A reproducible means of assessing the metabolic heat statusof preterm neonates

• Published in: Medical physics (Lancaster) 2007-12, Vol.35 (1), p.89-100
• Main Authors: Museux, Nathanaëlle, Cardot, Virginie, Bach, Véronique, Delanaud, Stéphane, Degrugilliers, Loïc, Agourram, Bouchra, Elabbassi, Elmountacer Billah, Libert, Jean-Pierre
• Format: Article
• Subjects: energy expenditure; indirect respiratory calorimetry; nursing care; partitional calorimetry; thermal mannequin
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.2815966

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   m 2 ; 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 ( V ̇ O 2 ) and carbon dioxide production ( V ̇ CO 2 ) were measured in 20 preterm neonates exposed to thermoneutral ( 32.3 ° C ) and to slightly cool environments ( 30.2 ° 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 V ̇ O 2 and V ̇ CO 2 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.