Continuous Interscalene Blocks and Rebound Pain

The number of patients requiring shoulder replacements for many different indications, including osteoarthritis, cuff arthropathy and acute fractures has continually grown in the last 15 years, as suggested by a recent international meta-analysis. While there is no designated Canadian database specific to total shoulder arthroplasty compiled by the Canadian Institute for Health Information (CIHI), international data suggests that the expansion of the indications for reverse total shoulder replacements has contributed to the increase in the total amount of patients that undergo such procedure, with an estimated growth of 6-15% between 2011 and 2019. Moreover, there has also been a four-fold increase in the proportion of outpatient shoulder arthroplasty cases in an ACS-NSQIP database from 2015-2019, without a notable increase in adverse patient events, highlighting a shift towards a more ambulatory approach to total shoulder arthroplasty (TSA).

As this procedure becomes mostly ambulatory, new challenges arise regarding the best pain management modality to limit the overall need for opioids and reduce their side effects including respiratory depression, pruritis, nausea and vomiting, as well as increasing patient satisfaction and recovery. There are multiple anesthetic techniques described in the literature to aid in multimodal analgesia, the most commonly used being the interscalene block (ISB), as a single-shot (sISB) or as a continuous infusion (cISB), often combined with multimodal analgesia with dexamethasone and dexmedetomidine. Other techniques include superior trunk blocks, as well as suprascapular nerve block, often used as an alternative when respiratory complications are a major concern due to phrenic nerve blockade. Most regional analgesia techniques detailed above have shown superior pain management compared to local infiltration alone.

Although the interscalene block is clearly established as standard of care for all patients undergoing shoulder surgery, numerous studies have compared the efficacy of sISB versus catheter-based cISB, with variable results favoring either modality in terms of pain management, opioid consumption and patient-related side effects. A more recent systematic review and meta-analysis of over 1000 patients in 20 trials on the effects of single-injection vs. continuous brachial plexus blocks for shoulder surgeries on patient-reported outcomes published in June 2026 has highlighted better pain management for cISB than sISB, especially during the 12- to 48-hour period, although most of the regimens showing better analgesia also included patient-controlled boluses. Notably, mean pain at rest was lower in the cISB group, with a particular benefit in the 24-48 hour period, a period where the concept of "rebound pain" can occur with single-shot modalities.

This concept has been defined in some studies as the "the transition from well-controlled pain (numerical rating scale [NRS] ≤3) while the block is working to severe pain (NRS ≥7) within 24 h of block performance.", with an estimated occurrence of 49.6%. Some identified contributors were younger patients, female gender, surgery involving bone, the absence of IV dexamethasone, as well as upper limb surgery. A possible explanation relies on a "supply-vs-demand" mismatch, where the possible analgesic block could be of insufficient length compared to the patient's needs, especially in the at-risk populations. A study realized in 2007 on femoral nerve block proved that prolonging a nerve block with a catheter based infusion did reduce the apparition of rebound pain. This concept has yet to be formally evaluated in upper limb surgeries and blocks, including in total shoulder arthroplasty.

Inclusion criteria

• Adults aged >18 years of age
• ASA I-III
• Scheduled for elective ambulatory total shoulder arthroplasty.

Exclusion criteria

• ASA IV
• Revision surgery
• Contraindication to regional anesthesia (such as allergy to local anesthetics, systemic anticoagulation, local infection)
• Preoperative chronic pain or opioid use
• Preoperative drug dependency
• Severe respiratory disease or contralateral diaphragmatic paralysis
• Patient refusal.