Auricular vagal stimulation halved rebound pain after interscalene block

Design

Single-centre randomised, participant- and assessor-blinded, sham-controlled trial

Population

120 adults having arthroscopic shoulder surgery with single-shot interscalene block

Primary outcome

Rebound pain within 24 hours

Effect

20.0% vs 43.3%; ARR 23.3% (7.2–39.5); NNT 4.3; RR 0.46 (0.26–0.82)

Rebound pain when a single-shot interscalene block wears off can erase much of its benefit. This single-centre, participant- and assessor-blinded, sham-controlled trial randomised 120 adults having arthroscopic shoulder surgery under ultrasound-guided single-shot interscalene block to active transcutaneous auricular vagus nerve stimulation (taVNS) or sham, perioperatively and on the first two postoperative days.

Rebound pain within 24 hours fell from 43.3% with sham to 20.0% with taVNS (absolute reduction 23.3%, 95% CI 7.2% to 39.5%; number needed to treat 4.3; RR 0.46, 0.26 to 0.82). Pain scores were lower at rest (−0.50) and on movement (−0.39), recovery (QoR-15) and sleep were better, and opioid use was lower but not significantly (GMR 0.67, 0.44 to 1.01). No stimulation-related adverse events occurred.

It is an interesting, low-risk adjunct, but the pain-score differences were small and the device is not in routine use. The more immediate lesson is that rebound pain is common enough — four in ten here — to plan for.

• Warn patients that pain may rise sharply when a single-shot block wears off, typically overnight.
• Start regular oral analgesia before the block is expected to recede, not after pain returns.
• Consider a perineural catheter or adjuvants such as dexamethasone where rebound pain is likely.
• Treat taVNS as promising but not yet standard; the evidence is one single-centre trial.

Why it matters

Rebound pain affected over 40% of controls, so the benefit of a single-shot block depends on what happens when it ends.

Don't overread it

One Chinese centre; pain-score differences of about half a point are below what most patients notice.

The statistics, in plain English

An NNT of 4.3 means about one patient in every four treated avoided rebound pain. The confidence interval for the NNT (2.5 to 13.9) is wide, so the true benefit could be considerably smaller.

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