Erector spinae plane blocks for cardiac surgery: Are we comparing apples to oranges?

In this month's issue of the Journal of Cardiac Surgery, King et al. report “a systematic review and meta‐analysis” of erector spinae plane blocks (ESPB) for patients undergoing median sternotomy. Using their described methodology, the authors found 498 articles through June 2021 and after excluding duplicate and irrelevant studies, completed 17 full article reviews, ultimately including 5 in their final analysis. They report no difference in postoperative pain scores, intraoperative opioids, time to extubation, and intensive care unit (ICU) length of stay in patients receiving ESPB versus no ESPB. The intent of the article is laudable and we congratulate the authors on identifying the need for a better understanding of the impact and practice of ESPB in cardiac surgery. Similar meta‐analyses have been published on ESPB in noncardiac and mixed population surgery, typically examining postoperative pain scores or opioid requirements, all with conclusions generally supportive of ESPB. However, there have been no meta‐analyses specifically examining the role of these blocks in the population undergoing median sternotomy. There is one systematic qualitative review that reported favorable results but explicitly stopped short of conducting a meta‐ analysis due to significant heterogeneity in the literature. A systematic review provides a summary of existing published research on a specific topic in a methodical, rigorous, and reproducible form. As systematic reviews include multiple studies, they can form a stronger evidence base for a particular topic than is available from individual studies alone. Further analysis of the included studies may then be conducted, examining heterogeneity, population characteristics, interventions, controls, and outcomes of the included studies. This statistical analysis is referred to as a meta‐analysis, typically including only randomized control trials (RCTs), and usually presenting specific outcomes weighted by sample size in a forest plot, providing a summary estimate of any treatment effect. While King and colleagues state they performed a systematic review and meta‐analysis, we believe this manuscript may be better viewed as a narrative review, consisting of three RCTs, a case‐control study of eight patients, and an observational study. To their credit, the authors did report significant heterogeneity among their selected studies, however, we feel it is important to highlight some of these differences. Among the RCTs, each used a different control group. The observational study evaluated the effects of a comprehensive enhanced recovery protocol, so compared to the nonintervention group, patients in the enhanced recovery group received substantially different treatment beyond the addition of ESPB. In four studies, single shot technique was used while the remaining study placed a catheter for continuous local anesthetic infusion. Surgical populations also varied, with one study only enrolling patients undergoing off‐pump coronary artery bypass grafting. Finally, one study included in the final analysis was not published as a full manuscript but instead as a letter to the editor. Beyond the decision to perform a single shot or infusion catheter technique, anesthesiologists that confer with colleagues at other institutions would anecdotally report that there are many additional variations of how to perform an ESPB, and these differences are also reflected in the available literature. These subtle differences could feasibly alter the clinical effect. Variations include the location of local anesthetic injection, local anesthetic choice (drug, volume and concentration) as well as the timing of the block (preinduction, postinduction, pre‐emergence). It is particularly important to consider these differences when evaluating outcomes that are likely