The feasibility of micro-ultrasound as a tool to image peripheral nerves Chandra, A.; Eisma, Rosine; Felts, P.; Munirama, S.; Corner, G. A.; Demore, Christine; McLeod, Graeme Published in: Anaesthesia DOI:10.1111/anae.13708 Publication date: 2017 Document Version Peer reviewed version Link to publication in Discovery Research Portal Citation for published version (APA):Chandra, A., Eisma, R., Felts, P., Munirama, S., Corner, G. A., Demore, C. E. M., & McLeod, G. (2017). The feasibility of micro-ultrasound as a tool to image peripheral nerves. Anaesthesia, 72(2), 190-196. DOI: 10.1111/anae.13708 General rights Copyright and moral rights for the publications made accessible in Discovery Research Portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from Discovery Research Portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain.• You may freely distribute the URL identifying the publication in the public portal. Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. uk/2013-R1This is the peer reviewed version of the following article: 'The feasibility of micro-ultrasound as a tool to image peripheral nerves' Anaesthesia, which has been published in final form at http://dx.doi.org/ 10.1111/anae.13708. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving. 2 Keywords:Regional anaesthesia: mechanism of injury Peripheral nerves: anatomy Ultrasound structures: echogenicity SummaryThe incidence of transient and permanent nerve damage during regional anaesthesia has not changed despite widespread use of ultrasound imaging for needle guidance over the last decade. Current clinical ultrasound has insufficient anatomical resolution, and anaesthetists have difficulty judging the precise location of the needle tip relative to the epineurium. In view of the controversy surrounding intraneural injection, there is a need to understand the structural changes caused by subepineural and subperineural needle penetration. We present micro-ultrasound imaging, which offers anatomical resolution better than 100 m, as a tool suitable for visualising neural anatomy and deformation caused by needle insertion. We imaged nine nerves from fresh and soft embalmed Thiel cadavers.Fascicles > 0.4 mm in width were identified. Subepineural needle placement was associated with denting, rotation and elastic deformation of fascicles, whereas subperineural needle insertion split fascicles permanently. . Micro-ultrasound using a single element transducer has been used to identify the epidural space [12], demonstrated in a needle to aid neurosurgical guidance ...

IntroductionAlthough administration of regional anesthesia nerve blocks has increased during the COVID-19 pandemic, training opportunities in regional anesthesia have reduced. Simulation training may enhance skills, but simulators must be accurate enough for trainees to engage in a realistic way—for example, detection of excessive injection pressure. The soft-embalmed Thiel cadaver is a life-like, durable simulator that is used for dedicated practice and mastery learning training in regional anesthesia. We hypothesized that injection opening pressure in perineural tissue, at epineurium and in subepineurium were similar to opening pressures measured in experimental animals, fresh frozen cadavers, glycol soft-fix cadavers and patients.MethodsWe systematically reviewed historical data, then conducted three validation studies delivering a 0.5 mL hydrolocation bolus of embalming fluid and recording injection pressure. First, we delivered the bolus at 12 mL/min at epimysium, perineural tissue, epineurium and in subepineurium at 48 peripheral nerve sites on three cadavers. Second, we delivered the bolus at using three infusion rates: 1 mL/min, 6 mL/min and 12 mL/min on epineurium at 70 peripheral nerve sites on five cadavers. Third, we repeated three injections (12 mL/min) at 24 epineural sites over the median and sciatic nerves of three cadavers.ResultsMean (95%) injection pressure was greater at epineurium compared with subepineurium (geometric ratio 1.2 (95% CI: 0.9 to 1.6)), p=0.04, and perineural tissue (geometric ratio 5.1 (95% CI: 3.7 to 7.0)), p<0.0001. Mean (95%) injection pressure was greater at 12 mL/min compared with 1 mL/min (geometric ratio 1.6 (95% CI: 1.2 to 2.1), p=0.005). Pressure measurements were similar in study 3 (p>0.05 for all comparisons).DiscussionWe conclude that the soft-embalmed Thiel cadaver is a realistic simulator of injection opening pressure.

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