Ultrasound guidance and success rates of axillary brachial plexus block - II

Abstract

1 study comparing ultrasound with nerve stimulation for axillary plexus block. Despite increased use of ultrasound in regional anesthesia, randomized trials comparing this approach with modern nerve stimulation techniques are relatively few.2 However, in our opinion this study missed an opportunity to fully investigate the role of ultrasound for axillary block.Unfortunately, ultrasound in Chan et al.'s 1 study did not utilize current nerve stimulation modalities for axillary block.3-5 The authors reported a success rate of 62.9% for median, ulnar and radial sensory block, which is relatively low compared with currently published data (> 92% success rates) and our clinical experience. 6Despite this discrepancy, the authors conclude that ultrasound "significantly improves the success rate." We also note a slight error in Table II for "Successful surgical anesthesia without supplementation".1 For the ultrasound group, we believe the reported percentage should have been 92.2% rather than 95% (59 of 64, not 62 patients). This changes the P value (but not overall significance) from 0.07 to 0.26.Studies demonstrating success rates of 91-97% have accepted a distal response as the only endpoint for radial nerve stimulation. Coventry et al.3 performed triple stimulation axillary block (25 mL lidocaine 1.5% with epinephrine), reporting 100% sensory blockade of median, ulnar and radial nerves to pinprick at 30 min. Sia et al. 4 performed triple stimulation axillary block (36 mL lidocaine 2% and bupivacaine 0.5%). He reported success rates of 93% for median and ulnar sensory block (cold at 30 min) and 95% for the radial nerve. Chan et al.1 accepted triceps rather than distal responses as an appropriate endpoint in 85% of patients despite Sia 5 demonstrating a significant difference in sensory radial nerve blockade when comparing a proximal (triceps) with a distal (wrist/fingers) endpoint (81% vs 95%). The accompanying editorial alluded to the low success rate, but the findings were explained by "rigid definitive endpoints of complete pinprick", and despite stating that the proximal response "may have been detrimental", concluded "clearly, ultrasound visibility of the nerve will enhance success".

The Role of Continuous Peripheral Nerve Blocks

“…Unfortunately, a nonending dispute between nerve stimulation and ultrasound has distracted the focus of interest from clinically important questions [ 85 , 86 ]. Almost all comparative studies violate in a way or another at least one of the crucial points for correct nerve stimulation mentioned above and have been subject to criticism [ 87 – 89 ]. The recent review by Abrahams et al [ 90 ] dealing with this topic emphasized the superiority of ultrasound according to the present “evidence” and was severely disputed in web publications of letters to the editor [ 91 ].…”