Erector Spinae Plane Block — FRCA Final MCQ
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Correct answer: E — Fascial-plane spread with diffusion to dorsal rami and variable involvement of ventral rami
Explanation lettering: E = shown as A · C = shown as B · D = shown as C · A = shown as D · B = shown as E
B is correct. An ESP block deposits local anaesthetic in the fascial plane deep to erector spinae, producing longitudinal spread and diffusion to nearby neural structures. Dorsal rami are involved consistently; spread towards ventral rami and other adjacent compartments is variable. Its precise mechanism remains incompletely defined. Direct intercostal blockade is not the defining mechanism because injection is not made within the intercostal neurovascular plane. Paravertebral spread may occur but is inconsistent and therefore cannot be described as obligatory passage through costotransverse foramina. Epidural spread is reported less commonly and is not the primary mechanism. Sympathetic effects may accompany anterior spread, but the ESP block is not a selective sympathetic-chain block and clearly has somatic analgesic effects.
Reference: Chin KJ, El-Boghdadly K. Mechanisms of action of the erector spinae plane (ESP) block: a narrative review. Canadian Journal of Anesthesia. 2021;68:387–408. https://pubmed.ncbi.nlm.nih.gov/33403545/