We thank Hunter et al.,1 Kuiper,2 and Slikboer et al.3 for their interest in our new approach for radial artery cannulation in pediatric patients,4 and it is our great honor to respond the questions and comments raised by them.
In response to the comment by Hunter et al.,1 our new approach is featured by adding two more isolation lines to the ultrasonic probe. These two developing lines were placed on the ultrasonic probe before applying the coupling agent (fig. 1). In addition, placing these two developing lines takes less than 5 s. For less experienced practitioners, this method may shorten the time taken for both locating the targeted artery and puncturing it.
In response to Kuiper,2 we admit that air may be trapped in the space between the two gauze wires and sterile probe cover. However, this situation can be overcome by filling the space with the coupling agent. In fact, in the current study, we first placed the two developing lines and then applied the coupling agent (fig. 1). Thereafter, we wrapped the probe with a 3M Tegaderm (3M Company, 3M Health Care, USA) transparent film to maintain aseptic conditions. We found that the developing effect was not related to the type of wire used; rather, it is associated with its diameter. Use of extremely fine wire (e.g., surgical suture) might result in poor developing effect. Thus, we utilized the wire from the surgical gauze because of its superior developing effects, rather than its metallic nature.
Based on our experience, preparations for this method should not take longer than 5 s because the developing lines do not have to be placed under sterile conditions. After placing the two developing lines and applying the coupling agent, we wrapped the ultrasound probe with a 3M Tegaderm transparent film to maintain aseptic conditions. Moreover, the M-mode draws a line in the center of the ultrasound image, but the needle often overlaps with the M-line during the procedure. Our method is better than those using M-mode because the targeted vessels are located by the two developing lines, and the shade of the needle can be visualized between these two lines.
In response to the comment and concern by Slikboer et al.,3 as we have mentioned above, our settings take no longer than 5 s to prepare. The wires from the surgical gauze need not be aseptic and can be reused multiple times. After placing the two developing lines and applying the coupling agent, the ultrasonic probe is wrapped in a 3M Tegaderm transparent film to maintain aseptic conditions.
The surgical gauze that contains the metal-containing wire (developing line) can be taken from the anesthesia toolbox rather than from the operating theatre. In addition, the wires do not require sterilization.
Since 2013, the research team has mainly used a modified out-of-plane approach (with a developing line tied to the midpoint of the ultrasound probe) for artery puncture,5 rather than the traditional out-of-plane approach. Therefore, the slightly lower accuracy of the first attempt may be related to the practitioners’ familiarity with one approach over the other.
Previous studies have shown that for ultrasound-guided vascular puncture, the first attempt success rate of the conventional out-of-plane approach does not differ significantly from that of the conventional in-plane approach.6–8 However, compared to the conventional out-of-plane method, our newly developed out-of-plane method significantly improves the first attempt success rate. We also appreciate the suggestion of a combined short- and long-axis approach for radial artery puncture. It will help to reduce the incidence of unwanted posterior wall puncture. In addition, based on our experience, the short-axis, out-of-plane approach is more applicable for puncturing shallow vessels with small diameters, whereas the long-axis in-plane approach is more applicable for puncturing deep vessels with a large diameters. Nevertheless, if the targeted vessel is fine and deep, a combined short- and long-axis approach should be used.
Figure 3 in our original article4 was generated using a vascular puncture model rather than a radial artery model. Therefore, the display scale does not accurately match the actual image. We used the vascular model for better illustration of the display of our method. The actual image is shown in figure 2B in the article.4
Dr. Zhang reports financial support from Beijing Municipal Science and Technology Commission (No. Z171100001017036). The other authors declare no competing interests.