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Redistribution of heat from the core to the cool peripheral compartments of the body causes hypothermia during epidural anesthesia. Diminishing the temperature gradient between the core and peripheral tissues by warming the body via the skin before anesthesia should prevent this hypothermia. We measured core temperature, skin temperatures, and cutaneous heat loss in seven volunteers who received two lidocaine epidural injections during a single study day. One epidural injection was given after the volunteer had rested in a cool room (approximately 22 degrees C) ("no prewarming") for 2 h, and one injection was given after the volunteer had been covered with a forced air warming mattress (approximately 38 degrees C) ("prewarming") for 2 h. Skin temperatures were higher after prewarming. The decrease in core temperature during epidural anesthesia was smaller after prewarming [mean within patient difference (prewarming-no prewarming): 0.41; P = 0.003]. However, heat loss was greater after prewarming (mean within patient difference: 26.4; P = 0.02). Shivering was less after prewarming. We conclude that prewarming decreases redistribution hypothermia caused by epidural block. These results support the hypothesis that redistribution of heat within the body, not heat loss, is the most important etiology of hypothermia from epidural anesthesia.

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