To the Editor:—
I read with interest the article by Bigeleisen.1In this article, the author presented a prospective study of ultrasound-guided axillary blocks and determined the incidence of nerve puncture, intraneural injection of local anesthetics, and transient or permanent nerve injuries. After reading this well-written article it occurred to me that there are some points that may add to discussion. Damage may be caused to peripheral nerves after regional anesthesia techniques by mechanical, chemical, or ischemic injuries, which may occur alone or in combination.2Iohom et al. 2reported that intraneural injection of ropivacaine in rat sciatic nerve, in a concentration routinely used in clinical practice, caused no deleterious effect on motor function. Hadzic et al. 3reported varying degrees of damage to the neural architecture after high-pressure injection of local anesthetic in dog sciatic nerve. This damage ranged from mechanical disruption and delamination to fragmentation of the myelin sheath and marked cellular infiltration. They also reported severe and persistent motor deficits.3
Since the introduction of ultrasound-guided peripheral nerve blocks at my institution, I frequently observe nerve puncture during this procedure. In my experience, the combination of electrical stimulation does not result always in motor response even if the needle tip is positioned intraneurally. In the same condition, I also sometimes observe no pain on intraneural injection. The advantage of ultrasound-guided nerve blocks in my practice is that I can watch the needle’s advancement in real time. Accordingly, in case I suspect nerve puncture, I slightly withdraw the needle and avoid intraneural injection to increase safety. In this study, the author excluded 22 patients from the study because of preoperative abnormalities in their motor and sensory examination. In daily practice, patients may present some degree of neurologic abnormalities before surgery. They may also be at high risk of nerve damage. Furthermore, intraneural injection in these patients may lead to an aggravating condition of their preexisting neuropathy. There are multiple causes and a combination of factors that may lead nerve injury after regional anesthesia techniques.4However, peripheral nerves have a dual blood supply of intrinsic exchange vessels in the endoneurium and an extrinsic plexus of supply vessels in the epineurial space that cross the perineurium to anastomose with intrinsic circulation.2Accordingly, nerve ischemia due to intraneural compression (local anesthetic volume or edema) and/or perineural compression (local anesthetic volume) may cause permanent or transient nerve damage.4Moreover, high-pressure intrafascicular or endoneural injection may also cause neural damage.3Consequently, the combination of ischemia, high-pressure intrafascicular or endoneural injection and local anesthetic toxicity could be deleterious to peripheral nerves.3,4
According to my experience, it is difficult to tell from the ultrasound image after apparent intraneural placement of the needle tip, whether the needle is positioned perineurially, epineurially, or endoneurially. The injection of the local anesthetic, even in a small quantity, in one of these positions may not lead to the same outcome. Furthermore, endoneural injection could result in nerve damage by promoting ischemic changes.2For this reason, I believe that avoidance of intraneural placement of the needle tip should be a major concern during ultrasound-guided peripheral nerve blocks. Moreover, performing a peripheral nerve block in real time and under direct vision gives us the possibility to correct the needle position, avoid intraneural injections, and avoid nerve injury.
In conclusion, although this study and other reports1,2suggested that nerve puncture and intraneural injection of low to moderate volumes of local anesthetic do not inevitably lead to neurologic injury, the role of ultrasound-guided peripheral nerve blocks is to increase safety. Even if we hypothesize that intraneural injections do not lead to neurologic damage, they present no advantage over perineural injections in rapidity of installation or in success rate after ultrasound-guided techniques. Finally, practitioners who have already experienced neurologic problems after regional anesthesia techniques always remember the difficulties encountered during the long way of patient care.
Clinique du Parc saint Lazare, Beauvais, France. firstname.lastname@example.org