# Comparative Study of Cold Sensation, Pinprick, and Perfusion Index in Evaluating the Quality of Ultrasound-Guided Supraclavicular Brachial Plexus Block: An Observational Study

## TL;DR

This study compares cold sensation, pinprick, and perfusion index to determine the best method for evaluating the success of ultrasound-guided brachial plexus blocks.

## Contribution

The study identifies perfusion index as a highly reliable early indicator of successful brachial plexus block with high sensitivity and specificity.

## Key findings

- Perfusion index (PI) showed significantly higher values in the blocked arm compared to the unblocked arm.
- PI had 100% sensitivity, specificity, and negative predictive value at 10 minutes with cut-off values of 3.25 and 2.75.
- The area under the ROC curve for PI was 0.983, confirming its reliability as an early indicator of block success.

## Abstract

Background

Ultrasound (USG)-guided brachial plexus block has become the preferred method for surgeries of the upper limb as it reduces the risks of pneumothorax, nerve injury, and local anesthetic toxicity. An objective, noninvasive technique for evaluating the block's effectiveness is the perfusion index (PI). An increased PI suggests a successful brachial plexus block.

Aims and objectives

The study aimed to evaluate and compare cold sensation, pinprick, and PI to determine the most effective indicator for assessing the quality of USG-guided supraclavicular brachial plexus blocks (SCBPBs).

Materials and methods

The study included 92 patients. Each patient received 25 mL of local anesthetics (10 mL of 0.5% bupivacaine, 10 mL of 2% lignocaine, and 5 mL of 0.9% normal saline) for USG-guided SCBPB. Responses to cold sensation, pinprick, and PI were noted for operative and control limbs starting right after block introduction till 20 minutes at intervals of 5 minutes. After 20 minutes, a modified Bromage scale was used to evaluate the motor block, and a 3-point scale was used to evaluate the block's quality. If the block quality was unsatisfactory or resulted in complete failure, such patients were considered for general anesthesia.

Results

Significantly higher PI in the blocked arm than the unblocked arm was observed across all periods. The PI and PI ratio cut-off values at 10 minutes were 3.25 and 2.75, respectively. At 10 minutes, the PI's sensitivity, specificity, and negative predictive value (NPV) were 100%. At 10 minutes, the sensitivity of the pinprick and cold sensation was 75% and 82%, respectively, and at 20 minutes, it reached 100%. All three methods' positive predictive value was 100% at 10 minutes. The NPV for cold sensation and pinprick gradually increased, reaching 100% at 20 minutes. Area under the receiver operating characteristic curve (AUROC) analysis showed that the PI reached a value of 0.983 by 10 minutes.

Conclusion

PI values were significantly higher in the blocked arm than in the unblocked arm. A successful block can be predicted with 100% sensitivity and specificity at 10 minutes if the PI is more than 3.25 and the PI ratio is more than 2.75. The AUROC analysis confirms that PI values are reliable early indicators of block success.