Heat balance in premature infants: comparative effects of convectively heated incubator and radiant warmer, with without plastic heat shield. Energy metabolism and substrate utilization in low birth weight neonates under radiant warmers. Minimal oxygen consumption in infants cared for under overhead radiant warmers compared with conventional incubators. Oxygen consumption and insensible water loss in premature infants under radiant heaters. Relative efficacy of an incubator and an open warmer in producing thermoneutrality for the small premature infant. A clinical comparison of radiant warmer and incubator care for preterm infants from birth to 1800 grams. Comparison of heated water-filled mattress and space-heated room with infant incubator in providing warmth to low birthweight newborns. A double-walled incubator alters the partition of body heat loss of premature infants.
Insensible water loss, oxygen consumption, and carbon dioxide production were measured in eight premature infants under four different conditions: in conventional single-walled incubator with and without plastic heat shield, and under radiant warmer with and without heat shield. IWL was greater under the radiant warmer (3.40 +/- 1.50 ml/kg/hour, mean +/- SD) than in the incubator (2.37 +/- 1.15 ml/kg/hour) when both were compared without heat shield. Addition of the heat shield reduced IWL in the incubator (2.13 +/- 0.76 ml/kg/hour) but not under the radiant warmer (3.37 +/- 0.94 ml/kg/hour). There were no significant differences in VO2 or respiratory quotient between any two of the four study conditions. We evaluated the metabolic response to the thermal demands of an open radiant warmer device, as distinct from convection incubator, in 13 healthy premature infants (1.395 +/- 169 g, 28 +/- 12 days of age, mean +/- SD). Metabolic rate was 10% higher for infants under the radiant warmer than in the incubator (2.60 +/- 0.4 v 2.36 +/- 0.3 kcal/kg/h; P less than .05). The radiant warmer also induced a small (4%), but significant, increase in nonprotein respiratory quotient (0.94 +/- 0.1 v 0.90 +/- 0.1; P less than .05) and a 13% increase in carbon dioxide production (8.26 +/- 1.1 v 7.31 +/- 1.1 mL/kg/min; P less than .05). Subcutaneous fat accumulation (estimated from 60-second skin-fold thickness measurements) was greater under the radiant warmer than in the incubator (0.08 +/- 0.05 v 0.04 +/- 0.04 mm/d; P less than .05). Under the warmer, the infant's mean skin temperatures and core temperatures were normal and similar to those found in the incubator, but the foot temperature was on average 0.6 degrees C cooler. The average rate of weight gain (18 g/kg/d) was the same in the radiant environment. The pattern of the elevated metabolic rate, shift of respiratory quotient coupled with the accumulation of subcutaneous fat, and cool extremities of infants under the radiant warmer may represent a physiologic adaptive response to thermal stress. However, the reasons for the elevated metabolic rate are unclear, because activation of the sympathetic nervous system with the release of catecholamines is not apparently involved.(ABSTRACT TRUNCATED AT 250 WORDS) Infants under radiant warmers have large increases in insensible water loss compared with infants in single wall incubators. To answer the question of whether or not a minimal rate of oxygen consumption could be achieved under overhead radiant warmers, we measured oxygen consumption, carbon dioxide production, and abdominal skin, cheek, rectal, thigh, and environmental temperature in ten healthy newborn infants in incubators and radiant warmers, using each infant as his/her own control. The minimal VO2 ranged from 4.41 to 8.87 and from 4.35 to 9.06 cc/kg/minute in the incubator and radiant warmer, respectively. The differences were clearly not significant (paired Student t-test, P greater than 0.60). There were no significant differences between the respiratory quotients, VCO2, or abdominal skin, check, rectal or environmental temperatures. These data support the hypothesis that a thermoneutral environment can be provided with a radiant warmer and imply that large increases in insensible water loss can occur without affecting minimal oxygen consumption. 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. To determine which warming system more closely approximates a neutral thermal environment, the oxygen consumption of 16 premature babies, weighing less than 1,500 gm each, was measured in a convectively heated incubator and under an open radiant warmer. Both systems were controlled to maintain a skin temperature of 36 C. The oxygen consumption of the infants was significantly higher under the radiant warmer. This result is in agreement with published data for this group of premature infants. The objective of this study was to compare radiant warmer and incubator care for preterm infants from birth with respect to temperature control and weight gain.
                Sixty preterm infants <33 weeks' gestation were randomized at birth to radiant warmer or incubator care. The initial goal was to maintain abdominal temperature at 36.8 degrees C in both groups and axillary temperature at 36.8 to 37.3 degrees C; air servocontrol was used for incubator infants. Infants in both groups received added humidity for 5 days if their weight was <1000 g and for 3 days if they weighed between 1000 and 1249 g. During a 3-hour period on days 1 to 7, recordings of abdominal, forehead, and foot temperatures were obtained. The percentage of the recording time during which the abdominal temperature was in the target range of between 36 degrees C and 37.5 degrees C was determined as an indicator of temperature control. Weight gain from birth to 1800 g was compared. Secondary outcomes included fluid balance and clinical events.
