Anesthesia & Analgesia:
Monitoring Intraneural Needle Injection: Work in Progress
Abdallah, Faraj W. MD*; Chan, Vincent W. S. MD, FRCPC†
From the *Department of Anesthesia and Keenan Research Centre in the Li Ka Shing Knowledge Institute, St. Michael’s Hospital and †Department of Anesthesia, Toronto Western Hospital (University Health Network), University of Toronto, Toronto, Ontario, Canada.
Accepted for publication November 26, 2013.
Funding: This work was supported by departmental funding.
Conflict of Interest: See Disclosures at the end of the article.
Reprints will not be available from the authors.
Address correspondence to Vincent W. S. Chan, MD, FRCPC, Department of Anesthesia and Pain Management, Toronto Western Hospital, 399 Bathurst St., Toronto, Ontario M5T 2S8, Canada. Address e-mail to Vincent.Chan@uhn.ca.
Our objective to accurately localize the needletip during peripheral nerve block is primarily safety driven because we realize that unintentional intraneural needle injection can result in nerve injury.1,2 An intraneural injection, whether intrafascicular or extrafascicular (interfascicular), always indicates a violation of the epineurium boundary. Although the mechanisms of nerve injury are many and not fully understood, clinical manifestation of neurologic deficit is thought to be more likely to occur when trauma is inflicted on nerve fascicles.3 The threat of an intrafascicular needle puncture is raised especially in nerves with a high nerve fascicle to connective tissue ratio, for example, proximal nerve root.4 Although an extrafascicular intraneural injection may have no neurologic sequelae,5,6 we must recognize that current methods of needle guidance, whether nerve stimulation or ultrasound, cannot distinguish between a hazardous intraneural injection and one that is safe.
Electrical stimulation is an improved method of nerve localization over paresthesia,7 but its accuracy in detecting needle-to-nerve contact remains suboptimal, as shown in both animal8,9 and human studies.10 A threshold stimulating current, 0.2 mA ≤ intensity ≤ 0.5 mA, is often considered the optimal extraneural stimulating end point for peripheral nerve block.11–13 However, human study data indicate otherwise and reveal the following: (1) there is a wide interindividual variability in the intensity of stimulating current required to evoke a motor response7; (2) different nerves (e.g., radial and ulnar nerves at the elbow) in a given individual may have different stimulation thresholds10; (3) the same nerve in a given individual may have different stimulation thresholds at different body locations (e.g., median nerve in the axilla versus wrist) due to different tissue-specific electrical impedances14; and (4) higher stimulation thresholds are observed in patients with neuropathy (e.g., diabetes).6
Most importantly, a threshold stimulating current >0.5 mA does not always exclude intraneural needle placement.12 For example, the reported intraneural stimulation threshold of the popliteal sciatic nerve ranges from 0.35 to 1.2 mA (mean, 0.58 mA) in humans12 and 0.08 to 1.8 mA in pigs, with 12.5% requiring current ≥0.8 mA.9 Nerve tissue architecture can influence the stimulation threshold by virtue of the proportion of connective tissue within the nerve4,15 and around it.16 Furthermore, a threshold stimulating current of 0.2 mA ≤ intensity ≤ 0.5 mA cannot exclude intraneural needle placement. Sala Blanch et al.13 observed similar stimulating current thresholds when the needle was positioned intraneurally and extraneurally (mean, 0.33 vs 0.35 mA, respectively) in human sciatic nerve.
In this issue of Anesthesia & Analgesia, Wiesmann et al.17 went one step further and demonstrated that even a stimulating current intensity <0.2 mA could not discern an extraneural from an intraneural needle insertion. By applying electrical stimulation of varying pulse durations (0.1, 0.3, and 1 milliseconds) to the terminal branches of the brachial plexus in an open dissection pig model, the authors found that the minimal stimulating current was indistinguishable between needle position inside a nerve and in direct nerve contact (a mean intensity of 0.12 mA in both cases, with 0.1-millisecond pulse duration). However, the stimulating current was higher (mean, 0.28 mA) when the needle was 1 mm away from the nerve. The findings of this study are in contradistinction to past pig8,18 and human6 data in that the stimulating current required for both intraneural and direct extraneural stimulation of the brachial plexus was significantly and consistently lower (<0.2 mA vs >0.5 mA). The authors attribute this observation to differences in experimental conditions among studies and the lack of hyperpolarization “stimulation block.”
