Background and Aims The Erector Spinae Plane block (ESPB) is an increasingly used to provide analgesia for surgeries involving the chest wall, rib fractures and even cancer pain. Although several meta-analyses that demonstrated the effectiveness of this block, its mechanism of action is still unclear. Anatomical studies on this ESPB injectate spread have found inconsistent results. This systematic review was conducted to summarize the current knowledge about the injectate spread following ESPB.
Methods Pubmed, Scopus and EMBASE were searched. All studies that examined the injectate spread after a thoracic ESPB involving the use of either dissection or imaging were included. The primary outcome was the presence of injectate spread in the various anatomical planes.
Results This review included 29 studies involving 113 cadaveric and 79 live subjects. The proportion of subjects with injectate spread in the erector spinae plane(ESP), intercostal space(ICS), epidural space(ES) and paravertebral space(PVS) was 1(95%CI: 0.97-1), 0.51(CI:0.38-0.64), 0.38(CI:0.28-0.5) and 0.57(0.49-0.64) respectively. The mean spread of injectate in the ESP, ICS, ES and PVS were 9.1(CI:5.1-13.2), 4.7(CI:2.0-9.3), 3.1(CI 0.1-3.6) and 3.5(CI: 0-7.3. Compared to cadavers, a larger proportion of patients had injectate spread in the ICS.
Conclusions Based on this study, the likely mechanism of action of the ESPB is via its spread into the intercostal, paravertebral and epidural compartments. While this correlates with current studies showing superiority of ESPB over placebo/control, it also raises the possibility that the clinical effect of ESPB is likely to be unpredictable.
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