EPIDURAL-ANESTHESIA AND THE THERMOREGULATORY RESPONSES TO HYPERTHERMIA - PRELIMINARY-OBSERVATIONS IN VOLUNTEER SUBJECTS

Background: Clinical reports associate the use of epidural anesthesia with an increase in core temperature in women in labor. We tested the hypothesis that epidural anesthesia alters thermoregulatory responses to hyperthermia in human volunteers. Methods: Each of four volunteers were studied on two days: Control and Anesthesia. On the Control day, the subject was warmed via the skin, and the core (esophageal) tempera ture threshold for sweating (detected on the forehead) was determined. The subject was then cooled until sweating stopped. The subject was w armed again, and a second sweating threshold was determined. The diffe rence between the first and second sweating thresholds was noted. On t he Anesthesia day, two sequential sweating threshold measurements were obtained in a similar fashion; however, a mid-thoracic level of epidu ral anesthesia was established before the second sweating threshold me asurement. The first and second sweating threshold differences were co mpared between the two study days. The presence or absence of sweating on the thigh was noted during all four warming periods. Results: Aver age skin temperatures were similar (about 37 degrees C) during all fou r sweating threshold measurements. On the Control day, the second swea ting threshold value was always slightly less than the first (average difference (mean+/-SD): -0.18+/-0.14 degrees C). in contrast, on the A nesthesia day, the second sweating threshold value (determined with an epidural block) was always greater than the first (average difference : +0.37+/-0.16 degrees C). Epidural anesthesia, therefore, increased t he sweating threshold by 0.55+/-0.27 degrees C. Epidural anesthesia bl ocked sweating in the thigh in two of the subjects.Conclusions: An epi dural block alters the thermoregulatory responses to warming by increa sing the threshold for thermoregulatory sweating and, in some cases, p reventing leg sweating.