Ultrasound, another nerve localization method, allows needle and nerve visualization, and thus presumably increases the sensitivity of detecting needle-to-nerve contact.7 Past cadaver and animal studies have demonstrated the usefulness of ultrasound in intraneural needle detection, but this happens often after initiation of an intraneural injection, resulting in sonographic evidence of nerve expansion and a change in nerve echogenicity.13,19 Clinical incidents of unintentional intraneural needle placement are attributed to poor needle tracking skills and failure to identify the needletip in real time.20,21 Realizing these limitations, it may be prudent to accept an injection end point (satisfactory local anesthetic spread around the nerve) rather than to always seek a needle position end point (direct needle-to-nerve contact) during ultrasound-guided regional anesthesia. Applying the hydrodissection technique with repeated small volume injections to open the path for needle advancement and to achieve a perineural injection without direct needle-to-nerve contact may improve safety. Recent clinical outcome data also suggest enhanced benefits when nerve stimulation and ultrasound are combined.22,23
Injection pressure monitoring is another potential safeguard against intraneural injection. Data extracted from animal models suggest that injection pressure is higher with intrafascicular compared with extrafascicular injection and that high pressure (>20–25 psi) results in histologic and functional nerve damage.24–26 Because the anesthesiologist’s ability to perceive injection pressure during peripheral nerve block is highly variable, the proposition of using pressure monitoring devices to keep the injection pressure to <15 psi is attractive. However, the fact that low pressure has been observed during intrafascicular injection (<11 psi) in 42%25 to 60%26 of cases underscores the need for more vigorous studies to further examine the sensitivity, specificity, and limitations of this monitoring tool. Peak injection pressure may also vary as a function of nerve size, nerve composition (connective tissue to nerve fascicle ratio), needle size, injection rate, injection volume, and perhaps animal species. For example, the peak pressure for intrafascicular injection (mean ± SD) was 10.9 ± 3.6 psi for rabbit sciatic nerve,24 29.7 ± 7.4 psi for dog sciatic nerve,26 and 48.9 ± 10.2 psi for human cadaver brachial plexus nerve root,27 measured under different experimental conditions. In addition, peak pressure is achieved often seconds after initiation of an injection (not immediate) and is likely influenced by the volume and rate of injection. The initial high resistance to injection encountered during the isostatic phase of pressure testing (before injection)24–27 is often due to needle–fascial sheath contact and not intraneural needle placement, as visualized under ultrasound.
We believe that the endeavor to monitor and prevent intraneural needle trauma and neurologic injury is still a work in progress. The search for a consistently effective monitor continues as evidenced by the development of other novel technologies, for example, electrical impedance monitoring,28 high-definition imaging,29 electromagnetic needle tracking,30 acoustic radiation force impulse imaging,31 and tissue sensing technology.32 At the present time, perhaps the strategy of depositing local anesthetic around the nerve without direct needle-to-nerve contact, whenever possible, is the best safeguard against nerve trauma while waiting for the “perfect” monitor.
Name: Faraj W. Abdallah, MD.
Contribution: This author helped write the manuscript.
Attestation: This author approved the manuscript.
Conflicts of Interest: The author has no conflicts of interest to declare.
Name: Vincent W. S. Chan, MD, FRCPC.
Contribution: This author helped write the manuscript.
Attestation: This author approved the manuscript.
Conflicts of Interest: Dr. Vincent Chan receives equipment support for research from BK Medical, Philips Medical Systems, SonoSite, and Ultrasonix.
This manuscript was handled by: Terese T. Horlocker, MD.
