Low Ambient Temperature Exposition Impairs the Accuracy of a Non-invasive Heat-Flux Thermometer.

Background: Indirect core body temperature (CBT) monitoring from skin sensors is gaining attention for in-field applications thanks to non-invasivity, portability, and easy probe positioning. Among skin sensors, heat-flux devices, such as the so-called Double Sensor (DS), have demonstrated reliability under various experimental and clinical conditions. Still, their accuracy at low ambient temperatures is unknown. In this randomized cross-over trial, we tested the effects of cold temperature exposition on DS performance in tracking CBT.

Methods: Twenty-one participants were exposed to a warm (23.2 ± 0.4°C) and cold (-18.7 ± 1.0°C) room condition for 10 min, following a randomized cross-over design. The accuracy of the DS to estimate CBT in both settings was assessed by quantitative comparison with esophageal (reference) and tympanic (comparator) thermometers, using Bland-Altman and correlation analyses (Pearson's correlation coefficient, , and Lin's concordance correlation coefficient, ).

Results: In the warm room setting, the DS showed a moderate agreement with the esophageal sensor [bias = 0.09 (-1.51; 1.69) °C,  = 0.40 ( = 0.069), CCC = 0.22 (-0.006; 0.43)] and tympanic sensor [bias = 2.74 (1.13; 4.35) °C,  = 0.54 ( < 0.05), CCC = 0.09 (0.008; 0.16)]. DS accuracy significantly deteriorated in the cold room setting, where DS temperature overestimated esophageal temperature [bias = 2.16 (-0.89; 5.22) °C,  = 0.02 (0.94), CCC = 0.002 (-0.05; 0.06)]. Previous exposition to the cold influenced temperature values measured by the DS in the warm room setting, where significant differences ( < 0.00001) in DS temperature were observed between randomization groups.

Conclusion: DS accuracy is influenced by environmental conditions and previous exposure to cold settings. These results suggest the present inadequacy of the DS device for in-field applications in low-temperature environments and advocate further technological advancements and proper sensor insulation to improve performance in these conditions.