# Effectiveness of Perfusion Index ratio and End-Diastolic Velocity ratio in evaluating the efficacy of Interscalene Brachial Plexus Block: a prospective observational study

## TL;DR

This study shows that the Perfusion Index ratio is more effective than the End-Diastolic Velocity ratio for early evaluation of interscalene brachial plexus block success.

## Contribution

The study introduces the use of PI and EDV ratios as early indicators for assessing the success of interscalene brachial plexus blocks.

## Key findings

- The PI ratio at 5 minutes had an AUROC of 0.894, indicating strong predictive value for successful block.
- The EDV ratio had lower specificity (50%) compared to the PI ratio at 5 minutes (85.7%).
- PI ratio at 5 minutes outperformed EDV ratio in evaluating block efficacy.

## Abstract

There is a lack of reliable indicators for evaluating the success of ultrasound-guided Interscalene Brachial Plexus Block (ISBPB). This study investigates the effectiveness of Perfusion Index (PI) ratio and End-Diastolic Velocity (EDV) ratio for early assessment of ISBPB effects.

Eighty-nine patients, aged 18–65 with BMI 18–24 kg/m2 and ASA grade I or II, underwent elective unilateral shoulder arthroscopic surgery. They received ultrasound-guided ISBPB with 15 mL local anesthetic (10 mL ropivacaine, 5 mL lidocaine). Patients were categorized into successful and failure groups based on needle test results after 30 min. PI and EDV of the brachial artery were recorded at baseline and at 5, 10, 15, 20, 25, and 30 min post-block. PI and EDV ratios were calculated by dividing values at each time by baseline. ROC curves were plotted at 5 and 10 min, and AUROC with 95% CI was calculated to assess block efficacy.

Of 89 patients, 3 were excluded due to data loss and 2 withdrew, leaving 84 patients. Of these, 70 (83.3%) had successful blocks. In the successful group, both PI and EDV ratios on the blocked side significantly increased 5 min after the procedure. The PI ratio at 5 min had an AUROC of 0.894 (95% CI: 0.816–0.972), with a threshold of 1.22, sensitivity of 84.3%, and specificity of 85.7%. The EDV ratio had an AUROC of 0.706 (95% CI: 0.553–0.860), with a threshold of 1.32, sensitivity of 92.9%, and specificity of 50%. At 10 min, the PI ratio for assessing ISBPB impact had an AUROC of 0.901 (95% CI: 0.828–0.974), with a threshold of 1.4, sensitivity of 74.3%, and specificity of 92.9%. The AUROC for the EDV ratio was 0.799 (95% CI: 0.6788–0.921) with a threshold of 1.54, sensitivity of 92.9%, and specificity of 57.1%. The PI ratio at 5 min had a significantly higher AUROC than the EDV ratio, but no significant difference was found between PI ratios at 5 and 10 min.

Both PI ratio and EDV ratio assess ISBPB efficacy. The PI ratio provides a more precise evaluation, with optimal assessment at 5 min post-procedure.

Chinese Clinical Trial Registry: ChiCTR2200066874.