Using pupillary pain index to assess the analgesic effect of interscalene block in arthroscopic rotator cuff repair under sevoflurane anesthesia: A prospective observational study

The combination of interscalene brachial block (ISB) combined total intravenous general anesthesia has been recommended for arthroscopic rotator cuff repair (ARCR) to enhance pain relief and reduce the need for additional analgesics after surgery. We aimed to explore the feasibility of using pupillary pain index (PPI) to evaluate the analgesic effect of ISB in patients undergoing ARCR under sevoflurane anesthesia. This prospective, observational, single-center study took place between October 26, 2022, and October 11, 2023. We included 34 adult patients scheduled for ARCR under combined ipsilateral ISB and sevoflurane anesthesia. Prior to surgery, a single-shot unilateral ISB was performed under ultrasound guidance using a 15 mL mixture containing 7.5 mL of 2% lidocaine and 7.5 mL of 0.5% ropivacaine. PPI was measured twice for each patient: first, after the induction of general anesthesia, and second, at the end of surgery, with a standard stimulus applied to both the ISB and control sides of the C5 and C6 dermatomal level of patient's shoulder region. The primary endpoint was the difference in PPI between the ISB and control sides, and the secondary endpoint was the correlation between postoperative numeric rating scale (NRS) and PPI on the ISB side. The Wilcoxon signed-rank test demonstrated that on the initial PPI measurement, the PPI on the ISB side was significantly lower than that on the control side (Median: 1.5 vs 7, P < .001). Similar results were observed for the second PPI measurement, with the PPI on the ISB side significantly lower than that on the control side (Median: 1 vs 6, P < .001). There was a moderate, positive relationship between the postoperative NRS and the PPI on the ISB side at the end of surgery, indicated by a Spearman coefficient of 0.39 (P = .022). At an age-adjusted MAC of 0.3 for sevoflurane, a significant difference was observed between the PPIs on the blocked and unblocked sides. The PPI exhibits potential as an objective tool for measuring the analgesic efficacy of ISB in patients undergoing ARCR under sevoflurane anesthesia.