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.