## 4 How to Solve (at Least in Part) These Problems
### Applications and Research Perspectives  
In clinical situations, the models can thus be used easily to define the optimal temperature at which a neonate should be nursed [30; 31; 32] for the optimization of body growth and survival. The models can also be used to make recommendations for avoiding hypothermia or hyperthermia. Lastly, the models can calculate body heat storage in various hyperthermia-promoting scenarios and can estimate the likely time until death. Thus, [PERSON] [20] showed that the effect of increased blanket thickness is always less than that caused by reduced skin exposure, and that hyperthermia only develops when the head and neck are entirely covered. [PERSON] et al. [32] defined the highest tolerable air temperature for a given set of clothes and/or covers. [PERSON] et al. [33] showed that a combination of a bonnet and a polyethylene bag (a commonly used method for preventing evaporative heat loss [3; 34] can result in hyperthermia but only when metabolic heat production rises while the skin temperature falls, as sometimes happens in newborns with fever [35]. [PERSON] et al. also reported on the time required to reach lethal thresholds in various clinical situations [33]. All the models show that when an infant is heavily dressed, additionally covering the head with a bonnet can trigger lethal hyperthermia. The heat loss is lower when the head in is a face-down position or is covered by bedding. All the studies emphasize that a neonate with fever should be less extensively wrapped, rather than more extensively. The heat exchanges for a thermal mannequin representing a small-for-gestational-age premature infant (weighing 900 g or 1500 g; see Figure 3) were quantified in a closed incubator (the Satis\({}^{+}\) from Mediprema, Tauxigny, France) before and after phototherapy (Lullaby LED Phototherapy System, GE Medical Systems, Laurel, MD, USA). The device was located 35 cm above the mannequin, as recommended by the manufacturer. The incorporation of preliminary data into the predictive model [30; 31] showed that in order to achieve an optimal thermal environment during phototherapy, the mean \(\pm\) standard deviation (SD) incubator air temperature can be decreased by 0.68 \(\pm\) 0.15 (for the  
Figure 4: Optimal incubator air temperatures (T\({}_{\mathrm{inc}}\)) in a mathematical model as a function of postnatal age for two neonates (body mass: 655 g and 1980 g, respectively). T\({}_{\mathrm{inc}}\) was calculated using the mean radiant temperature measured with a standard black- globe thermometer (\(\overline{\mathrm{T}}_{\mathrm{r}}\) –standard, dotted line) or using a thermal mannequin (\(\overline{\mathrm{T}}_{\mathrm{r}}\) –mannequin, full line). The relative humidity levels are those commonly recommended by [PERSON] et al., (2008) [29] in the incubator for these populations of neonates. 900 g neonate) and 0.72 \(\pm\) 0.07 \({}^{\circ}\)C (for the 1500 g neonate) in the first days of life. These preliminary data must now be confirmed in clinical trials. Since cold stress on admission increases the risk of hypothermia in the first 3 h of life [36], broader application of the models will need to improve the thermal performance of transport incubators via the inclusion of the outside air temperature (T\({}_{\text{out}}\)); the cool incubator wall enhances radiant heat loss when the neonate is transported in a cold environment. Although the influence of radiant heat loss can be an estimation using [PERSON]'s equation for the mean radiant temperature T\({}_{\text{r}}\) (based on the incubator's T\({}_{\text{a}}\) and T\({}_{\text{out}}\)), this approach has yet to be validated in a premature neonate [23].