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Ultrasound vs Neurostimulation for Wrist Blocks

Title
Ultrasound or nerve stimulation-guided wrist blocks for carpal tunnel release: a randomized prospective comparative study
Authors
Macaire P et al.
Journal
Regional Anesthesia and Pain Medicine2008;33: 363-8.

 

Study Summary

 

This article nicely illustrates the utility of ultrasound-guidance in performing forearm blocks of the median and ulnar nerve. The authors studied 60 adult patients undergoing carpal tunnel surgery and randomized them to either ultrasound-guided or neurostimulation-guided median and ulnar nerve blocks in the forearm. The endpoint of the ultrasound-guided technique was adequate local anesthetic spread, and the endpoint of the neurostimulation technique was motor or sensory response to a minimum current threshold of 0.5mA.
The authors looked at individual as well as total block performance time, which included scanning and injection time.

 

The nerves were located very quickly; scanning time for nerve location took an average of 12 seconds (10-20 seconds). Block performance time was shorter in the ultrasound-guided group for the median nerve (55 vs. 100 sec) and the ulnar nerve (58 vs. 80 sec). Interestingly, onset time was longer in the ultrasound-guided group (370vs 254 sec for median nerve, 367 vs. 241sec for ulnar nerve). The authors observed a high incidence of intraneural injection (evidenced by nerve expansion on ultrasound) in the neurostimulation group and postulated that this might account for the faster onset. This is in keeping with other reports by Bigeleisen and Rodriguez, which suggest that rapid onset may be a consequence of intraneural injection.

 

Given that the difference in onset was not clinically significant, and the success rates were equivalent, ultrasound-guidance appears to be preferable, especially if intraneural injection is to be avoided.

 

References

 

  1. Bigeleisen, P. E. (2006). "Nerve puncture and apparent intraneural injection during ultrasound-guided axillary block does not invariably result in neurologic injury." Anesthesiology 105(4): 779-83.
  2. Rodríguez J, Taboada M, Blanco M, Oliveira J, Bárcena M, Alvarez J. Intraneural catheterization of the sciatic nerve in humans: a pilot study. Reg Anesth Pain Med. 2008 Jul-Aug;33(4):285-90.