## 4 Discussion  
The use of a thermal manikin and the calculation of a premature neonate's heat exchanges with the environment enables us to make several practical observations of value  
Figure 3: The change over time in the mean body temperature (\({}^{\circ}\)C) for three levels of metabolic heat generation (colored lines) at a T\({}_{\rm a}\) of 20.9 or 25.9 \({}^{\circ}\)C and for the two thermal insulation conditions of (a sheet alone or sheet + blanket). The horizontal yellow and red lines indicate the thresholds for moderate hypothermia (35 \({}^{\circ}\)C), and severe hypothermia (32 \({}^{\circ}\)C), respectively. with regard to the modalities of early SSC (i.e., an hour of SSC immediately after delivery). It should be borne in mind that the present study's findings are limited to neonates dried at birth, wearing a cap and a diaper, and who are morphometric (i.e., a body temperature between 36.5 and 37.5 \({}^{\circ}\)C) at birth. Our results suggest that with a T\({}_{\rm a}\) of 25.9 \({}^{\circ}\)C, SSC can warm up the neonate when the thermal insulation provided by the neonate's covering and clothing is moderate (a sheet alone; I\({}_{\rm cl}\) = 0.15 m\({}^{2}\)\({}^{\circ}\)C/W; T\({}_{\rm b}\): 37.09 \({}^{\circ}\)C) or substantial (i.e., a sheet + blanket; I\({}_{\rm cl}\) = 0.21 m\({}^{2}\)\({}^{\circ}\)C/W; T\({}_{\rm b}\): 36.52 \({}^{\circ}\)C) but only when the neonate's level of metabolic heat production is high. Maintaining the T\({}_{\rm a}\) recommended by the WHO would indeed reduce the incidence of neonatal hypothermia. Regardless of the level of metabolic heat production, a T\({}_{\rm a}\) of 20.9 \({}^{\circ}\)C cannot be recommended. However, this value is often selected by the nursing staff for their own thermal comfort. Our experiments showed that after one hour, a T\({}_{\rm a}\) of 20.9 \({}^{\circ}\)C induces a state of moderate hypothermia with T\({}_{\rm b}\) ranging from 32.79 \({}^{\circ}\)C to 34.40 \({}^{\circ}\)C. Under this condition, the threshold for moderate hypothermia (35 \({}^{\circ}\)C) is reached after 28 and 48 min of exposure, respectively. However, a T\({}_{\rm a}\) of 25.9 \({}^{\circ}\)C alone is not sufficient. Our simulation showed that neonates whose metabolic heat generation cannot compensate for body heat losses (M < 2.7 W/kg) are likely to develop moderate hypothermia. Hence, SSC can only be recommended for thermally stable infants with a T\({}_{\rm b}\) of at least 37 \({}^{\circ}\)C at birth and a particularly active energy metabolism. This might explain the estimated inter-infant differences in the effectiveness of SSC and why some moderately hypothermia but well-covered premature infants require additional oxygen [13]. Many researchers have observed large interindividual differences in the cold resistance of preterm infants. Metabolic heat production depends on the nervous system's maturity and the mass of brown adipose tissue; hence, during cold exposure, metabolic activity sometimes fails to increase or can even decrease. [PERSON] et al. [34], thus, reported that the absence of a metabolic response was due to a lack of brown adipose tissue. These considerations are especially relevant in premature neonates. A study in the rat [35] showed that in individuals with intrauterine growth retardation, high adenosine levels inhibited lipolysis during fetal growth [36]. This mechanism would explain the lack of brown adipose tissue in a premature neonate. In an infrared thermography study of cold exposure in newborns with a gestational age below 30 weeks, [PERSON] et al. [37] claimed that brown adipose tissue could not produce enough heat to be effective against body cooling until the third trimester of pregnancy. Inter-infant differences in brown adipose tissue might, thus, be able to compensate (or not) for the infant's heat loss. The effectiveness of vasomotor mechanisms should also be considered.