Permanent Diaphragm Paralysis after Shoulder Rotator Cuff Repair: Interscalene Block Is Not the Only Factor

We read with interest the case series “Surgical Treatment of Permanent Diaphragm Paralysis after Interscalene Nerve Block for Shoulder Surgery.”1 We agree with the conclusion made by authors that the current practice of regional anesthetic blocks should continue to focus on technical accuracy, including use of ultrasound guidance. We would like to point out that in 3 of the 14 patients listed in the authors’ report, no guidance was used (either ultrasound or nerve stimulation) for performing the interscalene brachial plexus block (ISB). This is not a currently accepted standard of practice.2 Apart from the factors mentioned in the report, there are several other etiological factors that one needs to consider with regard to phrenic nerve injury in this subset of patients. These may include use of superficial cervical plexus block along with ISB, presence of local or systemic sepsis, intraoperative stretch during arthroscopic surgery, effect of excessive irrigating fluid near the nerves, and occult preexisting neurapraxia. The information on these factors is not available from the case series. We also notice that in 6 of the 14 patients, epinephrine-containing solutions were used for the block which may worsen the ischemic injury to the nerve.3 Eight patients had continuous catheter that might have been a factor for triggering fibrosis around the nervous tissue.4 Some centers use superficial cervical plexus block in addition to ISB for shoulder analgesia, this could contribute to direct injury to phrenic nerve as the phrenic nerve lies in close proximity to superficial cervical plexus.5 In the case series, the patients with preexisting neuropathy had poorer outcome after corrective surgery which may highlight the safety aspect of ISB in this subset of patients. Another important factor predisposing to chronic phrenic nerve palsy is the presence of cervical spine disease, which although not mentioned in the report needs to be considered while performing ISB.6 The most interesting finding in the case series is that all the patients referred with hemidiaphragm paralysis were male patients with higher body mass index who had undergone shoulder rotator cuff repair. The authors point out the patients with higher body mass index might have coexisting conditions predisposing to phrenic nerve paresis. They did not state that the patients with higher body mass index are more likely to be symptomatic due to an already burdened respiratory system and are therefore more likely to need referral for surgical treatment. So the presented cases may actually underestimate the prevalence of hemidiaphragm paralysis after shoulder surgery. In obese patients with short neck, repeated attempts are common with potential for nerve injury and irritation as well as contamination of the site with bacteria as well as the antiseptic solution.7,8 There are no data presented as to the evidence of low-grade or full-blown catheter/block site infection in the postblock period in this subset of patients.Patient positioning during arthroscopic shoulder surgery has been associated with various nerve injuries.9 The lateral decubitus position has been associated with the potential for peripheral neurapraxia, brachial plexopathy, and direct nerve injury. The beach-chair position has been associated with cervical neurapraxia and pneumothorax. The rotator cuff injuries themselves can result in clinical or subclinical reflex sympathetic dystrophy,10 which can have a component of phrenic nerve palsy. In fact, ISB may benefit this subset of patients.11 Because data on preexisting phrenic nerve paresis, chronic pain issues, or measures to evaluate the same in the patients mentioned in the study are lacking, directly blaming these cases to ISB without definitive evidence may be inappropriate. It would be informative to the readers to mention that multifactorial etiology is more likely the cause of such an event especially in susceptible population, therefore caution should be used while preforming ISB for such patients and the recommendation for performing the block should be made on case-to-case basis.We believe that the anesthesiologists should focus on strategies to provide phrenic nerve sparing ISB to avoid phrenic nerve involvement altogether. This includes performing ISB at lower level (C7 level), injecting local anesthetic posterior to plexus, using lower volumes and concentrations of local anesthetic.12–14 It will be useful to know the volumes and doses of local anesthetic used in this subset of patients. Some local anesthetic agents are considered more myotoxic than others and their toxicity is proportional to the duration of exposure and the dose.15 It would be advisable to use the least myotoxic local anesthetic agent for ISB and consider use of neuroprotective adjuvants.16We would like to clarify to the readers that the case series presented does not establish a cause and effect relationship between ISB and permanent diaphragmatic paralysis. As suggested in the editorial17 accompanying the case series, until such studies are available, it would be reasonable to continue offering ISB to patients undergoing shoulder surgery. We must congratulate the authors for having elegantly shown us that even delayed surgical release is beneficial in improving phrenic nerve function and thus may reduce disability caused by hemidiaphragmatic paralysis.The authors declare no competing interests.

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