perfusion index as a predictor of successful pns-guided supraclavicular block: a prospective study

Background: the perfusion index (pi) is a simple, non-invasive measure obtained via pulse oximetry that reflects peripheral blood flow changes. alterations in pi can signify shifts in perfusion dynamics during a brachial plexus block. this study aims to evaluate the efficacy of pi and the pi ratio as reliable indicators of successful supraclavicular brachial plexus blocks, performed under the guidance of a peripheral nerve stimulator (pns).objectives: the primary objective of this study was to assess the value of pi as a predictor of successful pns-guided supraclavicular block and to determine threshold values for pi and pi ratio that could accurately predict block success.methods: in this prospective, randomized, double-blind study, 70 patients scheduled for upper limb orthopedic surgeries were included. the sample size was powered to detect significant differences in pi between successful and unsuccessful blocks with a 5% significance level and 80% power. patients were randomized using a computer-generated sequence. pi measurements were recorded at baseline, then every two minutes for the first 10 minutes post-block, and every five minutes thereafter until 30 minutes post-block. sensory block was assessed using a three-point scale (0=normal sensation, 1=loss of pinprick sensation, 2=loss of touch sensation), while motor block was evaluated with the modified bromage scale (0=full movement, 1=partial movement limited to fingers/wrist, 2=complete motor block). confidence intervals (cis) for mean pi values were calculated to assess precision. receiver operating characteristic (roc) curve analysis was used to identify threshold values for pi and the pi ratio in predicting block success.results: significant increases in pi were observed in the blocked limb at multiple intervals compared to the unblocked limb (p < 0.05). at 10 minutes, the mean pi in the blocked limb was 8.26 (95% ci: 7.30 to 9.22), compared to 2.94 (95% ci: 2.55 to 3.33) in the unblocked limb. roc curve analysis identified a pi threshold of 2.80 and a pi ratio threshold of 2.45 as strong predictors of successful block.conclusion: the pi and pi ratio, particularly at the 10-minute mark, serve as reliable, non-invasive indicators of successful pns-guided supraclavicular brachial plexus blocks. these metrics provide clinicians with a quick and practical tool for evaluating block efficacy in real-time, potentially improving clinical outcomes.