We were interested to read Kaufman et al.’s1  article on the surgical treatment of 14 cases of permanent diaphragm paralysis after shoulder surgery, but dismayed to read the editorial that accompanied it,2  in which it was stated that the diaphragmatic paralysis was “clearly due to phrenic nerve damage after interscalene brachial plexus block.” This assertion is open to question and is not supported by the data presented by Kaufman et al.1 

There is a remarkable similarity between this assertion and that made for many years that the ulnar neuropathy suffered by some patients after surgery was clearly due to errors in on-table positioning that resulted in external nerve compression. The finding that there was a preponderance of obese male patients suffering ulnar nerve neuropathy led to a view that although direct compression may be a factor, other factors such as ulnar nerve stretching and inadequate blood supply to the ulnar nerve were more likely to be of significance.2–8  All Kaufman’s patients were male; all were overweight or obese; their mean age was 58 yr. Phrenic nerve lesions may be associated with degenerative cervical spine disease, trauma, and compression,9–13  and it is possible that these factors played a significant part in the cases described by Kaufman. Rotator cuff repairs are now commonly performed arthroscopically—these are often lengthy procedures performed with the patient in the lateral position and with traction applied to the arm, and in which swelling in the neck commonly results from saline infused under pressure into the joint for prolonged periods. It may well be that the combination of obesity, degenerative spine disease, nerve traction, and nerve compression were therefore significant factors in these cases.

We agree that the performance of an interscalene block may have been a factor (all 14 had blocks), but details of the approach used would have been informative, as a standard lateral, that is, modified Winnie, technique or out-of-plane ultrasound-guided approach brings the needle tip closer to the phrenic nerve compared with the currently popular in-plane ultrasound-guided needle approach through the middle scalene muscle. It may well be that the use of a Tuohy needle and a catheter (the majority of cases) were also factors. However, it is incorrect to assume that the block was the only factor—statistical association does not imply causation. Furthermore, if local anesthetic-induced myotoxicity is implicated as an important cause of nerve damage, why do we not see it more regularly around the many other small nerves that we regularly block?

Hogan’s conclusion that the cause of the phrenic nerve damage is local anesthetic injection is premature, and his suggestion that interscalene block be replaced for these procedures by “peripheral application of local anesthetic” is not supported by the data presented. As ever, we need to know more before we reach conclusions.

The authors declare no competing interests.

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