**3. Complications**

US-assistance has dramatically increased the safety and efficiency of RA techniques resulting in improved outcomes. Reports of complications are scarce and unsystematic. Although local anesthetic systemic toxicity (LAST) is virtually a shared complication of all blocks, it may be more often reported with blocks performed in highly vascular compartments. That was the case with PVB in a case series of eight patients undergoing coronary artery bypass grafting (CABG), where potentially toxic ropivacaine concentrations were reportedly common [80]. Of note, PVB were performed using a landmark technique, and catheters were placed in all patients. Similarly, Lockwood et al. cautioned that systemic absorption after PVBLM is highly probable, especially with continuous catheter infusions [81]. Such findings are compelling enough to consider, regardless of block location and technique, the following precautions: (1) do not exceed the maximum recommended LA dose (see also Table A1); (2) addition of epinephrine to delay systemic absorption; (3) be ready to monitor, recognize and treat LAST; and (4) consider US to enable precise needle advancement [82].

Sympathectomy varies in extent and intensity and is common with posterior nerve blocks, mostly bilateral PVB. Compared to PVB, posterior CWFPB seem less associated with hypotension and bradycardia [83], probably because the epidural spread is lower than initially thought [84].

Performance of PVB and CWFPB can, in theory, result in iatrogenic pneumothorax. Nevertheless, the incidence of this will remain undefined given that chest tubes are invariably present in CS with median sternotomy.

Although PVB are formally contraindicated with CPB anticoagulation regimens, the same recommendations may not apply to the more superficial CWFPB. To date, there are no reported hemorrhagic complications after any of the CWFPB, with anecdotal evidence supporting their use in contexts otherwise prohibitive for classical neuraxial techniques [85].

## **4. Perspective**

The best way to provide RA as part of cardiac ERAS strategies has become a topic of considerable interest. Future trials are needed to compare currently available USRA techniques (e.g., PVB versus posterior and anterior CWFPB), establish the optimum time to start the nervous blockade (i.e., pre- versus postoperatively) and understand the role of various perineural adjuvants. This last issue could have momentous consequences as it may enable prolonged duration of single-injection nerve blocks and circumvent the use of catheters [86]. Catheter-free RA is faster to implement, more tolerable and perceivably safer. Furthermore, a simplified technique without additional catheter attempts may promote adherence and widespread use amongs<sup>t</sup> anesthesiologists.

Monitoring regional blockade can be difficult under general anesthesia. With conscious, awake patients, preemptive blockades could be assessed by sensory testing (i.e., pinprick or cold stimulus), but this would delay the operation by at least twenty minutes. Intraoperative nociception monitors could help run an individualized and precise opioid-sparing strategy starting with induction. One trial is currently underway to evaluate the efficacy of ESPB on perioperative opioid consumption in CS with sternotomy during goal-directed anti-nociception using the Nociception Level (NOL) index (NCT04338984).

## **5. Conclusions**

USRA favors improved outcomes coupled with an excellent safety profile and has gained considerable momentum in fast-track cardiac surgery over the last decade. Young adults (i.e., mean age 50 years) undergoing elective cardiac surgeries with relatively short aortic cross clamp times seem to derive the greatest benefits, including opioid sparing, reduced time to extubation, earlier mobilization and improved perioperative pain control. Upcoming trials are expected to provide the missing links needed to standardize the integration of RA in cardiac ERAS pathways. Until such time, USRA remains a valuable adjunct in cardiac perioperative care that calls for a personalized application encompassing both anesthesiologist's expertise and patient's characteristics.

**Author Contributions:** C.B. wrote the concept and first draft. All other authors reviewed and edited the manuscript. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** The authors would like to thank Adrian Wong, Department of Intensive Care Medicine and Anesthesia, King's College Hospital, Denmark Hill, London, UK for constructive criticism of the manuscript.

**Conflicts of Interest:** The authors declare no conflict of interest.




pectoralis major muscle; PMINOR, pectoralis minor muscle; SAM, serratus anterior muscle; EIM, external intercostal muscle; INNIM, innermost intercostal muscle; TTM, thoracic

transversus muscle; LTN, long thoracic nerve; TDN, thoracodorsal nerve; ICN, intercostal nerve; ULB, unilateral block; BLB, bilateral block.
