Axillary Temperature, as Recorded by the iThermonitor WT701, Well Represents Core Temperature in Adults Having Noncardiac Surgery

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 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 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 and Altman methods. We apriori 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 ±05°C.

RESULTS: There were 3,339 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% CI: 88%, 93%).

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