EPIDURAL EPINEPHRINE AND CLONIDINE - SEGMENTAL ANALGESIA AND EFFECTS ON DIFFERENT PAIN MODALITIES

Background: It is not known whether epidural epinephrine has an analge sic effect per se. The segmental distribution of clonidine epidural an algesia and its effects on temporal summation and different types of n oxious stimuli are unknown. The aim of this study was to clarify these issues. Methods: Fifteen healthy volunteers received epidurally (L2-L 3 or L3-L4) 20 ml of either epinephrine, 100 mu g, in saline; clonidin e, 8 mu g/kg, in saline; or saline, 0.9%, alone, on three different da ys in a randomized, double-blind, cross-over fashion. Pain rating afte r electrical stimulation, pinprick, and cold perception were recorded on the dermatomes S1, L4, L1, T9, T6, T1, and forehead. Pressure pain tolerance threshold was recorded at S1, T6, and ear. Pain thresholds t o single and repeated (temporal summation) electrical stimulation of t he sural nerve were determined. Results: Epinephrine significantly red uced sensitivity to pinprick at L1-L4-S1. Clonidine significantly decr eased pain rating after electrical stimulation at L1-L4 and sensitivit y to pinprick and cold at L1-L4-S1, increased pressure pain tolerance threshold at S1, and increased thresholds after single and repeated st imulation of the sural nerve. Conclusions: Epidural epinephrine and cl onidine produce segmental hypoalgesia Clonidine bolus should be admini stered at a spinal level corresponding to the painful area. Clonidine inhibits temporal summation elicited by repeated electrical stimulatio n and may therefore attenuate spinal cord hyperexcitability.