Aural thermometry during profound hypothermia

External auditory canal temperature changes during profound hypothermia were studied experimentally in ten dogs and clinically in 20 patients undergoing open-heart surgery. The results were compared with nasopharyngeal and lower oesophageal temperatures. Tympanic membrane temperature provided a better approximation to brain temperatures measured in four dogs to below 20 degrees C than did either of the other two methods. In patients, auditory canal temperature showed less variability with respect to oesophageal temperature and fell at a faster rate than did nasopharyngeal temperature. It did not appear to be subject to positional or other artefacts but four patients showed evidence of auditory canal trauma. The precise relationship between auditory canal or tympanic membrane temperature and brain temperature during profound hypothermia is not established. Routine otoscopic examination should accompany the use of an ear probe.