Neuraxial (spinal and epidural) anesthesia also impairs central thermoregulatory control via mechanisms that remain unclear. Regional anesthesia also causes a sympathectomy that prevents lower-body vasoconstriction and paralysis that prevents lower-body shivering. Consequently, hypothermia during neuraxial anesthesia is as common, and nearly as serious, as during general anesthesia.
Daniel I. Sesler, M.D.
Australian and New Zealand College of Anaesthetists.
http://www.anzca.edu.au/events/asm/asm2007/Sessler3.htm