Perfusion index and perfusion index ratio as predictive tools for block success: A prospective observational study on ultrasound-guided supraclavicular brachial plexus block.

Background: The supraclavicular brachial plexus block is widely used for upper limb surgeries due to its effectiveness in providing anesthesia. Conventionally, success is gauged through sensory and motor assessments, which are not only subjective but also require active patient cooperation. This poses challenges for patients who are sedated or under general anesthesia. Additionally, repeated sensory testing can be uncomfortable. Therefore, an objective and noninvasive method to assess block success is needed. Perfusion index (PI), derived from pulse oximetry, reflects peripheral perfusion changes following sympathetic blockade and could serve as a useful surrogate marker. This study aimed to assess the utility of PI and the PI ratio as early indicators of successful block onset and to identify optimal threshold values correlating with effective anesthesia. Methods: Seventy patients undergoing elective upper limb orthopedic procedures received ultrasound-guided supraclavicular blocks. Data for PI were collected from the affected and unaffected limbs at the initial time point and again at 10, 15, and 20 minutes after the block was given. The PI ratio was derived by comparing values between limbs at each time point. Results: In successful blocks, the PI increased significantly in the affected limb. A PI > 2.94 showed 50% sensitivity and 91.67% specificity, while a PI ratio > 1.25 offered 50.78% sensitivity and 100% specificity at 10 minutes, confirmed by receiver operating characteristic (ROC) analysis. Conclusion: Both PI and PI ratio are effective in predicting block success, with the PI ratio proving more reliable, especially at the 10-minute mark.