Effects of epidural anesthesia on thermal sensation

Background and objectives: Epidural anesthesia decreases the core temperatu res triggering vaso constriction and shivering, presumably by increasing ap parent (as opposed to actual) lower-body temperature. We therefore tested t he hypothesis that epidural anesthesia also increases the overall perceptio n of warmth. Methods: We studied 8 volunteers in a randomized, cross-over protocol separ ated 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 te mperature and upper-body skin temperatures (33 degreesC) were kept constant throughout. Lower-body skin temperature was set in a random order to 31 de greesC, 32 degreesC, 33 degreesC, 34 degreesC, 35 degreesC, and 36 degreesC and maintained by circulating water and forced air. At each temperature, t he volunteers rated their thermal sensation with a visual analog scale (0 = cold, 100 = hot). Core temperature was 36.8 +/- 0.1 degreesC on the contro l day and 36.7 +/- 0.1 degreesC on the epidural day. Results: Scores for thermal sensation on the epidural day were near 47 min at each lower-body skin temperature. On the control day, visual analog scor es at a lower-body skin temperature of 31 degreesC were 16 +/- 10 mm. and i ncreased linearly to 61 +/- 6 nun at 36 degreesC. Control thermal sensation scores thus equaled those during epidural anesthesia when lower-body skin temperature was near 34 degreesC. Conclusions: Thermal sensation with and without epidural anesthesia was com parable at a lower-body temperature near 34 degreesC, which is a normal leg skin temperature. This suggests that autonomic and behavioral thermoregula tory consequences of epidural anesthesia differ - or that the current expla nation for reduced vasoconstriction and shivering thresholds during epidura l anesthesia is incorrect.