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

Abstract

Heat losses from a baby in an incubator were studied. The mean radiant temperature of surrounding surfaces other than those vertically below the manikin was measured. The coefficients A_f and h_r were calculated as though this was the mean radiant temperature of the whole environment. The fraction (A_f) of the body surface area which exchanged radiant energy with the surroundings increased from 0.48 for a foetal posture of 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 (h_r) was from 3.1 to 4.9 W m^-2 K^-1. The coefficient for convection (h_c) increased from 4.0 to 5.4 W m^-2 K^-1 due to a decrease in effective body diameter as the limbs moved away from the trunk. These changes in A_f, h_r and h_c 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.