After selecting the target transverse process for the block, place the transducer in a paramedian sagittal orientation, approximately 2 cm away from the midline (spinous processes), and try to visualize the transverse process.
ESSENTIAL FACT: At higher thoracic levels, e.g., above T5; trapezius, rhomboid major and erector spinae muscles can be identified as three layers superficial to the transverse processes. In the lower and mid-thoracic levels, only trapezius and erector spinae muscles can be seen.
Probe position and ultrasound image for an erector spinae block at the level of T5. Typically the rib-transverse process complex should be identified as a flat squared hyperechoic line with an acoustic shadow behind. Note that the pleura should not be visualized at the level where the block is performed. TP, transverse process; PVS, paravertebral space; Cr, cranial, Cd, caudad; A, anterior; P, posterior.
- If the transducer is placed too medial, the thoracic laminae will be visualized as flat hyperechoic lines. To fix: Slowly slide the transducer laterally.
- When the transducer is placed too lateral, ribs will be visualized as rounded acoustic shadows with an intermediate hyperechoic pleural line. To fix: Slowly slide the transducer medially.
Ultrasound imaging for an ESPB. Figure A. Transducer is placed too medial. Figure B. Adequate transducer position for an ESPB. Figure C. Transducer placed too lateral. ESP, erector spinae; TP, transverse process; PVS, paravertebral space. Cr, cranial, Cd, caudad; A, anterior; P, posterior.
- Insert the needle in-plane from a cranial to caudad direction until the needle tip contacts the transverse process.
- Inject 1-3 mL of local anesthetic to confirm proper injection plane by visualization of a spread deep to the erector spinae muscles and superficial to the transverse process.
- Complete the block with 20-30 mL of local anesthetic.
Reverse ultrasound anatomy of an ESPB with needle insertion in-plane from a cranial to caudad direction. The spinal nerve is exiting the paravertebral space (PVS) with the dorsal ramus branching and traveling posterior to innervate the posterior back muscles. TP, transverse process; PVS, paravertebral space. Cr, cranial, Cd, caudad; A, anterior; P, posterior.