1. Selander D, Brattsand R, Lundborg G, Nordborg C, Olsson Y. Local anesthetics: importance of mode of application, concentration and adrenaline for the appearance of nerve lesions. An experimental study of axonal degeneration and barrier damage after intrafascicular injection or topical application of bupivacaine (Marcain). Acta Anaesthesiol Scand. 1979;23:127–36
2. Hogan QH. Pathophysiology of peripheral nerve injury during regional anesthesia. Reg Anesth Pain Med. 2008;33:435–41
3. Jeng CL, Torrillo TM, Rosenblatt MA. Complications of peripheral nerve blocks. Br J Anaesth. 2010;105(Suppl 1):97–107
4. Moayeri N, Groen GJ. Differences in quantitative architecture of sciatic nerve may explain differences in potential vulnerability to nerve injury, onset time, and minimum effective anesthetic volume. Anesthesiology. 2009;111:1128–34
5. Bigeleisen PE. Nerve puncture and apparent intraneural injection during ultrasound-guided axillary block does not invariably result in neurologic injury. Anesthesiology. 2006;105:779–83
6. Bigeleisen PE, Moayeri N, Groen GJ. Extraneural versus intraneural stimulation thresholds during ultrasound-guided supraclavicular block. Anesthesiology. 2009;110:1235–43
7. Perlas A, Niazi A, McCartney C, Chan V, Xu D, Abbas S. The sensitivity of motor response to nerve stimulation and paresthesia for nerve localization as evaluated by ultrasound. Reg Anesth Pain Med. 2006;31:445–50
8. Chan VW, Brull R, McCartney CJ, Xu D, Abbas S, Shannon P. An ultrasonographic and histological study of intraneural injection and electrical stimulation in pigs. Anesth Analg. 2007;104:1281–4, tables of contents
9. Tsai TP, Vuckovic I, Dilberovic F, Obhodzas M, Kapur E, Divanovic KA, Hadzic A. Intensity of the stimulating current may not be a reliable indicator of intraneural needle placement. Reg Anesth Pain Med. 2008;33:207–10
10. Sauter AR, Dodgson MS, Stubhaug A, Cvancarova M, Klaastad O. Ultrasound controlled nerve stimulation in the elbow region: high currents and short distances needed to obtain motor responses. Acta Anaesthesiol Scand. 2007;51:942–8
11. Bigeleisen PE, Moayeri N, Groen GJ. Extraneural versus intraneural stimulation thresholds during ultrasound-guided supraclavicular block. Anesthesiology. 2009;110:1235–43
12. Robards C, Hadzic A, Somasundaram L, Iwata T, Gadsden J, Xu D, Sala-Blanch X. Intraneural injection with low-current stimulation during popliteal sciatic nerve block. Anesth Analg. 2009;109:673–7
13. Sala Blanch X, López AM, Carazo J, Hadzic A, Carrera A, Pomés J, Valls-Solé J. Intraneural injection during nerve stimulator-guided sciatic nerve block at the popliteal fossa. Br J Anaesth. 2009;102:855–61
14. Sauter AR, Dodgson MS, Kalvøy H, Grimnes S, Stubhaug A, Klaastad O. Current threshold for nerve stimulation depends on electrical impedance of the tissue: a study of ultrasound-guided electrical nerve stimulation of the median nerve. Anesth Analg. 2009;108:1338–43
15. Moayeri N, van Geffen GJ, Bruhn J, Chan VW, Groen GJ. Correlation among ultrasound, cross-sectional anatomy, and histology of the sciatic nerve: a review. Reg Anesth Pain Med. 2010;35:442–9
16. Andersen HL, Andersen SL, Tranum-Jensen J. Injection inside the paraneural sheath of the sciatic nerve: direct comparison among ultrasound imaging, macroscopic anatomy, and histologic analysis. Reg Anesth Pain Med. 2012;37:410–4
17. Wiesmann T, Bornträger A, Vassiliou T, Hadzic A, Wulf H, Müller HH, Steinfeldt T. Minimal current intensity to elicit an evoked motor response cannot discern between needle-nerve contact and an intraneural needle insertion. Anesth Analg. 2014;118:681–6
18. Altermatt FR, Cummings TJ, Auten KM, Baldwin MF, Belknap SW, Reynolds JD. Ultrasonographic appearance of intraneural injections in the porcine model. Reg Anesth Pain Med. 2010;35:203–6
