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Ultrasound is better than injection pressure monitoring detecting the low-volume intraneural injection
  1. Pierre Goffin1,2,
  2. Jorge Mejia3,
  3. Alberto Prats-Galino4,
  4. Lorena Morales1,
  5. Miriam Panzeri3 and
  6. Xavier Sala-Blanch3,4
  1. 1 Masters Degree in Advanced Medical Skills. Regional Anesthesia Based on Human Anatomy, University of Barcelona, Barcelona, Barcelona, Spain
  2. 2 Anesthesia and Intensive Care, MontLégia Hospital, Groupe Santé CHC, Liège, Belgium
  3. 3 Human Anatomy and Embryology, Universitat de Barcelona, Barcelona, Spain
  4. 4 Human Anatomy and Embryology, University of Barcelona Faculty of Medicine, Barcelona, Spain
  1. Correspondence to Dr Jorge Mejia, Anesthesiology, Hospital Clinic de Barcelona, Barcelona 08036, Spain; jmejiak{at}


Introduction Inadvertent intraneural injection is not infrequent during peripheral nerve blocks. For this reason, injection pressure monitoring has been suggested as a safeguard method that warns the clinician of a potentially hazardous needle tip location. However, doubts remain whether it is superior to the sonographic nerve swelling in terms of earlier detection of the intraneural injection.

Methods An observational cadaveric study was designed to assess injection pressures during an ultrasound-guided intraneural injection of the median nerve. We hypothesized that the evidence of nerve swelling occurred prior to an elevated injection pressure (>15 pound per square inch) measured with a portable in-line monitor. 33 ultrasound-guided intraneural injections of 11 median nerves from unembalmed human cadavers were performed at proximal, mid and distal forearm. 1 mL of a mixture of local anesthetic and methylene blue was injected intraneurally at a rate of 10 mL/min. Following injections, specimens were dissected to assess spread location. Video recordings of the procedures including ultrasound images were blindly analyzed to evaluate nerve swelling and injection pressures.

Results 31 injections were considered for analysis (two were excluded due to uncertainty regarding needle tip position). >15 pound per square inch was reached in six injections (19%) following a median injected volume of 0.6 mL. Nerve swelling was evident in all 31 injections (100%) with a median injected volume of 0.4 mL. On dissection, spread location was confirmed intraneural in all injections.

Discussion Ultrasound is a more sensitive and earlier indicator of the low-volume intraneural injection than injection pressure monitoring.

  • nerve block
  • peripheral nerve injuries
  • regional anesthesia
  • ultrasonography

Data availability statement

No data are available. Not applicable.

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Data availability statement

No data are available. Not applicable.

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  • Contributors PG and JM contributed equally to this paper and share first authorship. PG designed and conducted the study, analyzed and interpreted the data, and helped write the manuscript. JM analyzed and interpreted the data, and wrote the manuscript. JM acts as the corresponding author and guarantor. AP-G, LM, and MP helped in design and acquisition of data. XS-B designed and conducted the study, and helped write the manuscript.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.