Evidence for the Use of Ultrasound in Neuraxial Blocks

Goals: To summarize the existing evidence behind the role of ultrasonography in neuraxial anesthesia techniques. Methods: A literature search of the MEDLINE, PubMed, ACP Journal Club databases, and the Cochrane Database of Systematic Reviews was performed using the term ultrasonography combined with each of the following: spinal, intrathecal, epidural, and lumbar puncture. Only studies related to regional anesthesia or acute pain practice were included. Case reports and letters to the editor were excluded. Seventeen relevant studies were identified and included in this review. Results: Neuraxial ultrasonography is a recent development in regional anesthesia practice. Most clinical studies to date come from a limited number of centers and have been performed by very few and highly experienced operators. The existing evidence may be classified in 2 main content areas: (a) ultrasound-assisted neuraxial techniques and (b) real-time ultrasound-guided neuraxial techniques. (a) Ultrasound-assisted neuraxial techniques: Two scanning planes have been identified to offer useful acoustic windows for the assessment of spinal sonoanatomy providing complementary information: A parasagittal scanning plane (paramedian, longitudinal window) and an axial plane (transverse midline window). A preprocedure ultrasound can more accurately determine the location of a specific vertebral interspace than physical examination alone. The epidural and intrathecal spaces may be identified by ultrasonography, and the skin-to-epidural space or skin-to-intrathecal space distances may be accurately predicted. The use of a preprocedure ultrasound is associated with a lower number of attempts and a lower number of interspaces attempted by experienced anesthesiologists inserting an epidural catheter for labor analgesia. It may improve learning curves of junior trainees. (b) Real-time ultrasound-guided neuraxial techniques: Fewer and more recent studies report the use of this modality, mostly in the pediatric population. When performed by experienced anesthesiologists on selected patients with otherwise normal anatomy, the resulting efficacy is similar to that of standard techniques, but it may result in a shorter procedure time and less instances of "bony contact." A paucity of data exists in the nonobstetric adult population and on the impact of ultrasound use on safety profile. Conclusions: Neuraxial ultrasonography has been recently introduced to regional anesthesia practice. The limited data available to date suggest that it is a useful adjunct to physical examination, allowing for a highly precise identification of regional landmarks and a precise estimation of epidural space depth, thus facilitating epidural catheter insertion. Further research is needed to conclusively establish its impact on procedure success and safety profile, particularly in the adult nonobstetric population.