Temperatures measured by a deep body thermometer (Coretemp) compared with tissue temperatures measured at various depths using needles placed into the sole of the foot.

Continuous monitoring of body temperature during anaesthesia is a widely accepted clinical practice for which a variety of techniques are used. In this study, the accuracy of the deep body thermometer (Coretemp) was compared with temperatures measured by needle thermocouples. With IRB approval and informed consent, seven ASA physical status I and II patients undergoing otolaryngeal surgery were studied. General anaesthesia and neuromuscular blockade were induced with thiamylal and vecuronium. Anaesthesia was maintained with isoflurane at an end-tidal concentration of 1.0-2.0% and 66% nitrous oxide in oxygen. After induction of general anaesthesia, subcutaneous temperature was measured at the sole of the left foot using a Coretemp. Additionally 8-, 18-, and 38-mm-long needle thermocouples were inserted into the the sole of the left foot close to Coretemp and skin-surface temperature was also recorded adjacent to the needles. The Coretemp measurement (Tc) correlated best with 18-mm-deep needle temperature (r2 = 0.87). There was also a good correlation between Tc and 38-mm-deep needle temperature (r2 = 0.83). Skin and 8-mm-deep needle temperatures correlated poorly or only moderately with Tc (r2 = 0.67, 0.75, respectively). These results indicate that temperatures measured by Coretemp well reflect the temperatures at a depth of 18 mm or more from the skin into the foot.