Sensory & motor block

Mechanisms of nerve blockade and distribution of the local anesthetic are not consistent.

Studies suggest that local anesthetic after ESPB spreads in a cephalocaudal distribution, reaching mainly the dorsal rami and rarely the ventral ramus of the spinal nerves, and intercostal spaces. Distribution into the paravertebral space, and sympathetic chain is questionable. 

Sensory distribution of an ESPB comprising blockade of the dorsal rami. These rami carry visceral motor, somatic motor, and sensory information to and from the skin and deep muscles of the back. The extent of the block and its analgesic efficacy is variable due to the variability in the craniocaudal distribution of the local anesthetic.