BACKGROUND:

Core temperature can be accurately measured from the esophagus or nasopharynx during general anesthesia, but neither site is suitable for neuraxial anesthesia. We therefore determined the precision and accuracy of a novel wireless axillary thermometer, the iThermonitor, to determine its suitability for use during neuraxial anesthesia and in other patients who are not intubated.

METHODS:

We enrolled 80 adults having upper abdominal surgery with endotracheal intubation. Intraoperative core temperature was measured in distal esophagus and was estimated at the axilla with a wireless iThermonitor WT701 (Raiing Medical, Boston MA) at 5-minute intervals. Pairs of axillary and reference distal esophageal temperatures were compared and summarized using linear regression and repeated-measured Bland–Altman methods. We a priori determined that the iThermonitor would have clinically acceptable accuracy if most estimates were within±0.5 C of the esophageal reference, and suitable precision if the limits of agreement were within±0.5 C.

RESULTS:

There were 3339 sets of paired temperatures. Axillary and esophageal temperatures were similar, with a mean difference (esophageal minus axillary) of only 0.14 C±0.26 C (standard deviation). The Bland–Altman 95% limits of agreement were reasonably narrow, with the estimated upper limit at 0.66 C and the lower limit at− 0.38 C, thus±0.52 C, indicating good agreement across the range of mean temperatures from 34.9 C to 38.1 C. The absolute difference was within 0.5 C in 91% of the measurements (95% confidence interval, 88%–93%).

CONCLUSIONS:

Axillary temperature, as recorded by the iThermonitor WT701, well represents core temperature in adults having noncardiac surgery and thus appears suitable for clinical use.