To the Editor:
I read with interest the publication by Quan et al. on a simple and effective method for lining up an ultrasound probe to the radial artery for its cannulation in pediatric patients in the November issue of Anesthesiology.1 Their cannulation method using acoustic shadowing proved to be highly effective for first pass success.1
Two things need clarification for correct interpretation of their described technique. First, air is a poor conductor of ultrasound waves. The authors state, “The developing lines are made of metal-containing strands taken from x-ray–detectable surgical gauze.” Lines from highly reflective metal are not immediately apparent in figure 3. Perhaps the metal strands are very small, and they are essentially artificial air pockets, which cause the shadowing. Second, preparing and setting up this method must take time. The difference of the median time to locate the artery between the traditional and the novel technique was 12 s. Getting the gauze wires lined up nicely in a parallel fashion on the probe while maintaining sterility seems challenging and would probably lose the seconds gained. Besides, we do not want an air bubble to get trapped between the two gauze wires because of poor application of the sterile probe cover, as it will obscure the underlying tissue in shadows.
There are also other approaches. On some ultrasound machines, M-mode draws a line in the center of the ultrasound image, before displaying the M-mode trace of the tissue on that line (fig. 1). Once this M-line goes through the middle of the artery, one aligns the catheter with the center marker on the probe and attempts to cannulate the artery. The instruction manual of the ultrasound machine used by Quan et al. has a similar feature.
In the end, Quan et al. have shown us that a proper ultrasound alignment and artery cannulation technique diminishes the complication rate.1 This is a result that counts.
Dr. Kuiper received payment for lectures from Danube University Krems, Krems an der Donau, Austria, outside the submitted work.