ABSTRACT: Deep body temperature is an important and accepted index of health status in newborn infants. There are no easily used accurate methods for continuous deep body temperature measurements. Oral and tympanic membrane temperatures correlate well with rectal temperature but are not easily adapted to continuous measurement. We devised a noninvasive transcutaneous temperature sensor for continuous deep body temperature measurement that relies on the principle that, under steady state conditions, the temperature at the thermally insulated surface of a warm body, i. e. a zero heat loss surface, will be in equilibrium with the warmest part of the body. We used a standard clinical temperature probe placed between the skin and the mattress and attached to the skin with a foam adhesive disk. We used standard skin temperature probe attachment disks, which are also designed to provide thermal insulation to the skin temperature probe. We tested the hypothesis that this transcutaneous temperature would track body temperature as indicated by rectal temperature. In six anesthetized (pentobarbital) newborn piglets (1600 ± 200 g) placed on their abdomen in a convectively warmed infant incubator, we measured continuously the following temperatures for 5 h: transcutaneous over lower and upper abdomen, brown fat, rectal, and descending aorta. To examine the influence of environment, we varied the incubator air temperature between 32° and 36°C. Both transcutaneous temperatures tracked the rectal temperature, within 0.2°C for transcutaneous over lower abdomen and within 0.3°C for transcutaneous over upper abdomen. Aortic artery temperature was always lower than rectal. We conclude that transcutaneous temperature has the potential to be used reliably as a noninvasive replacement for continuous rectal temperature monitoring.
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