioeconomic and environmental factors. We found a similar association between fruitpurée consumption and autonomic functioning, further suggesting that the association between breastfeeding and infant autonomic functioning is noncausal.     

Survival of very low birthweight and very preterm infants in a geographically defined population

Objective : To determine in a geographically defined population 1 year survival of infants with a birthweight of less than 1500g or gestational age less than 32 weeks, and to establish the effect of postnatal age on predicted survival. Design : Cohort analysis of 72427 births to Welsh residents in 1993-94. Deaths were identified using the All Wales Perinatal Survey, a population-based surveillance of mortality between 20 weeks of gestation and 1 year of age. Main outcome measures : Birthweight- and gestation-specific infant mortality, and the effect of postnatal age, gender, and multiple pregnancy on predicted survival. Results : In normally formed infants 1 year survival at 24–25 weeks gestation was 35%, compared to 75% at 27–28 weeks, and 95% at 30–31 weeks. In infants with a birthweight of 500-699g 1 year survival was 18% compared to 70% at 800-999g, and 97% at 1300-1499g. The chances of survival improved markedly with increasing postnatal age; at 24–25 weeks gestation it was 35% at birth, 50% at 12 h, 66% at 7 days and 78% at 4 weeks. Infant mortality was higher in males, but multiple pregnancy had no effect. Conclusions : Up-to-date birthweight- and gestation-specific survival rates are essential for predicting the outcome of a newborn infant. The rapid change in the chances of survival with increasing postnatal age emphasises especially the importance of revising the prediction as the infant gets older, particularly during the first few days of life,