Cervical erector spinae plane block: a cadaver study

Abstract

BackgroundCervical erector spinae plane (ESP) block has been described to anesthetize the brachial plexus (BP), however, the mechanism of its clinical effect remains unknown. As the prevertebral fascia encloses the phrenic nerves, BP and erector spinae muscles to form a prevertebral compartment, a local anesthetic injected in the cervical ESP could potentially spread throughout the prevertebral compartment. This study utilizes cadaveric models to evaluate the spread of ESP injections at the C6 and C7 levels to determine whether the injection can reach the BP and its surrounding structures.MethodsFor each of the five cadavers, an ESP injection posterior to the transverse process of C6 was performed on one side, and an ESP injection posterior to the transverse process of C7 was performed on the contralateral side. Injections were performed under ultrasound guidance and consisted of a 20 mL mixture of 18 mL water and 2 mL India ink. After cadaver dissection, craniocaudal and medial-lateral extent of the dye spread in relation to musculoskeletal anatomy as well as direct staining relevant nerves was recorded. The degree of dye staining was categorized as “deep,” “faint,” or “no.”ResultsThe phrenic nerve was deeply stained in 1 injection and faintly stained in 2 injections. Caudally, variable staining of C8 (100%) and T1 (50%) roots were seen. Faintly staining at C4 root was only seen in one sample (10%). There was variable staining of the anterior scalene muscles (40%) anterior to the BP and the rhomboid intercostal plane caudally (30%).ConclusionsUltrasound-guided cervical (C6 and C7) ESP injections consistently stain the roots of the BP and dorsal rami. This study supports the notion that the cervical ESP block has the potential to provide analgesia for patients undergoing shoulder and cervical spine surgeries.

Analgesic effects of erector spinae plane block can differ according to needle size

“…However, in a cadaver study, when 20 mL dye mixture was injected at the C6 or C7 level, the phrenic nerve was stained by 3 of 10 injections. [ 8 ] In our case, phrenic nerve and brachial plexus block were observed in 1 (case 1) of 2 patients who had an excellent analgesic effect. For this reason, we believe that ESPB at the C7 level may be more likely to cause diaphragmatic paralysis.…”

Mechanisms of action of the erector spinae plane (ESP) block: a narrative review

“…24 A final consideration is that extent of dye spread is determined by macroscopic visual inspection of the results of dissection or imaging, and more subtle boundaries of spread may not be evident. In some cadaveric studies, a distinction is made between heavy or faint dye staining of nerves, 25 but it is unclear how this correlates with anesthetic effect in living subjects. As will be discussed, even very low concentrations of local anesthetic in the vicinity of a nerve may exert a physiologic effect.…”

“…93 Similarly, cadaveric injection at the C6 and C7 level consistently produced staining of the C5-C8 nerve roots, as well as the suprascapular, dorsal scapular, and long thoracic nerves that innervate the shoulder girdle. 25…”

Anatomic and radiological correlation of injectate spread from first thoracic costotransverse junction in cervical erector spinae plane

“…8,9 A cadaveric study using injections of MBD dorsal to C6 TP demonstrated consistent stain of ventral nerve roots in all specimens and phrenic nerve in one specimen. 11 The study involved injection and dissection in a prone position and then repositioned to supine followed by anterior dissection. This could lead to the spread of dye to unwanted areas affecting the analysis.…”