What do systematic reviews say?

Double vs single‐injection technique

Double showed no clear difference in complete failure of block3 compared with single‐injection technique (low certainty).

• Single, double or multiple‐injection techniques for non‐ultrasound guided axillary brachial plexus block in adults… 2016 · Cochrane Headline outcomes only
  RR 1.29 [0.33, 5.01]
  7 studies · 368 participants
  Low