Non-Axillary Chest Skin Temperature Underestimates Core Temperature During Redistribution Hypothermia Following Spinal Anesthesia

Accurate temperature monitoring is essential for detecting perioperative hypothermia during spinal anesthesia, where rapid redistribution of body heat commonly occurs. Although zero-heat-flux (ZHF) thermometry has emerged as a noninvasive method for estimating core temperature, the reliability of chest skin temperature monitoring in this context remains unclear. In this prospective observational study, temperature measurements were obtained at 5-minute intervals using a forehead ZHF sensor, an infrared tympanic thermometer, and a non-axillary chest skin probe in patients undergoing orthopedic surgery under spinal anesthesia. Agreement between methods was evaluated using Bland-Altman analysis for repeated measurements, the proportion of paired measurements within ±0.5°C, and Lin's concordance correlation coefficient. Ninety-nine patients completed the study. ZHF and tympanic temperatures showed good agreement, with a mean difference of 0.04 ± 0.35°C, limits of agreement from -0.63°C to 0.72°C, and 89% of paired measurements within ±0.5°C. In contrast, chest skin temperature demonstrated poor agreement with both ZHF and tympanic measurements. The mean difference between ZHF and chest skin temperature was 0.99 ± 1.11°C, with wide limits of agreement (-1.18°C to 3.17°C), and no measurements met the predefined ±0.5°C threshold. Similar discrepancies were observed when chest skin temperature was compared directly with tympanic temperature. These findings indicate that non-axillary chest skin temperature does not reliably reflect core temperature during redistribution hypothermia under spinal anesthesia and should not be used as a surrogate. ZHF thermometry showed substantially better agreement with tympanic temperature and may provide a more reliable noninvasive alternative for perioperative temperature monitoring.