Shoulder surgery is one of the most frequent and painful surgeries performed in traumatology. Using locoregional anesthesia as a part of multimodal pain management strategy is mandatory. the interscalene brachial plexus block (ISB) is the most used nerve block in shoulder surgery. ISB is considered the gold standard for its efficacy and analgesic quality, both intra and postoperatively. However, it is not free of risks, among them, the high rate of phrenic nerve block that produces hemidiaphragmatic paralysis (HDP) and in some patients, it could trigger a postoperative respiratory failure (PRF). Several strategies are described to reduce the rate of HDP.

Before performing a technique with potential hemidiaphragm compromise, the first strategy consists of evaluating the risk of developing PRF due to an HDP. According to this risk, we will decide the most effective and safe locoregional technique for our patient. the main reason to look for techniques that do not produce HDP is to avoid a PRF. This is the commonest postoperative pulmonary complication, with an incidence in general surgical populations that ranges between 0.2 and 3.4%. It is diagnosed when the gas exchange does not meet metabolic needs, leading to hypoxemia with or without hypercapnia after a surgical procedure, and as a result of the changes induced by anesthesia and surgery.

The multiple-hit theory stratifies risk at two stages. the first stage would consider threats associated with the patient’s condition and the surgical procedure. the second would consider intraoperative events and management, which would modulate the first-hit risk and indicate the patient’s definitive risk. It can translate this concept of multiple-hit theory to the patient scheduled for shoulder surgery. the risk of PRF is produced by combining several preoperative characteristics of the patient (ie, Age, ASA, Congestive heart failure, Chronic obstructive pulmonary disease, Diabetes mellitus, Current smoker, Dyspnea, Hypertension, Renal failure, Surgery type…) along with a second phase that encompasses intraoperative procedures (i.e., Hemidiaphragm palsy, Pulmonary drive pressure, Inspired oxygen fraction, Duration of surgery…). HDP is just one more risk factor, like others, this explains why most isolated HDP does not produce PRF in patients with few risk factors. However, when HDP is combined with more risk factors can lead to PRF. In these cases, it is essential to avoid evitable threats like HDP.

We must not forget that the overall risk of PRF is formed by a set of risk factors. Therefore, perform a locoregional block despite the risk of HDP (one risk factor) compared to general anesthesia with neuromuscular blockade and abundant opioids for pain control (three risk factors) seems an excellent way to reduce the overall risk. the key is to use locoregional blocking strategies to reduce the HDP rate. Using risk scales of postoperative pulmonary complications is a good idea to know and predict the risk of our patients before deciding to perform a particular locoregional block. a final step in risk stratification consists of the functional assessment of the diaphragm, before the era of ultrasound it was complex to perform this evaluation bedside. Diaphragm ultrasound evaluation (diaphragm POCUS) lets evaluate the degree of diaphragmatic excursion and the thickening fraction of each hemidiaphragm detecting paralysis or weakness with high specificity and sensitivity. as a resume, risk stratification scales and Diaphragm-POCUS will help us to decide the impact of a possible HDP, and complete our overall risk of PRF.

The blocks above the clavicle include ISB and supraclavicular brachial plexus block (SCB), they remain the most used blocks for shoulder surgery, including ambulatory surgery, despite its high rate of HDP. the ISB injecting between 30–45 ml can produce up to 100% incidence of HDP, this occurs from 2 possible mechanisms: local anesthetic (LA) spread toward the C3-C5 nerve roots or LA migration from the interscalene toward the phrenic nerve.

The most important strategy to limit the anterior and cephalad LA spread, is reducing the volume of LA. the volume injected will also influence the diffusion of LA to the phrenic nerve, with greater volume, greater diffusion through the tissues, facilitating contact with the phrenic nerve. as an example, using the same puncture point LA administration of 45 ml produces 100% rate of HDP compared to 5 mL, this US-guided low-volume injectates result in a 50% decrease in the rate of the ipsilateral phrenic nerve block.

Another important strategy to reduce LA spread is the place where LA is administered. ISB are commonly performed at the C6 level (cricoid cartilage). In this location, the phrenic nerve is situated near to the brachial plexus at only 0.18 cm. as the two neural structures move caudally, they diverge from each other at a rate of 3 mm for every centimetre below the cricoid cartilage. Although the more distal the ISB the less HDP. In this sense, the C7 block strategy (LA placed lateral and posterior to the C7 nerve root)would result in a decreased incidence of phrenic blockade compared with classical ISB-C7 root block was associated with a lower rate of HDP (13% vs 93%; P< 0.001) and when using this block with a volume below 6 mL, there was no instance of phrenic block occurred in this series. When LA was deposited at the C5-C6 nerve root, two strategies show a reduction in HDP. First, an injection target behind the C5–C6 nerve roots between the brachial plexus and the middle scalene muscle, this has reported a 27% incidence of HDP (using ropivacaine 0.75% [8]. Another strategy is an extrafascial injection of LA; this consist of LA deposition in a target point situated 4 mm lateral to the sheath of the brachial plexus at the level of C5-C6 roots [9]. Extrafascial injection strategy compared to LA deposition between the C5–C6 roots (subfascial injection) reported comparable postoperative analgesia with a significant decrease in the incidence of HDP with extrafascial LA injection (21% vs 90%; P < 0.001).

