THE USE OF ultrasound imaging for vascular access increasingly is becoming the standard of care, increasing firstpass efficacy and minimizing complications. 1-5 Recently, Arora et al. conducted a randomized, prospective, observational cohort study at a single institution, with the aim of determining whether ultrasound-guided out-of-plane imaging was superior to in-plane imaging for radial artery cannulation for patients undergoing cardiac surgery. 6 These investigators should be congratulated for this contribution, as the body of literature examining the benefits of ultrasound for arterial cannulation is considerably smaller compared with the literature describing ultrasound for central venous cannulation. 3 In their cohort of 84 patients, the firstpass success rate was higher for the in-plane technique compared with the out-of-plane technique (85.7% v 57.1%; p = 0.007). This observation supported their conclusion that the in-plane technique is superior for ultrasound-guided radial artery cannulation. 6 In their clinical trial, an experienced operator, who had performed more than 50 radial artery cannulations with each technique, conducted each arterial cannulation with a linear highfrequency ultrasound probe and a 20-gauge arterial catheter. 6 The study subgroups were balanced, with 42 patients randomly assigned to each group. The trial endpoints included number of first-pass successes, catheter redirections, skin punctures, hematomas, and cannulation failures. 6 The low first-pass success rate in the out-of-plane group was striking, when compared with the published evidence. 7,8 Sethi et al. have reported first-pass success rates for both in-plane and out-of-plane techniques to be greater than 80% (80% and 82.6%, respectively), and Quan et al. demonstrated first-pass success rates with the out-of-plane technique as high as 88.9% compared with 73.2% with the in-plane technique. 7,8 In both of these studies, the overall first-pass success rate was higher than the 57.1% firstpass success rate observed in the randomized trial by Arora et al. 6-8 The high first-pass success rates noted in these studies was congruent with the reviewed literature about first-pass :