Predicting Successful Supraclavicular Brachial Plexus Block in Adults using Pulse Oximetry Perfusion Index: A Prospective Observational Study

Abstract

Background: SCBPB is widely used for upper limb surgeries; however, objective and early confirmation of block success remains challenging. The PI derived from pulse oximetry, reflects sympathectomy-induced vasodilation and may serve as an early indicator of block success. Conventional sensory and motor assessments are subjective and operator-dependent. This study aimed to evaluate PI as an objective predictor of successful ultrasound-guided SCBPB, determine its optimal cut-off, and identify the earliest reliable time point for prediction.

Materials and Methods: This prospective observational study included 62 adult patients (ASA I–II, aged 18–60 years) undergoing elective upper limb surgeries under ultrasound-guided SCBPB. The block was performed using 30 mL of 0.5% ropivacaine with 8 mg dexamethasone. Perfusion index (PI) was recorded at baseline from the unblocked limb and from the blocked limb at 2, 4, 6, 8, 10, and 15 minutes post-injection. Sensory and motor block were assessed at regular intervals. The predictive accuracy of PI was evaluated using ROC analysis, and optimal cut-off values were determined.

Results: Block success was achieved in 96.8% of patients. PI increased significantly from baseline to 15 minutes (p < 0.001) and demonstrated high predictive accuracy, with AUROC of 0.958 at 6 minutes and 0.983 at 15 minutes. Sensory block showed moderate early accuracy, peaking at 10 minutes (AUROC = 0.971), but was less reliable than PI at earlier time points. Motor block showed poor early predictive performance across all intervals.

Conclusion: PI showed promising early changes following successful supraclavicular brachial plexus block, with high observed diagnostic accuracy. However, the small number of block failures limits the precision of these estimates. Larger studies with more failure events are needed to validate the observed PI thresholds and determine their clinical applicability.