Clonidine added to bupivacaine enhances and prolongs analgesia after brachial plexus block via a local mechanism in healthy volunteers.
OBJECTIVE
The addition of clonidine to local anaesthetics enhances pain relief after peripheral nerve block, but the site of action is unproven.


METHODS
Seven healthy volunteers underwent three brachial block procedures using bupivacaine 0.25% 1 mg kg(-1) + epinephrine 1:200,000 (=local analgesic) in a randomized, double-blind cross-over fashion: (a) control treatment: local analgesic with 0.9% sodium chloride solution for the block and an intramuscular injection of saline; (b) intramuscular treatment: local analgesic with 0.9% NaCl for block and an intramuscular injection of clonidine 2 microg kg(-1) and (c) block treatment: local analgesic with clonidine 2 microg kg(-1) for block and an intramuscular injection of saline.


RESULTS
The onset and duration of complete blockade (sensory/motor/temperature) was evaluated in the four nerve regions of the hand and forearm. Additionally, sedation score, blood pressure, heart rate and plasma clonidine concentrations were determined. The median duration of complete sensory blockade was 270 min (range 0-600) for block treatment compared to 0 min (range 0-480) for intramuscular treatment (P < 0.05) and 0 min (range 0-180) for control treatment (P < 0.05). Motor and temperature blockade exhibited similar results. Administration of clonidine was associated with sedation and a decrease in heart rate and blood pressure independent of the route of administration. Plasma clonidine concentrations were lower for block compared to the intramuscular treatment.


CONCLUSIONS
The admixture of clonidine to bupivacaine plus epinephrine prolongs and enhances brachial plexus blockade. Lower clonidine plasma concentrations for block treatment strongly suggest a local effect.
Hutschala
D
D
University of Vienna, Department of Cardiothoracic Anesthesia, Austria.
Mascher
H
H
Schmetterer
L
L
Klimscha
W
W
Fleck
T
T
Eichler
H G
HG
Tschernko
E M
EM
D000328:Adult; D000700:Analgesics / Q000008:administration & dosage* / Q000097:blood; D000779:Anesthetics, Local / Q000008:administration & dosage*; D001794:Blood Pressure / Q000187:drug effects; D001917:Brachial Plexus; D002045:Bupivacaine / Q000008:administration & dosage*; D003000:Clonidine / Q000008:administration & dosage* / Q000097:blood; D018592:Cross-Over Studies; D004311:Double-Blind Method; D004338:Drug Combinations; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D007273:Injections, Intramuscular; D008297:Male; D008475:Median Nerve / Q000187:drug effects; D009407:Nerve Block; D010146:Pain / Q000517:prevention & control; D011826:Radial Nerve / Q000187:drug effects; D013997:Time Factors; D014459:Ulnar Nerve / Q000187:drug effects
D000700:Analgesics; D000779:Anesthetics, Local; D004338:Drug Combinations; D003000:Clonidine; D002045:Bupivacaine