Effects of anatomic site, oral stimulation, and body position on estimates of body temperature

Background: A prior investigation characterized the range of body temperature in healthy young adults and established the importance of diurnal variations in defining the febrile state. Methods: Sequential rectal, oral, and tympanic membrane temperature measurements were performed on 22 healthy subjects to determine the quantitative effects of anatomic site, oral stimulation, and body position on estimates of body temperature. Results: Mean rectal temperatures exceeded concurrent oral readings by 0.4 degrees C +/- 0.4 degrees C (0.8 degrees F +/- 0.7 degrees F), which, in turn, exceeded concurrent tympanic membrane readings (obtained with a digital thermometer [IVAC Corp, San Diego, Calif]) by 0.4 degrees C +/- 1.1 degrees C (0.7 degrees F +/- 2.0 degrees F). Tympanic membrane readings were significantly more variable (both intrasubject and intersubject) than rectal or oral readings, especially when cerumen was present in the external ear canal being examined (P<.05). Mastication and smoking both caused significant increases in oral temperature that persisted for greater than 20 minutes. Drinking ice water caused a significant but more transient decrease in oral temperature. Of these activities, only mastication appeared to influence tympanic membrane readings. Body position exerted a modest effect on rectal temperature readings, but did not significantly affect oral or tympanic membrane readings. Conclusions: These findings indicate that, in addition to diurnal fluctuations in body temperature, the effects of anatomic site, oral stimulation, and body position should be considered in establishing criteria for the febrile state.