Agreement between zero-heat-flux and tympanic thermometry in preschool children undergoing tonsillectomy: a prospective observational study

Abstract Background Continuous core temperature monitoring helps prevent perioperative complications in preschool children, but available noninvasive methods have important limitations. Zero-heat-flux (ZHF) thermometry is an alternative; however, evidence remains limited in preschool children during the developmental period of frontal sinus pneumatization. This study evaluated the clinical agreement of ZHF thermometry (TSpotOn) against tympanic temperature (Ttymp) in this developmental cohort. Methods We conducted a prospective observational study of 154 preschoolers undergoing tonsillectomy. Intraoperative temperatures were recorded at 5-min intervals using ZHF, tympanic, and axillary (Taxilla) methods, for 1468 paired measurements in total. Agreement was assessed using repeated-measures Bland–Altman analysis, and within-participant association was evaluated using repeated-measures correlation. A ±0.5 °C difference was prespecified as an agreement criterion. Results TSpotOn agreed closely with Ttymp, the repeated-measures correlation was strong ( r = 0.753, 95% CI 0.729–0.776; P < 0.001), and the mean bias was 0.06 °C. The 95% limits of agreement (− 0.35 °C to 0.47 °C) fell within the predefined ±0.5 °C agreement criterion. Taxilla, in contrast, showed a systematic underestimation (mean bias: −0.50 °C) with wider limits of agreement (− 1.09 °C to 0.09 °C) that exceeded this threshold. Conclusions ZHF thermometry showed close agreement with tympanic thermometry while providing continuous, noninvasive temperature monitoring in preschool children within the expected developmental period of frontal sinus pneumatization. Given its closer agreement with tympanic thermometry than axillary monitoring, ZHF thermometry may be a practical option for continuous perioperative temperature monitoring in preschool children.