Phrenic nerve considerations in continuous brachial plexus blocks for shoulder surgery

We read with interest the systematic review and meta-analysis by Chong et al., which showed patient-reported benefits of continuous compared with single-injection brachial plexus blocks after shoulder surgery [1]. The review is valuable because it moves the discussion beyond technical success and opioid consumption to outcomes experienced by patients. At the same time, the main analgesic benefit was most evident for pain at rest and early opioid consumption, whereas pain on movement and longer term recovery remained less certain. We believe that the duration of phrenic nerve involvement and its respiratory implications deserve explicit consideration when continuous techniques, particularly continuous interscalene brachial plexus block, are selected. Ipsilateral hemi-diaphragmatic paresis remains a well-recognised consequence of interscalene brachial plexus blockade. The incidence may be high with standard interscalene approaches, and associated reductions in vital capacity of approximately 25–30% have been reported [2]. This reduction is usually tolerated by healthy individuals undergoing ambulatory shoulder surgery. It becomes more relevant when an infusion maintains analgesia for 24–48 h, the same interval during which the analysis found the most pronounced benefit of continuous brachial plexus blockade. Patients with pre-existing respiratory disease, morbid obesity, obstructive sleep apnoea or contralateral diaphragmatic dysfunction may have less physiological reserve. In a multicentre analysis of continuous interscalene brachial plexus blockade for shoulder arthroplasty, obesity and pre-existing pulmonary disease were associated with clinically significant respiratory complications [3]. A striking case report further illustrated that even a single-injection interscalene brachial plexus block with liposomal bupivacaine resulted in prolonged intensive care unit admission for respiratory failure in a patient with subclinical baseline respiratory compromise [4]. The potential for sustained phrenic nerve involvement during a 48-h continuous infusion in such patients demands explicit clinical consideration. This issue is not a criticism of the review, but a limitation of how the available trials can be translated to routine practice. Most included trials used interscalene approaches, whereas phrenic nerve palsy, diaphragmatic excursion and respiratory symptoms were not reported as patient-centred or safety outcomes. Consequently, the recommendation to offer continuous brachial plexus block selectively is sound for analgesic efficacy, but less informative for patients in whom an interscalene catheter may carry a higher respiratory risk. This limitation is particularly relevant because several phrenic nerve-sparing alternatives to the interscalene technique are now supported by trial evidence. The superior trunk block has been shown to provide non-inferior surgical anaesthesia and analgesia with a significantly lower rate of hemi-diaphragmatic paralysis (4.8% vs. 71.4%), representing a clinically viable alternative [5]. Continuous catheter delivery via this approach, as well as via high-thoracic erector spinae plane block, has been explored, although patient-reported outcome data remain limited. Future trials should therefore report respiratory outcomes systematically; stratify high-risk patients or define clear exclusion criteria; and compare continuous interscalene catheters with phrenic-sparing catheter techniques when feasible. To conclude, the practical question is not simply whether continuous brachial plexus blocks provide better analgesia, but for whom and by which approach. Incorporating diaphragmatic function and respiratory recovery into future trials and consensus frameworks would help clinicians preserve the analgesic advantages shown in the systematic review and meta-analysis while individualising the safety profile for the growing population of older and comorbid patients undergoing shoulder surgery.