Validation of the Zero-Heat-Flux thermometer (SpotOn®) in major gynecological surgery to monitor intraoperative core temperature: a comparative study with esophageal core temperature.

Background: The Zero-Heat-Flux technology of the SpotOn® sensor to measure core temperature has been validated in vascular and cardiac surgery. Our aim was to assess its validity in gynecological surgery in terms of time of measurement, thermic status (hypo-, normo-, or hyperthermia) and the use of different warming devices.

Methods: Prospective study in patients scheduled for major gynecological surgery using three warming systems (Snuggle Warm®, Lithotomy Underbody Blanket® and Warmtac Pad®). Intraoperative temperature was simultaneously monitored using the SpotOn® sensor and a Dräger® esophageal probe; measurements were taken after induction (T0), between 0 and 60 min (T1), between 60 and 120 minutes (T2) and after 120 minutes (T3). We calculated the level of correlation between pairs of measurements both overall and in subgroups with an acceptable difference of less than 0.5 °C. We built Bland-Altman plots, and calculated the Pearson correlation (PC) and intraclass correlation coefficient (ICC) to test our data.

Results: We recruited 70 patients and included 66 for analysis, giving a total of 401 paired measurements. Overall, the PC and ICC for paired temperature readings were 0.82 and 0.90, respectively. The lowest levels of correlation were observed after intubation, when a convective blanket was placed under the patient, and in hypothermic patients. The highest correlations were observed at T2, and in normothermic patients.

Conclusions: We found a high overall correlation between the SpotOn® and the esophageal probe, with negligible differences and almost perfect agreement. The warming system used, time of measurement, and thermic status appear to influence the level of correlation, but these differences were not clinically significant.