For example, the ear canal’s structure, probe design and probe positioning affect how well the canal is sealed from ambient influences and what parts of the tympanic membrane, ear canal wall, and perhaps skin surface, are in the thermometers field of view ( 32). Most researchers advise eliminating these adjusted modes and simply using unadjusted ear temperature ( Table 1) ( 16, 18, 21).įactors related to the patient, instrument, technique and environment contribute to the variability of ear-based temperature measurements. However, the data used to develop these offsets may not be readily applicable to the paediatric population. The offsets are based on an algorithm that transforms a subject’s tympanic temperature to that found at either the oral or rectal site. These conversion scales (known as ‘offsets’) convert the measured ear temperature to one that would be found at a different site, allowing a user to define more easily a fever from a measurement in the ear. Because estimates of core temperature measured at different body sites will vary, an effort has been made by manufacturers of IREDs to correlate tympanic readings to rectal or oral equivalents ( 16). Given the variations of temperature ranges with each of these methods and the limitations of their accuracy discussed above using any one method as a ‘benchmark’ or ‘gold standard’ is misleading. Most studies that compare the accuracy of tympanic thermometers with other classical measures of body temperature evaluate the reliability of tympanic readings by comparing them with rectal, oral or axillary measurements. Terms of reference used to evaluate tympanic thermometry Both methods have demonstrated comparable accuracy. A pyeloelectric sensor, which is a heat flow detector that measures the speed at which the thermal energy flows through a sensor, takes a ‘snapshot’ of the heat that it records from the TM, just like photographic film. A thermopile sensor detects the level of heat in the area directly proximal to the TM by taking multiple readings very quickly. Crying, otitis media or earwax have not been shown to change tympanic readings significantly.Īn IRED can measure the infrared radiation of the TM in two ways. It is, therefore, an ideal location for core temperature estimation ( 25, 26). In contrast with other sites of temperature measurement, the TM’s blood supply is very similar in temperature and location to the blood bathing the hypothalamus, the site of the body’s thermoregulatory centre. Because the amount of thermal radiation emitted is in proportion to the membrane’s temperature, IRED accurately estimates TM temperature ( 16). Instead of being in direct contact with the TM, today’s tympanic thermometers measure the thermal radiation emitted from the TM and the ear canal, and have therefore been called infrared radiation emission detectors (IRED). However, thermistors in direct contact with the TM are not practical for everyday use. In 1969, it was shown that such a device measured core temperature better than a rectal thermometer ( 24). The first devices used to measure tympanic membrane (TM) temperature did so by being in direct contact with the tympanic membrane. It is, therefore, essential that the measurement of a fever be accurate, reliable and reproducible from infancy through adolescence. Finally, an appropriate recording of the absence of a fever reassures both parents and health care providers who seek to diminish fever phobia, and inappropriate medical consultations and investigations ( 12). The definition of a fever of unknown origin also relies on stringent diagnostic criteria (ie, a fever lasting more than 14 days with no etiology found after routine tests), and depends on precise temperature recordings ( 9– 11). However, the presence of a normal or subnormal temperature in children younger than three months of age can also be associated with severe infections in the presence of other appropriate signs and symptoms. The presence of a fever in children younger than three months of age triggers a thorough investigation into the source of the infection ( 7, 8). In febrile children younger than 36 months of age, most serious illnesses are caused by infectious agents ( 3– 6). Despite the fact that temperature measurement in children seems so simple – a wide variety of devices are available to record a fever from skin, oral or rectal mucosa or the tympanic membrane – the choice for health professionals and parents has never been so complicated.Īccording to traditional teaching, the normal body temperature is 37☌ (98.6☏), but it is generally accepted that a temperature of 38☌ (100☏) or greater, as measured by a rectal thermometer, represents a fever ( 1, 2).
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