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Ultrasound scanning (US) can offer several advantages when used to guide placement of the needle for centroneuraxial blocks (CNBs). It is noninvasive, safe, simple to use, can be performed expeditiously, provides real-time images, is devoid from adverse effects, and it may be beneficial in patients with abnormal or variant spinal anatomy. When used for chronic pain interventions, US also eliminates or reduces exposure to radiation. In expert hands, the use of US for epidural needle insertion was shown to reduce the number of puncture attempts,1–4 improve the success rate of epidural access on the first attempt,2 reduce the need to puncture multiple levels,2–4 and improve patient comfort during the procedure.3 These advantages led the National Institute of Clinical Excellence (NICE) in the United Kingdom to recommend the routine use of ultrasound for epidural blocks.5 Incorporating these recommendations into clinical practice, however, has met significant obstacles. As one example, a recent survey of anesthesiologists in the United Kingdom showed that >90% of respondents were not trained in the use of US to image the epidural space.6 In this chapter, we describe techniques of US imaging of the spine, the relevant sonoanatomy, and practical considerations for using US-guided CNB and nerve blocks close to the centroneuroaxis.

Bogin and Stulin were probably the first to report using US for central neuraxial interventional procedures.7 In 1971, they described using US to perform lumbar puncture.7 Porter and colleagues, in 1978, used US to image the lumbar spine and measure the diameter of the spinal canal in diagnostic radiology.8 Cork and colleagues were the first group of anesthesiologists to use US to locate the landmarks relevant for epidural anesthesia.9 Thereafter, US was used mostly to preview the spinal anatomy and measure the distances from the skin to the lamina and epidural space before epidural puncture.10,11 More recently, Grau and coworkers, from Heidelberg in Germany, conducted a series of studies, significantly contributing to the current understanding of spinal sonography.1–4,12–15 These investigators described a two-operator technique consisting of real-time US visualization of neuraxial space using a paramedian sagittal axis and insertion of the needle through the midline to accomplish a combined spinal-epidural block.4 The quality of the US image at the time, however, was substantially inferior to that of today's equipment, thus hindering acceptance and further research in this area. Recent improvements in US technology and image clarity have allowed for much greater clarity during imaging of the spine and neuraxial structures.16,17

Basic Considerations

Because the spine is located at a depth, US imaging of the spine typically requires the use of low-frequency ultrasound (5-2 MHz) and curved array transducers. Low-frequency US provides good penetration but unfortunately, it lacks the spatial resolution at the depth (5–7 cm) at which the neuraxial structures are located. The osseous framework of the spine, which envelops the neuraxial structures, reflects much ...

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