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Opening injection pressure monitoring using an in-line device does not prevent intraneural injection in an isolated nerve model
  1. Jorge Mejia1,
  2. Victor Varela2,
  3. Javier Domenech1,
  4. Pierre Goffin3,4,
  5. Alberto Prats-Galino5,6 and
  6. Xavier Sala-Blanch1,7
  1. 1Anesthesiology, Hospital Clinic de Barcelona, Barcelona, Spain
  2. 2Master in Advanced Medical Skills in Regional Anesthesia based in Anatomy, University of Barcelona, Barcelona, Catalunya, Spain
  3. 3Anesthesia and intensive care, MontLégia Hospital, Groupe Santé CHC, Liège, Belgium
  4. 4Masters Degree in Advanced Medical Competences, Regional Anaesthesia Based on Human Anatomy, Universitat de Barcelona, Barcelona, Catalunya, Spain
  5. 5Human Anatomy and Embryology, Universitat de Barcelona, Barcelona, Spain
  6. 6Institut d'Investigacions Biomèdiques August Pi i Sunyer, Barcelona, Catalunya, Spain
  7. 7Anatomy and Embriology Department, Universitat of Barcelona, Barcelona, Spain
  1. Correspondence to Dr Xavier Sala-Blanch, Department of Anesthesiology, Hospital Clínic of Barcelona, 08036 Barcelona, Spain; xavi.sala.blanch{at}


Background Injection pressure monitoring using in-line devices is affordable and easy to implement into a regional anesthesia practice. However, solid evidence regarding their performance is lacking. We aimed to evaluate if opening injection pressure (OIP), measured with a disposable in-line pressure monitor, can prevent intraneural (subepineural) injection using 15 pound per square inch (PSI) as the reference safety threshold.

Methods An isolated nerve model with six tibial and six common peroneal nerves from three unembalmed fresh cadavers was used for this observational study. A mixture of 0.5% ropivacaine with methylene blue was injected intraneurally at a rate of 10 mL/min, to a maximum of 3 mL. OIP was recorded for each injection as well as evidence of intraneural contrast. Injected volume at 15 and 20 PSI was recorded, and when it leaked out the epineurium, if it occurred.

Results In all cases, OIP was<15 PSI and intraneural contrast was evident before the safety threshold. The 15–20 PSI mark was attained in 5 of 12 injections (41%), with a median injected volume of 0.9 mL (range 0.4–2.3 mL). Peak pressure of >20 PSI was reached in two injections (at 0.6 mL and 2.7 mL). Contrast leaked out the epineurium in 11 of 12 injections (91%) with a median injected volume of 0.6 mL (range 0.1–1.3 mL).

Conclusions Our results suggest that in-line pressure monitoring may not prevent intraneural injection using an injection pressure of 15 PSI as reference threshold. Due to the preliminary nature of our study, further evidence is needed to demonstrate clinical relevance.

  • nerve block
  • ultrasonography
  • technology
  • outcomes

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  • Contributors JM, PG, and AP-G was involved with review of the data and preparation of the manuscript. VV was involved with planning and design of the study, and preparation of the manuscript. JD helped in preparation of the manuscript. XS-B involved with conception, planning, design and conduction of the study, review of the data, and preparation of the manuscript.

  • Funding Supported by funding from the Department of Anatomy and Embriology, School of Medicine. Universitat of Barcelona. Spain.

  • Competing interests None declared.

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