Body temperature measurement in paediatrics: Which gadget should we believe?

Abstract

Many decisions regarding the investigation and treatment of paediatric patients are determined by body temperature. In the 21st century, we still struggle to find a quick and convenient method that parents and health care workers can use to measure body temperature accurately.The goal of measuring body temperature is to approximate the core temperature, which is the temperature of the blood that bathes the temperature-regulating centre in the hypothalamus. However, there is a gradient between every body site where temperature can be measured and the hypothalamus. Contrary to popular dogma, this gradient is not constant (ie, rectal temperature is not reliably 1°C higher than axillary temperature). Therefore, it is difficult to choose a body site to use as the reference standard for comparing readings obtained by different instruments or at different sites.The following sites have been used in studies of body temperature measurement in children:• Pulmonary artery (PA): This site is vascular, and it is anatomically relatively close to the hypothalamus. In adults, PA readings are only 0.18°C lower than readings from blood returning from the brain in the high internal jugular vein (1). PA catheters are usually only placed in children during cardiac surgery, but this remains the best site to use as the reference standard for core temperature in studies comparing measurements taken from other body sites and with different instruments.• Distal esophagus: This site is easily accessible in sedated patients, and readings in paediatric patients are closer to PA readings than are rectal, axillary, bladder or tympanic readings (2). Therefore, this site is a good choice for temperature measurement in sedated patients or for use as a reference standard when PA readings are not practical.• Rectal: Although used as the reference standard in many previous studies, the rectum is a long distance from the hypothalamus. Decreased splanchnic flow can result in falsely low readings and rectal temperature is slow to respond to changes in core temperature, especially if stool is present in the lower rectum (2,3). There is often reluctance on the part of parents and older children to measure rectal temperature, and nosocomial infections have been attributed to the use of rectal thermometers in hospital (4). There are rare case reports of rectal perforation caused by rectal thermometers in neonates and the safety of doing rectal temperatures in neutropenic patients has not been established.• Bladder: Urinary catheters with thermistors are available, but the results of studies are disparate as to whether bladder temperatures are closer to PA readings than rectal temperatures (2,5). Readings may be falsely low if urine output is decreased.• Nasopharyngeal: In the only paediatric study (5) to date that compared nasopharyngeal temperature with other sites, mean difference from PA temperature was 0.43°C, which was higher than the difference for bladder temperatures, but lower than the difference for rectal, tympanic or axillary temperatures. Ind...

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