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

Abstract

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 model's 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

“…The validity of the results reported in the present study depends on the accuracy of the parameters governing the heat transfer equations. In the present study, this difficulty was partly resolved using various heat exchange coefficients that had already been experimentally determined with the manikin, thus reducing the uncertainty and the number of empirical assumptions (Chessex et al 1988; Adams et al 2000; Lyon and Oxley 2001; Elabbassi et al 2004; Belghazi et al 2006; Agourram et al 2010). Moreover, the use of infrared thermometry enabled us to take account of the intersegment thermal heterogeneity of each neonate and thus obtain a more accurate measurement of the mean skin temperature than with spot measurements at several body sites.…”

“…The manikin represents a small-for-gestational-age neonate with a body surface area of 0.086 m 2 and a simulated weight of 900 g. The body shape reproduces the fingers, toes, eyes, mouth, ears and nose—each with the appropriate body angles. It has been extensively validated and described in detail elsewhere (Elabbassi et al 2004; Belghazi et al 2006; Museux et al 2008). The nude manikin was placed in a relaxed supine position on the mattress, with the face turned to the side (with the arms parallel to and 1.0 cm away from the trunk and the legs spread apart at 1.7 cm from the axis).…”

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.…”

“…Les pertes évaporatoires par les voies respiratoire (E resp ) et transcutanée (E) sont : E = h e ωA c (P sH20 − P aH20 ) F pcl (7) h e = coefficient de transfert de chaleur par évaporation (W/mb/m 2 ) calculé par la relation de Lewis (h e = 1,67 h c ), = mouillure de la peau (sans dimension) égale à 0,35 (dans les premiers jours de vie afin de tenir compte de la grande perméabilité de la peau de l'enfant) puis 0,08 car l'activité sudorale est nulle [16], P sH20 − P aH20 = différence de pression partielle entre la peau (pression saturante pour la température cutanée moyenne) et l'air de l'incubateur (mb), F pcl = coefficient de réduction des échanges de chaleur latente due à la vêture (sans dimension). Le facteur F pcl agissant sur l'évaporation est déter-miné avec le mannequin dont la surface est totalement mouillée ( = 1) à partir du rapport entre l'évaporation mesurée sur le modèle vêtu et le modèle nu [15,17].…”

Can Mathematical Models of Body Heat Exchanges Accurately Predict Thermal Stress in Premature Neonates?

“…Electrical wires placed inside each of the mannequin's members can be used to simulate the regional skin temperature heterogeneity ( Figure 3b) recorded (using infrared thermography) for real neonates. In a study of a thermal mannequin simulating a neonate with very low birth weight, Belghazi et al [27] also included a sweating feature. Firstly, the mannequin's surface was covered with a black cotton stocking, in order to simulate water evaporation from the surface.…”