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Vol. 7, Issue 1, January-March 2013 Saudi Journal of Anaesthesia

Safety of intraneural injection of local anesthetic

Abdelazeem Eldawlatly, Ammar Al Rikabi1, Shady Elmasry2

Departments of Anesthesia and 1Histopathology, College of Medicine, 2Anesthesia, King Khaled University Hospital, King Saud University, Riyadh, Saudi Arabia

A B S T R A C T

There  is  conflicting  information  in  the  literature  regarding  nerve  damage  following regional anesthesia. Intraneural injection of local anesthetic was described as a safe practice in regional anesthesia. This review focuses on the histopathological and functional assessment of peripheral nerve function following intraneural injection of local anesthetics.

Key words: Intraneural injection, local anesthetics, neurobehavior

removal of the sciatic nerve for histologic assessment was the inability to assess the neurobehavioral consequences of the neurotoxic effects of local anesthetics.

RESULTS

Inanunpublishedresultsonfivemalebeagledogsundergeneral anesthesia, bilateral posterior tibial nerves (PTN) were dissected and exposed to bupivacaine local anesthetic forupto48hatdifferentconcentrations0.25and0.5%.Longitudinal nerve specimens were taken from the PTN and sent for histologic analysis. Nerve inflammation wasdefinedbythepresenceof perineuralorintraneuralmacrophages, lymphocytes, neutrophils, granulation tissue, orreactivefibroblasts.Thepresenceof eachinflammatorymarker was graded as “none” (if no inflammatory reactionwasseen),“mild”(if theinflammatoryinfiltratewas seen in one high-power microscopic field), or “moderate” (if the inflammatory infiltratewas seen intwo high‑powermicroscopic fields).Mild tomoderateperineural inflammation at 48 h of 0.25%bupivacaineexposure was noticed [Figure 1]. Also the same reaction with fat necrosiswas seen 48 h of 0.5% bupivacaineexposure [Figure 2]. These unpublished data demonstrated varyingdegreesof mildtomoderateinflammatorychangesin the dog nerve specimens exposed to bupivacaine at 24h,whichbecamemoreevidentat48h.Thesefindingsare in keeping with other studies where prolonged exposure of rat sciatic nerve with either bupivacaine or ropivacaine induced significant nerve demyelinationand infiltrationwith inflammatory cells.[8,9] Intraneural needle placement, without injection, was described to

INTRODUCTION

Thereisconflictinginformationintheliteratureregardingnerve damage following regional anesthesia. Intraneural injection of local anesthetic was described as a safe practice in regional anesthesia. However, in one study it was concluded that a small volume of local anesthetic injected intraneurally may not invariably result in nerve injury.[1] In a prospective study on the neurological complications of 1000 ultrasound (US) guided peripheral nerve blocks (PNB), a low-rate of neurological complications was described.[2]Despitethefactthat,inthefieldof PNBthere was a transition from eliciting paresthesia to the use of electric nerve stimulation and most recently the use of US technology, the reported incidence of new neurological deficitsafterorthopedicsurgeryconductedunderPNBmaybeashighas15%atlessthan2weekspost‑operatively,but it doesn’t mean they were all due to PNB.[3] For ethical reasons studies, on histologic changes associated with nerve damage are limited to animal experimental studies. Correctly administered local anesthetics of clinical concentration are safe, but animal data indicate that all local anesthetics are potentially neurotoxic.[4-7] The limitation of the previous animal experiments using a rat model and

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DOI:

10.4103/1658-354X.109821

B R I E F R E P O R T

Address for correspondence: Prof. Abdelazeem Eldawlatly, King Saud University, Riyadh, Saudi Arabia. E-mail: dawlatly2@yahoo.com

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Saudi Journal of Anaesthesia Vol. 7, Issue 1, January-March 2013

Eldawlatly, et al.: Neurotoxicity of local anesthetics

cause non‑specificmechanical disruption andmarkedcellular infiltration.[10,11] In another study, intraneural needle placement without local anesthetic injection was described to cause pathophysiologic changes in the form of inflammatorycellsinfiltrationandaxonaldegeneration.[12] A functional consequence of intraneural injection of local anesthetic was described in one.[13] In a previous study on gel-nerve contact, we have reported limping as well as a consequence of nerve trauma.[14] Histologic changes of the spinal cord following intrathecal injection in the form of axonal degeneration was observed in an experiment on rats treatedwithgreaterthan16%prilocaineormepivacaineorwithgreaterthan4%bupivacaine.[15] In another similar animal study on electrophysiologic histopathologic and behavioral changes; bupivacaine was described as safer local anesthetic compared to lidocaine.[16-18] The neurotoxicity of local anesthetics can be demonstrated in vitro by the collapse of growth cones isolated from chick embryo and neurites in cultured neurons. In that regard, it was found that lidocaine was more toxic than bupivacaine and ropivacaine. Furthermore, it was found that mepivacaine, which is pharmacologically similar to lidocaine, has the least-adverse effects on cone growth among the clinically used local anesthetics.[19,20] Since the use of US guidance in regional anesthesia became more popular it seemed that intraneural puncture and injection of local anesthetics was much more common than previously thought. Various studies demonstrated that if intraneural puncture occurred the needle usually took a path away from the fascicles, while intraneural trans-fascicular puncture seemed relatively rare and intraneural intra-fascicular placement of the needle even more uncommon. As long as the needle is placed intraneurally but in an extra-fascicular fashion a safe injection and the absence of neurologic damage can be assumed. However, if nerve fascicles are

affected neurologic dysfunction can occur.[21] In a recent study conducted to determine the incidence of US-guided intraneural injection of local anesthetics, it was found to be ashighof 16.3%fortheUS‑guidedsubglutealapproachto the sciatic nerve.[22]

Sciatic nerve function as a method of functional evaluation was used in some animal studies. Sciatic function index (SFI) was used for such purpose and found that in a rat model following ropivacaine toxicity, 0.2 and 0.75%ropivacainehadnodeleteriouseffect.[23] There are significant concernswithoverrelianceon theSFI as anoutcome measure. Traditional SFI data lack resolving power and are prone to fail to detect a difference, even when significantdifferencesaredemonstratedbyothermethodsof evaluation. Although, the SFI is useful for detecting severe injuries, such as a complete nerve transaction, it has low-sensitivity for partial loss of nerve function.

CONCLUSION

Histologic changes following needle-nerve trauma eitherwithorwithout local anesthetic are non‑specific.However, intraneural injection of local anesthetics should be discouraged because the functional neurobehavioral consequences are not fully understood. Furthermore, the histopathological perineural changes following bupivacaine injection are not certain and further studies are needed in thatfield.

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Figure  1: Nerve specimen showing mild to moderate perineural inflammatory reaction. Note the presence of chronic inflammatory cells (arrow head)

Figure 2: Nerve specimen showing perineural inflammation (arrow head) with fat necrosis. Note the presence of distorted fat cells

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Eldawlatly, et al.: Neurotoxicity of local anesthetics

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How to cite this article: Eldawlatly A, Rikabi AA, Elmasry S. Safety of intraneural injection of local anesthetic. Saudi J Anaesth 2013;7:80-2.Source of Support: Nil, Conflict of Interest: None declared.

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