A Study to Evaluate the Change in Perfusion Index as an Indicator of Successful Ultrasound-guided Supraclavicular Block

BACKGROUND: The use of ultrasound guidance for supraclavicular brachial plexus blocks (SCB) enhances the precision and success of nerve blocks by improving visualization. Despite this, methods to assess block success, such as pin-prick tests, remain subjective. The perfusion index (PI), which measures blood flow changes, has emerged as an objective and noninvasive indicator of block efficacy. OBJECTIVE: This study aims to evaluate PI and PI ratio (PIR) as predictors of successful SCB and establish cutoff values for PI to determine block success. METHODS: A prospective, observational study was conducted with 40 patients scheduled for upper limb surgeries. PI was measured using pulse oximeters at baseline and intervals after the block. The primary outcome was to establish cutoff values of PI and PIR at 10 min to predict block success, and secondary outcomes included comparing PI values between successful and failed blocks. RESULTS: PI increased significantly in the blocked arm compared to the unblocked arm, with a statistically significant difference from the 6-min mark onward. A PI value >6.10 and a PIR >3.90 at 10 min were 90.9% sensitive and 100% specific in predicting block success. Receiver-operator characteristic analysis confirmed the discriminative utility of PI and PIR. CONCLUSION: PI and PIR are effective noninvasive predictors of SCB success, with specific cutoff values offering high sensitivity and specificity for determining block efficacy. Further studies are needed to validate these findings in patients with conditions that may affect PI values.