Influence of low ambient temperature on epitympanic temperature measurement: a prospective randomized clinical study

BACKGROUND: Epitympanic temperature (T(ty)) measured with thermistor probes correlates with core body temperature (T(core)), but the reliability of measurements at low ambient temperature is unknown. The aim of this study was to determine if commercially-available thermistor-based T(ty) reflects T(core) in low ambient temperature and if T(ty) is influenced by insulation of the ear. METHODS: Thirty-one participants (two females) were exposed to room (23.2 ± 0.4 °C) and low (−18.7 ± 1.0 °C) ambient temperature for 10 min using a randomized cross-over design. T(ty) was measured using an epitympanic probe (M1024233, GE Healthcare Finland Oy) and oesophageal temperature (T(es)) with an oesophageal probe (M1024229, GE Healthcare Finland Oy) inserted into the lower third of the oesophagus. Ten participants wore ear protectors (Arton 2200, Emil Lux GmbH & Co. KG, Wermelskirchen, Switzerland) to insulate the ear from ambient air. RESULTS: During exposure to room temperature, mean T(ty) increased from 33.4 ± 1.5 to 34.2 ± 0.8 °C without insulation of the ear and from 35.0 ± 0.8 to 35.5 ± 0.7 °C with insulation. During exposure to low ambient temperature, mean T(ty) decreased from 32.4 ± 1.6 to 28.5 ± 2.0 °C without insulation and from 35.6 ± 0.6 to 35.2 ± 0.9 °C with insulation. The difference between T(ty) and T(es) at low ambient temperature was reduced by 82 % (from 7.2 to 1.3 °C) with insulation of the ear. CONCLUSIONS: Epitympanic temperature measurements are influenced by ambient temperature and deviate from T(es) at room and low ambient temperature. Insulating the ear with ear protectors markedly reduced the difference between T(ty) and T(es) and improved the stability of measurements. The use of models to correct T(ty) may be possible, but results should be validated in larger studies.