Deep-forehead temperature correlates well with blood temperature

Purpose: To evaluate the accuracy and precision of "deep-forehead" temperature with rectal, esophageal, and tympanic membrane temperatures, compared with blood temperature. Methods: We studied 41 ASA physical status 1 or 2 patients undergoing abdominal and thoracic surgery scheduled to require at least three hours. "Deep-forehead" temperature was measured using a Coretemp(R) ther mometer Terumo, Tokyo, Japan). Blood temperature was measured with a thermistor of a pulmonary artery. Rectal, tympanic membrane, and distal esophageal temperatures were measured with thermocouples. All temperatures were recorded at 20 min intervals after the induction of anesthesia. We considered blood temperature as the reference value. Temperatures at the other four sites were compared with blood temperature using correlation, regression, and Bland and Altman analyses, We determined accuracy (mean difference between reference and test temperatures) and precision (standard deviation of the difference) of 0.5 degrees C to be clinically acceptable. Results: "Deep-forehead" temperature correlated well with blood temperature as well as other temperatures, the determination coefficients (r(2)) being 0.85 in each case. The bias for the "deep-forehead" temperature was 0.0 degrees C, which was the same as tympanic membrane temperature and was smaller than rectal and esophageal temperatures. The standard deviation of the differences for the "deep-forehead" temperature was 0.3 degrees C, which was the same as rectal temperature. Conclusions: We have demonstrated that the "deep-forehead" temperature has excellent accuracy and clinically sufficient precision as well as other three core temperatures, compared with blood temperature.