Nerve block, nerve damage and fluid injection pressure: overturning the myth

Graeme McLeod, Miguel Angel Reina

Research output: Contribution to journalArticlepeer-review


Histological and micro-ultrasound evidence rebuffs deep-rooted views on the nature of nerve block, nerve damage, and injection pressure monitoring. We propose that the ideal position of the needle tip for nerve block is between the innermost circumneural fascial layer and outer epineurium, with local anaesthetic passing circumferentially through adipose tissue. Thin, circumferential, subepineural expansion that is invisible to the naked eye was identified using micro-ultrasound, and could account for variability of outcomes in clinical practice. Pressure monitoring cannot differentiate between intrafascicular and extrafascicular injection. High injection pressure only indicates intraneural extrafascicular spread, not intrafascicular spread, because it is not possible to inject into the stiff endoneurium in most human nerves.
Original languageEnglish
JournalBritish Journal of Anaesthesia
Early online date5 Jan 2024
Publication statusE-pub ahead of print - 5 Jan 2024


  • anatomy
  • epineurium
  • histology
  • injection pressure
  • nerve block
  • ultrasound-guided regional anaesthesia


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