title: Ultrasound-guided approach to nerves (direct vs. tangential) and the incidence of intraneural injection: a cadaveric study.
abstract: This study evaluated the incidence of nerve puncture and intraneural injection based on the needle approach to the nerve (direct vs. tangential). Two expert operators in regional anaesthesia performed in-plane ultrasound-guided nerve blocks (n = 158) at different levels of the brachial plexus in cadavers, aiming either directly for the nerve (n = 77) or tangentially inferior to the nerve (n = 81). After reaching the outer limit of the nerve, the needle was intentionally advanced approximately 1 mm in both approaches, and 0.2-0.5 ml of saline was injected. Each operator classified (in real time) the needle tip and injectate as intraneural or not. Video clips showing the final position of the needle and the injection were evaluated in the same manner by seven independent expert observers who were blinded to the aims of this study. In addition, 20 injections were performed with ink for histological evaluation. Intraneural injections of saline were observed by the operator in 58% (45/77) of cases using the direct approach and 12% (10/81) of cases using the tangential approach (p < 0.001). The independent observers agreed with the operator in a substantial number of cases (Cohen's kappa index 0.65). Histological studies showed intraneural spread in 83% (5/6) of cases using the direct approach and in 14% (2/14) of cases using the tangential approach (p = 0.007). No intrafascicular injections were observed. There was good agreement between the operators' assessment and subsequent histological evaluation (Cohen's kappa = 0.89). Simulation of an unintentional/accidental advancement of the needle 'beyond the edge' of the nerve suggests significantly increased risk of epineural perforation and intraneural injection when a direct approach to the nerve is used, compared with a tangential approach.
authors.affiliation: Antwerp University Hospital, Antwerp, Belgium.
authors.forename: L A
authors.initials: LA
authors.lastname: Sermeus
authors.affiliation: University of Barcelona, Barcelona, Spain.|Hospital Clinic, Barcelona, Spain.
authors.forename: X
authors.initials: X
authors.lastname: Sala-Blanch
authors.affiliation: National University of Ireland and Clinical Research Facility, Galway University Hospitals, Galway, Ireland.
authors.forename: J G
authors.initials: JG
authors.lastname: McDonnell
authors.affiliation: Anaesthesiology Service of Hospital das Forças Armada/Polo Porto, Porto, Portugal.
authors.forename: C A
authors.initials: CA
authors.lastname: Lobo
authors.affiliation: Taunton and Somerset NHS Foundation Trust, Taunton, UK.
authors.forename: B J
authors.initials: BJ
authors.lastname: Nicholls
authors.affiliation: Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
authors.forename: G J
authors.initials: GJ
authors.lastname: van Geffen
authors.affiliation: Lapeyronie University Hospital, Montpellier, France.
authors.forename: O
authors.initials: O
authors.lastname: Choquet
authors.affiliation: University Hospital and University College Cork, Cork, Ireland.
authors.forename: G
authors.initials: G
authors.lastname: Iohom
authors.affiliation: Hospital Sant Joan de Deu, University of Barcelona, Spain.
authors.forename: B
authors.initials: B
authors.lastname: de Jose Maria Galve
authors.affiliation: Centre for Oncological Research Antwerp, University of Antwerp, Antwerp, Belgium.
authors.forename: C
authors.initials: C
authors.lastname: Hermans
authors.affiliation: Department of Pathology, Antwerp University Hospital, Antwerp, Belgium.
authors.forename: M
authors.initials: M
authors.lastname: Lammens
mesh_terms: D001917:Brachial Plexus / Q000000981:diagnostic imaging; D065527:Brachial Plexus Block / Q000009:adverse effects*; D002102:Cadaver; D006801:Humans; D015994:Incidence; D019300:Medical Errors / Q000706:statistics & numerical data; D009339:Needles; D009407:Nerve Block / Q000009:adverse effects*; D015588:Observer Variation; D010525:Peripheral Nerves / Q000000981:diagnostic imaging*; D012584:Sciatic Nerve / Q000000981:diagnostic imaging; D018084:Ultrasonography, Interventional / Q000379:methods*
keywords: intraneural injection; needle approach; peripheral nerve blocks; ultrasound