We thank Swenson, Davis, Albrecht, Riazi, and Brull for their comments on our study, which have given us an opportunity to contribute additional thoughts on this subject.1 

Swenson and Davis point out that our article does not provide convincing evidence that intraneural injection is safe, specifically citing the small sample size. We agree and also advise against the practice of intraneural injections as unnecessary and potentially hazardous. Several recent studies reported that as little as 1 ml, or 0.1 ml/mm of square surface of the nerve of local anesthetic injected perineurally, is sufficient for timely onset of successful nerve block.2,3If so, what can be gained by a targeted intraneural injection, except an unnecessary risk? However, an injection within the epineurium during popliteal sciatic block has been a norm before ultrasound, and should probably continue with ultrasound-guided blocks as well, provided adequate monitoring, as discussed below.4,,7 

We share the concerns of Swenson and Davis that there is a possibility that the title of the article may be misinterpreted by some as a “tacit approval of a practice which may result in disabling complications.” The fundamental problem is in the lack of the standardized nomenclature of what constitutes an intraneural versus  perineural injection. Importantly, for the purpose of our study, “intraneural” was defined as injections that occurred within the epineurium and not within the perineurium.8However, the predicated reports on the subject used the term “intraneural” for injections that took place within any connective tissue of the nerves or plexuses.8As a result, the peer-review process favored “intraneural” in our title, although a more appropriate title would have been “intraepineural” or “subepineural.” In our recent review, however, we attempted to standardize nomenclature of the sites of nerve injection to help reduce the future confusion in the literature.9We also agree with Swenson and Davis in that technology is now available to decrease the risk of intraneural injection and needle trauma. There is sufficient evidence suggesting that combination of ultrasound guidance, electrophysiologic monitoring (avoidance of evoked motor response at less than 0.3 mA), and avoidance of resistance to injection (more than 15 psi) may decrease the risk of an intrafasciular injection altogether.9 

Albrecht et al.  question whether additional electrophysiologic testing or data analysis would have an impact on the incidence of neurologic outcome of the subepineural injections reported in our study. We do not have a reason to doubt the sensitivity and the timing of the electromyography testing to detect significant subclinical nerve injury in our study. Electromyography is simply the most suitable method currently available to assess postblock nerve injury.10The choice of electrophysiologic data presented in our article was collaboratively made with reviewers through the peer-review process. Reporting more data would have unnecessarily cluttered the article since analysis of pre- and postinjection electrophysiologic data at all three data points (baseline, 1 week, and 4 weeks postblock) did not yield a signal prompting further exploration. As opposed to the report by Albrecht et al. ,11none of our patients had symptoms or signs of nerve injury.

Sala-Blanch X, López AM, Pomés J, Valls-Sole J, García AI, Hadzic A: No clinical or electrophysiologic evidence of nerve injury after intraneural injection during sciatic popliteal block. ANESTHESIOLOGY 2011; 115:589–95
Eichenberger U, Stöckli S, Marhofer P, Huber G, Willimann P, Kettner SC, Pleiner J, Curatolo M, Kapral S: Minimal local anesthetic volume for peripheral nerve block: A new ultrasound-guided, nerve dimension-based method. Reg Anesth Pain Med 2009; 34:242–6
O'Donnell BD, Iohom G: An estimation of the minimum effective anesthetic volume of 2% lidocaine in ultrasound-guided axillary brachial plexus block. ANESTHESIOLOGY 2009; 111:25–9
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
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
Tran de QH, Dugani S, Pham K, Al-Shaafi A, Finlayson RJ: A randomized comparison between subepineural and conventional ultrasound-guided popliteal sciatic nerve block. Reg Anesth Pain Med 2011; 36:548–52
Sala-Blanch X, De Riva N, Carrera A, López AM, Prats A, Hadzic A: Ultrasound-guided popliteal sciatic block with single injection at the sciatic division results in faster block onset than classical nerve stimulator technique. Anesth Analg; 2012 (in press)
Bigeleisen PE, Moayeri N, Groen GJ: Extraneural versus  intraneural stimulation thresholds during ultrasound-guided supraclavicular block. ANESTHESIOLOGY 2009; 110:1235–43
Sala-Blanch X, Vandepitte C, Laur JJ, Horan P, Xu D, Reina MA, Karmakar MK, Clark TB, Hadzic A: A practical review of perineural versus  intraneural injections; A call for standard nomenclature. Int Anesthesiol Clin 2011; 49:1–12
Borgeat A, Aguirre J: Assessment and treatment of postblock neurologic injury. Anesthesiol Clin 2011; 29:243–56
Albrecht E, Niederhauser J, Gronchi F, Löcherbach C, Kombot C, Rossat J, Gilliard N, Kuntzer T: Transient femoral neuropathy after knee ligament reconstruction and nerve stimulator-guided continuous femoral nerve block: A case series. Anaesthesia 2011; 66:850–1