CLONIDINE DOES NOT IMPAIR REDISTRIBUTION HYPOTHERMIA AFTER THE INDUCTION OF ANESTHESIA

Clonidine is commonly given for premedication, and it impairs normal t hermoregulatory responses to warm and cold stimuli while depressing sy mpathetic tone. We studied the effect of premedication by clonidine on redistribution hypothermia induced by the induction of anesthesia. Si xteen ASA physical status I or II patients were randomly assigned to r eceive either clonidine 150 mu g or a placebo. Anesthesia was induced 45 min later by thiopental, fentanyl, and vecuronium IV and was mainta ined by the administration of 0.6% isoflurane. We monitored central co re (tympanic) temperature and skin surface temperatures at the forearm and the fingertip during the 2 h after the induction of anesthesia be fore surgery. We estimated skin blood flow at the level of the forearm by using laser Doppler during the same period. The core temperature d ecreased comparably in the two groups of patients, from 37.1 +/- 0.2 d egrees C to 35.3 +/- 0.4 degrees C and from 37.1 +/- 0.2 degrees C to 35.5 +/- 0.3 degrees C in the clonidine and placebo groups, respective ly. The forearm-fingertip surface temperature gradient decreased simil arly in the two groups. There was no evidence of cutaneous vasoconstri ction. The laser Doppler index at the fingertip increased similarly in the two groups, as did the forearm-fingertip temperature gradient. We conclude that premedication with clonidine does not significantly imp air the profile of central hypothermia induced by heat redistribution after the induction of anesthesia. Implications: The induction of gene ral anesthesia is associated with redistribution hypothermia. This stu dy shows that premedication with oral clonidine does not worsen the de crease in core temperature resulting from general anesthesia.