Energy Metabolism and Substrate Utilization in Low Birth Weight Neonates Under Radiant Warmers.

Abstract. 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 < .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 < .05) and a 13% increase in carbon dioxide production (8.26 +/- 1.1 v 7.31 +/- 1.1 mL/kg/min; P < .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 < .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 Celsius 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. We speculate that change in metabolic activity is more likely related to alterations in sleep and/or behavior patterns in the exposed environment. Given this relatively short-term study of healthy premature infants receiving an excellent caloric intake (120 kcal/kg/d), we conclude that radiant... [ABSTRACT FROM AUTHOR]