Indocyanine green: evidence of neurotoxicity in spinal root axons.
BACKGROUND
The inadvertent intravascular injection of a local anesthetic during epidural anesthesia is an uncommon but potentially serious complication. Epinephrine, the most commonly used marker, does not provide sufficient sensitivity to exclude intravascular injection in all patient populations. The dye indocyanine green (ICG) has been proposed as an alternative marker. It has been demonstrated that ICG could be used to detect intravascular injections with a simple transcutaneous spectrophotometric technique. Although the safety of intravenous ICG is well documented, its neurotoxic potential requires careful study given the probability of inadvertent intrathecal injection during test injections used to verify epidural catheter placement.


METHODS
In this study, the authors investigated the neurophysiologic effects of clinically relevant concentrations of ICG (range, 28.6-286 microm) on single myelinated and unmyelinated dorsal root axons in rats by measuring effects on impulse generation and conduction.


RESULTS
In contrast to the apparent absence of toxicity when injected intravenously, ICG applied to intact dorsal roots at concentrations likely to be encountered with an epidural test dose produced long-lasting conduction block (21 of 26 axons) or spontaneous bursting activity (7 of 26 axons) in myelinated and unmyelinated dorsal root axons.


CONCLUSIONS
Given this apparent neurotoxicity, ICG should not be used when intrathecal or nerve root injection is possible.
Dietz
Friederike B
FB
Department of Anesthesiology, Heinrich-Heine-University Dusseldorf, Germany.
Jaffe
Richard A
RA
D000767:Anesthesia, Epidural / Q000009:adverse effects; D000818:Animals; D001369:Axons / Q000187:drug effects; D004396:Coloring Agents; D004558:Electric Stimulation; D004837:Epinephrine / Q000097:blood; D007208:Indocyanine Green / Q000009:adverse effects; D008297:Male; D009413:Nerve Fibers, Myelinated / Q000187:drug effects; D009431:Neural Conduction / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D013126:Spinal Nerve Roots / Q000187:drug effects*
D004396:Coloring Agents; D007208:Indocyanine Green; D004837:Epinephrine