Epinephrine increases the neurotoxic potential of intrathecally administered lidocaine in the rat.
BACKGROUND
Epinephrine is commonly added to lidocaine solutions to increase the duration of spinal anesthesia. Despite this common usage, the effect of epinephrine on the neurotoxic potential of this anesthetic is not known. The current experiments investigated whether adding epinephrine increases functional impairment or histologic damage induced by spinal administration of lidocaine in the rat.


METHODS
Eighty rats were divided into four groups to receive an intrathecal injection of normal saline containing either 5% lidocaine, 5% lidocaine with 0.2 mg/ml of epinephrine, 0.2 mg/ml of epinephrine, or normal saline alone. Animals were assessed for persistent sensory impairment using the tail-flick test administered 4 and 7 days after infusion. Animals were then killed, and the spinal cord and nerve roots were prepared for neuropathologic evaluation.


RESULTS
Rats given 5% lidocaine developed persistent sensory impairment and histologic damage, and the addition of epinephrine resulted in a further significant increase in injury. Sensory function in animals given epinephrine without anesthetic was similar to baseline and did not differ from saline. Histologic changes in animals treated with epinephrine alone did not differ significantly from saline controls.


CONCLUSIONS
The neurotoxicity of intrathecally administered lidocaine is increased by the addition of epinephrine. When making clinical recommendations for maximum safe intrathecal dose of this anesthetic, one may need to consider whether the solution contains epinephrine.
Hashimoto
K
K
Department of Anesthesia and Perioperative Care, University of California, San Francisco, USA.
Hampl
K F
KF
Nakamura
Y
Y
Bollen
A W
AW
Feiner
J
J
Drasner
K
K
D000775:Anesthesia, Spinal; D000779:Anesthetics, Local / Q000633:toxicity*; D000818:Animals; D004357:Drug Synergism; D004837:Epinephrine / Q000633:toxicity*; D008012:Lidocaine / Q000633:toxicity*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time / Q000187:drug effects; D013116:Spinal Cord / Q000187:drug effects* / Q000473:pathology / Q000502:physiology
D000779:Anesthetics, Local; D008012:Lidocaine; D004837:Epinephrine