# Assessment of the Optimal Distal End Length of Echogenic Perineural Catheters to Facilitate Successful Coiling: A Regional Anesthesia Simulator-Based Technical Study

## TL;DR

This study determines the best length for a flexible part of a medical catheter to coil properly near a nerve, using a simulator.

## Contribution

The study introduces specific lengths for catheter flexibility that maximize successful coiling in nerve block procedures.

## Key findings

- Retracting the stylet by 7 cm achieves 90% coiling success.
- An 8.1 cm retraction achieves 95% coiling success.
- Saline injection was successful in 92% of unobstructed catheters.

## Abstract

Introduction: We investigated the optimal length of a flexible end-portion of an echogenic-straight perineural catheter that would facilitate a catheter’s flexible distal portion to coil behind the sciatic nerve in a Blue Phantom nerve block simulator (Elevate Healthcare, Sarasota, Florida, United States).

Methods: In 80 20G perineural echogenic catheters, the integral stylet was retracted at various lengths (from 3 cm to 10 cm) so that the optimal catheter’s flexible length that enables the catheter’s flexible end portion (3-10 cm) to coil could be evaluated. Ten perineural catheters were allocated per cm of retraction. In our binary format, two variables were included: the first was the length of the catheter’s distal flexible end, and the second was whether the catheter’s distal end was coiled or not coiled. Optimal probabilities (90% and 95%) predicting the catheter’s optimal flexible distal length that facilitates successful coiling or not were evaluated by probit regression.

Results: Overall, 64 of the 80 perineural catheters were coiled. Analysis showed that withdrawing the integral stylet of a perineural catheter by 7 (6.1-9.4) cm and 8.1 (6.9-11.3) cm resulted in an optimal successful coiling with 90% and 95% probability (p<0.001). Injection of normal saline through the 60 unobstructed catheters contacted with the sciatic nerve in 55 cases (92%).

Conclusion: Retracting the integral stylet of a perineural catheter by specific lengths facilitates the coiling of its flexible distal end with high probability. This configuration could provide a functional buffer of catheter length, mitigating the risk of tip dislocation from its intended position.