A simplified standardized ultrasound-guided plane block for the Intercostobrachial nerve: Effective volume of 0.5 % ropivacaine determined by Dixon's up-and-down method.

OBJECTIVE

The success rates of the intercostobrachial nerve (ICBN) blocks varied from 51 % to 100 % by different techniques, which required rich expertise from the operators and/or high-resolution ultrasound. We proposed a simplified ultrasound-guided plane block and explored the 50 % effective volume (EV50) and the 95 % effective volume (EV95) with corresponding 95 % confidence intervals.

METHODS

We recruited patients undergoing surgery of the upper limb and performed the simplified block. The needle target was positioned at 3 cm caudal to the centre of the axillary artery on the anterior surface of the conjoint tendon. The EV of 0.5 % ropivacaine was determined by Dixon's up-and-down method with an initial volume of 5 mL, and a successful or failed block could produce a 0.5 mL decrement or increment. Probit regression was fitted to determine the EV. To enhance robustness, a bootstrap analysis with 1000 resamples was performed. We recorded the block performance and adverse events.

RESULTS

A total of 28 patients were included. The EV50 calculated by the Dixon's up-and-down method was 3.29 ± 0.60 mL. Based on Probit regression analysis, the EV50 and EV95 were 3.31 (3.09-3.53) and 3.94 (3.46-4.42) mL. The bootstrap-derived EV50 and EV95 were 3.32 (3.05-3.52) and 3.90 (3.54-4.41) mL. No adverse events occurred.

CONCLUSIONS

This simplified standardized ultrasound-guided plane block can provide a reliable anesthesia of the intercostobrachial nerve, with an EV50 of 3.31 mL and an EV95 of 3.94 mL for 0.5 % ropivacaine. This approach may enhance teaching and clinical practice by improving ergonomics, procedural efficiency, and reproducibility, while minimizing local anesthetic dosage and enhancing safety.