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LETTER TO THE EDITOR

Does Excessive "Searching" Increase the Risk of Neural Trauma in Peripheral Nerve Blockade?

Department of Anesthesiology and Critical Care Medicine; Medical University Innsbruck; Innsbruck, Austria; wolfgang.voelckel{at}uibk.ac.at

In Response:

Chin et al. (1) address the possible cause-effect relationship between repeated attempts to puncture the neurovascular sheet and subsequent nerve damage. It appears obvious that repetitive withdrawal and repositioning of the needle increases the likelihood of a direct needle-nerve contact. Nevertheless, we doubt that the actual number of stimulation attempts causes nerve damage because most unsuccessful attempts, by definition, are well away from the nerve bundle. The needle may need to be repositioned to approach the desired structure. Moreover, another key question is still unanswered—namely, whether a direct nerve puncture is necessarily harmful if drugs are not injected intraneurally. If the latter fact were true, the technique of eliciting paresthesias would have resulted in an extensive number of minor and major complications during the last decades.

In our current study, we sought to assess histologic findings after both ultra-low current stimulation and injection of a local anesthetic (2). As such, although a sufficient motor response (current <0.5 mA) had already been obtained, we further advanced and/or repositioned the needle, intentionally minimizing the needle-nerve distance as indicated by the decline of stimulation current. Unfortunately, we were unable to report on the actual number of needle maneuvers needed to achieve a motor response <0.2 mA. Given the fact that the sciatic nerve is a well-embedded structure of significant size, we speculate that a direct needle-nerve contact may be more harmful in this case than other peripheral nerve blocks. Most recently, Hadzic and Vloka's (3) review of the possible risk factors of peripheral nerve injury outlined six major issues: 1) intraneural injection, detectable by pain on injection, the intensity of the stimulating current or the resistance to injection; 2) needle design and direct needle trauma; 3) toxicity of the injected drug; 4) neuronal ischemia; 5) compressive hematoma; and 6) tourniquet neuropathy. Bearing these issues in mind, we still consider peripheral nerve blocks to be safe and effective when the local anesthetic is carefully injected during peripheral nerve stimulation with a current between 0.3 and 0.5 mA. The clinical relevance of our observing signs of inflammation remains unknown.

REFERENCES

1. Chin KJ, Chee VWT. Does excessive "searching" increase the risk of neural trauma in peripheral nerve blockade? Anesth Analg 2006;103:780–1.[Free Full Text]
2. Voelckel WG. Klima G, Krismer AC, et al. Signs of inflammation after sciatic nerve block in pigs. Anesth Analg 2005;101:1844–6.[Abstract/Free Full Text]
3. Hadzic A, Vloka J. Peripheral nerve blocks: principles and practice. New York: McGraw-Hill, 2006.

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