Energy balance in the newborn baby: use of a manikin to estimate radiant and convective heat loss.

Convective and radiant heat loss from a baby in an incubator were studied using a heated manikin. The mean radiant temperature of surrounding surfaces other than those vertically below the manikin was measured. The coefficients Af and hr were calculated as though this was the mean radiant temperature of the whole environment. The fraction (Af) of the body surface area which exchanged radiant energy with the surroundings increased from 0.48 for a foetal posture to 0.76 for a spreadeagle posture due to a decrease in radiant exchange between opposing body surfaces. The corresponding increase in the coefficient for heat exchange by radiation (hr) was from 3.1 to 4.9 Wm-2 K-1. The coefficient for convection (hc) increased from 4.0 to 5.4 WM-2 K-1 due to a decrease in effective body diameter as the limbs moved away from the trunk. These changes in Af, hr and hc show that posture is important in regulating heat loss from a baby. As the radiant temperature of the incubator canopy was between 2 and 4K below incubator air temperature, a baby loses more heat by radiation than by convection.