19. Moayeri N, Krediet AC, Welleweerd JC, Bleys RL, Groen GJ. Early ultrasonographic detection of low-volume intraneural injection. Br J Anaesth. 2012;109:432–8
20. Sites BD, Spence BC, Gallagher JD, Wiley CW, Bertrand ML, Blike GT. Characterizing novice behavior associated with learning ultrasound-guided peripheral regional anesthesia. Reg Anesth Pain Med. 2007;32:107–15
21. Chin KJ, Perlas A, Chan VW, Brull R. Needle visualization in ultrasound-guided regional anesthesia: challenges and solutions. Reg Anesth Pain Med. 2008;33:532–44
22. Orebaugh SL, Kentor ML, Williams BA. Adverse outcomes associated with nerve stimulator-guided and ultrasound-guided peripheral nerve blocks by supervised trainees: update of a single-site database. Reg Anesth Pain Med. 2012;37:577–82
23. Sites BD, Taenzer AH, Herrick MD, Gilloon C, Antonakakis J, Richins J, Beach ML. Incidence of local anesthetic systemic toxicity and postoperative neurologic symptoms associated with 12,668 ultrasound-guided nerve blocks: an analysis from a prospective clinical registry. Reg Anesth Pain Med. 2012;37:478–82
24. Selander D, Sjöstrand J. Longitudinal spread of intraneurally injected local anesthetics. An experimental study of the initial neural distribution following intraneural injections. Acta Anaesthesiol Scand. 1978;22:622–34
25. Hadzic A, Dilberovic F, Shah S, Kulenovic A, Kapur E, Zaciragic A, Cosovic E, Vuckovic I, Divanovic KA, Mornjakovic Z, Thys DM, Santos AC. Combination of intraneural injection and high injection pressure leads to fascicular injury and neurologic deficits in dogs. Reg Anesth Pain Med. 2004;29:417–23
26. Kapur E, Vuckovic I, Dilberovic F, Zaciragic A, Cosovic E, Divanovic KA, Mornjakovic Z, Babic M, Borgeat A, Thys DM, Hadzic A. Neurologic and histologic outcome after intraneural injections of lidocaine in canine sciatic nerves. Acta Anaesthesiol Scand. 2007;51:101–7
27. Orebaugh SL, Mukalel JJ, Krediet AC, Weimer J, Filip P, McFadden K, Bigeleisen PE. Brachial plexus root injection in a human cadaver model: injectate distribution and effects on the neuraxis. Reg Anesth Pain Med. 2012;37:525–9
28. Tsui BC, Pillay JJ, Chu KT, Dillane D. Electrical impedance to distinguish intraneural from extraneural needle placement in porcine nerves during direct exposure and ultrasound guidance. Anesthesiology. 2008;109:479–83
29. Karmakar MK, Shariat AN, Pangthipampai P, Chen J. High-definition ultrasound imaging defines the paraneural sheath and the fascial compartments surrounding the sciatic nerve at the popliteal fossa. Reg Anesth Pain Med. 2013;38:447–51
30. Brinkmann S, Vaghadia H, Sawka A, Tang R. Methodological considerations of ultrasound-guided spinal anesthesia using the Ultrasonix GPS™ needle tracking system. Can J Anaesth. 2013;60:407–8
31. Palmeri ML, Dahl JJ, MacLeod DB, Grant SA, Nightingale KR. On the feasibility of imaging peripheral nerves using acoustic radiation force impulse imaging. Ultrason Imaging. 2009;31:172–82
32. Brynolf M, Sommer M, Desjardins AE, van der Voort M, Roggeveen S, Bierhoff W, Hendriks BH, Rathmell JP, Kessels AG, Söderman M, Holmström B. Optical detection of the brachial plexus for peripheral nerve blocks: an in vivo
swine study. Reg Anesth Pain Med. 2011;36:350–7
© 2014 International Anesthesia Research Society
What does "Remember me" mean?
By checking this box, you'll stay logged in until you logout. You'll get easier access to your articles, collections,
media, and all your other content, even if you close your browser or shut down your
To protect your most sensitive data and activities (like changing your password),
we'll ask you to re-enter your password when you access these services.
What if I'm on a computer that I share with others?
If you're using a public computer or you share this computer with others, we recommend
that you uncheck the "Remember me" box.
Data is temporarily unavailable. Please try again soon.
Readers Of this Article Also Read