Effectiveness of Perfusion Index ratio and End-Diastolic Velocity ratio in evaluating the efficacy of Interscalene Brachial Plexus Block: a prospective observational study - Hu, Li; Sun, Jintao; Zhang, Bin; Ye, Xiaoyan; Lu, Jian; Zhu, Zhipeng; Zhou, Hongmei (Frontiers in Medicine, 2025)