Evidence of Nerve Puncture during Ultrasound-guided Peripheral Nerve Blocks

The article by) Bigeleisen1is a nice illustration of gross anatomical changes that may occur in a nerve during performance of a peripheral nerve block (PNB) and highlights the emerging role of ultrasound in the performance of PNB. The author used a 10-MHz linear transducer to demonstrate the findings. Transducers with higher frequencies are now becoming increasingly available and will in the future provide better definition of the anatomic details, particularly when superficial nerves are imaged.

However, we have a few comments. (1) In this study, patients were sedated with 1–2 mg midazolam and 50–100 μg fentanyl, which may have interfered with the ability to report paresthesia during performance of the PNB. Because the nerves were identified by the report of paresthesia by the subject or the feeling of a pop, one would like to know the distribution of the techniques in identifying the nerves. (2) The title is misleading. Although the author uses the phrase “ultrasound-guided axillary block” in the title, according to the methods, the actual nerve was identified (according to the author) only “when a paresthesia was elicited or a pop was felt.” The author does not report the plane at which the needle was advanced in relation to the ultrasound beam in the methods section. If the needle was advanced perpendicular to the beam at any time, it might have been difficult to comment on whether the needle entered the substance of the nerve. (3) No age range of patients was reported in the results section.

We do agree with the author that intraneural injection may not always lead to nerve injury. We work in a tertiary care pediatric center and perform almost all of our PNBs during general anesthesia. Most of our PNB are increasingly being performed with ultrasound guidance in conjunction with a nerve stimulator. We would like to report a case where a left femoral nerve block was performed during general anesthesia for postoperative analgesia in a 12-yr-old, 33-kg girl who underwent a left distal femoral and proximal tibial epiphysiodesis. The femoral nerve block was performed using a nerve stimulator with ultrasound guidance. Thirty milliliters ropivacaine, 0.1%, was injected in increments without resistance via  a 22-gauge Braun Stimuplex needle (B. Braun Medical, Bethlehem, PA) at a stimulation threshold of 0.31 mA. Postoperatively, the patient had complete sensory blockade in the distribution of the left femoral and lateral cutaneous nerve of the thigh and did not need any opioids for 23 h. The patient had no residual numbness (after 24 h), paresthesia, or dysesthesia. A review of the ultrasound images obtained during the block showed swelling of the nerve after injection of the local anesthetic (figs. 1A and B, similar to the images obtained by Bigeleisen.1 

As reported by Bigeleisen,1the occurrence of intraneural injection during PNB is probably not uncommon, and only a larger series can determine the consequences of intraneural injection noted on ultrasound.

*The Children’s Hospital of Philadelphia and University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania. ganesha@email.chop.edu