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Background |
Epitympanic temperature (Tty) measured with thermistor probes correlates with core body temperature (Tcore), but the reliability of measurements at low ambient temperature is unknown. The aim of this study was to determine if commercially-available thermistor-based Tty reflects Tcore in low ambient temperature and if T... |
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. Tty was measured using an epitympanic probe (M1024233, GE Healthcare Finland Oy) and oesophageal temperature (Tes) with an oesophageal probe (M1024229,... |
Results |
During exposure to room temperature, mean Tty 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 Tty decreased from 32.4 ± 1.6 to 28.5 ± 2.0 °C without insulation and from 35.6 ± 0.6 to 35.2 ± 0.... |
Conclusions |
Epitympanic temperature measurements are influenced by ambient temperature and deviate from Tes at room and low ambient temperature. Insulating the ear with ear protectors markedly reduced the difference between Tty and Tes and improved the stability of measurements. The use of models to correct Tty may be possible, bu... |
Background |
Accurate measurement of core body temperature (Tcore) can be fundamental for guiding treatment and triage decisions in emergency care of patients. Although invasive techniques remain the gold standard for Tcore measurement (pulmonary artery or lower third of the oesophagus) these sites are not practical in emergency si... |
Temperature at the tympanic membrane was originally proposed as a less invasive alternative for estimation of Tcore [2, 3]. Previous investigations have shown that with precise placement in the lower anterior quadrant of the tympanic membrane, tympanic temperature is highly correlated with intracranial temperature and ... |
Methods |
Design, setting and participants |
Volunteers were recruited from the local mountain rescue organization. Written informed consent was obtained from all participants prior to participation in the study. The study was approved by the Ethics Committee of the Regional Hospital of Bolzano, Italy. Participants were in good cardiopulmonary health; a clinical ... |
We used a randomized cross-over design. Participants were randomly assigned to group A or B; group A was exposed to low temperature first followed by room temperature (n = 15); group B was exposed to room temperature first followed by low temperature (n = 16). A climate chamber with controlled temperature settings was ... |
Monitoring |
An oesophageal probe (9F general purpose sterile probe M1024229, GE Healthcare Finland Oy) was inserted via the naris into the lower third of the oesophagus [15] after anesthesia of the nasal and pharyngeal mucosa with topical 2 % lidocaine solution. An epitympanic probe (M1024233, GE Healthcare Finland Oy) was inserte... |
Protocol |
Probes were placed after at least 30 min of rest. After placement of the probes in the medical examination office, participants were guided to the first test setting. Measurements were recorded every 5 s for a total duration of 10 min for each location (participants were in a seated position for the testing duration). ... |
Data analysis |
Descriptive data are reported as mean ± standard deviation unless otherwise indicated. The Wilcoxon signed-rank test was used to compare (i) Tes and Tty in the same person at a specified duration of exposure and (ii) Tes or Tty in the same person between the first and last measurement. The Wilcoxon-Mann–Whitney test wa... |
Results |
There were 31 participants (two females) with mean age 38 ± 12 years (range 22–61 years). The ambient air temperature in the room temperature setting was 23.2 ± 0.4 °C and in the low temperature setting was −18.7 ± 1.0 °C. In one participant the oesophageal probe was displaced after 5 min at room temperature and the la... |
Measurements at room temperature |
Temperature measurements during testing at room temperature are shown in Fig. 1a. Mean Tes was 36.8 ± 0.4 °C at 0 min and 36.8 ± 0.3 °C at 9:35 min (n = 30, p = 0.124). Without insulation of the ear, mean Tty increased from 33.4 ± 1.5 °C at 0 min to 34.2 ± 0.8 °C at 9:35 min (n = 21, p = 0.004). With insulation of the ... |
Fig. 1 |
figure1 |
Epitympanic temperature (Tty) at room temperature (a; 23.2 ± 0.4 °C) and low temperature (b; −18.7 ± 1.0 °C) in relation to exposure time in minutes. Data are displayed for group A (solid lines; exposure to low followed by room temperature), group B (dotted lines; exposure to room followed by low temperature), with ins... |
Based on a Bland-Altman plot (Fig. 2), the mean difference between Tty without insulation of the ear and Tes was 2.9 °C and the correlation was weak (CCC = 0.03, 95 % confidence interval [CI] 0.00–0.06, n = 21). The mean difference was less with insulation of the ear (1.5 °C) and the correlation was not significant (CC... |
Fig. 2 |
figure2 |
Bland-Altman plots of individual data for mean Tes and Tty at room temperature (a, without insulation of the ear; b, with insulation) and low temperature (c, without insulation of the ear; d, with insulation). The solid line is the mean of differences and the dashed lines are the limits of agreement (mean ± 1.96 standa... |
