Infrarot-Temperaturmessung im Gehörgang mit dem DIATEK 9000 Instatemp und dem DIATEK 9000 Thermoguide Einflußgrößen und Vergleich mit anderen Methoden der Temperaturmessung des Körperkerns

Zusammenfassung

Zwei Infrarot-Gehörgangsthermometer – DIATEK 9000 Instatemp und DIATEK 9000 Thermoguide – wurden unter zwei Hauptgesichtspunkten untersucht: „Wie groß sind die Unterschiede zu anderen Messungen der Körperkerntemperatur?“ bzw. „Welche Variablen beeinflussen das Meßergebnis?“. Bei der Untersuchung der Einflußvariablen zeigte sich, daß zum Erzielen optimaler Meßergebnisse eine Mindestpause von 2 min zwischen zwei Messungen am selben Ohr einzuhalten ist und unnötig lange Verweilzeiten der Geräte im Ohr zu vermeiden sind. Die mit den Infrarotgeräten im CAL-Modus gemessenen Temperaturen lagen mit ca. 0,4 °C signifikant niedriger als die Kontaktmessungen am Trommelfell. Die Unterschiede zur Rektal- bzw. Ösophagealtemperatur betrugen im Mittel −0,19 °C (Rektalmodus) bzw. −0,13 °C (Coremodus). Die Ergebnisse zeigen, daß mit den Geräten nicht die reine Trommelfelltemperatur, sondern vielmehr auch die Temperatur des angrenzenden Gehörgangs miterfaßt wird. Zur Kompensation der systematischen Unterschätzung der Kerntemperatur werden die gemessenen Werte geräteintern in Körperkerntemperaturäquivalente umgerechnet, was zu einer deutlichen Verringerung der systematischen Abweichungen zwischen den Methoden führt.

Abstract

Temperature of the tympanic membrane is recommended as a “gold standard” of core-temperature recording. However, use of temperature probes in the auditory canal may lead to damage of tympanic membrane. Temperature measurement in the auditory canal with infrared thermometry does not pose this risk. Furthermore it is easy to perform and not very time-consuming. For this reason infrared thermometry of the auditory canal is becoming increasingly popular in clinical practice. We evaluated two infrared thermometers – the Diatek 9000 Thermoguide and the Diatek 9000 Instatemp – regarding factors influencing agreement with conventional tympanic temperature measurement and other core-temperature recording sites. In addition, we systematically evaluated user dependent factors that influence the agreement with the tympanic temperature.

Materials and Methods. In 20 volunteers we evaluated the influence of three factors: duration of the devices in the auditory canal before taking temperature (0 or 5 s), interval between two following recordings (30, 60, 90, 120, 180 s) and positioning of the grip relative to the auditory-canal axis (0, 60, 180 and 270°). Agreement with tympanic contact probes (Mon-a-therm tympanic) in the contralateral ear was investigated in 100 postoperative patients. Comparative readings with rectal (YSI series 400) and esophageal (Mon-a-therm esophageal stethoscope with temperature sensor) probes were done in 100 patients in the ICU. The method of Bland and Altman was taken for comparison.

Results. Shortening of the interval between two consecutive readings led to increasing differences between the two measurements with the second reading decreasing. A similar effect was seen when positioning the infrared thermometers in the auditory canal before taking temperatures: after 5 s the recorded temperatures were significantly lower than temperature recordings taken immediately. Rotation of the devices out of the telephone handle position led to increasing lack of agreement between infrared thermometry and contact probes. Mean differences between infrared thermometry (Instatemp and Thermoguide, CAL-Mode) and tympanic probes were −0.41±0.67 °C (2 SD) and −0.43 ±0.70 °C, respectively. Mean differences between the Thermoquide (Rectal-Mode) and rectal probe were −0.19±0.72 °C, and between the Thermoguide (Core Mode) and esophageal probe −0.13±0.74 °C.

Discussion. Although easy to use, infrared thermometry requires careful handling. To obtain optimal recordings, the time between two consecutive readings should not be less than two min. Recordings should be taken immediately after positioning the devices in the auditory canal. Best results are obtained in the 60° position with the grip of the devices following the ramus mandibulae (telephone handle position). The lower readings of infrared thermometry compared with tympanic contact probes indicate that the readings obtained represent the temperature of the auditory canal rather than of the tympanic membrane itself. To compensate for underestimation of core temperature by infrared thermometry, the results obtained are corrected and transferred into core-equivalent temperatures. This data correction reduces mean differences between infrared recordings and traditional core-temperature monitoring, but leaves limits of agreement between the two methods uninfluenced.