Source: Sia et al. Reg Anes Pain Med 2001; 26(6): 499-503

Reviewer:  R. Prasad, MD

Summary:

• Nerve stim technique
• Local=1:1 mix of lido 2% and bupiv 0.5%. 4cc injected subcut over artery (block medial cut nn of arm & forearm) in all
• 2N (20ml at median & radial Nn) and 3N (10ml for musculucut ("MC"), 10 median, 20 radial nn) adequate for hand block; 90% success
• 3N better if need to block musculocutaneous (lateral forearm) distribution reliably (98% vs 80% success of MC block)
• primary block effectiveness = % with complete block of all 6 nerves after 30min
• study is underpowered to detect difference in this; needed 195 patients per group based on their pilot data

• I don't think there's really much new information here
• Nevertheless, it is additional evidence for efficacy of 3N technique

• 100 ASA-PS I and II for elective hand, wrist, or forearm surgery with block
• Fent 1mcg/kg & midaz 20 mcg/kg premed
• Randomly assigned 2N vs 3N
• All nerves found at 0.5mA. Blocks performed or supervised by Sia.
• Blocks assessed by blinded investigator:
• onset at 10, 20, and 30min after start (MC, rad, med, uln, med cutaneous nn of arm & forearm distributions checked)
• if no block at 30min, missed nn blocked more distally; tested at 40 and 50min
• latency time = time ready for surgery
• Sample size based on expected chance of blocking MC from pilot study: assuming 97% vs. 80%, needed 47 pts in each group for 80% power with p<0.05.

• 90% block of 3n to hand in both groups
• 10pts needed supplementary blocks (all successful)
• 2N: 6pts
• 3N: 4pts
• similar onset time (~16±8min), latency time (~20±10min), venous puncture (4-5), motor block, tourniquet pain, sedation request, sx of IV injection, unintentional paresthesia
• Primary block success (after 30min, without addtl blocks). P<0.05 only for MusculoCut (*)