BACKGROUND: The aim of this study was to investigate the influence of epidural clonidine on the BIS, and its potential dose-sparing effect on the sevoflurane requirement for maintaining the BIS 50.

METHODS: Forty ASA I or II patients aged 20 to 65, undergoing lower abdominal, gynecologic surgery under general anesthesia, were randomly allocated to either a 10 ml epidural normal saline injection group (n = 20) or a 10 ml epidural clonidine 3µg/kg mixed with normal saline injection group (n = 20). They received 5 mg/kg thiopental sodium and 0.1 mg/kg vecuronium bromide for induction, with no premedication. After surgical incision, the sevoflurane concentration was controlled to maintain the BIS 50. Epidural saline or clonidine was then injected and end-tidal sevoflurane concentration to maintain the BIS 50, the heart rate (HR) and mean arterial pressure (MBP) were measured every 5 min over a 20 minute period.

RESULTS: The end-tidal sevoflurane concentration in the clonidine group decreased by 27.5% after the epidural clonidine injection (1.49 ± 0.23 vol% vs. 1.08 ± 0.27 vol%; P<0.05) compared with the saline group (1.36 ± 0.18 vol% vs. 1.33 ± 0.21 vol%; P>0.05). There were no changes in the heart rate and mean blood pressure in either group.

CONCLUSIONS: Epidural clonidine causes a significant decrease in the BIS, and lowers the end-tidal sevoflurane concentration required for maintaining the BIS 50.