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Anesth Analg 2001;93:466-471
© 2001 International Anesthesia Research Society

REGIONAL ANESTHESIA

Topical Application of Acidic Bupivacaine to the Lumbar Ganglion Induces Mechanical Hyperalgesia in the Rat

Jun-Ming Zhang, MS, MD*, Yuko Homma, MD*, William E. Ackerman, MD{dagger}, and Sorin J. Brull, MD*

*Department of Anesthesiology, University of Arkansas for Medical Sciences, Little Rock, Arkansas; and {dagger}Integrative Pain Medicine of Arkansas, Little Rock, Arkansas

Address correspondence and reprint requests to Jun-Ming Zhang, MS, MD, Department of Anesthesiology, Slot 515, University of Arkansas for Medical Sciences, 4301 W. Markham St., Little Rock, AR 72205. Address e-mail to ZhangJunming{at}uams.edu

To investigate the neurologic mechanisms of acidic local anesthetic-induced low back pain in humans, we administered bupivacaine and buffered saline at acidic or alkalinized pH at the L5 dorsal root ganglion (DRG) of rats via a hole drilled through the transverse process covering the DRG. Behavioral changes were tested before and after bupivacaine or saline administration. Results indicate that acute single-dose infusion of the DRG with bupivacaine (0.5%) at acidic pH (5.5) induced ipsilateral mechanical hyperalgesia that lasted for 7 days. Acute infusion of alkalinized bupivacaine (pH 7.2), however, caused only minor hyperalgesia that lasted <3 days. Similar results were obtained when bupivacaine was replaced with saline. Alternatively, chronic delivery of acidic saline to the DRG via a subcutaneously implanted osmotic pump resulted in a significant decrease in the withdrawal threshold on the ipsilateral hind paw that lasted for 10 days. In rats receiving chronic treatment of the DRG with alkalinized saline, mechanical hyperalgesia lasted for only 3 days. The results demonstrated that acidic bupivacaine deposited at the DRG causes pain and hyperalgesia when the effects of the local anesthetic have dissipated. These findings may explain the limited therapeutic effects of some acidic local anesthetics used for management of cancer-related and chronic back pain.

IMPLICATIONS: Acidic bupivacaine administered at the L5 lumbar ganglion causes pain and hypersensitivity of the hind paw in the rat. These findings may explain the limited therapeutic effects of some acidic local anesthetics used for treatment of cancer-related and chronic back pain.






Lippincott, Williams & Wilkins Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999 HighWire Press
Copyright © 2001 by the International Anesthesia Research Society.