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You are planning an erector spinae block on a 44-year-old patient with right-sided rib fractures. The ultrasound probe placement and resulting ultrasound image are shown below. As labeled in the ultrasound image, at which location would it be MOST appropriate to inject local anesthetic in order to achieve an erector spinae block?
Answer: C. Read the discussion below.
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The erector spinae block is a relatively newly described interfascial nerve block where local anesthetic is injected deep to the erector spinae muscle. Injection into this plane usually results in a spread of local anesthetic over several dermatomal levels, and has been used for analgesia for rib fractures as well as thoracic and lumbar surgeries. The purported mechanism of analgesic action is thought to be diffusion of local anesthetic into the rami of spinal nerves.
While several techniques have been described, the most common approach is using ultrasound guidance. After selecting the appropriate vertebral level, the ultrasound probe is placed in a paramedian sagittal orientation, approximately 2 to 3 cm off midline (Figure 1). Once the transverse process is identified, a needle is directed in-plane until it contacts the transverse process. At this point, a small amount of local anesthetic can be injected to confirm spread in a plane between the erector spinae muscle and the transverse process, followed by the remainder of the volume to be delivered.
Figure 1. Left: Placement of ultrasound probe for erector spinae block. Right: Ultrasound image showing transverse process and relevant anatomy. (A) A superficial interfascial plane. (B) Inside the erector spinae muscle. (C) The correct location to perform an erector spinae block. (D) Deep to the costal transverse ligament (the location to perform a paravertebral block). © 2020 American Society of Anesthesiologists.
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