Ultrasonography (US) as a means to guide peripheral nerve blockade (PNB) was first explored by anesthesiologists at the University of Vienna in the mid-1990s.1 Although radiologists had made use of ultrasound technology to guide needles for biopsy, the application of this imaging modality for PNB was novel at that time.2 The utility of ultrasound to facilitate a range regional anesthesia techniques including brachial plexus and femoral blocks was demonstrated.1,3 A decade later, colleagues from the University of Toronto, Canada, began to embrace this technology, further demonstrating its utility and describing in detail the sonoanatomy of the brachial plexus.4 A number of advances in technology took place in the meantime, including smaller and more mobile ultrasound platforms, improved resolution, and needle recognition software, all cumulatively leading to increased bedside utility of ultrasound by anesthesiologists.5
ADVANTAGES OF ULTRASOUND GUIDANCE
The previously used surface anatomy-based techniques, such as nerve stimulation, palpation of landmarks, fascial “clicks,” paresthesias, and transarterial approaches, did not allow for the monitoring of the disposition of the local anesthetic injectate. Ultrasound guidance, however, offers a number of important practical advantages for nerve blockade. Ultrasound allows visualization of the anatomy of the region of interest. This allows more informed guidance for the needle pathway to the target while avoiding structures that might be damaged by the needle.6 Ultrasound also allows visualization of the needle tip as it is passed through the tissues, confirming alignment with the intended path, again reducing the likelihood of inadvertent needle trauma to unintended structures. Perhaps most important, real-time ultrasound imaging permits continual visualization of local anesthetic solution delivery to ensure proper distribution, with the potential for adjustment of the needle tip position as necessary to optimize local anesthetic distribution.7 Introduction of ultrasound guidance in regional anesthesia has led to refinement of many nerve block techniques, expanded use of PNB, and greater acceptance by surgical colleagues and patients.
ULTRASOUND AND SONOANATOMY
Ultrasound-guided PNB may be broken down into two fundamental aspects: imaging structures in the plane of section, including the target nerve, and guiding the needle. Understanding and recognition of three-dimensional anatomic structures on a two-dimensional image requires training in the technology and sonoanatomy pattern recognition (Table 30–1). As anatomic recognition remains essential to placing blocks, even with real-time visual guidance, specialty society guidelines for training residents and fellows continue to stress the importance of anatomical dissection and gross anatomy training as an inherent component of learning ultrasound-guided regional anesthesia (UGRA).8 In a study conducted over a 1-month regional anesthesia rotation, residents demonstrated markedly improved recognition of relevant structures at the sites of several different PNBs, using ultrasound imaging.9 In an evaluation of ultrasound-guided interscalene block instruction, residents demonstrated increasing efficiency of sonoanatomy recognition as their experience over the course of the rotation increased.10
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