Lumbar Ultrasonography for Obstetric Neuraxial Blocks: Sonoanatomy and Literature Review

Abstract

Ultrasonography has gained popularity in recent years among anaesthesiologists and being used widely for regional blocks and central venous catheterization. Ultrasonography for neuraxial blocks was found beneficial especially for determining the correct needle insertion site and estimating the needle insertion depth of epidural space. In many recent studies, ultrasound guided epidural and spinal blocks have been evaluated among obstetric patients. Pre-procedural lumbar ultrasonography and real time ultrasound guidance for neuraxial blocks was the subject of these studies. We aimed to evaluate lumbar ultrasonography for obstetric neuraxial blocks. We describe the principles of lumbar ultrasound scanning techniques and present a practical review of lumbar sonoanatomy. We discuss the potential impact and benefits of the ultrasound-guided technique in improving obstetric neuraxial blocks and limitations of its use in clinical practice, based on previous studies.

Keywords: Lumbar ultrasonography; neuraxial block; obstetric anesthesia.

Figure 1

Positioning of the ultrasound probe for the transverse median approach

Figure 2

Visualisation of the spinal structures in the transverse median approach LF-D: ligamentum flavum-dura mater; VB-PLL: vertebral body-posterior longitudinal ligament; TP: transverse processes; AP: articular processes; DSac: dural sac; M: para-spinal muscles

Figure 3

Spinous process with underneath acoustic shadowing (transverse median approach)

Figure 4

a, b. Ultrasonographic measurement of epidural space depth using transverse median (a) and paramedian sagittal (b) approaches with the help of built-in calliper

Figure 5

Positioning of the ultrasound probe for paramedian sagittal oblique scanning

Figure 6

Visualisation of anatomical structures using the paramedian sagittal oblique approach. PC: posterior complex, consists of ligamentum flavum, epidural space and posterior dura mater. AC: anterior complex, consists of anterior dura mater, posterior longitudinal ligament, and posterior surface of the vertebral body or intervertebral disk L: lamina; DSac: dural sac (intrathecal space)

Figure 7

a, b. (a) Sacrum is usually seen as a hyperechoic flat or wedge-shaped structure (b) The exact vertebral interspace can be determined by counting vertebrae caudad-to-cephalad direction starting from the sacrum. The arrows are showing the gaps (acoustic windows) between vertebrae where anterior and posterior complex could be seen. The images are obtained using the paramedian sagittal oblique approach

Figure 8

a, b. (a) Saw-teeth pattern, which indicates the laminae interrupted by intervertebral spaces (b) The epidural space between the hyperechoic dura mater and the ligamentum flavum produces a thin hyperechoic parallel line seen as an equal sign. The images are obtained using the paramedian sagittal oblique approach

Figure 9

Positioning of the ultrasound probe for longitudinal median scanning

Figure 10

Visualisation of the spinal structures in the longitudinal median approach. The tips of spinous processes are seen as a series of hyperechoic lines with posterior acoustic shadowing