In Reply

I was pleased by the interest generated following publication of our article in Anesthesiology, August 2013, entitled, “Surgical Treatment of Permanent Diaphragm Paralysis after Interscalene Nerve Block for Shoulder Surgery.”¹ 

The responses by Drs. Uppal, Bellew, and Staff underscore the need to consider all potential etiological factors during assessment to better understand the underlying pathophysiology, and ultimately, take the necessary precautions to minimize future occurrences. I believe it is justified for there to be some hesitation in concluding there is a direct cause-and-effect relationship between interscalene nerve block (ISB) for shoulder surgery and a permanent phrenic nerve injury; however, as long as we are evaluating and treating patients who develop this complication, the priority is clearly to establish associated risk factors rather than attempt to ascertain whether ISB is directly or indirectly related to the problem.

Dr. Uppal mentions the possibility of phrenic injury being more likely in patients undergoing combined superficial cervical plexus block and ISB. He also discusses how patient positioning during shoulder surgery can be an independent risk factor for nerve injury. Dr. Bellew describes how rotator cuff procedures performed arthroscopically “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.”

Although the possibility remains that the surgical procedure itself, and/or patient positioning, results in phrenic nerve injury, the literature does not provide us with a clear correlation, and we have not seen phrenic nerve injuries after shoulder surgery in patients who received only general anesthesia without a regional block. Alternatively, we have evaluated and treated one patient who suffered combined brachial plexus and phrenic neuropathies after shoulder replacement surgery who did not receive ISB. Unlike rotator cuff surgery, total shoulder replacement has been associated with postoperative neurologic injuries.² 

Unfortunately, the small sample size in our study prevented direct conclusions regarding predisposing factors. All patients in the series did have increased body mass indexes; however, it is impossible to ascertain whether this can be explained by: (1) Greater technical difficulties causing a more traumatic ISB; (2) If they were more likely to report respiratory disturbances due to obesity (as stated by Dr. Uppal); or (3) If they also had metabolic syndrome with concomitant neuropathic changes.

The notion of other factors predisposing the phrenic nerve to injury is of great interest to the authors and will be a focus of future investigation. Dr. Uppal mentions the possibility of occult or undiagnosed phrenic nerve paralysis, especially related to underlying peripheral neuropathy. Both Drs. Uppal and Bellew discuss possible susceptibility in patients with underlying degenerative cervical spine disease.

It is the opinion of the authors that degenerative changes in the cervical spine are an independent risk factor for phrenic nerve injury and may be the cause of occult or undiagnosed phrenic nerve injury. Our extensive experience in evaluating (n = >300) and treating (n = >100) patients with phrenic nerve injuries from a variety of iatrogenic and traumatic causes has provided an opportunity to better understand the neuropathic process. Patients undergo cervical spine magnetic resonance imaging as part of a comprehensive evaluation, especially when the etiology is unclear. The vast majority will have abnormal findings in C3-5 even when the symptomatology is limited to respiratory abnormalities.

Upton and McComas introduced the concept of a double-crush phenomenon 30 yr ago.³  They hypothesized that a proximal level of compression could predispose distal sites to be more sensitive to compression. A clinical correlate would be the case of cervical radiculopathy that predisposes for development of a more peripheral nerve compression. These authors noted a high incidence of carpal and cubital tunnel syndrome with associated cervical nerve root injuries. A double-crush phenomenon may explain permanent phrenic injury in patients with asymptomatic (or symptomatic) cervical radiculopathy who undergo ISB.

Our study raised the possibility of phrenic nerve injury resulting from either mechanical trauma (direct or indirect) or pharmacological toxicity. Although it would be helpful to distinguish the underlying cause, the resulting neuropathic process may be similar. Mechanical injury leads to an inflammatory process with compressive adhesions (or as Dr. Staff discusses, “nerve microvasculitis” as an alternative response to perioperative inflammation) and segmental ischemia, whereas pharmacological toxicity causes a chemical neurotoxicity that likely involves disruption of blood flow to the axons.⁴  A segmental phrenic nerve injury in the cervical region would be the result in both cases.

Given the possibility of either (or both) mechanisms involved in the pathologic process, preventive measures should continue to focus on atraumatic methods and modified analgesic dosing. Neuro-anatomy can vary from patient-to-patient; therefore, it is logical that ultrasound guidance and nerve stimulators be standard of care. In having performed over 100 phrenic nerve procedures, it is evident that the anatomical relationship between the brachial plexus and phrenic nerve is not consistent, thus standard landmarks to achieve a safe ISB can sometimes be misleading.

From the standpoint of a reconstructive microsurgeon specializing in peripheral nerve surgery, either mechanism results in a deficit that may be amenable to surgical repair. A large cohort study reporting our outcomes after phrenic nerve reconstruction is published in Annals of Thoracic Surgery, and indicates efficacy and safety of this procedure when compared with nonsurgical treatment or diaphragmatic plication.⁵