We appreciate the letter by Gopalasingam et al.1 regarding our recently published study.2 Reports on ultrasound-guided vascular access have been increasing dramatically. However, before evaluating those data, we must consider several important factors, such as patients’ ages, sizes of vessels, quality of the ultrasound images, ultrasound application method and operator skill. Although Gopalasingam et al.1 commented that the low first attempt success rate was evidence of lack of an optimal technique, they should have considered the patients’ ages and ultrasound application method before comparing the data. We grouped study participants according to their age in the short and long-axis approach groups: infants (mean age, 5.6 months) and children (mean age, 40.8 months). Therefore, comparisons should be made with reports of similar demographics using the same technique. In our study, the first attempt success rate using the short-axis approach in children was 68%, similar to 67% (mean age, 40.3 months) and 76.3% (median age, 18.4 months) in previous studies.3,4
One more thing to be considered is the technique itself. We did not apply dynamic needle tip positioning (DNTP) to compare conventional short-axis and long-axis approaches. The disadvantage of the short-axis approach is the difficulty in finding the needle tip precisely. Moreover, we did not use the ultrasound transducer marked at a centreline and we inserted the needle with bevel-up orientation. Therefore, the posterior wall was more likely to be punctured with the conventional short-axis approach. The DNTP technique might overcome this weakness.5 However, DNTP is not a routine method for ultrasound-guided arterial cannulation. Furthermore, the usefulness of DNTP has not been validated for paediatric patients. Considering the small-sized, superficially lying, and easily-compressible vessels in paediatric patients, tracking the needle into the target vessel with proximal shifting of the transducer may be a challenge. Sloth et al.6 suggested the DNTP-para vessel approach for paediatric patients. Nevertheless, more studies are required to investigate outcomes when using DNTP in paediatric patients. In addition, we believe that the long-axis/in-plane approach is better than DNTP in not puncturing the posterior wall, because the needle tip can be more easily identified.
To avoid posterior wall puncture using the short-axis/out-of-plane approach in paediatric patients, additional movements of the needle and ultrasound transducer are necessary and we did not take this technique into account in our study. If we had applied DNTP, the results would have been totally different and the time required to obtain and adjust both the ultrasound image and needle might have been prolonged. Thus, it seems inappropriate to determine inadequate operator skills by simply comparing numbers without considering the meanings behind them.
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1. Gopalasingam N, Juhl-Olsen P, Sloth E. Posterior wall puncture during ultrasound-guided arterial cannulation suggests inadequate operator skills. Eur J Anaesthesiol
2. Song IK, Choi JY, Lee JH, et al. Short-axis/out-of-plane or long-axis/in-plane ultrasound-guided arterial cannulation in children: a randomised controlled trial. Eur J Anaesthesiol
3. Schwemmer U, Arzet HA, Trautner H, et al. Ultrasound-guided arterial cannulation in infants improves success rate. Eur J Anaesthesiol
4. Ishii S, Shime N, Shibasaki M, et al. Ultrasound-guided radial artery catheterization in infants and small children. Pediatr Crit Care Med
5. Clemmesen L, Knudsen L, Sloth E, et al. Dynamic needle tip positioning: ultrasound guidance for peripheral vascular access. A randomized, controlled and blinded study in phantoms performed by ultrasound novices. Ultraschall Med
6. Sloth E, Gopalasingam N, Obad DS, et al. Dynamic needle tip positioning-para vessel approach. Paediatr Anaesth