Pain Medicine and Management

The paravertebral spread that occurs after erector spinae plane block may be volume-dependent. This cadaveric study was undertaken to compare the extent of paravertebral spread in erector spinae plane block using different dye volumes. After randomization, fourteen erector spinae plane blocks were performed bilaterally with either 10 ml or 30 ml dye at the level of  T5 in seven un-embalmed cadavers. Direct visualization of paravertebral space by endoscopy was performed immediately after injections. The back regions were also dissected and dye spread and nerve involvements were investigated. A total of five 10 ml injections and seven 30 ml injections were completed for both endoscopic and anatomical evaluations. No paravertebral spread was observed by endoscopy after any of the 10 ml injections. Dye spread to spinal nerves at intervertebral foramen was identified by endoscopy at adjacent levels of T5 (median: three levels) in all 30 ml injections. Upon anatomical dissection, all blocks were consistently associated with posterior and lateral spread to back muscles and fascial layers, especially in 30 ml injections, which showed greater dye expansion. In one 30 ml injection, sympathetic nerve involvement and epidural spread was observed at injection site level. Although paravertebral spread following erector spinae plane block increased in a volumedependent manner, this increase was variable and not pronounced. As injectate volume increased for erector spinae block, injectate spread to the back muscles and fascial layers seemed to be more predominantly increased, rather than the extent of paravertebral spread.