Quantitative evaluation of the effects of interscalene block on physiological responses to the balance between nociception and anti-nociception among inpatients undergoing total shoulder arthroplasty under general anesthesia.

Although the suppression of physiological responses to the balance between nociception caused by surgical trauma and anti-nociception due to anesthesia during total shoulder arthroplasty (TSA) is relevant for better perioperative managements, quantitative evaluations of the effects of ultrasound-guided interscalene brachial plexus block (ISB) on physiological responses have not been performed. Physiological responses were assessed using the nociceptive response (NR) index. In this multi-institutional observational study, associations between ISB and NR values were examined among inpatients undergoing TSA under general anesthesia between March 2019 and January 2021. The effects of ISB on acute postoperative pain and major complications within 30 days after surgery were also examined. NR values after skin incision clearly showed significant suppressions of physiological responses in patients undergoing TSA with ISB (n = 60), compared to those without ISB (n = 24). Acute postoperative pain on the day of surgery was also significantly less in patients with ISB than in those without ISB. Postoperative complications, classified by Clavien-Dindo grades, showed no significant differences between patients with and without ISB. A propensity score-matched sensitivity analysis confirmed the same results in patients with (n = 21) and without ISB (n = 21). In conclusion, suppression of physiological responses to the balance between nociception and anti-nociception by ISB can be quantitatively evaluated by NR index during TSA.