The impact of environmental factors in pre-hospital thermistor-based tympanic temperature measurement: a pilot field study

BACKGROUND: Few pre-hospital services have the possibility to accurately measure core temperature (T(core)). Non-invasive estimation of T(core) will improve pre-hospital decision-making regarding the triage and management of hypothermic patients. Thermistor-based tympanic temperature (T(tymp)) correlates well with T(core) in controlled studies; however, little is known about the feasibility of using T(tymp) under field conditions. This study assessed the impact of pre-hospital environmental factors on the accuracy of T(tymp). Deep rectal temperature (T(rect)) was used as a substitute for T(core). METHODS: Normothermic volunteers (n = 13) were exposed to four simulated field conditions producing local cooling of the head and ear canal. After exposure, T(tymp) was recorded every 15 s for 10 min and compared with T(rect). Descriptive analysis and Bland-Altman plots were used to assess agreement. RESULTS: Immediately after exposure mean T(tymp) was low, but increased rapidly and reached an apparent steady state after 3–5 min. After 5 and 10 min, the mean temperature difference (∆T(rect-tymp)) ranged from 1.5–3.2 °C (SD = 0.5) and 1.2–2.0 °C, respectively. T(rect) remained unchanged throughout the study period. CONCLUSIONS: After surface cooling of head and neck, T(tymp) did not accurately reflect core temperature within the first 10 min of measurement. The variation of ∆T(rect-tymp) was low after 10 min, regardless of the initial degree of cooling. With the risk of over-triage, T(tymp) may at this point provide an indication of T(core) and also exhibit a trend. TRIAL REGISTRATION: ClinicalTrials.gov: NCT02274597 ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s13049-015-0148-5) contains supplementary material, which is available to authorized users.