Evaluation of Perfusion Index as a Tool for Early Detection of Ulnar Nerve Sparing after Brachial Plexus Block Through Supraclavicular Approach: A Prospective Observational Study

Introduction: Supraclavicular Brachial Plexus Block (SPB) is a common anaesthesia method for upper limb surgeries. However, ulnar nerve sparing can occur, leading to patient discomfort and surgical delays. Traditional assessment methods are subjective and time-consuming. The Perfusion Index (PI) has been shown to be an effective, objective, non-invasive tool for assessing peripheral nerve blocks. Aim: To evaluate PI as a tool for early detection of ulnar nerve sparing after SPB. Materials and Methods: This prospective observational study included 60 patients undergoing upper limb orthopaedic surgery under SPB. PI readings were taken at the index and little fingers at baseline and at regular intervals after the block for 30 minutes. Clinical assessment of the block was also performed. Data normality was tested using the Shapiro-Wilk test, and categorical data were compared using the Chi-square test. Results: Out of 60 patients, 44 (73.33%) had successful blocks, and 16 (26.67%) had ulnar nerve sparing. Demographic characteristics (age, weight, height, sex, ASA grade, and type of surgery) as well as baseline PI at the index and little fingers were comparable between patients with successful blocks and those with ulnar nerve sparing. PI at the little finger was significantly higher in successful blocks compared to ulnar sparing cases from two minutes onwards, reaching a maximum at 30 minutes (7.39±0.80 in successful block vs 1.68±0.27 in ulnar sparing, p<0.001). The PI ratio at the little finger showed statistically significant differences from one minute onwards, also reaching a maximum at 30 minutes (6.08±1.63 in successful block vs 1.52±0.30 in ulnar sparing, p<0.001). In ulnar sparing cases, PI and PI ratio were significantly higher at the index finger compared to the little finger (Mean PI at 30 minutes: index finger 9.22±1.71 vs little finger 1.68±0.27, p<0.001; Mean PI ratio at 30 minutes: index finger 8.08±1.15 vs little finger 1.52±0.30, p<0.001). The area under the Receiver Operating Characteristic (ROC) for PI at the little finger reached 1.0 at seven minutes, demonstrating 100% sensitivity and specificity for detecting ulnar sparing. Conclusion: PI measured at the little finger is a highly reliable, non-invasive tool for early detection of ulnar nerve sparing following SPB. It provides objective, real-time monitoring and can detect ulnar sparing as early as seven minutes post-block with high accuracy. Incorporating PI monitoring into routine anaesthesia practice can improve early detection of failed blocks, reduce surgical delays, and enhance patient comfort.