We thank Drs. Gray and Schafhalter-Zoppoth for their interest in our article 1and confirming the usefulness of ultrasound imaging for nerve localization based on their own experience. The value of ultrasound technology is obvious when the technical skill is acquired.
Drs. Gray and Schafhalter-Zoppoth raised concerns about potential danger of the technique we proposed for advancing the needle in the lateral to medial direction in the supraclavicular location. As stated in the text, this approach makes anatomic sense because the plexus is located lateral to the subclavian vessels; thus, needle will reach neural structures before the vessels. Ultrasound-guided nerve localization in this manner is safe, as demonstrated in our recent study. 2
Ultrasound imaging clearly defines the target nerves we wish to block and vital structures we wish to avoid, e.g. , pleura and vessels. We agree with Drs. Gray and Schafhalter-Zoppoth that “ultrasound-guided procedures are not without complications.” It is important to emphasize that the safety of ultrasound techniques relies on real-time observation of needle movement at the time of advancement. Without keeping the needle shaft and tip in constant view, needle penetration may be deeper than what is perceived on the monitor. With increased practice and technical experience over the past years, we are now confident in maintaining constant and proper needle–probe alignment to optimize needle visibility throughout the procedure. We have learned to make only purposeful needle movement and resist any advancement whenever needle tip visualization is in question. Another practical maneuver that helps to highlight needle tip position is injection of a small saline or air bolus through the needle so that an alert echo signal is generated in the tissue immediately adjacent to the needle tip. In our opinion, taking these cautionary steps during ultrasound-guided nerve localization is clearly a step in the right direction to combine accuracy with safety.
We also appreciate the comments from Dr. Sandhu, who expressed concern about our high failure rate of imaging the brachial plexus with the L12–L5 MHz probe in the infraclavicular region, creating a false impression that the plexus is very difficult to image in this area. This is not true. We have clearly pointed out in the Discussion that one must find the optimal balance between image quality and the depth of penetration when selecting a probe for brachial plexus scanning. Although the high-frequency L12–L5 MHz probe generates brachial plexus images with superb resolution in superficial locations (e.g. , interscalene, supraclavicular, axillary, and midhumeral), it has limited tissue penetration capability, precluding its usefulness at the deeper infraclavicular coracoid location. To scan deep-seated structures, probes of lower frequency (e.g. , in the 4-to 7-MHz range) are necessary.
We agree with Dr. Sandhu that the brachial plexus seems hyperechoic in the infraclavicular region, whereas it is hypoechoic in the other four superficial locations examined. With clinical experience, we can now visualize the brachial plexus in the infraclavicular location using a linear 4-to 7-MHz probe and achieve consistent block success. It is important to point out that probe frequency (high vs. low) is only one of several important determinants of image clarity on ultrasound. Technological advance such as real time compound imaging with the Philips HDI 5000 unit (ATL Ultrasound, Bethell, WA) also adds to the image quality we observed, 1significantly superior to that seen in earlier studies. 3,4
Toronto Western Hospital, University Health Network, Toronto, Ontario, Canada. vincent.chan@uhn.on.ca
