Predicting the Success of Ultrasound-Guided Supraclavicular Brachial Plexus Block Using Pulse Oximeter Perfusion Index

Background Early and objective assessment of peripheral nerve block success remains a clinical challenge despite the widespread use of ultrasound guidance. The perfusion index (PI), derived from pulse oximetry, reflects changes in peripheral blood flow following sympathetic blockade and may serve as an early indicator of block success. This study aimed to evaluate the utility of pulse oximeter-derived PI in predicting the success of ultrasound-guided supraclavicular brachial plexus block. Methods This prospective observational study included 121 adult patients undergoing elective upper limb surgery under ultrasound-guided supraclavicular brachial plexus block. PI was recorded in both blocked and unblocked arms at baseline and at five-minute intervals for 30 minutes following block administration. Sensory and motor blockade were assessed using pinprick testing and the modified Bromage scale, respectively. Block success was defined by complete sensory blockade of C5-T1 dermatomes without the need for conversion to general anesthesia. Changes in PI, PI ratios, and their correlation with block success were statistically analyzed. Results PI in the blocked arm increased significantly from a baseline value of 2.1±0.7 to 11.0±2.3 at 30 minutes, while PI in the unblocked arm remained unchanged (p<0.0001). The PI ratio in the blocked arm rose progressively to 5.8±2.0 at 30 minutes. Successful sensory and motor blocks were achieved at 16.1±4.8 minutes and 17.1±6.4 minutes, respectively. PI demonstrated a significant positive correlation with both successful sensory block (r=0.62) and motor block (r=0.716) (p<0.0001). Overall block success was achieved in 95.9% of patients (n=116). Conclusion Pulse oximeter-derived PI is a simple, non-invasive, and reliable early predictor of successful ultrasound-guided supraclavicular brachial plexus block. Its routine use as an adjunct to clinical assessment may enhance the early confirmation of block success, improve perioperative efficiency, and reduce unnecessary conversion to general anesthesia.