In the room temperature setting, Tty without insulation of the ear was lower at 0 min in group A (32.0 ± 0.9 °C; n = 10) compared to B (34.6 ± 0.7 °C; n = 11, p <0.001), but was not different with insulation of the ear (p = 0.476). |
Measurements at low temperature |
Temperature measurements during testing at low temperature are shown in Fig. 1b. Mean Tes was 36.7 ± 0.4 °C at 0 min and 36.8 ± 0.4 °C at 9:15 min (n = 31, p = 0.001). Without insulation of the ear, mean Tty decreased from 32.4 ± 1.6 °C at 0 min to 28.5 ± 2.0 °C at 9:15 min (n = 21, p <0.001). With insulation of the ea... |
Based on a Bland-Altman plot (Fig. 2), the mean difference between Tty without insulation of the ear and Tes was 7.2 °C and the correlation was not significant (CCC = 0, 95 % CI −0.01–0.01, n = 21). The mean difference was less with insulation of the ear (1.3 °C), which was similar to the mean difference at room temper... |
In the low temperature setting, Tty without insulation of the ear was lower at 0 min in group A (31.5 ± 1.4 °C; n = 10) compared to B (33.3 ± 1.3 °C; n = 11, p = 0.008), but was not different with insulation of the ear (p = 0.352). |
Individual variability in temperature |
To understand the influence of inter-individual variability, the difference between Tty and Tes at 3 min at room temperature was correlated to the difference between Tty and Tes at 3 min at low temperature for each individual. We chose 3 min to reduce the variability seen in some measurements in the first minutes after... |
Model for predicting core temperature |
Tty was corrected (Tty_c) using a linear regression model to predict Tes from Tty at 3 min . The model at room temperature was T ty_c = 32.32 + 0.134 * T ty without insulation of the ear and T ty_c = 26.394 + 0.295 * T ty with insulation. The model at low temperature was T ty_c = 37.025 - 0.008 * T ty without insulatio... |
Fig. 3 |
figure3 |
Bland-Altman plots of individual data for Tes and Tty_c at room temperature (a, without insulation of the ear; b, with insulation) and low temperature (c, without insulation of the ear; d, with insulation). The solid line is the mean of differences and the dashed lines are the limits of agreement (mean ± 1.96 standard ... |
Discussion |
We report the influence of low ambient temperature and individual factors on temperature measured epitympanically using a thermistor-based probe. We found a deviation from the reference Tcore that was markedly reduced with insulation of the ear from ambient air using an ear protector. We also propose a model to correct... |
Influence of ambient temperature |
Epitympanic measurements were influenced by ambient temperature. During exposure to room temperature, mean Tty increased by 0.8 °C, whereas it decreased by 3.9 °C during exposure to low temperature. Similarly, mean deviation from Tes was >50 % higher in the low temperature setting compared to the room temperature setti... |
Inter-individual variability |
We found that the degree of deviation of Tty from Tes in both ambient air settings was different between individuals, i.e. individuals with a large deviation in one setting also had a large deviation in the other setting. This is partially due to differences in placement of the probe. Temperature in the ear canal seems... |
Practical implications |
Measuring Tcore is the only way to accurately assess the severity of hypothermia. There are other commonly used scales to stage hypothermia based on clinical signs and symptoms, but these are not always reliable since there are differences in consciousness among patients at a given Tcore [19]. Patients with mild hypoth... |
The models to correct Tty seem to give a valid estimation of Tes for measurements at room temperature without insulation of the ear and at low temperature with insulation. It was unexpected that the correlation between Tty_c and Tes at room temperature with insulation was low and non-significant, though this is probabl... |
Limitations and further research |
The results are based on measurements in healthy, normothermic volunteers at rest in the two reported ambient temperatures and may not be applicable for other populations (e.g. patients in cardiac arrest, trauma) or ambient conditions. The models to correct Tty should be validated with a larger sample size. The lack of... |
Conclusion |
Epitympanic temperature measurements are influenced by ambient temperature and deviate from Tes at room temperature and low ambient temperature. Insulating the ear with standard industrial ear protectors markedly reduced the difference between Tty and Tes and improved the stability of measurements over the testing dura... |
Ethics, consent and permissions |
The study was approved by the Ethics Committee of the Regional Hospital of Bolzano, Italy. Written informed consent was obtained from all participants prior to participation in the study. |
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