**6. Diaphragm-sparing BP blocks**

Shoulder surgery is accompanied by severe acute postoperative pain that continues to be an unresolved problem. The gold standard for analgesia after this surgery is the ISBP. Unfortunately, this block is associated with a high incidence of ipsilateral phrenic nerve block and the consequent HDP, which restricts its use in patients with pre-existing pulmonary involvement, so it is prudent to consider the practical options to avoid or reduce the incidence of this complication. Nerve block techniques without diaphragmatic involvement such as supraclavicular blocks, upper trunk blocks, anterior suprascapular nerve blocks, costoclavicular blocks, and combined infraclavicular-suprascapular blocks are some of the possible alternatives. It has been suggested that costoclavicular blocks could provide postoperative analgesia similar to ISBP along with a 0% incidence of HDP. It is not clear whether costoclavicular blocks could achieve surgical anesthesia for shoulder surgery. The anterior suprascapular nerve blocks have been shown to provide

surgical anesthesia and analgesia similar to ISBP. However, the risk of HDP has not been adequately quantified. Of the remaining nerve blocks that preserve diaphragm function, supraclavicular blocks (with injection of posterolateral local anesthetic to the brachial plexus), upper trunk blocks, and combined anterior and infraclavicular suprascapular blocks achieve analgesia similar to ISBP, along with an incidence of HDP <10% [17, 25, 51].

### **7. Discussion**

Orthopedic surgeries are well known to be very painful. General anesthesia or regional anesthesia, or a combination of both, are optimal options for shoulder surgery. Regional nerve blocks are essential for postoperative analgesia and can be used alone or as a complement to GA, therefore the postoperative analgesia could be prolonged for 24 hours or more [49]. Regional anesthesia in the setting of GA has a relative contraindication but, with the use of USG, this statement has been challenged [52].

ISBP blockade is the most common approach and a highly effective technique, but with a high incidence of HDP, that contraindicates it in patients with lung disease or contralateral PN paralysis [25, 51]. Supraclavicular blocks vs. ISBP, result in similar pain control and patient satisfaction, but with an incidence of HDP exceeding 60%, when LA is injected intracluster, vs. 9% depositing LA posterolateral to neural cluster (in this setting, cluster refers to the confluence of trunks and divisions of BP) [25, 28].

UT block targets C5-C6 nerve fibers traveling with SSN and AN, producing analgesia not inferior to ISBP block and a 75% incidence reduction of PN involvement [21–24]. The HDP occurs with an incidence of 5% [25].

AN block (posterior access) plus SSN block (sub supraspinous muscle access) produces a good analgesic effect in minor surgeries, compared to ISBP block, but spares the AN anterior articular branches, the lateral pectoral nerve articular branch, and subscapular nerve [25, 41, 45] and is inferior in terms of analgesia when compared to ISB in major surgeries. SSN block at sub omohyoid level extends to the UT almost always and occasionally to the middle trunk, with almost no PN block [33–35, 37]. It provides surgical anesthesia and similar analgesia to ISB [25]. It remains necessary to formally quantify the incidence of HDP. Both blocks should be accompanied by a supraclavicular nerve block at the lateral edge of the SCM to give analgesia to the skin over the shoulder and its contribution to the acromioclavicular joint [29].

AN block may be performed at the axillary fossa, producing anesthesia/analgesia that includes the anterior and posterior branches, with the advantage that intercostobrachial nerve block may be performed with the same puncture [38]. Access to the AN by anterior route is easy to perform and has the possibility of extending to the musculocutaneous nerve, superior subscapular nerve, lateral pectoral nerve and through the clavipectoral fascia, to the lateral supraclavicular nerve [41]. Clavipectoral fascia and peri clavicular block can provide anesthesia and analgesia for fractures of the middle third of the clavicle, without PN paralysis [44–46].

To date, the strategy that achieves analgesic equivalence with ISB with a 0%-incidence of HDP is the costoclavicular block. In 2019, Aliste et al. [53] compared ISB and costoclavicular block in 44 patients undergoing arthroscopic surgery, finding equivalent analgesia in both groups. Moreover, there is no evidence that this block results in surgical anesthesia [25]. Supraclavicular blocks (with LA injection posterolateral to the BP), UT blocks, and combined infraclavicular-anterior suprascapular blocks have been shown to achieve similar analgesia to ISB [54], coupled with an HDP incidence <10%. Decreasing LA injectate volume could avoid HDP altogether and should also be investigated for the provision of surgical anesthesia [25].