Using SCB is itself another strategy to reduce the HDP rate compared to ISB-SCB does provide equivalent analgesia to ISB during the first 24 hours, with a reduce HDP compared to ISB, but it is unfortunately afflicted with a 9% incidence of HDP. US-guided classical SCB with 30 mL of LA has an incidence of 34% HDP. Again low volume and the place to LA depositions are the main strategies to reduce HDP. With a strategy of restricting LA injection to the corner pocket (the confluence of the first rib and subclavian artery) and limiting the LA volume to 20 mL, some authors perform ICB avoiding HDP. Another useful strategy is the bent-needle technique; this consists on needle insertion initially at the supraclavicular fossa and then positioning a catheter tip in the infraclavicular fossa, inferior and medial to the coracoid process and far from the phrenic nerve, with this strategy have been reported a 1% incidence of HDP after the initial LA bolus.

Nowadays, one of the most useful strategies to prevent HDP is the diaphragm-sparing nerve blocks for shoulder surgery. These techniques do not produce HDP because they are very far from the phrenic nerve. This prevents LA from spreading to the phrenic nerve. the shoulder is innervated by multiple peripheral nerves; they arise mainly from two plexus, brachial and cervical plexus (see table 1). Knowing shoulder innervation, we can plan different diaphragm sparing nerve block for shoulder surgery. the suprascapular nerve originates from the most proximal section of the brachial plexus (i.e., superior trunk) and it provides approximately 70% of the sensory innervation to the shoulder joint. the remaining 30% of sensory input to the shoulder is provided by the axillary, supraclavicular, subscapular, and pectoral nerves. These nerves originate from the more distal section of the brachial plexus (i.e., lateral and posterior cords), from lateral cord originates the lateral pectoral nerve, from the posterior cord originates the subscapular and axillary nerves. the cutaneous innervation overlying the shoulder joint is separate from the brachial plexus and mediated by the supraclavicular nerves (which originate from the superficial cervical plexus). According to shoulder neuroanatomy, suprascapular nerve block (SSNB) do not provide complete coverage or surgical anesthesia of the shoulder joint; they have been used for postoperative analgesia after shoulder surgery. a recent meta-analysis indicates that SSNB is not different from ISB concerning postoperative opioid consumption and total pain severity during the first 24 h after shoulder surgery. It is also not different from ISB concerning opioid-related side effects, analgesic duration, PACU analgesic consumption, and procedural discomfort. Also, ISB seems to offer minor analgesic advantages compared to SSNB, but they are transient and limited to the immediate postoperative period (PACU stay). In contrast, SSNB does appear to reduce the risk of respiratory complications, undesirable nerve blocks, and block-related complications.

Compared with SSNB alone, some authors found that combined axillary nerve block (AXB) with SSNB resulted in lower pain scores, improved patient satisfaction, and less rebound pain. However, when we need surgical anesthesia some authors have remarked that AXB-SSNB should be reserved for minor arthroscopic surgery because essential structures, like the rotator cuff, also receive supply from other nerves, which are not anesthetized with AXB-SSNB. Also compared with ISB, AXB-SSNB resulted in higher intraoperative opioid requirements, increased pain/opioid consumption in the postanesthesia care unit and decreased patient satisfaction at 6 hours. SSNB and AXB are a good diaphragm sparing block strategy for intraoperative and postoperative analgesia, but not as an alone anesthesia surgical technique.

Combine SSNB with an infraclavicular brachial plexus block (ICB) would target the brachial plexus at the level of the cords, providing an efficient method to block the lateral pectoral, subscapular, and axillary nerves. SSNB-ICB strategy blocks all the shoulder structures except the cutaneous region innervated by supraclavicular nerve, when we add this nerve block, we obtain a surgical anesthesia technique. In order to avoid, three different punctures, it has been described the combined retroclavicular approach that combines these three blocks (SSNB, retroclavicular ICB and supraclavicular nerve block) with only one cutaneous puncture. Some authors reported a 3% incidence of HDP with US-guided ICB (coracobrachial approach). However, these authors used a 30-mL volume of ropivacaine 0.5%. When ICB is used with less LA volume (15 mL) we have no HDP in a not published personal series. Recently, it has been suggested that the costoclavicular space (a variation technique of ICB) could also serve as a retrograde channel to supraclavicular brachial plexus blocks. 20 mL of LA injected in the costoclavicular space can reach the supraclavicular brachial plexus, achieving analgesic parity with a small-volume supraclavicular block while retaining the 0% incidence of HDP seen with infraclavicular blocks. Probably, SSNB and ICB have the key to resolve the best strategy as a diaphragm sparing nerves block for shoulder surgery. Research around this topic is granted.

In conclusion, when shoulder surgery is planned, there are many strategies to avoid HDP and PRF. the evaluation of the patient‘s risk and locoregional techniques appropriately used will increase safety, efficacy and satisfaction in our patients.

References

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