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) temperature threshold for sweating (detected on the forehead) was determined. The subject was then cooled until sweating stopped. The subject was warmed again, and a second sweating threshold was determined. The difference between the first and second sweating thresholds was noted. On the Anesthesia day, two sequential sweating threshold measurements were obtained in a similar fashion; however, a mid-thoracic level of epidural anesthesia was established before the second sweating threshold measurement. The first and second sweating threshold differences were compared between the two study days. The presence or absence of sweating on the thigh was noted during all four warming periods.

RESULTS

Average skin temperatures were similar (about 37 degrees C) during all four sweating threshold measurements. On the Control day, the second sweating threshold value was always slightly less than the first (average difference (mean+/-SD): -0.18+/-0.14 degrees C). In contrast, on the Anesthesia 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 the sweating threshold by 0.55+/-0.27 degrees C. Epidural anesthesia blocked sweating in the thigh in two of the subjects.

CONCLUSIONS

An epidural block alters the thermoregulatory responses to warming by increasing the threshold for thermoregulatory sweating and, in some cases, preventing leg sweating.