Comparison of Perfusion Index Ratio with Conventional Assessment for Early Detection of Supraclavicular Brachial Plexus Block Onset: An Observational Study

Abstract Objective: Supraclavicular brachial plexus block is widely used for upper-limb surgery, although conventional assessment of block onset is slow and patient dependent. The perfusion index (PI) has emerged as an objective marker of block success. We compared the PI and PI ratio (PIR) with conventional clinical assessments for early identification of block onset. Patients and Methods: This prospective observational study enrolled 70 patients scheduled for elective orthopedic upper-limb surgeries under ultrasound-guided supraclavicular nerve blocks. Block onset was assessed at 2-min intervals using conventional methods while simultaneously recording PI and ratio measurements. Parameters were obtained from the index finger of the blocked limb at baseline and every 2 min up to 20 min following block administration. Results: Baseline PI was 2.10 (interquartile range [IQR]: 1.50–2.80) and increased progressively in a near-linear manner to 10.05 (IQR: 9.10–11.00) at 20 min after block administration. A PIR >1.4 was identified in 47.1% of patients at baseline, rising to 94.3% by 6 min and reaching 100% by 14 min. Cold sensation testing demonstrated a comparable trajectory, with all patients testing positive by 10 min. In contrast, pinprick positivity reached 100% at 16 min, while complete motor block (modified Bromage grade 3) evolved more slowly and was achieved in 91.4% of patients at 20 min. Conclusions: The PIR provides an objective, early indicator of the onset of supraclavicular brachial plexus block and shows a strong correlation with traditional assessment measures, including pinprick sensation, cold discrimination, and motor blockade.