Perioperative measurement of core body temperature using an unobtrusive passive heat flow sensor

Clinicians strive to maintain normothermia, which requires measurement of core-body temperature and may necessitate active warming of patients. Monitoring temperature currently requires invasive probes. This work investigates a novel foam-based flexible sensor worn behind the ear for the measurement of core body temperature. This observational study uses the device prototype and clinical data to compare three methods for calculating the temperature from this sensor: a basic heat-flow model, a new dynamic model that addresses changing surrounding temperatures and one that combines the dynamic model with a correction for adhesive quality. Clinical validation was performed with 21 surgical patients (average length of surgery 4.4 h) using an esophageal temperature probe as reference. The operative period was divided into four segments: normal periods (with stable surrounding temperatures), surrounding temperatures increasing due to the use of the Bair Hugger™, stable periods during Bair Hugger™ use and surrounding temperatures decreasing due to its removal. The error bias and limits of agreement over these segments were on average of − 0.05 ± 0.28 °C (95% limits of agreement) overall. The dynamic model outperformed the simple heat-flow model for periods of surrounding temperature changes (12.7% of total time) while it had a similar, high, performance for the temperature-stable periods. The results suggest that our proposed topical sensor can replace invasive core temp sensors and provide a means of consistently measuring core body temperature despite surrounding temperature shifts.