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Chapter 37. Sonography of the Lumbar Paravertebral Space and Considerations for Ultrasound-Guided Lumbar Plexus Block

Which of the following statements is correct regarding lumbar plexus block (LPB)?

A. LPB is a superficial block.

B. LPB is accomplished by a small amount (less than 5 mL) of local anesthetic solution.

C. Traditionally, LPB has been performed under computed tomography or fluoroscopy guidance.

D. Ultrasound can monitor the needle path and final needle tip placement during LPB.

D is correct. Ultrasound (US) is increasingly being used to guide peripheral nerve blocks, and it is only logical that ultrasound-guided LPB is of interest because of the ever-increasing availability of US machines that produce high-quality images in the operating room. US has been used to preview the relevant anatomy, measure the depth to the transverse process, guide the block needle to the posterior aspect of the psoas muscle or the lumbar plexus in real time, and monitor needle–nerve contact or spread of local anesthetic during an LPB. Understanding the sonoanatomy of the lumbar paravertebral region is a prerequisite for US-guided LPB.

A is incorrect. The lumbar plexus lies deep to and within the psoas muscles.

B is incorrect. Because the roots of the lumbar plexus are located in the fascial plane within the posterior aspect of the psoas major muscle, an injection of a sufficient volume of local anesthetic (approximately 20–30 mL) to fill the compartment is required.

C is incorrect. Traditionally, LPB has been performed using surface anatomical landmarks to identify the site for needle insertion and eliciting quadriceps muscle contraction in response to nerve stimulation. The main challenges with accomplishing LPB with anatomical landmarks and peripheral nerve stimulation relate to the depth at which the lumbar plexus is located. Small errors in estimation of landmark or angle of needle insertion can lead to the block needle being directed away from the plexus, resulting in inadvertent deep needle insertion or renal or vascular injury. Therefore, real-time monitoring of the needle and local anesthetic injection during an LPB is desirable and may improve the accuracy and safety of the technique. Although computed tomography and fluoroscopy can be used to increase precision during LPB, these technologies are impractical in terms of cost- and time-effectiveness, and more importantly, exposure to radiation.

Where are the roots of the lumbar plexus located at the level of L3–L4?

A. Between the erector spinae and psoas major muscles

B. In the fascial plane within the psoas major muscle

C. Lateral to the quadratus lumborum muscle

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