A reproducible means of assessing the metabolic heat status of preterm neonates

Abstract

The aim of the present study was to validate the measurement of metabolic heat production using partitional calorimetry (PC) in preterm neonates exposed to a near-thermoneutral environment in an incubator. In order to reduce experimental uncertainty (due to the different variables involved in the calculation of body heat exchanges between the infant and the environment), the mean radiant temperature and the heat transfer coefficients for convection, radiation and evaporation were measured using a multisegment, anthropometric thermal mannequin which represents a small-for-gestational-age neonate (body surface area: 0.150 m2; simulated birth weight: 1500 g). The metabolic heat production calculated by PC was compared with the results of indirect respiratory calorimetry, which is rarely done in clinical setting since this method interferes with the neonate's environment and requires a high degree of technical preparedness. The oxygen consumption (VO2) and carbon dioxide production (VCO2) were measured in 20 preterm neonates exposed to thermoneutral (32.3 degrees C) and to slightly cool environments (30.2 degrees C). The mean skin temperature was measured by infrared thermography. The measurements were made during well-established periods of active and quiet sleep. Metabolic heat production was assessed by weighting each value of VO2 and VCO2 by the duration of the sleep stages. Our results showed that there was no significant difference between the two methods in terms of their estimation of metabolic activity at thermoneutrality (mean overall difference: 0.34 kJ h(-1) kg(-1)) and in the cool environment (0.26 kJ h(-1) kg(-1)). We observed significant interneonate variability. Partitional calorimetry enabled the prediction of body growth with a daily error of less than 5.3 g (2.38 kJ h(-1) kg(-1)) for all the neonates at thermoneutrality and for 85% of the subjects (3.03 kJ h(-1) kg(-1)) in the cool environment. Despite this limitation, we demonstrate here that PC provides reliable information for calculating the energy expenditure of individual preterm neonates on the basis of standard environmental input variables. We suggest that the technique can be advantageously used to assess the energy expenditure and normal growth of these infants.

Dynamics and complexity of body temperature in preterm infants nursed in incubators

“…Arguably, future real-time analysis of temperature time series in a longitudinal fashion might allow for quantitative assessment of maturation of the temperature control system and provide a rational basis for transfer of infants from an incubator to an open cot. Currently, this decision is primarily based on body weight of infants [41, 42], however, there is little evidence to suggest a specific body weight indicating readiness for transfer, i.e., such transfers are typically a matter of trial and error despite the fact that thermo-neutrality is important for adequate weight gain and has beneficial effects on other autonomic control systems such as breathing and heart rate [9, 43, 44]. …”

Conception d’un logiciel de calcul de la thermoneutralité dans les incubateurs fermés pour nouveau-nés prématurés (projet Pretherm®)

“…En effet, la difficulté majeure de cette conception réside dans le fait que le calcul des différents échanges de chaleur intervenant dans le bilan thermique de l'enfant prématuré reposait jusqu'à présent sur des incertitudes notamment en ce qui concernaient les coefficients d'échanges de chaleur et la température moyenne de rayonnement généralement calculés sur l'adulte. La conception dans notre laboratoire de mannequins calorimétriques ayant les formes anatomiques de nouveau-nés prématurés [15,17,18] a permis de résoudre ces problèmes.…”

“…h K = coefficient de transfert de chaleur par conduction [18], T m = température de surface du matelas.…”

Influence of Thermal Drive on Central Sleep Apnea in the Preterm Neonate

“…The value of T e is nearly equal to the body's internal temperature, ρ = volumetric mass of air (kg.m -3 ); C = h c (T a -sk ) F cl A c A D h c = the convective heat transfer coefficient (W·m -2 ·°C -1 ) = 2.38 ( sk -T a ) 0.25 , 29 as recommended for natural convection 29,30 , A c = the percentage of body surface area available for convective heat exchange (0.804). 31 The value was determined by taking into account the surface area contacting the mattress (0.104) and the surface area of the upper part of the trunk covered by the diaper (0.092), 31 F cl = the heat reduction factor due to clothing, which can be calculated as follows 32 : 29,33 I cl = the effective clothing thermal insulation of the diaper, which ranged from 0.021 to 0.064°C·m -2 ·W -1 according to the actual air temperature measured in each experimental condition.…”

“…31 The value was determined by taking into account the surface area contacting the mattress (0.104) and the surface area of the upper part of the trunk covered by the diaper (0.092), 31 F cl = the heat reduction factor due to clothing, which can be calculated as follows 32 : 29,33 I cl = the effective clothing thermal insulation of the diaper, which ranged from 0.021 to 0.064°C·m -2 ·W -1 according to the actual air temperature measured in each experimental condition. 31 The clothing surface area factor f cl is 1 + 1.97 I cl ; Radiant heat exchange (R) is calculated using the StephanBoltzmann law: R = h r A r [( r + 273) 4 -( sk + 273) 4 ] F cl A D A r = the effective radiating area (0.77), determined for a relaxed neonate 34 less the percentage of the surface area in contact with the mattress (0.104) and the upper part of the trunk surface area covered by the diaper (0.092), A r = 0.574, r = the mean radiant temperature of the environment (°C) 29 ;…”