To the Editor:— Perlas, Chan, and Simons should be congratulated for their interesting article on imaging of the brachial plexus. 1However, because they failed to image the infraclavicular plexus in 73% of the small number of cases in their study, they create the false impression that the plexus is very difficult to image in the infraclavicular area.
I have been able to visualize all three cords of the plexus with low-resolution, 2.5-MHz-frequency probes and to inject anesthetic around each nerve cord separately. This may not give publication-quality images, but is good enough for administering a block. 2Currently, I use a 4- to 7-MHz variable frequency probe, obtaining a good quality image in every patient, and the cords seem to be slightly hyperechoic in most adults. I have administered nearly 3,000 successful blocks with sonography alone, without using a nerve stimulator. The image of the nerve depends on the architecture of the nerve, the frequency of the transducer, the distance of the nerve from the probe, the angle between the nerve and the ultrasound beam, and the nature of the surrounding tissues.
The cords seem hyperechoic in the infraclavicular area and, being closer to the probe, seem hypoechoic in the axilla and the interscalene area. Perlas et al. were possibly looking for hypoechoic cords in the infraclavicular area. What they have labeled in the infraclavicular area is not likely to be a nerve because of its extremely small size; all the cords in the figure seem to be hyperechoic. This can be confirmed by obtaining a longitudinal image of the structure in question. It is not clear why they did not electrically stimulate the cords in the infraclavicular area. I have relabeled their figure 5, which is more like a medially placed sagittal section of the cords. By keeping the arm adducted and pronated, one can rotate the cords (fig. 1).
I disagree with their statement that earlier studies using a frequency less than 10 MHz have not seen nerves. The cords of the plexus can be clearly seen with 4–7 MHz (fig. 2). Ting and Sivagratnam 3showed images of different regions of the plexus with lower-resolution probes. Kapral et al. 4and others also obtained images of trunks and nerve branches in the supraclavicular and axillary areas, respectively.
As Greher and Kapral 5have rightly pointed out in their editorial, simply using a 12-MHz probe may not improve images in all areas. However, their criticism of Perlas et al. for keeping the needle under the ultrasound beam at all the times seems unfair. In Kapral’s technique, the needle and the ultrasound beam cross each other at only one point, and the needle will be seen as a speck, which may not necessarily be its tip. This, as well as a single injection, might be responsible for the prolonged onset time of 40 min in the study of Kapral et al. 4Keeping the needle under the beam allows visualization of the entire needle, the nerve, and the spread of the local anesthetic. The approach of Perlas et al. allows the needle to be seen at all times, adds safety, and allows multiple injections without moving the transducer or completely removing the needle. On the other hand, their use of a large-size probe requires a longer course by the needle through the soft tissues, which is a minor disadvantage as long as one can recognize images of important structures and avoid them, which can be accomplished by simply using a smaller probe.
New York University School of Medicine, New York New York. firstname.lastname@example.org