Incubation of very immature infants.

The range of thermal control and the thermoneutral range of preterm infants under 30 weeks' gestation was calculated by extrapolation of data from studies on more mature infants. Even assuming some thermoregulatory capacity, the range of control is less than 3 degrees C, the thermoneutral range is less than 0.5 degrees C, and both are greatly influenced by the rate of transepidermal water loss. Measurements of metabolic rate and effective thermal environment made on 6 infants under 30 weeks' gestation in the first week of life showed that the very preterm infant exerts little thermoregulatory control and that variations in transepidermal water loss are a major factor determining the appropriate thermal environment.

The heat balance of small babies nursed in incubators and under radiant warmers.

The heat balance of 12 healthy preterm babies (mean birth weight 1.58 kg, gestation 32 weeks, age 7 days) was studied first in an incubator and then under a radiant warmer during normal nursing. Heat production and heat loss by radiation, convection and evaporation were measured in presumed thermoneutral conditions. Although rectal and mean skin temperatures were normal and the same in both environments, there were important differences. Radiation was the major source of heat loss in the incubator and convective losses were low. Under the radiant warmer convection was the major source of heat loss and heat was gained by radiation. A small rise in metabolic heat production occurred under the radiant warmer. Respiratory water loss was low in both environments. Skin water loss was significantly higher under the radiant warmer. The most immature baby (gestation 28 weeks) could not be kept warm in the incubator despite high air temperature, because the evaporative heat loss from her skin was very high. Her body temperatures were normal under the radiant warmer. It is concluded that both devices provide acceptable thermal environments for most preterm babies but that incubators without humidification may be inadequate for immature babies with a high skin water loss.

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.