The blood supply of the tympanic membrane from the common carotid artery is shared with the hypothalamus. As the ear canal and tympanic membrane have no inherent metabolic activity, then the temperature of the tympanic membrane should be primarily determined by this blood supply. This means that the tympanic membrane temperature should in theory closely represent the hypothalamic temperature. As such, it is easy to understand why a number of studies find the tympanic thermometer can be a more accurate reflection of core temperature and a more accurate indicator of fever.
The tympanic thermometer uses infrared light to detect thermal radiation. Temperature is measured by inserting the probe into the auditory canal. The thermometer probe then scans and after a few seconds records the amount of infrared energy emitted by the tympanic membrane.
The tympanic or aural route has become popular in paediatrics and, provided correct technique has been used, it has a number of advantages over other methods of thermometry. Advantages include it being a more accurate reflection of core temperature, it is non-invasive, is quick and relatively easy to use and is comfortable for the child. Other advantages of tympanic or aural thermometry are that the procedure itself is more hygienic, less invasive and safer than other forms of thermometry.
Despite the increasing widespread use of tympanic or aural thermometry in paediatrics it is important that the nurse is aware that some studies have highlighted some limitations in its use. Some studies advise that tympanic thermometers should be used with extreme caution and only as an indication of temperature. For the tympanic thermometer to be more ‘accurate’, it must be placed in the ear canal correctly in order that it can ‘see’ the tympanic membrane. If the probe is not correctly placed this can result in the thermometer scanning the ear canal instead of the tympanic membrane and thus give a falsely low temperature reading. This can be more likely where there are multiple personnel taking temperatures.
Education of all staff using tympanic thermometers is essential to ensure reduction in user error and negative influence on temperature readings. Some studies have highlighted the fact that the ear canal in infants and children can be very different lengths, and as such the thermometer probes may be too large for smaller infants thus potentially influencing the accuracy of the temperature measurement.
Tympanic temperature readings may also be affected by the ambient temperature such as from incubators or may vary depending upon whether the ear used has been exposed to air or on a pillow or mattress.
There are conditions where tympanic thermometry may be contraindicated and these include the infant or child who has significant ear pathology, a foreign body in the ear or has moisture in the ear, such as cerebrospinal fluid or blood.
Remember that a tympanic thermometer must be cared for and stored correctly and some must be recalibrated every 12 months.
If the nurse finds any abnormal temperature measurements using the tympanic thermometer technique, then the nurse must recheck the temperature and also consider another method & site of thermometry. Any abnormality must be documented and reported to nurse-in-charge and doctor.