                There were 30 infants in each group; 48 were <1500 g (of whom 17 were <1000 g). There were no significant differences in birth weight, gestation, gender, or illness severity scores in the 2 groups. Significant differences in temperature control were noted on day 1. Although admission temperatures were similar, lower abdominal temperatures were noted in the first 2 hours of life in the incubator group (medians were 36.6 degrees C and 35.9 degrees C in the radiant warmer and incubator groups, respectively). Similarly, mean abdominal temperatures during the 3-hour recording on day 1 were lower in the incubator group, and infants in this group spent a significantly greater percentage of the recording time with temperatures outside the target range (17.3% compared with 0.88%). Other temperature recordings from the forehead and foot were not significantly different in the groups. Fluid intakes were higher for infants under radiant warmer on days 2, 3, and 4, and the difference amounted to a mean of 12.8 mL/kg/d. Maximum sodium levels in the first week were similar in the 2 groups. Mean weight gain was 17.4 g/kg/d for the radiant warmer group and 17.1 g/kg/d for the incubator group; days to regain birth weight and length of hospital stay were not significantly different. Greater numbers of infants in the radiant warmer group required phototherapy, and adverse events (which included death, necrotizing enterocolitis, chronic lung disease, grade 3 or 4 intraventricular hemorrhage, periventricular leukomalacia, or retinopathy requiring laser treatment) were less frequent in the radiant warmer group (1 infant compared with 8 in the incubator group; relative risk 0.1; 95% confidence intervals: 0.01-0.82).
                This study has shown differences in abdominal temperatures on day 1 and outcome, although the latter finding should be viewed with caution because of the sample size. The results indicate benefits for the initial use of the radiant warmer after birth. Although fluid requirements were higher in the radiant warmer group for days 2 through 4, the increased fluid volumes were given without apparent adverse effect. Prevention of excessive heat loss is fundamental to survival of low birthweight (LBW) newborns. The use of infant incubators (INC) is beyond the resources of developing countries, and the space-heated room (SHR) has been the only feasible means of providing thermal protection to LBW newborns. Recently a thermostatically controlled, heated, water-filled mattress (HWM) has been developed as a potentially simpler and affordable alternative.
                In a neonatal care ward of a referral hospital in Addis Ababa, 62 < 1 week old newborns, weighing 1000-1999 g, who were well enough to breathe comfortably in room air and tolerate oral feeds, were randomly allocated to INC, HWM or SHR and followed for 3 weeks. The level of cold stress as assessed by core-to-skin temperature gradient and the rate of weight gain were the main outcome measures.
                The level of cold stress was lowest in the INC, intermediate in the HWM and highest in the SHR. Relative to the INC group, the HWM group exhibited a modest increase in the occurrence of clinically important hyperthermic or hypothermic deviations in core temperature (rate ratio (RR) = 2.3; 95% CI: 0.9, 5.6), and the SHR displayed a definite increase (RR = 4.0; 95% CI: 1.7, 9.3). During the first week, the rate of weight gain was highest in the INC group (3.6 g/kg/day), lowest in the SHR group (-2.3 g/kg/day, P < 0.05 versus INC) and intermediate in the HWM group (1.6 g/kg/day, P > 0.1 versus INC).
                Care in the SHR produced clinically significant thermal stresses and was associated with deficient early neonatal growth, but the use of HWM may constitute a feasible and clinically acceptable alternative in providing warmth to LBW newborns during the neonatal period. Partitional calorimetry was used to assess the influence of a double-walled incubator (Air-Shields C-86 Isolette) on the body heat loss of eight premature newborn infants (birth weights 1.44-1.89 kg, ages 6-19 days). Each infant was studied in the same incubator with and without the inner wall. Incubator heater output was regulated by servocontrol to maintain the abdominal skin temperature at 36.5 degrees C. Operative environmental temperature was the same (mean 33.0 degrees C) in both incubators. There were no differences in body temperatures, oxygen consumption, carbon dioxide production, respiratory quotient, or evaporative water and heat losses. The double-walled incubator reduced radiant heat loss but increased convective heat loss, so that the total rate of body heat loss was unchanged.
Radiant warmers result in increased IWL compared to incubators. This needs to be taken into account when calculating daily fluid requirements. The results of this review do not provide sufficient evidence concerning effects on important outcomes to guide clinical practice. Further randomised controlled trials are required to assess the effects of radiant warmers versus incubators in neonatal care on important short and long term outcomes, with particular attention to extremely low birthweight infants in the early neonatal period.