In this prospective study, eight research dogs were used to compare temperature assessments made with a predictive rectal thermometer (the early rate of temperature change mathematically predicts the final temperature), an infrared auricular thermometer, and a subcutaneous temperature-sensing microchip. Core body temperature measured by a thermistor-tipped pulmonary artery catheter was used as a baseline or standard. For each dog, temperature was measured during four study periods over three days. Hypothermia was induced by anesthesia, and hyperthermia was induced by a low dose of endotoxin. When possible, the accuracy of the thermometer devices was evaluated by in vitro testing. Near-simultaneous duplicate measurements were recorded from the four devices during hypothermia, euthermia, and hyperthermia.
The results revealed that rectal temperature readings were closest in agreement with core body temperature measurements; the other devices generally underestimated the core body temperature. Variability between successive readings of the same device was greatest for the auricular thermometer and least for the intravascular catheter. Problems encountered with the auricular thermometer included positioning, delay in reading, and patient discomfort. The authors concluded that rectal thermometry was reliable and provided the most accurate assessment of core body temperature.
Traditionally, practitioners have relied on rectal thermometers to determine core body temperature. Advances in medical technology have led to the marketing of infrared auricular thermometers in the United States and of canine subcutaneous microchip temperature sensors in Europe and Asia. Theoretically, the speed of measurement by these two devices could overshadow their increased cost and their application requirements, especially when compared with rectal thermometry in fractious or diseased patients. However, the results of this study in inactive dogs supports the premise that predictive rectal thermometers are more useful than these technically advanced devices. It would be interesting to note if these data are supported by future studies involving more patients in a clinical setting.
Greer RJ, Cohn LA, Dodam JR, et al. Comparison of three methods of temperature measurement in hypothermic, euthermic, and hyperthermic dogs. J Am Vet Med Assoc 2007;230(12):1841-1848.