Unpredictable Injectate Spread of the Erector Spinae Plane Block in Human Cadavers

Abstract

We performed bilateral ultrasound-guided erector spinae plane blocks at the second and eighth thoracic vertebrae in 11 fresh frozen cadavers. Methylene blue dye spread variably and extensively deep to the erector spinae muscles fascia with involvement of the spinal rami and paravertebral space in 1 of 11 cadavers when injected at the eighth thoracic vertebra, and in 4 of 11 cadavers at the second thoracic vertebra, with crossover to the contralateral side of the spine. Our study demonstrates that in cadavers, an erector spinae plane block follows the fascial planes with unpredictable spread, which might explain its varying clinical efficacy.

Mechanism of action of the erector spinae plane block: distribution of dye in a porcine model

“…An interfascial cephalocaudal spread of dye with a median of 5 (range 4–7) segments was observed, which is shorter than the spread reported in human cadaveric studies 3 5 18. However, previous human studies bear a segmental incongruence in which the presence of dye on muscle surface is not always accompanied by compromise of the correspondent dorsal rami 3 5 18. For example, Ivanusic et al reports a distribution pattern from T1 to T12 in which only 3/12 segments the dorsal rami were stained in more than 50% of the injections 3.…”

“…Since the ESP block was first described by Forero et al in 2016, its therapeutic effect has been attributed to the cephalocaudal spread of local anesthetic in the musculofascial plane deep to the erector spinae muscle and its anterior diffusion into PVSs bathing the ventral and dorsal rami of the spinal nerves, the DRG and the rami communicantes 1 2. Although numerous clinical reports have endorsed the original theory,1 2 15 16 and some anatomical cadaveric studies demonstrate a scanty presence of dye in the thoracic PVS,3 5 17 there are, to date, no studies able to demonstrate either a systematic multisegmental involvement of the ventral rami of the spinal nerves or the communicating path between the ESP and the PVS 3 6 18…”

Comparison of ultrasound-guided erector spinae plane block and thoracic paravertebral block for postoperative analgesia after video-assisted thoracic surgery: a randomized controlled non-inferiority clinical trial

“…Adhikary et al 3 reported distribution of solution into the paravertebral space and epidural space whereas Ivanusic et al 5 reported that almost no solution reached the paravertebral space. Dautzenberg et al 23 also demonstrated that the dye distribution in ESPB was unpredictable, explaining its varied efficacy 23. In ESPB, if enough anesthetic solution had spread to the paravertebral or epidural space to reduce sensation at multiple intercostal levels, sensation should also have been reduced across multiple levels from the dorsal to the anterior cutaneous branch region (as occurred in the TPVB group).…”

Human volunteer study examining the sensory changes of the thorax after an erector spinae plane block

“…Cadaver studies examining local anesthetic spread post an ESP block have shown inconsistent spread of dye. If cadaver studies were a football match, it would be 3–2 to paravertebral spread, with no explanation of how the ball ended up in the goal 4–8…”