Pupillary Pain Index to Evaluate Interscalene Block and Postoperative Pain in Patients Underwent Shoulder Surgery

When an individual encounters nociceptive pain stimuli, the pupil dilates in a unique way called pupillary reflex dilation (PRD), which can be observed both when the individual is awake or under anesthesia. The degree of pupillary reflex dilatation can be further quantified into an objective parameter called the Pupillary pain index (PPI), which serves as a monitoring tool for the balance between nociception and antinociception in surgical patients. Larson studied 32 female breast surgery patients who received general anesthesia combined with thoracic paravertebral nerve block on the affected side. The results showed that the affected side of the nerve block had significantly lower pupillary reflex dilation than those without nerve block on the healthy side of the breast. The authors believed that this study confirmed the value of pupillary reflex dilation in monitoring the success rate of unilateral thoracic paravertebral nerve block during general anesthesia. In a prospective observational study of 26 patients undergoing neurosurgery under general anesthesia, Pupillary pain index at the end of surgical anesthesia and Numerical Rating Scale (NRS) during the recovery room were recorded separately, The results showed a significant correlation between the two parameters (rS = 0.62; P = 0.002). The authors concluded that the application of the measurement of pupillary reflex dilation may be useful in predicting and preventing acute postoperative pain. Shoulder rotator muscle repair is a common surgery in our hospital. Patients must receive general anesthesia, sometimes combined with scalene interscalene block (ISB), to improve postoperative acute pain ,help to perform passive shoulder rehabilitation exercises and prevent shoulder joint adhesions. Based on the above literature review, the motivation for this study was to investigate the feasibility of using pupillometry to assess acute pain after shoulder surgery. The objectives of the research project are as follows: 1. Can pupillary reflex dilation in patients undergoing general anesthesia be used to assess the analgesic effect of scalene nerve block? 2. Is the pupillary pain index (PPI) at the end of surgical anesthesia correlated with the first numerical pain scale (NRS) during the recovery room in such patients?

Inclusion criteria

• Patients who received general anesthesia combined with ipsilateral interscalene block
• Patients listed as a Class I/II physical condition of the American Society ofAnesthesiologists

Exclusion criteria

• Patients younger than 20 years of age
• The presence of ophthalmologic (recent eye surgery or cataracts) or neurologic diseases (diabetic neuropathy,or postherpetic neuralgia) that could interfere with Pupillometer