Patients having arthroscopic shoulder surgery are most commonly scheduled for day surgery, and admission to the hospital for hypoxia associated phrenic nerve paralysis is suboptimal. Patients with intrinsic lung disease are at risk for this complication. Patients who are morbidly obese are also at risk for this complication . Unfortunately, it is not always easy to tell ahead of the block who will develop clinically relevant complications as a result of phrenic nerve palsy after interscalene block. A large retrospective review was published on cases of outpatient interscalene catheter usage (n=509) . Adverse events were recorded in 6.7% of patients. Of these only 0.6% (3 patients) had problems or complaints of dyspnea all of which were after discharge to home. However, the mean BMI was 24, with no patient having a BMI greater than 29. In addition, all patients with any lung disease were not included in the study.
At the level of the interscalene block, the phrenic nerve lies in close association with the brachial plexus cords/trunks. (see fig 2). Its course is most proximate to the brachial plexus at the level of the interscalene block where it typically is 18 to 20 mm away from the C5 nerve root at the level of cricoid cartilage.
However, as one moves caudad, the phrenic nerve moves an additional 3 mm further away from the plexus for every cm that it descends over the anterior scalene muscle.
A review article on the options for avoidance of significant phrenic nerve block was published in the journal Anesthesiology in 2017 . This article is highly recommended for the practioner who desires a more in depth understanding of brachial plexus and phrenic nerve anatomy.
Patients who are obese are more likely to experience dyspnea in association with phrenic nerve palsy. Furthermore, it is likely that morbid obesity will also increase the risk of hypoxemia in association with dyspnea. There are several strategies to reduce the chances of this outcome and will be reviewed briefly. Traditional training of the ISB has recommeneded high volumes (30 to 40 mLs) to ensure complete blockaded of the brachial plexus. Reducing this amount could reduce the incidence of phrenic nerve palsy. However, most studies indicated that volumes of 20 mL or greater will inevitably result in phrenic nerve palsy if the injection occurs around the C5-C6 nerve roots. US guided techniques have allowed practitioners to be more precise in the placement of the local anesthetic permitting a lower volume to achieve shoulder analgesia after interscalene block. In particular, one study found that after 10 mL was injected, the chance of phrenic nerve palsy could be reduced from 100% to 60% . Reducing the injected volume to 5 mL can lower the chance of phrenic nerve palsy to as low as 27%  without compromising the block effectiveness for up to 24H. However, it is well known that introducing a greater volume tends to increase the chances for success, and therefore, using 5 mL as a routine is likely to lead to suboptimal outcomes in some cases. Furthermore, given the problems with admitting a patient from an outpatient facility to a hospital secondary to respiratory compromise, an incidence of phrenic nerve palsy of 27% may seem high. Nevertheless, further improvements seem possible if the concentration is reduced. To provide dense surgical anesthesia and prolonged dense post operative analgesia, I typically opt for 0.5% bupivacaine or Ropivacaine. By halving the concentration to 0.25%, AL-Kaisy et al was able to reduce the incidence of phrenic nerve palsy from 100% to 17% . However, this study only had 5 volunteers in each group. In a slightly larger group of patients (30), Thackeray et al. were able to reduce the incidence of phrenic nerve palsy from 78% to 21% by halving the bupivacaine concentration with a 20 mL injection. This reduciton in concentration seemed to come at the expense of more opioid requirements over a 72 hours time frame and also a shorter block duration (18 hr vs. 11.9 hr) . To add confusion to the previous studies, Zhai et al. couldn't find a significant differenence in phrenic nerve palsy when using a fixed dose of 50 mg of Ropivacaine for US guided interscalene block using concentrations of 0.25, 0.5 or 0.75% .
Perhaps more effective, is an injection of local anesthetic around the C7 nerve root. When using 5 mL of a 0.75% concentration of Ropivacaine, no patients (n=20) had any diaphragmatic paresis after 2 hours post injection . The calculated ED 95 was 3.6 mL of 0.75% ropivacaine for this study when injected around the C7 nerve root.
