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To the editor,
Erector spinae plane block (ESPB) is a recently described paravertebral interfacial plane block and has become popular among regional anesthetists. We have read with great interest the cadaver study by Ivanusic et al 1 that shows the distribution of local anesthetic drugs in ESPB and also the anatomical study of ESPB by Adhikary et al.2
In the Ivanusic et al study,1 they performed ESPB and administered 20 mL methylene blue at the T5 vertebral level and evaluated the distribution of dye in the cadaver. They reported that there was no distribution within the paravertebral plane and no distribution was observed at anterior regions of the transverse process. Adhikary et al 2 performed ESPB and retrolaminar blocks using 20 mL solution at T5 vertebral level and investigated the distribution of radiocontrast solution with MRI and anatomical dissection of cadavers. They reported distribution of the solution to the anterior region of the transverse processes. Thus, there is controversy in the results of these studies, where the same volume of solution was administered at same vertebral level. The difference in the distribution of the solution seen in these studies is significant and needs to be confirmed clinically.
There are multiple factors that may affect the distribution of local anesthetic solution in ESPBs. As Elsharkawy et al 3 expressed in their study, the deep plane consists of multiple layers, which prominently influence the spread of injected solution that is distributed within the layers. Local anesthetic injection point, local anesthetic volume, and the length of the transverse process also affects the distribution of local anesthetics and block effectiveness. Thus, we would like to discuss the distribution of local anesthetics in ESPB when performed at different vertebral levels and the possible difference of local anesthetic spread in thoracic and lumbar ESPB.
ESPB performed at the lumbar vertebral level is a promising method which has been shown to have sufficient analgesic effect in hip surgery.4 Lumbar ESPB differs technically and anatomically from ESPB that is performed at the thoracic level. Transverse process of thoracic vertebra ends at 2–3 cm lateral while transverse process of lumbar vertebra may reach up to 4–6 cm lateral. Thus, wide paravertebral distribution of injected solution is not likely in lumbar ESPBs. Our CT images of a patient on whom we have performed ESPB with administration of local anesthetic and radiocontrast solution mixture at L4 vertebrae level demonstrate an excessive distribution to the anterior region of the transverse process (figure 1) in contrast to the results of cadaver studies.5 In our observation, ESPB performed at thoracic vertebrae level has a clinical effect similar to an extended paravertebral block; meanwhile lumbar ESPB clinically acts as a lumbar plexus block. Local anesthetic solution surrounds the psoas muscle and extends from T12 up to L1 vertebra when injected at S1 to S2 level. In addition, the solution spreads markedly to dorsal region and shows an effect similar to thoracolumbar interfascial plane block (figure 1B).
We conclude that different distribution characteristics may be observed and result in different sensorimotor block properties when ESPB is performed at different vertebral levels. Clinical studies are needed to investigate the sensory and motor block characteristics of ESPB when different concentrations/volumes and block application techniques are used. We would like to emphasize the importance of specifying the block application point (eg, upper thoracic, lower thoracic, lumbar), which may significantly affect clinical results of the ESPB, in anatomical studies.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed
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