Trainee anaesthetist diagnosis of intraneural injection—a study comparing B-mode ultrasound with the fusion of B-mode and elastography in the soft embalmed Thiel cadaver model

Abstract Background The incidence of intraneural injection during trainee anaesthetist ultrasound guided nerve block varies between 16% in experts and up to 35% in trainees. We hypothesized that elastography, an ultrasound-based technology that presents colour images of tissue strain, had the potential to improve trainee diagnosis of intraneural injection during UGRA, when integrated with B-Mode ultrasound onto a single image. Methods We recorded 40 median nerve blocks randomly allocated to 0.25 ml, 0.5 ml, 1 ml volumes to five sites, on both arms of two soft embalmed cadavers, using a dedicated B-Mode ultrasound and elastography transducer. We wrote software to fuse elastogram and B-Mode videos, then asked 20 trainee anaesthetists whether injection was intraneural or extraneural when seeing B-Mode videos, adjacent B-Mode and elastogram videos, fusion elastography videos or repeated B-Mode ultrasound videos. Results Fusion elastography improved the diagnosis of intraneural injection compared with B-Mode ultrasound, Diagnostic Odds Ratio (DOR) (95%CI) 21.7 (14.5 - 33.3) vs DOR 7.4 (5.2 – 10.6), P P P Conclusions Fusion elastography improved the accuracy, reliability and confidence of trainee anaesthetist diagnosis of intraneural injection.