Performing a supraclavicular block as been studied as a method of reducing phrenic nerve palsy. More specifically, targeting the superior trunk of the brachial plexus (formed by the union of the C5/C6 nerve roots), has been reported in two case reports to provide analgesia after shoulder surgery without blocking the phrenic nerve. At this level the phrenic nerve has migrated away from the brachial plexus. An approach to target the superior trunk is to do a supraclavicular brachial plexus block. Mulltiple studies have looked at the supraclavicular block and the results are somewhat equivocal. For example, with injection volumes of 20 to 30 mL, phrenic nerve palsy occured in 25 to 51% of patients. Furthermore, in some of the studies, patients receiving a supraclavicular block had inferior post op analgesia. On the other hand, Kim et al. were able to show that a supraclavicular block performed equally to ISB for patients having shoulder surgery without GA in terms of conversion to GA (0 patients) or fentanyl requirements . Given the above data, I have begun to modify my block for shoulder surgery, seeking to do what I consider to be a high supraclavicular block or perhaps a low ISB. I further modify my block in patients who I consider to be at higher risk for phrenic nerve palsy by reducing the volume of local anesthetic and perhaps also decreasing the concentration.
The above techniques may reduce the incidence of phrenic nerve palsy, but don't seem to eliminate the risk altogether. The risk of phrenic nerve palsy may be completely eliminated by avoiding any injection around the brachial plexus. In 2012, Siegenthaler et al. desribed a novel approach to the suprascapular nerve . In their study, a comparison study was done between locating the suprascapular nerve in the supraclavicular space vs. in the suprasspinous fossa. They determined that suprascapular nerve identification was much better in the supraclavicular space (81% identified vs. 36%). In my own practice, attempts at identification of the correct space using the supraspinous fossa (also known as the suprascapular notch) proved very difficult due to the greater amount of thick tissue overlying the area. Furthermore, This approach requires a cooperative patient who can sit upright in order for the approach. Lastly, I found that due to the depth of the area to be blocked, an acute angle was required making visualization of the needle problematic for accurate injection.
The suprascapular nerve provides aproximately 70% of the innervation to the glenohumeral joint. The majority of the remaining 30% derives from the axillary nerve. Two recent studies published in Anesthesiology have looked at the effectiveness of suprascapular nerve block vs. interscalene block to determine non inferiority. One was a meta analysis comparing the two approaches . The meta analysis determined that a suprascapular nerve block alone was not inferior to an ISB. In this meta analysis, only one study utilized a supraclavicular block in the supraclavicular fossa (all other studies approached the nerve from supraspinous fossa). The primary outcome for which the blocks were compared and found to be similar were for post operative morphine consumption (24H) and the cumulative difference between ISB and SSNB in the area under the curve for rest pain during the first 24H interval. This meta analysis did note, however, that during a 1 hour interval in the PACU, ISB provided superior pain control. At 6,12,24, and 48hr there was no statistical difference. In this same meta analysis, it was found that ISB was associated with more respiratory complications, undesirable blockades, and block-related complications.
This month (july 2018), a head to head to head trial was published comparing analgesic efficacy between the anterior suprascapular, supraclavicular and interscalene nerve blocks . The primary outcome was pain scores in the PACU. The pain scores were 1.9,2.0 and 2.3 for the ISB, anterior suprascapular, and supraclavicular blocks respectively. The authors concluded that the anterior suprascapular nerve block was non inferior to the ISB. They also concluded that the supraclavicular block did not meet their prespecified criteria for non inferiority. They also found a significant decrease in respiratory function (measuring VC) for the ISB. (see fig 3).
In general, ISB is the gold standard for providing effective and consistent post op analgesia for shoulder surgery. However, in day surgery patients who are likely to become hypoxemic (sat less than 90%) on room air after phrenic nerve block, the ISB is a relative contraindication. Current research indicates that the only method found to virtually provide a 0% incidence of phrenic nerve palsy is a suprascapular nerve block. Fortunately, several studies indicate that this block is likely non inferior to ISB in providing ample pain control.
Technique-Anterior Surpascapular nerve block:
place US probe in standard location as you would for ISB. Move the probe in a caudad direction as you follow the brachial plexus. (see figures below).
After determining the location of isolated SCN, only 3 to 4 mL are required to block this nerve at this level. Furthermore, due to the location of the nerve, a catheter could easily be inserted and secured in this location.
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