Introduction: This narrative review summarizes the evidence derived from randomized controlled trials (RCTs) pertaining to the use of adjunctive ultrasonography (US) for neuraxial blocks.
Evidence acquisition: The literature search was conducted using the MEDLINE, EMBASE and PUBMED databases. For the MEDLINE and EMBASE searches, the MESH terms "ultrasonography" and key word "ultrasound" were queried; using the operator "and", they were combined with the MESH terms "neuraxial block," "epidural anesthesia," "epidural analgesia," "spinal anesthesia," "spinal analgesia," "intrathecal anesthesia," "intrathecal analgesia," "caudal anesthesia," and "caudal analgesia." For the PUBMED search, the search terms "ultrasound neuraxial," "ultrasound intrathecal," "ultrasound epidural" (limited to clinical trials), "ultrasound spinal" (limited to clinical trials), and "ultrasound caudal" (limited to clinical trials) were queried. Seventeen RCTs were retained for analysis.
Evidence synthesis: Compared to conventional palpation of landmarks, US assistance (i.e., preprocedural scanning) results in fewer needle passes/insertions and skin punctures for neuraxial blocks in obstetrical and surgical patients. These benefits seem most pronounced when expert operators carry out the sonographic exams and for patients displaying difficult spinal anatomy. Preliminary findings also suggest that US provides similar pain relief and functional improvement to fluoroscopy for epidural/caudal steroid injection in patients afflicted with chronic spinal pain. Although one trial demonstrated shorter needling time with US guidance (i.e., real-time scanning of needle advancement) compared to US assistance, these findings require further validation.
Conclusions: Published reports of RCTs provide evidence to formulate limited recommendations regarding the use of adjunctive US for neuraxial blocks. Further well-designed RCTs are warranted.