The WHO defines the normal temperature of a neonate at 36.5– 37.5°C, and gradations of hypothermia including mild (36-36.5°C), moderate (32-36°C) and severe (<32°C). Even at warm ambient temperatures, neonates can have difficulty retaining heat, especially as amniotic fluid evaporates off their skin. While hypothermia kills more infants, the effects of prolonged hyperthermia can also be devastating.
Thermometers are also helpful to diagnose maternal infection. A fever of greater than 100 degrees Farenheight is often indicative of an infection. Furthermore, fevers over 103 degrees can cause mental symptoms and become dangerous.
Mechanism of Action
Mercury and alcohol thermometers rely on the thermal expansion of liquid up a calibrated column. Digital thermometers typically rely on either a thermocouple or thermister for contact measurement. Axillary measurement is typically preferred for safety, hygiene, and ease. Tympanic thermometers detect infrared radiation from middle ear tissues and can give accurate readings in 1-2 seconds, but may be inconvenient in the immediate neonatal period if the tympanic membrane is inaccessible. Liquid crystal thermometers are usually plastic films which change color on the basis of temperature.
Current Use in High-Resource Settings
Digital and tympanic measurement tools are most common for spot checking neonatal temperature. Thermocouples or thermisters may be taped to the infant’s skin for continuous monitoring in intensive care settings. Digital pacifier thermometers are sometimes used in outpatient settings and as consumer products. For adults, gradations must be shown to understand the severity of the fever. Increasingly, disposable or digital thermometers are being used.
Application in Low-Resource Settings
The most prevalent technique to assess temperature in low-resource settings is human touch, which is typically more sensitive to hyperthermia than hypothermia. Low cost mercury thermometers are also commonly used, but are often fragile and require some degree of training.
In infants, the WHO recommends axillary placement of such thermometers for 5 minutes or rectal placement for three minutes (whereas digital thermometers may take a reading in less time). The liquid crystal ThermoSpot has been tested in urban and rural settings in India with promising results, especially for multi-day monitoring in environments where caregivers may not be trained to use mercury thermometers.