Background and Objectives Epidural anesthesia decreases the core temperatures triggering vasoconstriction and shivering, presumably by increasing apparent (as opposed to actual) lower-body temperature. We therefore tested the hypothesis that epidural anesthesia also increases the overall perception of warmth.

Methods We studied 8 volunteers in a randomized, cross-over protocol separated by at least 48 hours. On one day, epidural anesthesia was induced to a T11 sensory level; the other day was a control without anesthesia. Core temperature and upper-body skin temperatures (33°C) were kept constant throughout. Lower-body skin temperature was set in a random order to 31°C, 32°C, 33°C, 34°C, 35°C, and 36°C and maintained by circulating water and forced air. At each temperature, the volunteers rated their thermal sensation with a visual analog scale (0 = cold, 100 = hot). Core temperature was 36.8 ± 0.1°C on the control day and 36.7 ± 0.1°C on the epidural day.

Results Scores for thermal sensation on the epidural day were near 47 mm at each lower-body skin temperature. On the control day, visual analog scores at a lower-body skin temperature of 31°C were 16 ± 10 mm and increased linearly to 61 ± 6 mm at 36°C. Control thermal sensation scores thus equaled those during epidural anesthesia when lower-body skin temperature was near 34°C.

Conclusions Thermal sensation with and without epidural anesthesia was comparable at a lower-body temperature near 34°C, which is a normal leg skin temperature. This suggests that autonomic and behavioral thermoregulatory consequences of epidural anesthesia differ — or that the current explanation for reduced vasoconstriction and shivering thresholds during epidural anesthesia is incorrect.