[Temperature measurement in the ear canal: comparison of an infrared thermometer with conventional temperature probes and evaluation of clinical factors on infrared measurement].

PURPOSE: We compared the readings of the GENIUS 3000A FirstTemp infrared thermometer with a conventional temperature probe (MON-A-THERM tympanic) placed in contact with the tympanic membrane. We also systematically evaluated user-dependent factors influencing the infrared readings.

METHODS: In 100 postoperative patients we investigated the repeatability of the infrared measurements and the agreement with tympanic thermocouple probes in the contralateral ear regarding the degree of auditory canal contamination. In 20 volunteers we evaluated the influence of three factors: interval between consecutive measurements, dwell time in the auditory canal before reading the temperature, and positioning of the grip. Finally, we compared the infrared readings in the same ear of 20 different users who were not familiar with this new method.

RESULTS: Comparison with the tympanic contact probes revealed a mean difference of -0.67 degree C (+/-0.65 degree C 2 SD). The infrared thermometer significantly underestimated the temperature of the thermocouple probes. Repeatability was +/-0.3 degree C. The presence of cerumen in the auditory canal had no influence on the infrared readings. Shortening of the interval between two consecutive readings (30 and 60 s.) led to increasing differences between the two measurements with the second reading decreasing. After positioning the infrared thermometer in the auditory canal 5 seconds before taking temperatures, the recorded temperatures were significantly lower compared to the immediate temperature recordings. Rotation of the device out of the telephone handle position led to an increasing lack of agreement between infrared thermometry and thermistor probes. In 20 inexperienced operators agreement with the thermocouple probe was -0.80 degree C (+/-0.60 degree C 2 SD) and repeatability was +/-0.6 degree C.

CONCLUSION: Although easy to use, infrared thermometry requires careful handling and experienced users. To get optimal recordings, the time between consecutive measurements should not be less than 90 seconds. Recordings should be taken immediately after positioning the device in the auditory canal. Best results are obtained when the grip of the device follows the ramus mandibulae like a telephone handle. The lower readings of the infrared thermometer compared to tympanic contact-probes indicate that the obtained readings represent the temperature of the auditory canal rather than of the tympanic membrane itself.