L. Ghyselen

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.

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.

Effect of posture on the thermal efficiency of a plastic bag wrapping in neonate: Assessment using a thermal “sweating” mannequin

To assess the various heat exchanges with the environment a multisegment, anthropometric, thermal mannequin representing a neonate with a birth weight of 900 g has been designed. The mannequin simulates not only dry heat loss (radiative+conductive+convective body heat exchanges) but also the evaporative skin water loss which can be encountered in low-birth-weight neonates. The model was placed in the supine or prone position in a closed incubator (air temperature, 33 C; relative air humidity, 50%; air velocity below 0.1 m s(-1)). Experiments were performed with the mannequin either naked or wrapped in a flexible, plastic bag (with the head exposed) used to prevent excessive body water loss at delivery and during the following hours About 30% of the models total surface was wetted with water. Our results demonstrated that body position does not modify dry and evaporative heat losses, whatever the experimental conditions. The plastic bag acts rapidly and reduces total heat loss by 30% to 34%, primarily through a reduction in evaporative water loss (between 5.4 and 6.7 g kg(-1) h(-1)). When the bag is present, the uncovered surface of the head accounts for about 50% of the total heat loss. This simple and inexpensive solution can be used to prevent thermal stress and dehydration in very small premature neonates.

Assessment of radiant temperature in a closed incubator

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

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

(\overline{T}_{r} )

Polyethylene bag wrapping to prevent hypothermia during percutaneous central venous catheter insertion in the preterm newborn under 32 weeks of gestation.

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

[Noise level in the NICU: Impact of monitoring equipment].

\overline{T}_{r}