Opening injection pressure monitoring using an in-line device does not prevent intraneural injection in an isolated nerve model

Abstract

BackgroundInjection 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.MethodsAn 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.ResultsIn 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).ConclusionsOur 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.

Ultrasound is better than injection pressure monitoring detecting the low-volume intraneural injection

“…In particular, opening injection pressure (OIP)—pressure required to start injection—should act as an objective warning that helps avoid the intraneural injection altogether. However, recent experimental data indicate otherwise: pressures may rise, but only when injection is underway 10. Our results ratify this perception, and suggest that US may be superior: indeed, OIP was <15 PSI in all cases, and only six injections (19%) reached ≥15 PSI requiring 0.6 mL of median injected volume, compared with a 100% detection of the sonographic nerve swelling with a median 0.4 mL of injected volume.…”

“…Though not widely used, the novel in-line monitors provide a simple and affordable method for clinicians to measure injection pressures in the clinical setting. However, doubts remain on their ability to prevent the intraneural injection, and their applicability in straightforward blocks performed by experienced practitioners is still debatable 10. Indeed, no study to date has evaluated if injection pressure monitoring is superior to US in terms of earlier detection of the intraneural injection.…”

Response to Dr Costa

“…We would like to thank Costa et al 1 for their interest in our study 2. We fully agree, as previously outlined, that pressure monitoring plays an important role in the prevention of nerve injury, and our results should not discourage from progressing in this direction 3.…”

Opening injection pressure as a part of multimodal monitoring to detect intraneural injections

“…We read with great interest the technical report from Mejia et al 1 as they provide interesting insights regarding the use of opening injection pressure (OIP) to detect intraneural injection during peripheral nerve block. The authors conclude that in-line pressure monitors may not prevent intraneural injection based on an isolated cadaveric nerve models (tibial and common peroneal nerves).…”