Loïc Dégrugilliers

Échanges thermiques et thermorégulation chez le nouveau-né

The newborns energy expenditure is used in order of priority for: (i) basic metabolism; (ii) body temperature regulation and (iii) body growth. Thermal regulation is an important part of energy expenditure, especially for low birth-weight infants or preterm newborns. The heat exchanges with the environment are greater in the infant than in the adult, explaining the increased risk of body hypo- or hyperthermia. The newborn infant is a homeotherm, but over a long period of time, he cannot maintain the thermal processes. Further developments are expected to improve the infants thermal environment, with assessment of the various heat exchange mechanisms by conduction, convection, radiation and evaporation. The quantification of the respective parts of these exchanges would improve nursing care through clinical procedures or equipment used to ensure the control of the optimal thermohygrometric conditions in incubators, especially when the likelihood of excessive body cooling is high. The present review focuses on the various body heat exchange mechanisms, the thermoregulation processes of the newborn, and their implications in clinical usage and limitations in the neonatal intensive care unit.

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

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 neonates 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.

Variations in incubator temperature and humidity management: a survey of current practice

Aim:  To describe and assess routine procedures and practices for incubator temperature and humidity management in France in 2009.

Relationship Between Functional Residual Capacity and Oxygen Desaturation During Short Central Apneic Events During Sleep in “Late Preterm” Infants

Apneic episodes are frequent in the preterm neonate and particularly in active sleep (AS), when functional residual capacity (FRC) can be decreased. Furthermore, FRC may be inversely correlated with the speed of blood-O2-desaturation. We evaluated the potential involvement of FRC in the mechanisms responsible for blood-O2-desaturation during short central apneic events (>3 s) in “late-preterm” infants and analyzed the specific influence of sleep state. Apneic events were scored in 29 neonates (postmenstrual age: 36.1 ± 1.2 wk) during AS and quiet sleep (QS). FRC was measured during well-established periods of regular breathing. Apneas with blood-O2-desaturation (drop in SpO2 >5% from the baseline, lowest SpO2 during apnea: 91.4 ± 1.8%) were more frequent in AS than in QS, whereas no difference was seen for apneas without desaturation. The magnitude of the FRC did not depend on the sleep state. In AS only, there was a negative relationship between FRC and the proportion of apneas with desaturation. Even in late preterm infants who do not experience long-lasting apnea, blood-O2-desaturation during short apneic events is related (in AS but not QS) to a low baseline FRC. Sleep stage differences argue for a major role of AS-related mechanisms in the occurrence of these apneas.

Assessment of radiant temperature in a closed incubator

In closed incubators, radiative heat loss (R) which is assessed from the mean radiant temperature

Quantitative Imaging of Regional Aerosol Deposition, Lung Ventilation and Morphology by Synchrotron Radiation CT

(\overline{T}_{r} )

A mean body temperature of 37°C for incubated preterm infants is associated with lower energy costs in the first 11 days of life

accounts for 40–60% of the neonate’s total heat loss. In the absence of a benchmark method to calculate