Perfusion Index as a Parameter for Effectiveness ofUltrasound-guided Supraclavicular Brachial Plexus Block

Abstract

Background: Ultrasound-guided (USG) supraclavicular brachial plexus block (SCBPB) in upper extremity surgery is a popular approach. Conventional methods for the evaluation of block success are time-consuming and need the patient’s cooperation. The perfusion index (PI) is an oximetry reliability indicator, available on many monitors as a non-invasive parameter, indicating the ratio of arterial blood flow (pulsatile flow) to venous, capillary, and tissue blood flow (non-pulsatile blood flow), which is a more sensitive and earlier indicator of sympathetic blockade than temperature measurement. The main objective of this study is to evaluate the success of the supraclavicular block by using the perfusion index (PI) as a parameter. Methods: This study was carried out between January, 2021 and January, 2022 at Dhaka Medical College in the orthopedics operation theatre. Patients received a total of 20 ml of 0.5% Bupivacaine for ultrasound guided supraclavicular brachial plexus block (SCBPB). Perfusion index was recorded on the index finger before & just after performance of SCBPB, after achieving complete sensory & motor block, after performance of SCBPB and at the time of the end of surgery. Comparison was done between the PI before SCBPB and just after SCBPB, after complete loss of sensory & motor function, and at the time of the end of surgery. Chi-square test was done for qualitative variables, and t-test was done for quantitative variables. A receiver operating characteristic (ROC) curve was used to determine the sensitivity and specificity of PI and to determine the cut-off point. Results: A total of 90 patients were enrolled in the study. Considering PI just after SCBPB, at the time of complete sensory block, at the time of complete motor block, and at the time of the end of surgery with baseline PI, it was found statistically significant as p<0.05. While the area under the curve (95%CI) = 0.924(0.9-1.0) of PI at the time of complete motor block was greater than AUC (95%CI) = 0.913(0.9-1.0) of PI at the time of complete sensory block in the ROC curve. Perfusion index at the time of complete motor block has a higher 95.74% sensitivity and 97.3% specificity with 97.8% positive predictive value and 94.7% negative predictive value. Accuracy value 97.6%. And the cutoff value was >5.43. Where PI at the time of complete sensory block has 92.74% sensitivity and 97.56% specificity with 98.3% positive predictive value and 87.5% negative predictive value. Accuracy value 94%. And the cut off value was > 4.23. Mean PI value at the time of complete motor block 6.47±1.42 with percentage (%) change of PI from base line 197.6±18.6% was higher than mean PI value at the time of complete sensory block 5.47±1.12 and percentage (%) change of PI from base line 169.8±16.7%. Conclusion: PI provides a real-time, objective, and continuous display, unlike intermittent, subjective clinical testing. It enables early identification of successful blocks, reducing operating time spent on sensory/motor assessments. So, PI can be used as a parameter of successful SCBPB.

Bangladesh Society of Anaesthesiologists. 2023;36(2).:5-13