Critical review: evolution and impact of ultrasound guidance on brachial plexus anaesthesia.
McCartney, Colin John Lindsay
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Brachial plexus block (BPB) techniques provide significant benefits including better pain control, faster discharge and reduced adverse effects compared to general anaesthesia. Prior to 2005 BPBs were performed using landmark, paraesthesia or electrical nerve stimulation (PNS) methods and were associated with reasonable success (70-80%) but were still associated with risk of failure and complications. Use of ultrasound (US) to guide local anaesthetic injection was first reported in 1989 but until 2004 remained unexplored. From 2004 we aimed to explore the feasibility, success and safety of ultrasound-guided brachial plexus block (USBPB) compared to techniques guided by anatomical landmarks or peripheral nerve stimulation. We hypothesized that USBPB would be feasible, have greater success and safety compared to standard methods. In 2004 we identified the possibility of using US to place infraclavicular block (ICB) and identified a pattern of local anaesthetic spread that predicated successful block. A subsequent randomized trial found improved success of US compared to existing methods. We examined success of US-guided axillary brachial plexus block (ABPB) and found that performance time and success were improved. In a large retrospective review of ABPB techniques we identified that US techniques were faster to perform, had a higher success and were safer compared to standard methods. We also assessed existing nerve localization methods in an observational study and found that both have poor sensitivity and specificity possibly explaining some of the limitations of these techniques. A bench study examining local anaesthetic injection using ultrasound found that both novices and experts could accurately determine local anaesthetic spread. In practice this is a useful marker for safe injection and could explain findings of increased safety with ultrasound methods. we systematically reviewed the literature for studies examining USBPB and this demonstrated that US improved block success and performance time. Subsequent pilot work indicated that US, in addition to improves block success and performance time. Subsequent pilot work indicated that US, in addition to improving quality, could also reduce volume of local anaesthetic required for successful block and we hypothesized that for certain techniques such as interscalene block this may improve safely. we compared US-guided interscalene block (ISB) using traditional volumes (20ml) and compared with a low volume (5ml) of ropivacaine 0.5%. Results demonstrated no difference in efficacy or duration but significant reduction in respiratory (and other) complications with lower volumes. We then compared US-guide ISB to PNS using and Up and Down Sequential Allocation design to estimate the minimum effective anaesthetic volume (MEAV50) for ropivavaine 0.5% for major shoulder surgery. Our findings indicated that volumes of local anaesthetic could be dramatically reduced with US (0.9 vs 5.4ml) whilst still providing effective pain relief. In the last ten years the cases and studies described have demonstrated that US improves BPB success and safety. For ISB US reduces volumes of local anaesthetic required for success whilst also reducing respiratory and other complications.