Der Anaesthesist | 2021
Why erector spinae plane block is more efficient than midtransverse process to pleura block in lumbar spinal surgery
Abstract
I have read with great interest the recently published article written by Eskin et al. about “Ultrasound-guided erector spinae block versus midtransverse process to pleura block for postoperative analgesia in lumbar spinal surgery”. Their findings showed that both erector spinae plane (ESP) and midtransverse process to pleura (MTP) blocks provided effective pain relief after lumbar spinal surgery but the ESP blockwas superior to MTP block regarding postoperative analgesia in the first 12h. I would like to thank the investigators for their well-designed analysis. I also wish to give my opinion with respect to the primary outcome measure of the study. The data presented by the authors suggests that postoperative visual analogue scale (VAS) scores were significantly lower in the ESP group compared to the MTP group at every time point during the first 12h, after which the VAS scores were similar between the two groups and both were superior to the control group. To explain these findings, the authors hypothesized that the difference between ESP and MTP blocks in this study could be due to a better local anesthetic (LA) spread of the ESP block to multiple levels. According to the authors, LA in MTP block spreads more in the anteroposterior plane than in the craniocaudal plane, which resulted in a decrease of LA spread to higher dermatome levels. I wish to share my opinion about three other possibilities that could explain these results. First of all, the ESP blockswere performed in the middle of the incision line. It could be that ESP block worked as a local wound infiltration analgesia method as well. The second possibility is explained by the nature of the plane where the LA is injected and the LA absorption via the vascular bed within the injected plane. I have previously published a paper pointing out that the plasma LA concentration is likely to be higher following ESP block than in paravertebral block [1]; the erector spinae muscle being highly vascularized and presenting a large surface area of contact in contrast to a limited space containing principally fatty loose tissue. Similarly, MTP block is performed in an area (we have previously proposed the term retroparavertebral space to characterize this region [2]) mainly containing connective and fat tissues. Therefore, an increase in plasma concentration of LA observed after ESP block may have influenced thesystemicanalgesia. Thevascular absorption of LA and the systemic effect would have been further increased with